Innovative high temperature and mechanical descaling (HIDES).
Date: 2013-12-02
Institutions: Directorate-General for Research and Innovation
Subjects: industrial electric machinery, industrial research, iron and steel industry, quality standard, railway industry, research and development, research project, research report, resistance of materials, technological process, use of water

European Commission

Research Fund for Coal and Steel

Innovative high temperature  
and mechanical descaling

(HIDES)

D. Espinosa, G. Lannoo, H. Uijtdebroeks, P. Pouteau, X. Peng

Centre de Recherches Métallurgiques ASBL (CRM)

Avenue du Bois Saint-Jean 21, 4000 Liège, BELGIUM

D. Farrugia, P. Yates, M. Bugdol, M. Whitwood, E. McGee and C. Izzard

Tata Steel UK (TATA STEEL)

Moorgate Road, Rotherham, South Yorkshire S60 3AR, UNITED KINGDOM

A. David, T. Muller, T. Prezeau

WINOA (Wheelabrator Allevard Corporate WA) 

Avenue de Savoir 528, 38570 Le Cheylas, FRANCE

A. Erz, J. Hoffmeister

Karlsruher Institut für Technologie (KIT) – Institute for Applied Materials (IAM)

Kaiserstrasse 12, 76131 Karlsruhe, GERMANY

Grant Agreement RFSR-CT-2009-00009 
1 July 2009 to 31 December 2012

Final report

Directorate-General for Research and Innovation

2013 

EUR 26177 EN

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Luxembourg: Publications Office of the European Union, 2013 

ISBN 978-92-79-33229-6 
doi:10.2777/4304 

© European Union, 2013 
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TABLE OF CONTENT 
1.  FINAL SUMMARY 
2.  Scientific and technical description of the results 

2.1. 
2.1.1. 
2.1.2. 
2.1.3. 
2.2. 
2.2.1. 
2.2.2. 
2.2.3. 
2.2.4. 
2.2.5. 
2.2.6. 
2.2.7. 
2.2.8. 
2.3. 
2.3.1. 
2.3.2. 
2.3.3. 

2.3.4. 
2.3.5. 
2.4. 
2.4.1. 

2.4.2. 
2.5. 
2.5.1. 
2.5.2. 
2.6. 
2.6.1. 
2.6.2. 
2.6.3. 

5 
15 
15 
WP1: Envelope of current Industrial Conditions and Material Preparation 
15 
Task 1.1 Steel Compositions 
15 
Task 1.2 Envelope of HPW descaling processing conditions 
26 
Task 1.3 industrial oxide scale characterisation 
29 
WP2: Water-based descaling process 
29 
Task 2.1 Pulsating/fluctuating water jet 
30 
Task 2.2 High pressure/low flow rate 
30 
Task 2.3 Particular water jet 
31 
Task 2.4 Double descaling 
33 
Task 2.5 Latest Descaling nozzle technology 
34 
Task 2.6 Effect of nozzle geometry 
41 
Task 2.7 Modelling 
55 
Task 2.8 Cross performance comparison of water-based technology 
59 
WP3: Water-free descaling process - high temperature shot blasting 
59 
Task 3.1: Development and test of heat-resistant blasting media grade 
Task 3.2: Preliminary trials of hot temperature blasting operations 
62 
Task 3.3: Definition of an experimental procedure to assess the high temperature resistance 
73 
of the blasting media 
73 
Task 3.4: Validation of the water-free descaling process in online conditions 
75 
Task 3.5 Modelling of high temperature shot blasting 
83 
WP4: Characterization of surface state and properties 
Task 4.1 Characterisation oxide/surface/sub-surface and Task 4.2 Analyse of the 
83 
primary/secondary scale growth and adhesion. 
86 
Task 4.3 Surface temperature during descaling 
89 
WP5: Process efficiency comparison and implications 
89 
Task 5.1 Assessment of optimum descaling techniques 
89 
Task 5.2 Detailed comparison water-based / water free descaling on selected grade 
99 
WP6: Regime maps, sensitivities and industrial validation for optimum descaling 
99 
Task 6.1 Regimes maps of innovative mechanical descaling techniques 
Task 6.3 Industrial testing of selected techniques 
103 
Task 6.2 comparative assessment of upscaling new descaling techniques and guidelines 109 
117 
119 
121 
125 
129 
131 
133 
137 
139 

3.  Conclusions 
4.  Exploitation, impact and transferability of the research results 
5. 
6.  List of figures 
7.  List of tables 
8.  List of acronyms and abbreviations 
9.  List of references 
Appendix 1: Descaling basic formula 
Appendix 2: Pareto charts and 2D Regime maps 

conformity with the plan 

3 
 
 
 
 
 
 
 
 
 
 
 
1.  FINAL SUMMARY 

General objectives:  

This project aims to address the surface quality problems associated with descaling efficiency through 
the development of new integrated routes involving the use of new water-free descaling techniques and 
optimisation of current water-based descaling processes. Two main branches have been explored: 

1)   More  efficient  water-based  descaling:  Primary  and  secondary  scale  water-based  descaling 

techniques have been optimised by changing the descaling parameters.  

2)  New descaling media: Different steel shot blasting concept was developed by changing the steel 
shot  (size  and  hardness),  the  descaling  temperature,  the  shot  blasting  parameters  (depth 
intensity, cover rate, impact pressure, etc.) and mechanical descalability assessed and compared 
with current state of the art high pressure water-based descaling processes. 

Descaling particular steel compositions was investigated in order to determine the most feasible 
methods of descaling according to the scale formed in a range of specific steel compositions of interest 
with focus on high alloyed steels.  

The  project  is  divided  into  6  work  packages.  The  main  interaction  between  the  work  packages  are 
shown in Figure 1.  

WP 1
Industrial conditions and
material preparation

WP 2
Water-based descaling
processes

WP 3
Water-free descaling
process - High
temperature shot blasting

WP 4
Characterisation of
surface state and
properties

WP 5
Process efficiency
comparison and
implication

WP 6
Industrial validation for
optimum descaling

Figure 1 Diagram illustrating interaction between work packages 

WP1: Envelope of current industrial conditions and material preparation  
The  objective  of  this  work  package  was  to  select  and  acquire  the  range  of  steel  grades  under 
investigation  (especially  high  alloys  steels  (Si,  Al)),  and  the  envelope  of  processing  laboratory 
conditions in line with industrial applications. A suitable window of process conditions (temperature, 
pressure,  etc)  for  conditioning  the  oxide  scale  (composition,  thickness,  etc)  was  selected.  This  work 
package gives the envelope of thermo-mechanical conditions and materials to water-based and water-
free descaling systems.  
Industrial materials have been selected (task 1.1): Rail steel as-cast bloom of 298Q quality (high C, Si) 
steel (SRSM mill), valve spring bloom of VS56 quality (medium C, Si, Cr) steel (SRM mill), electrical 
steel  of  UT23  prior  and  after  tunnel  furnace,  and  UT12  quality  (ULC,  Si,  Al)  steel  (DSP  mill)  and 
LFCS steel in as-cast condition.  

Laboratory cast melts have been produced according to industrial chemical composition to enlarge the 
range of alloy content with respect to Si and Al up to nearly 6% Si and 2.4% of Al. The specific steel 
composition of all the industrial and lab materials are given in Table 3.  

Sample  preparation  is  one  of  the  main  objectives  of  this  work  package  (task  1.3),  not  only  the  steel 
selected  here  above  were  prepared  for  the  test  to  perform  along  the  project,  but  also  the  selection  of 
special materials like Aluminium for erosion test and simulation materials like HPDE and Teflon was 

5 
 
an  important  task.  Aluminium  and  plate  board  materials  were  used  to  study  at  room  temperature  the 
different  parameters  of  HPW  (High  pressure  water)  and  shot  blasting  process  in  dynamic  and  static 
tests.  

The  water-based  descaling  has  been  studied  in  this  work  package  (task  1.2),  the  objective  was  the 
identification of the main parameters and concepts having the bigger impact on the descalability of the 
steel  surface.  It  was  found  that  mechanical  impact,  speed  through  descaler  and  thermal  effect  prior, 
during  and  after  descaler  are  intrinsically  linked  to  pump-flow  characteristics.  Nozzle/filter  type  and 
throughput/pacing and constraint through the mill depend on mill configuration. 

In  general  the  HPW  descalability  is  linked  to  impact  force  [N],  impact  pressure  (IP)  [MPa],  specific 
water impingement (SWI) [l/m²], descaling energy [kJ/m²] and coverage in terms of spray width [mm], 
overlap  [mm]  and  wash  [mm].  These  concepts  will  give  also  the  link  for  cross  comparison  with  the 
water free shot blasting process. The variables that play an important role in the definition of the above 
mentioned  parameters  are  the  nozzles  geometry  and  set-up,  standoff  distance,  the  flow  rate  and  the 
product speed. The nozzles position and geometry are defined by four angles (spray, depth, offset and 
rake angle) and from them other important characteristics are deduced (spray width, overlap distance, 
spray length, etc). It can be said that a good descalability requires a good overlap defined at 8 to 15% of 
spray width, a regular spray width, a small spray thickness, an efficient spray angle ideally max 30° and 
a relative small standoff distance to ensure perfect laminar flow and maximum impact. The project has 
developed  an  approach  based  on  key  independent  and  dependent  parameters  which  characterise  the 
process and its variability as well as the efficienty of descaling under known well established theorie. 
This  approach  is  based  on  design  of  experiment  (DoE)  which  has  as  objective  to  define  the  most 
significant parameters and their interaction on descalability.  

A mapping of the main important reheating and descaling conditions in HPW was done based on the 
parameters  used  in  the  primary  descaling  installations  considered  in  this  project  (MSM,  SRM  and 
tunnel  DSP  furnace).  The  conclusions  of  this  study  are  that  prior  descaling  and  reheating  furnace 
conditions are  critical  in  terms  of  conditioning  the  primary  oxide  scale  and  oxide/metal  interface and 
that  the  average  resident  time,  max  heating  rate/surface,  soaking/discharge  temperature  and  oxidising 
atmosphere are the most critical input factors for the reheating conditions. From descaling conditions 
the study could be summarised saying that IP from all three primary decalers vary from 0.1 to 2MPa, 
SWI  from  3  to  40l/m²,  descaling  energy  vary  from  0.2  to  85kJ/m²,  fluid  velocity  vary  from  120  to 
212m/s and impact force vary from 67 to 223N.  

After the identification of the main parameters, conditions and variables of the HPW, the next objective 
is the characterisations of the primary scale morphology prior descaling (task 1.3) within the operation 
windows of the three reheat furnaces of interest (MSM, SRM and tunnel DSP furnace). To fulfil this 
objective  a  series  of TGA  tests  (Thermogravimetric  Analyses)  was  done  using  extreme  conditions  of 
production reheat exhaust gas composition (low, medium, and high). The results provided an oxidation 
rate curve and scale morphologies to be used as benchmark samples for the HPW descaling lab test.  

The main results of the TGA tests are summarised as follow: for rail steel (298Q) with 0.27%Si the time 
temperature profile of 1220°C has no large difference in oxidation for the different furnace atmosphere 
conditions and surface state. Reheating temperature has a large influence mostly above 1220°C and the 
scale thickness has an average of 970µm.  

For  the  rail  steel  lab  material  2217  with  1.23%  Si,  the  total  weight  gain  in  the  oxide  curves  for  the 
different temperature goes up to 60%. The scale shows complex oxides, internal scale spallation, cracks 
and magnetite are also present. For the modified DSP steel with 5.9% Si and 2.13% Al, the results show 
a  drastic  effect  of  Al  on  oxidation,  this  also  associated  with  Si  content.  Al  in  combination  with  Si 
reduces  the  eutectic  fayalite  temperature  increasing  liquid  oxide  penetration.  For  the  steel  LFCS,  the 
results of TGA test show a scale thickness of 1450µm giving a similar oxidation rate to modified rail 
steel (2217) and higher than rail steel with 0.23% Si.  

WP2: Water based descaling process 
The objective of this work package is to test new water based descaling processes using laboratory pilot 
descaling  based  on  industrial  conditions  from  WP1.  Several  different  descaling  conditions  are 
investigated in order to improve current descaling performance. These are cross-compared for a specific 
set of conditions with conventional water-based system currently used in industrial conditions.  

6 
 
To  carry  out  this  objective  the  revamp  of  the  HPW  descaling  rig  was  necessary  to  achieve  a  system 
pressure up to 500bar/low flow and a flexible set-up for nozzles testing. The control of the atmosphere, 
to  work  as  close  as  possible  to  industrial  values,  was  improved  as  well,  the  reheating  now  could  be 
carried  out  in  air  or  atmosphere  from  stoichiometric  combustion  giving  ~9%CO2,  17%H2O  at  2% 
excess of O2 or 10% excess air.  

In  view  of  some  delay  encountered  at  the  start  of  the  project  (descaling  expert  retiring,  delay  in  rig 
revamp, some capability limitation post descaling (evaporation, applications system and mixing/dosing 
facility for particulate), it has not been possible to study the effect of particulate descaling (task 2.3). 
Priority was given to comparing/benchmarking both HPW and hot shot blasting descaling with a shift 
on effort in running prototype trials (WP6) and characterisation of finished products.  

The  first  task  (task  2.1)  of  this  work  package  is  the  study  of  the  pulsating/fluctuating  water  jet,  the 
technology  is  based  on  capitalizing  the  impact  shock  or  water  hammer  pressure  mostly  at  the  initial 
phase  of  the  impact.  By  pulsing  the  jet,  the  material  is  exposed  to  higher  impact  pressure  at  shorter 
period  of  time.  Limited  tests  were  performed  to  promote  system  pressure  oscillation,  but  this 
technology seems to have slow progress with the nozzles manufactures, due to difficulty of control at 
high pressure and not enough better quality of descaling with single nozzle.  

High pressure/low flow rate test were performed in this work package (task 2.2), the capability of the 
rig to deliver depending on flow-pressure characteristics of nozzles could reach up to 500bar in single 
nozzle configuration and 440bar in dual nozzle  mode. Several Al erosion test to assess high pressure 
low flow conditions for nozzles DNM0325 (DSP plant) were carried out. The nozzles DNM0325 could 
deliver 40.2l/min at 500bar.  

Double  descaling  concept  was  tested  to  assess  efficiency  compared  to  single  descaling  for  difficult 
grades  (task  2.4),  comparison  with  TGA  results  was  also  performed  here  to  analyse  the  scale 
morphology of primary scale obtained during pilot descaling test.  

Scale morphology was similar for TGA and pilot descaler test. Double descaling did not show a marked 
effect compared to single descaling but it was found that for double descaling some parameters should 
be adapted to scale morphology, heat losses, production considerations, water supply, etc. In general for 
being effective, double stationary offset headers can be utilised often with first header operating at low 
pressure-low  flow  to  condition  the  scale.  For  a  reversing  mill  (such  as  plate  rougher)  wash  box 
descaling units can be utilised in double descaling mode.   For the Si high Al steel, little benefits could 
be gained in view of level of entanglement, but tests carried out were only a fraction of the envelope of 
descaling (still low pressure) which could be considered. 

The latest descaling nozzle technology was also studied in this work package (task 2.5), which includes 
improved stabiliser, orifice shape and material design. The improved technology and manufacturing has 
resulted in reduction of spray depth or thickness and width. Now options for short, long, and extra-long 
stabiliser are available. New Lechler Scalemaster superior HPS series, DNM and latest DNEX nozzle 
technology have been tested.  

An important task of this work package was to study in depth the effect of the nozzle geometry on the 
descaling efficiency (task 2.6). Spray height and various angles are key variables in the header design 
that will affect descaling performance. Not only the study of parameters or geometry is important but 
also  the  interaction  and  influence  on  each  other  parameters  have  to  be  considered.  The  efficiency 
depends on spray angle and spray height. The impact density, pressure and impact are affected by the 
spray  angle.  The  normal  distribution  of  impact  pressure  is  influenced  by  the  depth  angle.  The  offset 
angle  is  a  key  to  prevent  spray  interference  as  well  as  directing  oxide  scale  and  water  away;  it 
influences  directly  the  amount  of  wash  and  the  temperatures  losses.  A  rake  angle  different  to  0°  is 
required to avoid scale in the roll bite. The standoff has a direct influence on the impact pressure and it 
is also related to the spray angle. The header angle represents the fixed referential point for all the other 
angle parameters. The influence of the nozzle filters was also analysed, the use of short or long filters 
could increase the impact pressure by at least 20%. The wear of the nozzle is also an important factor, it 
is related to the design of the orifice tip and the nozzle tip material; the wear will influence the spray 
pattern and potentially the droplet size which increases as water flow increases. The number of nozzles 
and the nozzle pitch are related as well, in general, smaller the pitch, higher the number of nozzles, this 
is a key parameter to be controlled. Overlap and wash are influenced by pitch, standoff, system pressure 

7and rake; the overlap has to be controlled otherwise descalability can be drastically reduced with spray 
interference and increased cooling.  

The study of nozzle geometry and efficiency was done by static and dynamic erosion test, impact force 
measurements  and  Almen  strip  deflection  test.  The  nozzles  used  were  new  nozzles  from  Everloy 
DNM0325/0833/1225  with  short,  long  and  extra-long  filters  and  Lechler  HPS  6P3.567.  The  main 
conclusions  could  be  mentioned  as  follow:  No  erosion  at  130bar,  erosion  increases  as  standoff 
decreases, erosion decreases with short filters and Al thickness. Min difference is visible between long 
and extra-long filters.  

The interaction of parameters between two nozzles was studied as well, a large set of Al erosion test 
was done to study the influence of geometry on overlap and wash during descaling, the results of the 
study were clear, when overlap is reduced by 3mm the impact force could be increased in the secondary 
spray from 0.2 to 0.8MPa.  

The model of the water based process was done too (task 2.7), it was done by analytical calculations, 
further developments of FEM based models for the mechanical components and development of more 
advance  fluid  based  models  using  a  CEL  (coupled  Eulerian  Lagrangian)  formulations  to  model  the 
spray and impact target of the descaling process.  

The  FEM  HPW  descaling  modelling  addresses  the  thermal  and  mechanical  side  as  well  as  new 
developments for accounting for fluid-structure interaction (mechanical side only). After the validation 
of  the  analytical  models  it  can  be  concluded  that  IP  is  overestimated  at  small  standoff  in  view  of 
potential error in spray form. The IP calculations give better predictions for short filters, long and extra-
long  filters  give  increased  IP  in  good  agreement  with  moderate  to  high  pressure  and  standoff  above 
93mm.  The  benefits  of  extra-long  filters  were  not  realised  in  view  of  the  length  of  header  and  water 
supply. Analytical predictions of spray width are in good agreement with those measured from impact 
force and Al at the highest pressure. Overlap is better predicted as system pressure is ramped up and 
standoff increases.  

And finally a cross performance of single/double descaling and descaling function of impact pressure 
was done (task 2.8). The main conclusions are that as-cast reheat surface especially for electrical steel 
are  the  most  difficult  surface  to  descale.  Fayalite  formation  for  electrical  steel  and  valve  spring 
decreases descability. Double descaling can be beneficiary for some grades, for example for High Si, 
but more work is required, it could be recommended to use as pre-cracking of scale using low pressure 
sprays to avoid heat losses, and then followed by high pressure descaling.  

WP3: Water-free descaling process – high temperature shot blasting 
The  objective  of  this  work  package  is  to  test  new  water  free  descaling  processes.  Several  different 
descaling conditions are investigated in order to improve descaling performance.  

The different parameters of blasting media were studied in order to select the adequate metal shots for 
testing at high temperature. Shape, size, hardness and distribution of operating mix are the main criteria 
for  blasting  media.  Shapes  of  media  are  round  or  angular  particles  and  size  is  defined  by  normal 
dimension, both shape and size are defined by the SAE J444 standard designation. The hardness range 
depends on the shot application. The operation mix is a mixture of particles used in a blasting machine, 
it is characterised by size distribution, abrasive type and quantity as well as blasting parameters. 

One of the main tasks of this work package was to study the need of the development of heat-resistance 
blasting  media  grade  (task3.1).  It  was  expected  that  the  steel  abrasive  media  would  show  lower 
efficiency  when  used  at  high  temperature.  After  lab  trials  and  pilot  industrial  trials  together  with 
numerical simulations and slow motion videos the need of new abrasive media grade was not found, all 
the  results  showed  that  the  abrasive/substrate  contact  time  is  very  short  and  that  the  temperature 
increment  of  the  shots  after  descaling  hot  parts  was  from  11°C  to  22°C  far  under  the  tempered 
temperature ~400°C. 

In order to perform the preliminary shot blasting trials (task 3.2) at hot temperature the key parameter of 
blasting operations and the effects on descaling efficiency was identified. Coverage rate is associated to 
the  descaling  efficiency;  it  is  the  ratio  of  the  area  covered  by  hits  expressed  in  percentage  and  it  is 
correlated to surface deformation. The type of blasting system has an effect on the coverage area: in the 

8 
 
 
wheel blasting system the media is propelled by a bladed wheel rotating thanks a motor. This method 
has  a  lot  of  advantages  such  as  the  easy  control  of  shot  velocity,  high  production  capacity  and  high 
efficiency blasting operation with recyclable media. In the air blasting system the shots are introduced 
by direct pressure or by gravity into a stream of compressed air directly through a nozzle onto work, the 
main advantages of this system are the flexibility and the easiness, but it is not easy to control the shot 
velocity and flow.  

Other important parameters to take into account are the media velocity, type of media, mass flow rate 
and  impact  angle. The  media  velocity  has  an effect on  the  kinetic  energy.  The  type  of  media,  shape, 
size, mass and hardness affect the coverage rate. The mass flow rate defines the time required to obtain 
the specific coverage rate and the impact angle affects the transfer energy from shot to work piece and it 
is also an important parameter for rebound and recyclability.  

Taking  profit  of  the  flexibility  of  the  air  blasting  system,  a  small  air  blast  device  was  designed  and 
installed in CRM lab to perform test of descaling at high temperature. The air blasting device allows 
performing test only in static mode. Different parameters were chosen in the first set of trials, shot size 
WS170  and  WS230,  low  and  high  pressure,  low  and  high  flow  and  soft  and  standard  media.  The 
objective  of  working  with  several  shots,  pressures,  flows  and  hardness  is  the  pre-selection  of  best 
parameters  at  high  temperatures.  The  size  will  affect  the  coverage  speed  and  the  quantity  of  impact, 
important parameter for economic reasons. Big shots have higher kinetic energy and have an effect on 
cleanliness.  The  pressure  affects  the  shot  velocity  which  increase  with  pressure,  the  efficiency  of 
descaling is affected and the risk of shot inlaying increases. The flow gives information about the size 
of  the  system  in  an  industrial  application;  low  flow  means  fewer  turbines  and  more  compact 
installations, other effect of flow is in the productivity, high flow enables shorter blasting times. And 
the hardness of the shots has an effect on the consumption and on the final quality of surface treated 
(shot inlaying, roughness, etc).  

Taking  into  account  all  the  parameters  described  above,  several  trials  have  been  done  using  the  air 
blasting pilot device. The test used the electrical furnace to heat up the samples up to 1200°C during 1 
hour, then shot blasting descaling in a static mode is applied on sample and finally cooled down in a 
nitrogen  box  to  avoid  further  oxidation  and  cracking  phenomena.  The  first  trials  were  done  without 
control  of  atmosphere  in  the  oven  in  order  to  see  the  behaviour  of  the  shots  and  to  calibrate  the  test 
selecting the best blasting parameters. The conclusions of the first tests could be summarised as follow:  
the  favourable  blasting  parameters  are  high  pressure  (higher  shot  velocity),  numerous  impact  (shot 
blasted  quantity)  and  shots  of  standard  hardness.  After  blasting  operation  no  variation  of  micro  or 
macrostructure of shots was observed.  

A second set of trials was performed in the same way as just described, but using controlled atmosphere 
in  the  reheating  furnace,  CRM  has  developed  a  new  controlled  reheating  atmosphere  setup 
corresponding  to  industrial  reheating  conditions,  during  the  trials  a  dew  point  of  57°C  was  set 
corresponding to 17% humidity and controlling the nitrogen flow an oxygen level in the range of 1.6% 
to 2.4% was measured which correspond to similar atmosphere in the Tata Steel furnace (WP2). The 
objective  of  this  test  was  to  use  the  already  selected  blasting  parameters  and  check  the  descalability 
efficiency in industrial reheating conditions of shot blasting on different steels. The material used was 
lab  cast  and  industrial  materials.  The  parameters  used  during  the  test  are:  max  pressure  and  high 
quantity of shots in order to increment as much as possible the impact energy and coverage rate. The 
main conclusions of the test are: for electrical steel, a clear impacted zone was created for all steels; the 
coverage  rate  was  between  50%  and  90%,  the  increase  of  shot  quantity  incremented  the  descaling 
efficiency  but  no  significant  effect  of  shot  size  was  observed.  For  rail  steels  both  industrial  and  lab 
material are 100% impacted but not completely descaled, this could be due to the steel composition and 
temperature.  

Extra test have been performed using the pilot air blasting at CRM and the wheel blasting machine at 
WINOA,  the  tests  were  done  with  Al  and  Almen  strips.  The  objective  of  the  trials  at  CRM  were  to 
check  shot  velocity  and  influence  of  shot  blasting  on  the  material  in  terms  of  impact  energy, 
topography, coverage, etc and transport the main values of parameters to a wheel blasting application. 
The  objective  of  the  trials  at  WINOA  was  to  get  information  about  the  shot  velocity  and  blast 
conditions as close as possible to industrial application. The main conclusions obtained are: the blasting 
transposition of parameters was achieved with success, no real impact of shot size on roughness found, 

9 
no real difference on surface state, coverage rate and impacted surfaces state between samples blasted 
by air or wheel machine and no embedded shots.  

One of the main advantages of the blasting descaling process is the possibility of recycling of shots, the 
abrasive were studied before and after hot sample blasting (task 3.3 and task 3.4). The measurements of 
sieve and hardness did not show significant difference, the hardness seems not to be affected by the hot 
material, and the sieve measurement did not show wear or breakage.  

In  this  work  package  the  modelling  of  abrasive  shot  blasting  was  also  performed  (task  3.5)  using 
ABAQUS/explicit. The basic structure of the model consists of bulk material with layered oxide scale 
and a number of shots that impact the surface. For the modelling some simplifications have to be made: 
only  a  small  section  of  the  work  piece can  be simulated  and  the  shots  are taken  as  rigid  bodies. The 
formulations  used  for  the  simulations  for  the  oxide  scale  are  tensile  and  brittle  damage;  the  bulk 
material is modelled with elastic-plastic material behaviour. Simulations with one shot and multi shots 
(4-shots) were done; different shot speeds (10, 40 and 75m/s), scale strengths (4 to 20MPa), shot size 
(WS170 and WS230) and scale thickness (250µm to 1000µm) have been investigated.  

The main results of this study can be summarised as follows: the simulations are in accordance with the 
experiments  in  terms  of  scale  removal.  The  brittle  formulation  is  more  stable,  the  influence  of  a 
particular shot size on scale thickness should be studied further because it there seems to exist an ideal 
shot size for a specific scale thickness, in terms of maximizing the damage done by a single shot. In 
addition it seems that faster shots do not always cause more damage than slower shots. Most damage 
achieved by the WS230 shots because of the higher kinetic energy; the scale is easier removed when 
oxide  thickness  increases  and  the  shots  are  big  enough  to  be  able  to  penetrate  the  oxide.  The  shots 
WS230  cause  a  lot  of  damages  at  the  interface  between  the  bulk  and  the  scale  due  to  the  plastic 
deformation of the bulk material. Damaging the interface is beneficial in terms of descaling, since this 
lead to ablation of the scale layer.  

WP4: Characterisation of surface state and properties 
Characterisation is performed for all the products obtained in the previous work-packages. The surface 
properties  and  oxide  scale  state  is  investigated.  Temperature  of  the  surface  during  descaling  is  also 
assessed. 

Primary scale obtained by TGA test WP1 and reheating test WP2 and WP3 under industrial conditions 
was investigated for all the steels studied in this project (task 4.1 and task 4.2). The main conclusions 
are: the primary scale is non-uniform and already fairly porous with spallation and through thickness 
cracks. Thickness for rail steel is 1050µm almost matching with scale thickness of 940µm formed under 
industrial reheating atmosphere validating so the procedure for reheating samples. The comparison of 
primary oxide layer achieved on lab steels in Tata Steel and in CRM reheating furnace shows a similar 
morphology and scale thickness. Oxide layer composition and thickness is not affected by surface initial 
state but after shot blasting the polished samples show lower roughness and best descability than as-cast 
samples.  

Scale after shot blasting test done in WP3 was analysed, from cross section results it could be said that 
for  the  low  Al  electrical  steels (lab  and  industrial  steels)  shot  blasted  with  6kg  and  9kg,  the  oxide  is 
descaled when high pressure is used 7.5 bar and no significant effect of the blasting parameters on the 
oxide layer is observed. For the high Al electrical steels, Al is enriched at the interface leading to spinel 
formation. The longer the duration of the shot blasting the less oxide layer remains on the metal surface; 
it seems that the bigger shots WS230 have a better descalability than the smaller ones WS170. In order 
to ensure descaling effect and reduce descaling time higher flow rate and shot velocity is necessary.  

The last task of this work package (task 4.3) was the study of the temperature evolution during water-
based and water free descaling. Test were performed to study the influence of heat losses during single 
and  double  water  descaling,  the  heat  loss/HTC  measurements  give  60  to  80°C  loss  at  0.12m/s  in  the 
range of 300 to 400bar on primary scale and with reduces heat losses on secondary scale but initially 
chilled surface of the order of 50°C.  
By means of thermocouple measurements, the temperature was also assessed during hot shot blasting 
test performed in WP3, the results are from static test with 6 and 9kg of shots corresponding to 40s and 
60s blasting time, such long blasting times are not compatible with the industrial practices but are due 

10 
 
 
 
 
to the limits of the shot blasting device. Nevertheless it is observed that the different blocks exhibit the 
same  cooling  rate  during  shot  blasting  which  is  around  5°C/s.  the  different  shots  types  have  no 
influence on the cooling rate and the shots temperature increases a couple of degrees after shot blasting 
process.  

WP5: Process efficiency comparison and implications 
The aim of this work package is to emphasis the benefits of each process in optimising scale removal in 
pilot experimental conditions.  

The assessment of optimum descaling techniques was the first objective of this work package (task 5.1). 
Based  on  all  the  study  done  in  WP1,  WP2  and  WP3  ,  for  the  water  based  descaling  the  optimum 
methodology requires: appropriate level of descaling energies based on grade and pump/water supply 
from  17  to  50kJ/m²,  to  increases  descaling  energy  and  taking  into  account  the  mill  layout,  feedstock 
speed can be adjusted and potentially reduced above the minimum speed; optimum selection of nozzles 
with  max  spray  angle  of  30°,  standoff  within  90  to  120mm  based  on  minimum  pitch  of  45mm  and 
minimum overlap/wash, the overlap to avoid overcooling could be between 7 to 15% spray width. The 
rotatory descaling should be selected for difficult to descale grades.  
For water free descaling the optimal parameters selected from lab trials are: line speed from 0.1 to 1m/s, 
shots size WS170 and WS230 with speed of 61m/s and 76m/s, conveyor speed of 2.9m/min to 7m/min, 
turbine angle of 37°, max flow rate of 90Kg/min and coverage width of 0.6 to 1m.  

Detailed  comparison  of  water-based/water  free  descaling  on  selected  grades  is  one  of  the  main 
objectives  of  the  project  (task  5.2);  the  comparison  of  the  two  processes  has  involved  modelling, 
experimental test and detailed surface characterisation.  
Modelling was here necessary due to the complexity of both processes and the need of determine a set 
of  common  parameters.  The  main  results  are  related  to  the  shot  and  water  velocity.  ~80m/s  shot 
velocity  corresponds  to  a  HPW  descaling  of  max  320bar  for  the  particular  nozzle  DNM0325  giving 
theoretical descaling IP of the order of 1.5-1.8MPa. The analytical depth is 0.1 to 0.3mm using water or 
metallic shot for 0.4mm diameter particle.  
Al erosion tests are a good method to evaluate the HPW parameters but for shot blasting this kind of 
test did not give positive results, from faro arm measurements on Al blasted samples the results showed 
that no erosion has occurred only material displacement (plasticity) under shot impact. For that reason 
plasterboard and Teflon shot blasting erosion test were also carried out to be able to compare the two 
descaling processes. 

Using appropriate masking in a dynamic mode (using wheel industrial blasting machine see WP6) at a 
given turbine rate and speed, several Teflon and plasterboard tests were performed, then compared to 
HPW descaling keeping line speed constant (0.12m/s). For HPW a pressure of 120bar is needed to give 
same erosion depth as shot blasting with turbine speed of 60Hz and a descaling energy of 40kJ/m², so 
fixing  the  line  speed  means  the  same  descalability  between  the  two  processes  should  be  reached  at 
120bar for the HPW descaling and 60Hz turbine speed, therefore a decreases ratio of 2.75 on system 
pressure. This highlights the importance of descaling and shot blasting energies and the speed through 
the process affecting also throughput.  

Steel samples obtained after high pressure water descaling in WP2 and shot blasting descaling in WP3 
were further analysed, it could be concluded that on lab scale test hot shot blasting descaling is at least 
as efficient as double high pressure water descaling in removing the primary scale.  

In this work package a series of trials using water based and water free descaling combined with hot 
rolling were performed in order to analyse the evolution of the surface after the different processes.  
The water based tests are performed with a new descaler box designed in CRM where standoff, speed, 
angles and overlap could be modified easily. The max IP is 0.45N/m² and pressure 130bar, with Lechler 
nozzles.  Industrial  materials  were  used  298Q  and  UT23.  The  samples  are  reheated  under  atmosphere 
control,  descaled  and  rolled  in  the  rolling  stand  with  a  max  rolling  force  of  400Ton,  the  rolling 
reduction used was 20%. After rolling the samples were taken inside a cooling nitrogen device.  From 
cross section results it can be said that after water descaling and hot rolling the material has still some 

11 
 
 
 
 
 
 
entanglement and internal oxidation, the descaler could not remove completely the scale formed in the 
reheating furnace, the remaining scale thickness is around ~20µm.  

Water free trials were performed under the same parameters of reheating, rolling and cooling conditions 
here  above  described,  the  samples  were  descaled  in  the  static  shot  blasting  pilot  device  with  shots 
WS230,  9kg  and  pressure  of  7.5bar.  Samples  were  observed  right  after  rolling  and  in  cross  section. 
After  rolling  the samples show  a  very  smooth  surface,  no cracks  or  shot inclusions  are  visible.  From 
cross  section  the  surface  after  shot  blasting  shows  a  waving  aspect  but  after  rolling  the  oxide  and 
substrate  is  deformed  to  a  smooth  surface  with  homogenous  oxide  layer.  Entanglement,  internal 
oxidations or cracks are not visible.  

WP6: Regime maps, sensitivities and industrial validation for optimum descaling 
The  objective  of  this  work  package  is  the  industrial  validation  of  selected  innovative  mechanical 
descaling technique.  

The regime maps for DSP and SRM based on descaling energies above 60kJ/m², impact force/mm and 
validation  up  to  400bar  were  constructed  in  this  work  package  (task  6.1).  For  the  regimes  maps 
designed for DSP it can be concluded that a minimum of 30l/min is required per nozzle in order to be 
able to descale uniformly and even higher flow-pressure for reaching the descaling energies required for 
very  difficult  grades.  Relations  between  IP  and  SWI  have  been  derived  and  should  be  implemented. 
Overlap is more difficult to predict but for a standoff between 88 and 93mm a correct overlap could be 
created. Validation of the maps was done with testing HPW descaling on UT23 material and Al erosion 
test.  

The  last  phase  of  the  project  was  the  industrial  validation  for  optimum  descaling  (task  6.3),  large 
experiments  trials  including  descaling  and  hot  rolling  with  large  scale  hot  shot  blasting  prototype 
developed by WINOA and CRM were performed at Tata Steel and compared with HPW descaling. The 
idea  was  to  perform  a  large  series  of  controlled  heavy  trials  as  close  as  possible  to  production  to 
compare efficiency of both processes.  
A  standard  wheel  blasting  machine  was  adapted  to  be  able  to  work  with  hot  samples.  On  top  of  the 
blasting cabinet was positioned a blasting wheel to access comparable angles to HPW, the turbine could 
be adjusted in 3 dimensions; the rake angle of the wheel has been custom-made designed and built for 
this application. A blasting wheel of 5.5kW with capacity of 90kg/min in term of flow rate was enough 
to  ensure  a  good  efficiency  and  productivity.  Blasting  speed  and  flow  were  monitored  with  an 
automation system, all the tests were performed under dynamic conditions and the media was reused for 
each sample.  The parameters were the optimum parameters obtained from WP3 and WP5.  

In the first set of trials HPW (pilot descaling rig) was compared to wheel blasting descaling, from visual 
observations  it  can  be  said  that  shot  blasting  seems  a  promising  way  to  water  free  descale  samples. 
From cross section analysis it can be confirmed that HPW descaling for pressure considered 200bar and 
high speed resulted in poor descability as compared to lower system pressure and low speed as already 
discussed in WP2. The  hot  shot  blasting  process  using  WS230  and  60Hz  turbine  speed created  some 
shot  indentation  to  the  steel  surface.  As  cast  surfaces  gave  the  worse  surface  finish  for  the  two 
processes.  

In the second set of trials not only the descaling efficiency of the two processes was compared but also 
the scale evolution was analysed, hot rolling was performed after water and shot blasting descaling. A 
detailed experimental plan was conceived to allow on one single large block to be hot shot blasted then 
flip  by  180°,  craned  to  the  roller table  of the  plate  mill  for  water  descaling  and  then  rolled  in  1 to  3 
passes,  all  within  the  safe  conditions  and  timing  (max  5min).  A  total  of  6  large  blocks  were  rolled 
encompassing UT23, UT12 and rail steel grades. All the large blocks were reheated with dummy bars 
for initial primary scale morphology in the large gas furnace of the plate mill (~6% to 8% excess O2). 
Post  rolling  these  large  blocks  were  either  cooled  in  the  large  argon  box  or  direct  quenched  in  the 
AC_DQ unit. Scale thickness profile was determined with Elcometer probe 455. After test samples for 
microscopic analysis were taken.  
The Elcometer results show that for UT12 scale thickness maps are fairly uniform with average rolled 
residual scale below 20µm after one rolling pass. For UT23 and rail steel higher remaining scale and 

12 
 
 
 
 
 
 
 
non-uniform  surface  state  is  found.  The  results  of  cross  section  and  SEM  show  that  regions  of  good 
descalability are regions of minimal internal oxidation and entanglement especially for electrical steels 
UT23.  Irrespectively  of  turbine  set-up,  the  scale  profile  seems  to  have  a  smoother  and  less  wavy 
interface when shot blasting except in areas where scale remains. In conclusions it can be said that the 
water based and water free descaling tried during the pilot industrial trials show a similar efficiency in 
terms  of  primary  scale  removal.  Similar  amount  of  scale  remaining  and  similar  morphology  of  scale 
after both processes is visible.  

The  last  task  of  this  work  package  (task  6.2)  is  the  up-scaling  and  the  cost  evaluation  for  a  possible 
industrial application of the improved water based descaling and the new water free descaling. Using 
the heavy pilot prototype data and work by WINOA to scale blasting unit to an industrial unit for use at 
two extreme plants and production (SRM rod mill 283 bloom and heavy plate mill Scunthorpe on slab) 
the calculations could be summarised in the following tables:  

Pilot data 
Industrial wheel blasting pilot 
parameters 
Impact 
Width 
m 

Speed 
m/s 

Turbine 
kW 

Initial situation 

Industrial need 

SRM bloom 

Primary descaling 

Secondary 
descaling 

HPM slab 

0.08-0.12 

0.6 -1 

1 x 5.5 

Size mm 

Flow 
=90kg/mi
n 

283x230 
Lg 9400 

Speed 
m/s 

0.2 

Size 
mm 
283x2
30 Lg 
9400 

Speed 
m/s 

1 

Size 
mm 
1900 x 
228 Lg 
3600 

Speed m/s 

0.5 

SRM bloom Primary descaling  SRM 

bloom 

secondary 

HPM slab 

Upscale equipment sizing 

Abrasive 
Flow  
Kg/min 
260 

# turbines 

descaling 
Abrasive  Flow 
Kg/min 

# turbines 

Abrasive  Flow 
Kg/min 

# turbines 

2 X 11kW 
or 4 X 5.5kW 

1300 

4 X 22kW  
or 8X11kW 

2400 

4 X 37kW 
or 6 X 30kW  
or 8 X 18.5kW 

Table 1 Up-scaling blasting descaling for industrial application 

The abrasive is recovered at the bottom of the cabinet, the media is recyclable hundreds of times, it is 
calculated  that  only  a  small  portion  of  the  abrasive  will  break  upon  each  impact,  it  is  measured  that 
450g are broken/eliminated per ton of abrasive projected.  

The  cost  estimation  considers  cost  of  energy,  water  and  shot,  type  of  product  for  full  descaling 
coverage, variable line speed, pump type and power and descaling time. It also accounts for wear rate of 
nozzle  via  an  increase  of  the  coefficient  of  discharge  CD.    It  however  simplifies  cost  for  water 
discharge, any water treatments, accumulators (case of plate mill), maintenance and operator cost, etc. 
The investment cost is not included, but the value is similar for both systems.   

Electricity rate (0.065 £/kWh or 0.076 €/kWh) was rather low. This is due to increase in the next years 
and  impacts  a  lot  more  the  HPW,  less  the  HSB.  Cost  is  based  on  24/7,  47w/year  running  for  water 
descaling the calculations are based on 8064h/year and for blasting only when needed by the process. 
Standby energy is estimated at 30% of running energy.  

Results show a higher annual cost for HPW compared to HSB.  All neglected costs are known to be 
higher with HPW than for shot blasting. Both cost calculations are based on the test done during this 
project, it is an estimation and not all the industrial values and conditions are taken into account, more 
test should be done to have a more real estimated cost. 

13 
 
 
 
 
 
Plant 

SRM secondary 
SRM secondary 
SRM primary 
SRM primary 
HPM slab 
HPM slab 

Feed frequency 
(s) 
20 
30 
20 
30 
360 
180 

HPW total annual cost 

48 707 € 
48 429 € 
75 716 € 
73 437 € 
294 293 € 
296 617 € 

Wheel blasting cost 
calculated 
39 321 € 
37 330 € 
28 529 € 
26 716 € 
40 800 € 
44 641 € 

Table 2 Economical calculations comparing HPW and blasting descaling for three plants 

14 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
2.  SCIENTIFIC AND TECHNICAL DESCRIPTION OF THE RESULTS 

2.1.  WP1: Envelope of current Industrial Conditions and Material Preparation 

The  objective  of  WP1  was  to  select  and  acquire  production  range  of  steel  grades  under investigation 
(especially  high  alloyed  steels  (Si,  Cr)),  and  the  envelope  of  processing  laboratory  conditions  in  line 
with industrial reheating and primary descaling applications. 

2.1.1.  Task 1.1 Steel Compositions  

The  project  has  focused  on  primarily  rail  grades  for  SRSM  rail  mill  Scunthorpe  and  electrical  steels 
from the Direct Sheet Plant (DSP) at Ijmuiden. The matrix was enlarged with valve spring steels from 
Scunthorpe Rod Mill (SRM), LFCS from Thrybergh combination Mill (TCM) and Laboratory cast from 
CRM based on compositional variants of rail and DSP electrical steels, studying primarily influence of 
Si and Al. 

Table 3 Chemical composition of Industrial steels and laboratory cast melts 

2.1.2.  Task 1.2 Envelope of HPW descaling processing conditions 

2.1.2.1. HPW descaling theory 

HPW descaling [see 33-90] can be best described as the process of removing oxide scale by spraying 
the  hot  steel  surface  under  a  range  of  moderate  to  high  pressure  using  stationary  (usually  flat  jet 
nozzles)  or  rotary  (rotor  descaler)  systems  under  a  given  feedstock  travelling  speed.    The  aim  is  to 
ideally  remove  loose  to  sticky  primary  to  tertiary  scale  under  optimum  impingement  and  surface 
chilling as well as power-water flow rate consumption, for improving surface quality and minimising 
roll  wear.  Complex  solid-fluid  thermal-mechanical  mechanisms  are  acting  through  the  scale,  scale 
interface and sub-surface of the steel substrate depending on the descaling process parameters imposed 
and  the  scale  morphology.  Now,  although  much  progress  has  been  made  to  enhance  the  range  of 
pressure-flow,  develop  better  nozzle  tips  (reduced  wear,  less  turbulence/straight  jet,  etc),  many 
unknowns still exist regarding the way specific mechanisms acting on the scale in combination/isolation 
could be used to target key oxide scale morphologies, especially in the presence of Si, Al and Cr.  

15 
 
 
 
 
 
2.1.2.2. HPW descaling components 

Main descaling components are: 

•  Type of descaler (e.g. stationary, rotary) which dictates the regime of flow-pressure-stand-off as 
well  as  additional  mechanisms  acting  at  steel  surface  (multi-shear).  Figure  2  illustrates  a 
comparison between stationary and rotary descaling. 

•  Header,  nozzle  and  filter  types  (e.g.  number,  spray  geometry  characteristics,  static  flat  jet 

versus pulsating nozzle, short and long filters, etc.) 

•  Water  delivery  systems  (pumps,  accumulator,  recirculation (D T))  and  water  quality  regarding 
pressure-flow  rate  capacity  and  temporal  variation,  maximum  system  pressure  from  relief 
valve, etc. 

•  Utilisation (single pass, double descaling), etc.  
•  Additional system components such as effect of roller table, pinch roll unit, etc. should also be 
considered  in  the  analysis  of  the  variability  of  the  system  operational  conditions  in  terms  of 
wear affecting stand-off or centrality of product. 

Figure 2 Comparison static versus rotary descaling 

2.1.2.3. HPW descaling parameters and concepts 

Descalability of steel surface [24,33,76-78,85] is intrinsically linked:  
Mechanical impact (normal/shear). Speed through descaler (i.e. time under spray but also before/after). 
Thermal  effect  prior/during  and  after  descaler.  Scale  morphology,  type  and  steel/metal  interface  and 
steel  sub-surface  (profile,  local  composition  (oxide,  fayalite),  entanglement,  oxidation,  flaws, 
decarburisation, etc.) 

Mechanical  impact,  speed  through  descaler  and  thermal  effect  are  intrinsically  linked  to  pump-flow 
characteristics and constraint (flow, pressure, coverage, etc.), nozzle/filter type and throughput/pacing 
and constraint through the mill depending on mill configuration, etc. 

Descalability of a steel surface depending on the length scale adopted can have various definitions. At 
macro level or plant level, can be defined as x% visual residual scale post descaling, at laboratory level 
as  minimum  average  residual  scale  thickness  which  has  been  one  of  the  approach  taken  to  assess 
efficiency  and  uniformity  of  both  HPW  descaling  and  hot  shot  blasting  but  depending  on  method  of 
characterisation could be further refined to consider for instance the geometrical, morphological state of 
the steel/metal surface interface, etc. 

However it is generally adopted that HPW descalability is intrinsically linked to four concepts: 

16 
 
 
 
 
 
1.  Impact force [N] and Impact Pressure (IP) [MPa] defined as the force of water (or indeed 

other fluid) over the impingement area.  

2.  Specific  Water  Impingement  (SWI)  (l/m2)  defined  as  the  area  of  the  feedstock  covered  in 

terms of volume of water per unit area.  

Adoption  and  combination  of concepts  1  and  2 lead  to  IP  –  SWI.  Usually  combining  both  IP  and 
SWI  gives  descalability  limits  with  complete  descaling  falling  above  the  limits  sets  by  plotting  IP 
function  of  SWI.  These  limit  lines  have  negative  slope  and  are  often  non-linear,  showing  inverse 
relationships between IP and SWI. These graphs have up to now been acquired within Tata Steel Figure 
3.  All  points  below  line  are  not  deemed  safe  but  approach  is  dependent  on  scale  conditioning  and 
morphology. 

Figure 3 Example of SWI function of IP for a SI-steel 

3.  Descaling energy as by product of Impact force and Specific Water impingement in (kJ/m2).  

4.  Coverage  in  terms  of  spray  width  (mm),  overlap  (mm)  and  wash  (mm)  describing 
geometrically  how  sprays  interact  between  pair  of  nozzles  with  respect  to  the  lead  and 
associated secondary nozzle.  

These concepts are important as providing a link for cross benchmarking with the water free shot 
blasting process (see Task 5.2). 
It should be noted that concepts 1, 2 and 3 are not independent as sharing flow rate and spray width 
as  main  input  variables,  but  are  established  concepts  describing  impact  force  from  the  water 
flow/droplet size and effect of cooling and time under the spray via the SWI quantity. Except for 
descaling  conditions  involving  very  high  pressure  where  a  step  change  in  flow  reduction  can  be 
achieved  (via  operating  at  reduced  stand-off),  in  the  current  range  of  industrial  descaling  conditions 
(100-300bar) and installation set-up (so called “conventional stationary descaler”), an optimum water 
impingement is required up to saturation to provide required descaling energy for a given range of steel 
grade and scale morphology.  

Other  concepts  have  been  derived  (see  Modelling  Task  2.7),  together  with  analytical  calculation  of 
many  other  quantities  such  as  water  evaporation  energy,  thermal  and  mechanical  stresses,  strain  for 
fracture, etc.  

These four concepts can be further decomposed as shown in Table 4 and Appendix 1.  

HPW descalability  
concepts 

Main  
Dependencies 

Secondary  
dependencies 

Main independent 
variable 

Impact 

1. 
(conventional) 
definition 1  

force 

Fi

.rrr r=

VfCvQ

.

.

1.1  fluid  density  r  (generally 
water at given temperature) 
1.2 flow rate Q 
1.3 Fluid velocity Vf  
Vf

.2.=
C

.
SPg

1.3.1 system pressure SP 

fluid density 

flow rate Q 
Flow rate Q f (nozzle 
type/orifice) 

17 
 
 
 
 
 
 
 
 
 
 
 
 
force 
Impact 
1’ 
(accounting for nozzle 
spray 
angle) 
definition 2 
Fi =

SPg
.

.2.

)2/

.2

Q

.

aaa a
sin(
aaa a

1´. Mean Impact 
pressure  
definition 1  
IP =1

Fi
A

For maximum impact 
pressure 
IPmax=IP1*2 

1’. Mean Impact 
pressure  
definition 2   

1´. Impact pressure 
 definition 3 

IP =
2

SPK
.(

)

5.0

Q
.
.

cos(

)

bbb b

2

(

xH
.)

aaa a
tan(

2

)

Leading to (main 
equation)  
bbb b
CDK
Q
.
.
cos(
aaa a
tan(
xH
)2/
.

5.0

2

IP =
2

2. Specific Water 
Impingement 

SWI

=

Q
BV
.

.60

gravitational 

With  C:  Flow  rate  coefficient 
(0.85) 
g: 
9.8m/s2 
1.4 
atmospheric 
deceleration coefficient  Cv 
Same as above 

constant 

velocity 

1.4.1 standoff distance H 

stand-off H 

spray angle a

2.1 impact Force Fi see 1 

See above 

spray angle a

See above 

2.2 impact Area 

2.2.1 spray width B 

B =

.2

H

.

aaa a
tan(

).2/

1
bbb b
cos(

)

2.2.2 spray thickness d 
1
bbb b
cos(

fff f
tan(

d =

).2/

H

.2

.

stand-off H 
spray angle a
rake angle b
standoff H 
Spray thickness angle f
(nozzle type, can be 
estimated via nozzle 
orifice diameter see 
Section A2.6) 
Rake angle b

)

2.1  coefficient  of  discharge 
nozzle CD 

Flow rate-system pressure 

flow rate Q 

2.2 flow rate Q 

2.3 rake angle b

)2/

2.4 stand-off H 

2.5 nozzle spray angle a

3.1 flow rate Q 

3.2  feedstock  velocity  through 
jet 

3.3 spray width 
B =

aaa a
tan(

).2/

H

.2

.

1
bbb b
cos(

)

stand off H 
spray angle a
rake angle b

3. Descaling Energy E 
E=IP(1 or 2)* SWI 

See above 

4. Coverage 

spray width 

Overlap D  

D = C-E   
with C = cosg. g. 
Wash 

g. g.  B             

stand off H 
spray angle a
rake angle b
spray width B 
Offset or twist angle g
Nozzle pitch E 

g  

Mainly via measurement 

Table 4 Dependencies of main HPW descaling 

flow rate Q 

rake angle b

stand-off H 

spray angle a

 (nozzle 

type) 

Flow rate Q 

Velocity V 

stand off H 
spray angle a
rake angle b

See above 
g  
twist angle g
Nozzle pitch E 

18 
 
 
 
 
 
 
 
 
 
a
a
a
 
 
a
a
a
 
 
 
 
 
 
 
 
 
 
a
a
a
 
b
b
b
 
 
 
b
b
b
 
 
 
 
 
 
 
 
 
b
b
b
 
 
b
b
b
 
 
a
a
a
 
 
a
a
a
 
 
 
 
 
a
a
a
 
a
a
a
 
b
b
b
 
b
b
b
 
 
 
 
a
a
a
 
b
b
b
 
 
 
g
g
g
g
 
Other definitions for Impact force/Pressure do exist such as the one used by Everloy considering system 
pressure, flow rate, diameter and speed of water droplet.  

From Table 4 it can be observed that the main independent variables come from: 
•  The nozzle geometry (spray angle in both width and thickness) 
•  The nozzle set-up relative to each other in terms of twist, rake and pitch on the header/ring 
•  The standoff distance  
•  The flow rate  
•  The product speed of travel.  
Nozzles are of flat jet geometry and are characterised by four angles which are independent but who 
will interact when located on header to influence the distribution of the standoff distance, the degree of 
overlap and spray destruction or wash. These are (see Figure 4): 
•  Spray angle a
•  Spray thickness (or depth) angle f f f  f 

 (parallel to direction of rolling DR) (generally between 1.5 
and  3o,  but  value  often  not  quoted  by  manufacturer  despite  its  criticality).  This  angle  can  be 
calculated from nozzle orifice and system pressure 

a (acting in cross width direction to DR) (generally between 15-45 o) 

g  (deviation from cross width direction) (generally 15°) 
b (inclination from DR, usually between 0 and 15o, max 30o) 

•  Nozzle offset angle g
•  Lead or rake angle b
From the knowledge of these angles and spatial location of the nozzles, key important characteristics of 
the spray can be deduced (Figure 4): 
•  The spray width B  
•  The spray width C  at 90o to the DR (cross width) 
•  The overlap distance D at 90o to the DR  
• 
• 
These are deduced from the two independent parameters: 

Spray length A 
Spray thickness assuming knowledge of spray thickness (or depth) angle 

•  Nozzle standoff distance H 
•  The nozzle pitch E 

Good descalability usually requires:  

•  A  good  overlap  defined  at  8  to  15%  of  spray  width.  The  overlap  should  compensate  for  any 

pressure drop at end of spray width.  

•  A rectangular spray width or at least minimising deflecting type spray pattern. The spray should 

be as even as possible  

•  A small spray thickness, therefore a small spray thickness or depth angle 
•  An  efficient  spray  angle  ideally  ~max  30o,  however  it  is  recognised  that  nozzle  section  will 
have to depend on installation and constraints (i.e. total flow rate versus coverage and standoff) 
and that stationary descaler units are usually compromised in terms of set-up  

•  A relatively small standoff distance to ensure perfect laminar flow and maximum impact 

(a) typical flat jet high pressure spray form 

(b)  schematic  of  spray  thickness  (or  depth)  and  width  with 
Al imprints  

19a
a
g
g
b
b
 
 
(c)  set-up  definition  with  all  major  angles  (except 
depth or thickness angle) 

(d)  cross  sectional  view  of  imprint  and  interaction 
based on pitch and 3 main angles 

(e) typical Al erosion two nozzle imprints with offset angle of 15o and plan view shape of nozzle tip/orifice 

(f) Schematic nozzle imprint with overlap 

(g) Overview of overlap and wash on Al erosion plate. 
Note  flat  spray  width  is  not  perfectly  even  (i.e. 
rectangular) 

Figure 4 Flat jet spray nozzle characteristics and significant parameters affecting descalability in 
stationary descaling rigs (DR: Rolling Direction) 

2.1.2.4. HPW descaling Approach 

The  project  has  developed  an  approach  based  on  key  independent  and  dependent  parameters  which 
characterise  the  process  and  its  variability,  as  well  as  the  efficiency  of  descaling  under  known  well 
established theories such as that of Impact Pressure (IP) - specific water impingement (SWI) curves and 
descaling energies. 

This approach is the basis of a Design of Experiment (DoE) to determine most significant independent 
factors and their interaction on descalability criteria which is the object of task 2.6 and 2.7.  

An  initial  list  (see  Table  5  and  Table  6)  of  output  and  input  parameters  is  presented  below  some  of 
which independent, dependent and others variables exploiting further the concept presented in Table 4.  
It can be observed that this list is extensive and complex mostly when variability is accounted for.  

20 
 
 
 
 
 
 
 
 
 
 
Descalability output parameters 
Impact force 
Impact pressure 
Impact energy or work 
Spray width 
Spray depth 
Spray impact area (inc. profile) 
Temperature losses (HTC, uniformity, recalescence, etc) 
Descalability (% residual scale, surface state (roughness, remant scale, cracking)) 

Table 5 Descalability output parameters 

Nozzle 

Pitch 
Spray angle 

Transverse or depth 
angle 
Offset angle 
Lead angle 
Type 
Overlap 
Wash 
Nozzle flow rate 
Stand off 

Independent 
Quasi-independent but from factor required and will be function of flow rate. 
Spray angle will change as wear rate increases 
Quasi – independent (function of flow rate) not published by nozzle 
manufacturer 
Independent 
Independent 
Independent 
Dependent f(pitch, spray width, offset angle) 
Dependent f(nozzle, wear, overlap, etc) 
Dependent on pressure 
Dependent on roller table height and product dimensions 

Short 
Long  

Filter (reduced turbulence, increase IP) 

Independent  
Independent 

Descaling process 

Speed (fixed/varied) 
Flow rate 
System pressure 
Single/double descaling 
Bloom/billet guiding 

Time to descaler 
Furnace atmosphere exhaust 
composition 
Cold/hot changing 
Heating rate and profile 
Heating and soaking time 
Furnace temperature 
Furnace pressure 
Furnace type 
Furnace control delta T 
Position in furnace 
Prior billet cooling 

Size and section (wxh) 
Composition inc. alloy (Si, Al, Cr, 
Ni, C, etc) 

Descarburisation (Y/ N) 

Strength / plasticity 

Independent  
Independent but dependent on pump 
Independent  
Independent 
Independent  

Prior descaling process 

Dependent f(speed) 
Independent 

Independent 
Independent 
Independent 
Independent 
Independent 
Independent 
Independent 
Dependent on throughput, mix, etc 
Dependent on oxide scale thickness, type, plasticity, cooling 
media, pacing (i.e. velocity) 

Product 

Independent 
Independent scale thickness, type and morphology but 
dependent on process conditions, time, temperature and 
atmosphere 
Dependent on time, temperature, atmosphere and composition 
(e.g. descarb thickness and properties) 
Dependent on temperature and composition 

21 
Temperature 
Head to tail temperature variation 
Skid mark / temperature variation 
Residual stress/stress state oxide 
and interface (thermal and growth 
stress of oxide) 
Grain size / type 
Coating (Y/N) 
EAF/BOS (Cu/Sn residual) 
Cast surface (Y/N) 
As-cast scale inc. mould powder 
Scale plasticity 
Scale porosity 
Scale morphology and type 

Dependent  
Dependent 
Dependent 
Dependent 

Dependent 
Independent 
Independent 
Independent 
Dependent 
Dependent 
Dependent 
Dependent 

Table 6 HPW descaling input parameters (controlled) 

Uncontrolled input parameters / variability 

Steel composition 
Stock size 
Mill/furnace pacing (delays) 
Wear (roller table, etc.) 
Descaling set-up (nozzle orientation) 
Furnace atmosphere (CV, gas) 
As-cast process (speed, secondary cooling, etc.) 
Wear nozzle 
Header alignment 
Nozzle orientation 
Nozzle blockage 
Flow-pressure variation 

Affects scale type/morphology/plasticity, etc. 
Affects stand, thermal capacity, guiding, etc. 
Affect temperature, scale, etc. 
Affects standoff 
Affects overlap, etc. 
Affects scale type / morphology / plasticity etc. 
Affects as-cast scale prior reheating 
Affects IP, wash, pressure drop, etc. 
Affects wash, overlap, etc. 
Affects wash, overlap, etc. 
Affect descalability, cooling 
Affects IP and descalability 

Table 7 HPW descaling input parameters (uncontrolled) 

This analysis has been enlarged to a certain extent with the characterisation of the oxide scale state and 
its  variability  prior  descaling  which  is  dependent  on  grade  composition  and  furnace/post-descaling 
conditions.  

2.1.2.5. Mapping of HPW descaling conditions 

Table  8  summarises  envelope  in  terms  of  min/max  reheating  and  descaling  conditions.  Prior  primary 
descaling, the reheating furnace conditions are critical in terms of conditioning the primary oxide scale 
and  oxide/metal  interface  with  average  resident  time,  max  heating  rate/surface  temperature, 
soaking/discharge  temperature  and  oxidising  atmosphere  being  most  critical  input  factors.  These  are 
also detailed here. 

-  Mixed Enriched Gas (MEG) 

a.  Typical combustion product composition 

Reheating 

Mill 

SRSM 
(rail 
mill) 

22 
 
 
 
 
5 to 50% excess air translating to 1 to 5% excess O2 

- 
-  Water vapour (5 to 17%) 
- 

200mins resident time (max 300mins) (Fig.b) 

b.  Typical reheating curve SRSM (rail) 

Primary Descaling 

3 x Inoxihp pumps each rated at 497litre/min at 250 bars. 

standoff distances ranging from 75mm to 125 mm 
pitch between 61 to 71mm 
rake or lead angle set at 10°  
nozzle twist angle set to 15° 

- 
-  maximum pressure of 206 bars (max flow rate 64.6l/min per nozzle) 
- 
- 
- 
- 
-  Lechler scalemaster 642/682 type (30 and 40 spray angle). Total No nozzles 24 
typical temperature at entry descaler are 950-9600C (scale) to 1120-1140oC with 
- 
bulk remaining at 1180-1200oC 
typical speed max 1m/s 
bloom type 355x305 

- 
- 

Assuming  centrality  envelope  of  processing  conditions    the  following  envelope  can  be 
determined 
IP(MPa) [0.67-1.18] @206bar 
Spray width(mm)  [68-82] 
Spray depth max(mm) 5 
Overlap ~10-13% 
Impact force (N)  [178-223] 
SWI (l/m2) [13-15.8] @ 1m/s  
Descaling energy(kJ/m2) [11-19] 

Reheating 

-  Mixed Enriched Gas (MEG): 5 to 10% air translating to 1 – 1.5% oxygen 
-  Water vapour (6 to 14%) 
- 

120mins average resident time (Fig.e) 

SRM 
(rod 
mill) 

c. 

typical reheating curve SRM (rod) 

23 
 
 
 
 
 
 
 
 
 
 
Primary Descaling 

3 x Inoxihp pumps each rated at 497litre/min at 250 bars. 

- 
-  maximum pressure of 206 bars (max flow rate 21.53l/min per nozzle), min 

pressure 110bar 
standoff distances ranging from 85mm to 160 mm 
pitch 55mm 
rake or lead angle set at 15°  
nozzle twist angle set to 15° 

- 
- 
- 
- 
-  Lechler scalemaster 694 type (30 spray angle)- total No of nozzles 18 
- 
- 

entry speed max 1m/s reducing to max 0.2m/s 
bloom type 283x230, billet 180x180 

Assuming  centrality  envelope  of  processing  conditions    the  following  envelope  can  be 
determined: 
Bloom: 
@206bar                                                                          @110bar 
IP(MPa) [0.4]                                                                    [0.2] 
Flow rate(l/min) [21.53]                                                     [15.73] 
Standoff(mm) [100,110] 
Spray width(mm)  [70-74]                                                [68-73] 
Spray depth max(mm) [3.5]                                             [3.7] 
Overlap ~17-23% 
Impact force (N)  [73]                                                       [39] 
Fluid velocity(m/s) [124, 172] 
SWI (l/m2) [5] @ 1m/s @0.2m/s [25]                               [4,18] 
Descaling energy(kJ/m2) [2-10]                                       [0.7-4] 
If not central  
@206bar                                                                          @110bar 
Side Standoff [85,132]  
IP(MPa) side [0.28,0.49]                                                   [0.15, 0.26] 
Spray width(mm) [61,87]                                                  [60,84] 
Spray depth  3-4.4mm                                                      [3.3,4.6] 
SWI (l/m2)  
[4,5.8] @1m/s                                                                   [3,4] @1m/s                                   
[20.6,29]@0.2m/s                                                              [15.6,22] @0.2m/s 
Descaling energy(kJ/m2)  
[1.15,2.8]@1m/s                                                               [0.4,1.1]@1m/s  
[5.7,14]@0.2m/s                                                               [2.3,5.7]@0.2m/s   

Billet 
@206bar                                                                             @110bar 
Standoff(mm) [100-160] 
IP(MPa) [0.2,0.4]                                                               [0.1, 0.2] 
Spray width(mm)  [70,101]                                                [68,98] 
Spray depth max(mm) [3.5,5]                                               
Overlap ~40% 
Impact force (N)  [72,73]                                                    [39] 
SWI (l/m2)  
[3.5,5]@ 1m/s                                                                    [2.7,3.8]@1m/s 
[18,25]@ 0.2m/s                                                                [13,19]@0.2m/s  
Descaling energy(kJ/m2)  
[0.7,2]@1m/s                                                                     [0.2,0.8] @1m/s 
[3.5,10]@0.2m/s                                                                [1.3,3.9]@0.2m/s 

If not central , reducing values of IP, SWI and descaling energy by 1% 

24 
 
 
 
Reheating 

The  Direct  Sheet  Plant  in  Ijmuiden,  the  Netherlands,  is  an  integrated  casting  and  strip 
rolling  plant.  (Fig.d).  On  exit  from  the  casting  mould  the  scale  starts  to  form  on  slab 
surface is in contact with oxidizing agents, it can be assumed that the scale starts to form 
from the exit of the mould. At this point, the steel surface is already in solid state and it is 
being continuously cooled by a series of water nozzles. 

d.  schematic of DSP and RSB scale breaker 

Temperature entry furnace is on average 950oC increasing to 1150oC average exit tunnel 
furnace. Atmosphere conditions are to be assumed as follows: 
2%free oxygen, 18% water vapour and 9%CO2 based on natural gas. In reality the 
thin  slab  is  submitted  to  very  high  humidity  level  during  secondary  cooling  and  at 
end of cooling prior to entering the tunnel furnace. 

Primary Descaling (RSB) 

DSP 
RSB 
descaler 

The RSB1 descaling headers are located adjacent to the tunnel furnace exit and operates at 
maximum of 400 bars giving 2520l/min but on average is set-up to work at 280 bar system 
pressure.  The  nozzles  (x35)  located  on  the  descaling  headers  are  set  at  rake  angles  and 
twist  angles  of  15°  using  Everloy  DNM0325  nozzles  with  long  filters  (nominal  spray 
angle 30o). The slab speed through the descaling jets varies from 0.13 to 0.4 m/s. The total 
width coverage from the spray jets is 1684 mm (Fig. e). 

e. 

 typical RSB top descaler set-up at standoff of 93mm 

The following parameters have been used to map the envelope of processing conditions 
Standoff 80 to 100mm 
System pressure from 160 to 320bars 
Pitch 48mm 
Offset and lead angle 15o  

Giving the range of: 
IP(MPa) [0.7-2] based on system pressure of 160 to 320bar 
Spray width(mm)  [44-56] 
Spray depth max(mm) 3-4 
Overlap ~ -12 to 10% 
Impact force (N)  [67-130] 
Fluid velocity (m/s)  [152-212] 
SWI (l/m2) [18-40] between 0.13 and 0.4 m/s @160bar 
SWI (l/m2) [24-40] between 0.13 and 0.4 m/s @280bar 
SWI (l/m2) [26-40] between 0.13 and 0.4 m/s @320bar 

25 
 
Descaling energy(kJ/m2) [15-33] between 0.13 and 0.4 m/s @160bar @ 93mm 
Descaling energy(kJ/m2) [34-57] between 0.13 and 0.4 m/s @280bar @ 93mm 
Descaling energy(kJ/m2) [42-65] between 0.13 and 0.4 m/s @320bar @ 93mm 

@min standoff 80mm, descaling energy at 320bar pressure can rise to 85kJ/m2 @0.13m/s 

Table 8 Summary of envelope of processing conditions 

In summary, IP from all three primary descalers vary from 0.1 to 2MPa, SWI from 3 to 40 l/m2 (value 
assumed to be taken as saturation value) and descaling energy from 0.2 to 85kJ/m2. Fluid velocity and 
impact force vary from 120 to 212m/s and 67 to 223N respectively.  

2.1.3.  Task 1.3 industrial oxide scale characterisation  

The  idea  behind  this  task  is  to  be  able  to  characterise  the  range  of  primary  scale  morphologies  prior 
descaling within the operating window of the three reheat furnaces of interest (MSM, SRM and tunnel 
DSP  furnace).  Some  effort  has  been spent in trying  to  acquire bloom  reheat  diverts  with  reheat scale 
preserved but this has proven to be difficult and prone to scale spallation/detachment,  

Therefore, it was decided to run a series of Thermogravimetric Analyses, TGA in short, using extreme 
conditions  of  production  reheat  exhaust  gas  composition  (low,  mid,  high).  The  aim  is  to  provide 
oxidation rate curve but mostly scale morphologies to be used as benchmark samples for the HPW and 
shot  blasting  descaling  lab  tests  which  should  encapsulate  the  extreme  range  of  reheat  conditions 
encountered in production, although influence of delays (time, temperature) should also be studied in 
more detail.  

•  TGA analysis 

The  STC  Thermobalance  comprises  a  vertical  tube  furnace  (55mm  bore)  with  a  maximum  operating 
temperature  of  1500oC.  A  sample  is  suspended  by  a  platinum-rhodium  wire  from  an  electronic 
microbalance that detects weight changes during the gravimetric oxidation test.  

Two  different finishes  were  studied, as-cast  and  ground  (usually  standard  applied  for TGA  analysis). 
On this basis and taking into account atmosphere described in Table 8a. the range of production steel 
grades of interest were studied. The main results are summarised here below: 

Si 
Surface 
state 

Prior 
TGA 
test 

TGA 
test  

Results 

0.27%  
Pre-machined to blocks 
As-cast and MC (Machined/ground) 
As-cast oxide and level of decarburation:  
as-cast  oxide  scale  (prior  reheat)  is  non-uniform  of  average  thickness  of  142  microns  and 
already  fairly  porous  with  spallation  and  through  thickness  cracks.  Some  level  of 
decarburisation is also evident along the sample faces. 

5%, 15% and 20% and 45% excess air for CMEG and AMEG gas 

The time-temperature profile of 1220oC, no large differences in oxidation rate (between 0.1 and 
0.11 g/cm2) exist from the extreme change of furnace atmosphere and surface state (as-cast v 
machined/ground).   

The  as-cast  finish  simply  slightly  retards/slows  down  oxidation  rate.  Gas  composition  has  a 
larger  influence  on  kinetics  with  CMEG  increasing  oxidation  rate  mostly  at  lower  level  of 
excess air. At 45% excess air, oxidation rate is fairly similar between the two enriched mixed 
gas compositions.  This is due to the increased moisture content of the CEMG gas as compared 
to AMEG. Reheating temperature, especially soaking has a large influence on oxidation mostly 
above 1220oC. Using a simple linear conversion between weight gain and scale thickness for 1g 
oxide  gain/cm2  equivalent  to  7230  microns  of  scale  thickness,  a  total  scale  thickness  can  be 
computed to around 870 microns [3]. Morphologies of oxidised rail production show the three 
‘conventional’  scale  layers  with  most  of  the  spallation,  in  view  of  the  highC  composition, 
occurring in the Wustite (FeO). Because the reheat temperature was above 1177oC, the Fayalite 

26 
 
 
eutectic  temperature  (FeO-Fe2SiO4)  (case  without  presence  of  Al),  fayalite  forms  as  nodules 
and  fingers  entangled  within  the  scale-metal  decarburised  interface.  Iron  sulphide  is  also 
formed within the steel substrate at the oxide scale interface owing to atmosphere considered 
The  scale is  highly  porous  and delaminated  which  will  have  had the  consequence  of limiting 
further  oxidation,  hence  the  limited  differences  in  oxidation  kinetics  at  a  given  temperature 
function of atmosphere. The outer layer will be easily descaled but consideration of influence of 
interface  properties  brought  about  by  decarburised  layer  and  fayalite  needs  to  be  considered. 
Assessment of scale thickness shows an average scale layer of 970microns, not too dissimilar to 
the one predicted by converting weight gain to scale thickness 
Decarburisation was also measured and appears larger at corner.  

Table 9 TGA Analysis:  Rail steel (298Q) – QA code B9S34 (Table 3) 

Si 
TGA test  

1.23%  
5% and 45% excess air for CMEG gas, whit high water vapour 
Increasing  the  Si  content  changes  drastically  the  oxidation  rate/kinetics  for  the 
temperature-time profile used (representing MSM). Large deviation in kinetics occurs 
with  the  larger  excess  oxygen  content  of  the  CMEG45  waste  gas  composition  as 
shown  in  Figure  5.  The  graph  also  includes  additional  data  of  oxidation  curves  at 
different temperature. Total weight gain went up by 60%. 

Results 
TGA Test 

SEM/EDA results 

Figure 5 CRM Lab cast – Effect of Si (%weight 1.23 versus 0.23) content on rail steel 
oxidation 
Complex  oxides,  large  nodules/rosette  clusters  (Fe,  Si  and  interface  (Fe2SiO4)  are 
formed  together  with  internal  scale  spallation.  Major  cracking  through  FeO  and 
magnetite is also present 

a)  2217 (5%) CMEG TGA                 b) 2217 (45%) CMEG TGA 

Figure 6 SEM/EPA analysis CRM lab cast rail steel variant 2217 (a) 5% CMEG TGA 
analysis (b) 45% CMEG TGA analysis 

Table 10 TGA analysis: Modified CRM Rail steel (2217) (Table 3) 

27 
 
 
 
 
 
Steel  

Si content 5.9% - C content 0.04%  
Al content 2.13% - C content 0.04% 
Compared to production grade UT23 B9S38 2.3%Si and 0.4%Al 
1120°C and 1150°C (isothermal) 

Temperature 
representative of the 
DSP tunnel furnace 
Atmosphere furnace  Natural gas 2% excess oxygen, 18% water vapour, 9% CO2 and balance N2 

Results  

Aluminium  has  a  drastic  effect  on  oxidation  rate  mostly  at  the  highest 
temperature.  This  is  to  be  associated  with  also  the  Si  content.  Al  should  be 
enriched  at  the  scale/metal  interface  reducing  the  metal/scale  adherence  and 
inducing  scale  spallation.  It  also  in  combination  with  Si  reduces  the  eutectic 
Fayalite  temperature  to  below  1177oC  (~1150oC)  therefore  increasing  liquid 
oxides penetration. 

Table 11 TGA Analysis:  Modified DSP electrical steel composition (Table 3) 

Waste gas 
composition 
Reheating 
temperature 

Results 

H2O % wet 17.19  and O2 %wet 1.74 -%dry 2.10 

1200°C 

Scale thickness experimentally is ~ 1450microns. This is not too different to the predicted 
oxidation thickness.  

Table 12 TGA Analysis:  LFCS 209/1 (Table 3) 

State material  Bloom divert, following production reheat from SRM 
Surface state 
TGA test 
with mixed 
gas 

as-cast 
Central MEG or Anchor MEG with min 5% excess air aimed giving CO2 between 12.5 
and 28 and H2O between 6 and 17% for excess O2 level of 0.9 to 1.5%. 

Results 

Decarburisation is seen at steel sub-surface on the as-cast reheat surface. 
Oxidation is greater than production rail steel and similar to 2217 CRM rail lab cast with 
CMEG mix 5% excess air. 

Table 13 TGA Analysis:  VS56 SRM (B9S33)  (Table 3) 

28 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
2.2.  WP2: Water-based descaling process 

The ability to carry out WP2 resides on the technical capability and range of processing conditions of 
the HPW descaling pilot rig. To achieve this, the STC descaler had to be revamped with a range of new 
base  equipment  (headers,  etc.)  and  ancillary  facilities.    The  HPW  descaling  rig  consists  of  a 
reciprocating  piston  three-plunger  pump,  a  new  twin  nozzle  descaling  header  with  full  adjustment 
(stand-off via LVDT, micrometric pitch, rake and twist), a stock carriage with variable imposed speed 
(from  0.1  to  4m/s)  and  a  sump.  The  45kW  pump  set-up  with  current  35mm  plunger  is  capable  at 
delivering ~86l/min max which depending on nozzle geometry will give a maximum system pressure of 
500bar. At this flow, ~ 2mins of HPW descaling time is possible.  

Specific attention has been spent in the control of the furnace atmosphere in terms of excess Oxygen 
function of reheating/oxidation together with detailed assessment of ramp rate of the furnace. Reheating 
can be carried out in air or atmosphere from stoichiometric combustion products of natural gas and air 
giving ~ 9%CO2, 17%H2O at 2% Excess O2 or 10% excess air.  

2.2.1.  Task 2.1 Pulsating/fluctuating water jet  

In view of delays at the start of project and the need to fully engineer the rig to study in detail Task 2.4 
but  also  WP6,  this  task  has  been  only  assessed  technically  and  via  a  simple  test  to  promote  system 
pressure  oscillation.  The  concept  feasibility  of  “water  hammer  or  cutting  technology”  effect  was 
discussed with suppliers (Lechler, Everloy) and key institutes such as Brno University. This technology 
is based on capitalizing on the impact shock or water hammer pressure mostly at the initial phase of the 
impact.  By  pulsating  the  jet,  the  material  is  exposed  to  higher  impact  pressures  at  shorter  period  of 
times. This technology although tested by Brno University at 20 kHz in collaboration with the Academy 
of  Science  of  Czech  Republic  [9]  has  not  seen  any  progress  with  the  nozzle  manufacturers  owing  to 
difficulty and control at high pressure and not enough significant better quality after hot descaling with 
single nozzle (Figure 7). The possibility to induce a pulsation through blocked nozzle stabilizer was 
however investigated but not taking the pulsation attenuator or damper from pump outlet. Other 
methods through a resonator chamber inserted into the nozzle have not been studied. 

a)

b)   c) 
Figure 7 (a) Pulsating nozzle (b) normal water jet spray (c) shock wave front theory [9] 

29 
2.2.2.  Task 2.2 High pressure/low flow rate  

This task has been completed with the capability to deliver depending on flow-pressure characteristics 
of  nozzle  up  to  500  bar  (single  nozzle  configuration)  and  440bars  in  dual  nozzle  mode.  Pressure 
between 150bar and 500bar have been tested for DNM0325 with the corresponding flow rate given in 
Table 14. In conclusion, erosion increases with time and pressure. Al strength reduces the erosion rate.   

Figure 8 High pressure – low flow testing validation with Erosion tests on Al function of pressure and 
time [150 to 400bar] DNM0325 Everloy nozzle inc. faro arm correlation see Task 2.6 

2.2.3.  Task 2.3 Particular water jet  

Table 14 DNM0325 flow-pressure 

Nanoparticles  and  colloidal  suspension  was  investigated  within  Tata  Steel  Europe  with  respect  to 
ISO14001  standard  and  water  discharged  to  drain  in  STC  HPW  descaler.    Carbon  nanotube  aqueous 
dispersion was purchased from Nanocyl (AQUACYL product) for incorporation in waterborne system 
with the  view  to  test applicability  post descaling.    Collaboration  with WINOA  was  initiated  with the 
potential  identification  of  micro  size  steel  shot  particles.  Issues  regarding  particle  feeding/mixing  to 
high pressure jet, has been reviewed to ascertain whether such trial is possible. It was not possible to 
mix directly to water tank with likely issues of wear/damage occurring within the pump/plunger/liner. 
New  cutting  nozzle  with  dosing/regulator  feeder  from  Accustream  was  investigating  but  applying  to 

30 
 
 
 
HPW  descaling  (larger  flow)  which  is  different  to  small  high  pressure  water  cutting  abrasive  nozzle 
requires  designing  /purchasing  specific  nozzle.  The  wok  by  Giraud  [10]  was  also  reviewed.  For 
carrying out these tests proper design, ventilation and extraction need to be design which is out of scope 
of this project in view of the initial delay to revamp the rig to high pressure set-ups. (Effort was also 
rescheduled to support the WP6 tasks in comparing in a large prototyping environment HPW descaling 
and hot shot blasting which should be more the focus and delivery of this project). 

2.2.4.  Task 2.4 Double descaling  

The  aim  of  this  task  is  to  assess  efficiency  of  double  descaling  versus  single  descaling  for  difficult 
grades. For each grade a post-reheated sample was also preserved. 

For this series of trials, the CRM DSP lab cast blocks id 2213 to 2215 (see composition Table 3). This 
task  was  completed  for  these  grades  inc.  detailed  morphology  characterisation  of  residual  scale  and 
comparison with TGA analysis.  

Conditions imposed were: 

•  Single/double descaling with positive rake angle (15o) 
•  High pressure 280 bar  (30l/min) DNM0325 single nozzle 93mm standoff 
•  ~30min reheat-60min soak from cold,1160oC 
•  O2 ~2% (monitored f(time)) 
• 
• 

2 blocks (1 block scale morphology prior descaling) 
IP ~1.36MPa, spray width ~50mm, impact Area 174mm2, 44kJ/m2, SWI 32l/m2, time under 
spray ~ 0.011s 

•  All samples cooled in Ar 
•  Manual operation between 2 passes (inter descaling time min 21s – 45s) 

Due to standoff selected, a non-descaled band of ~20mm is left on sample for detailed characterisation 
of  primary  reheated  scale  on  each  of  the  block  selected.  In  view  of  the  need  to  respect  positive 
descaling, the double descaled sample is single descaled, inch reversed (with water spray stopped) and 
then descaled again. Minimum inter descaling time is ~ 21s, allowing secondary scale to linearly grow 
(depending on block temperature) from scale free or remnant primary scale. 

The high Si (2214) variant created “powdery scale” as expected (above 3.5%Si) and that overall for this 
grade, double descaling was beneficial. For 2213 and 2215, double descaling does not seem to show a 
marked effect.   

Figure  9,  Figure  10  and  Figure  11  show  micros  at  50µm  magnification  for  all  reheated,  single  and 
double descaled sub-samples (~20mm width samples machined from initial block). In the In the Figures 
the  oxide  of  each  stage  is  shown,  from  reheating  furnace  the  primary  scale  is  visible,  large  scale 
thickness and entanglement which is the initial oxide state before descaling process. In the figures from 
single  descaling,  it  can  be  seen  that  the  primary  scale  is  removed,  so  some  remaining  oxide  is  still 
visible  attached  to  the  substrate.  And  the  figures  called  double,  are  the  oxide  remaining  after  double 
descaling, where also part of the primary scale is removed.  

For  the  descaled  samples,  two  regions  were  observed:  remnant  and  descaled  bands.  The  2213  DSP 
grade (closest to production grade except C content) show remnant primary/secondary scale of ~ 40m m 
where metal oxide growth at interface coupled with fayalite has not been descaled. (Figure 9) 

31 
 
 
 
2213 Single 
2213 Furnace 
Figure 9 Micros on reheated, single and double descaled samples – 2213 (DSP grade) 

2213 double 

The  2214  samples  show  low  metal  entanglement  due  to  potential  low  scaling  rate  and  formation  of 
SiO2 protective layer or less protective fayalite interlayer formation, mostly below the fayalite eutectic 
temperature. A sub-surface (below interface) of liquid fayalite running transversally is visible (Figure 
10).  Due  to  cooling  and  differential  thermal  expansion,  most  of  the  outer  scale  is  spallated.  Internal 
oxidation of up to 70microns is occurring for grade 2215. With the Al and Si addition, Fe-Si-Al oxides 
will form along Wustite grain boundaries, with also Al-Fe oxide (Figure 11). 

2214 Furnace 

2214 Single 
Figure 10 Micros on reheated, single and double descaled samples – 2214 High Si (DSP grade) 

2214 double 

2215 Furnace 

2215 Single 
Figure 11 Micros on reheated, single and double descaled samples – 2215 high Al (DSP grade) 

2215 double 

Comparison with initial TGA analyses is also presented below in Figure 12 re. scale morphology for 
2214  and  2215  with  those  obtained  during  pilot  descaler.  Overall,  although  total  reheating  time  was 
different  (longer  during  HPW  descaling  trials  90mins  v  75mins),  similar  scale  morphology  has  been 
obtained Figure 12.  

32 
 
 
 
 
 
 
 
 
 
 
 
TGA 

HPW descaler pilot furnace 

Grade 
2214 

2215 

Figure 12 Comparison reheated scale HPW descaler v TGA analysis (see Task 1.3) 

Double descaling needs to be adapted to scale morphology, heat losses, production consideration, water 
supply, etc. In general for being effective, double stationary offset headers can be utilised, often with 
first header operating at low pressure-low flow to condition the scale. For a reversing mill (such as plate 
rougher) wash box descaling units can be utilised in double descaling mode.   For the Si high Al steel, 
little benefits could be gained in view of level of entanglement, but tests carried out were only a fraction 
of the envelope of descaling (still low pressure) which could be considered. The reason of using 280 bar 
is that it is the average pressure for DSP (see Table 8) 

2.2.5.  Task 2.5 Latest Descaling nozzle technology  

Latest descaling nozzles include improved stabiliser, orifice shape and material design. The improved 
technology and manufacturing has resulted in reduction in spray depth or thickness and width. Options 
for short, long, and extra-long stabiliser are now available (Everloy). 

Nozzle efficiency and geometry is assessed part of a four-step procedure as follows: 

1.  Theoretical re. pressure-flow characteristics, predicted IP, descaling energy, etc.  
2.  Static erosion rate measurement and impact area assessment on Al plates: Most of the results 
have  been extracted from  the  soft  Al  erosion tests.  In  this  task  two  different  Al qualities  and 
gauge  have  been  used.  Al  1050  H14  35-40HV  (~90-100MPa)  and  Al  5251  H22  66HV 
(~200MPa). Figure 8 

3.  Impact  force  distribution  along  spray  width  and  spray  depth  for  a  given  descaling  set-up 
(standoff, system pressure, etc.). This measurement is deemed important as really mapping the 
full force distribution of the water jet within the spray impact area as well as the geometry of 
the water spray prior impact.  

4.  Dynamic  Cold/Hot  descaling  using  simulation  material  (ideally  cold)  or  steel  grade  and 

reheating atmosphere condition.  

DNM  and  latest  DNEX  nozzle  technology  from  Everloy  Systems  inc.  filters  has  been  tested.  Other 
nozzles were assessed in this project such as the new Lechler Scalemaster superior HPS series. Both the 
6P4 567 (30o spray angle), 606 (26o spray angle) an 808 (40o spray angle) have been tested. Figure 13 
shows the basic principles of the new Lechler HPS. 

33 
 
 
 
 
Figure 13 New Lechler HPS series (in particular 6P3.606.27) 

Experimental testing is being carried out according to a range of DoE matrix based on EISME design 
(Expected  Integrated  Mean  Square  Error)  [8]).  This  5-level  design  is  very  efficient  in  minimising 
number of tests whilst capturing the non-linear effects. 

Rotary systems by Hermetik AB were also investigated as shown in Figure 2. These systems operate at 
high pressure (450bar) low flow, low standoff (40mm) and as compared to a stationary descaling have 
multiple descaling passages/imprints and greater shear. But this type of systems was out of scope in this 
project.  

2.2.6.  Task 2.6 Effect of nozzle geometry  

2.2.6.1. Influence of nozzle angles, filters and set-up 

Current flat jet nozzles are used in HPW descaling, with most of the impingement force concentrated at 
the centre of the spray. Spray height and various angles as defined in Table 4 are key variables in the 
header design that will affect descaling efficiency.  

, depth angle f,  offset angle 

From  the  assessment  and  details  of  Table  4,  the  nozzle  geometry  is  characterised  by  4  angles  (spray 
angle a
g  and lead or rake angle b)  and by the interaction between stand-
off, pitch and angles when considering overlap and wash as well as varying pressure distribution across 
width. 

Other  parameters/variables  which  need  also  to  be  considered  are  spray  height  H  (mm),  -  nozzle  tip 
wear,  nozzle  tip  design,  header  angle,  influence  of  filter  (short/long)  in  straightening  the  flow  and 
changing the IP characteristics and nozzle pitch which influences overlap/wash 

34 
 
 
 
 
 
 
 
g
g
g
a  (deg) 

Spray  angle  a
this  is  an  inherent  characteristic  of  a  nozzle  and  will  affect  function  of  height 
(inverse square root relationship), the impact density, pressure and impact area. A larger angle reduces 
impact.  Efficiency depends on spray height and spray angles. 

Depth  angle  f f f  f (deg):  The  depth  angle  f is  not  usually  quoted  by  nozzle  manufacturer  but  values 
between  1.5 to  3  deg  can be  assumed  (on  average  20  is  usually  assumed). This is an important angle 
which imposes the normal (and steep) distribution of impact pressure/force.  

Offset  angle  g g g  g  (deg)  The  offset  angle  is  key  to  prevent  spray  interference  as  well  as  directing  oxide 
scale and water away. It influences directly the amount of overlap which should not be more than 10 to 
15% of spray width at max. It also compensates for pressure drop at end of spray width, but does not 
affect the spray width. If not set properly, will directly influence the amount of wash and temperature 
losses. Generally a 15o angle is selected assuming crossbar header is transverse to the rolling direction. 
The width of overlap (see Figure 4g) should be realistically equal to width of pressure drop from nozzle 
tip. Offset angle should be controlled/ maintained. There is an interaction between the rake and offset 
angle on spray distance and hence impact pressure. This is important mostly as standoff and rake are 
increasing. 

Lead or rake angle b b 
b  b (deg)  A rake angle different to 0o (0o in the vertical direction being normal to 
feedstock surface) is required to avoid scale in the roll bite, assuming descaling with a nozzle inverse to 
rolling  direction.  Typically  for  a  rake  angle  set-up  at  15o,  70%  of  the  flow  is  diverted  opposite  to 
direction  of  feedstock  travel.  Only  when rake  reaches  35o  and above,  that the water flow  tends to  be 
unidirectional. Therefore the rake angle will play an important role in preconditioning the oxide scale 
prior heating the spray impact as well as overall cooling post descaling. It will also influence the shear 
component within the scale and interface. Increasing the rake angle reduces the impact pressure. High 
rake creates also wash out. 

Standoff or spray height H (mm) Impingement area or pressure is directly inversely proportional to 
the square root of the stand-off distance. For a given nozzle, minimisation of air friction losses has to be 
done. Also as standoff distance increases, the spray tends to break from a nominal laminar jet (nominal 
distance ~ 100mm), and increasing stand-off has a lesser influence on impact pressure. It is intrinsically 
linked to spray angle and in general the smaller the spray angle is, the highest efficiency the nozzle will 
operate.  Reducing  stand-off  is  often  the  most  cost  effective  way  of  improving  descalability  (i.e. 
improving IP), however a good control of overlap/wash needs to be implemented. 

Header  angle  to  feedstock  Usually  a  90o  angle  is  applied  to  the  header  bar  where  nozzles  are 
configured, but this angle needs to be checked during maintenance as it represents the fixed referential 
point for all other angle parameters. 

Influence of nozzle filters (or strainer/stabiliser) Filters are added to reduce fluid flow turbulence by 
straightening  flow  therefore  replacing  need  for  long  pipes  which  will  increase the  standoff  distances. 
Depending on nozzle supplier, the use of short and long filters will increase impact pressure IP by at 
least 20%. The influence of nozzle strainer has been tested in this section for the Everloy DNM0325. 

(a) 

35a
a
 
 
 
 
 
 
 
 
(b) 

 (c) 

Results of comparison of each digging force. DNH type descaling nozzle, which has thinner spray 
thickness and stronger impact force, digs the lead plate more deeply. DNH nozzle with long filter digs 
further deeper  

Figure 14 Influence of nozzle filters (a) nozzle components (b) effect of filter in straightening flow (c) 
Influence of filter (short, long) on impingement area 

Influence  of  wear  (nozzle  tip)  Minimisation  of  nozzle  tip  wear  is  important  in  order  to  maintain  a 
steady state descalability performance. It is intrinsically linked to nozzle design, more specifically the 
design of the orifice tip, the nozzle tip material, etc. Wear occurs due to abrasion/erosion at the nozzle 
orifice creating a change in spray pattern and potentially droplet size, which tends to increase as water 
flow increases. Pressure drop will be most pronounced at tip extremity (mostly if tip is not self-aligning 
to nozzle base), which needs to be monitored as wear compounded by offset angle/overlap/wash will 
affect  the  severity  of  pressure  drop.  As  wear  increased,  the  coefficient  of  discharge  CD  increases 
requiring more flow i.e. more energy to sustain system pressure and therefore impact pressure. This is 
the way that maintenance (i.e. change) of nozzle versus increased energy spent can be estimated. 

Influence of nozzle pitch The nozzle pitch and number of nozzles inc. type define both coverage and 
interference as directly linked to overlap D. In general smaller the pitch, higher the number of nozzles 
and  smaller  the  spray  angles  and  higher  the  efficiency  if  overlap/wash  is  controlled  and  maintained. 
This is a key parameter to control and impose. 

36 
 
 
 
 
 
 
Overlap/wash As stated above, degree of overlap and wash is influenced by pitch, twist angle but also 
standoff, system pressure and rake. Good descaling (in stationary mode) has to have a degree of overlap 
but  it  needs  to  be  controlled  carefully  and  certainly  no  more  than  15%  of  spray  width  otherwise 
descalability  is  drastically  reduced  with  spray  interference  and  increased  cooling.  Not  controlling  the 
degree  of  overlapping  will  then  create  a  regime  of  wash  or  spray  interference  with  reduced  or 
annihilation of descaling and presence of overcooling. This is a key for electrical steel descaling. 

Figure 15 Overlap effect schematic inc. from reference [11] 

2.2.6.2. Detailed characterisation of nozzle geometry and efficiency 

(a) 

Static  Erosion  tests  are  common  practice  for  assessing  impingement  area,  degree  of  overlap  if 
operating  under  two  nozzle  configuration  as  well  as shape  and  depth  of imprints.  Usually  lead  or  Al 
strips  or  plates  are  used  under  static  impact  by  the  spray  nozzle(s).  By  selecting  carefully  the  room 
temperature simulation material, equivalent strength material can also be used to replicate steel strength 
at high temperature or indeed steel + oxide scale.  
Figure 16 shows various imprints on Al strip for different nozzles. Further refinement of characterising 
not only volume (or inverse 3D profile) and shape of imprint but also hardness profile have been carried 
out.  This  should  be  related  to  the  gauge  and  quality  of  Al  strips  from  say  1000  to  6000  series  and 
conditions  (H4  (half  hard)  to  H8  or  TB  (aged)).  Influence  of  gauge  has  also  been  investigated,  re. 
saturation, erosion, plasticity. 

Figure 16 Typical Al imprints from erosion test 

A  series  of  new  nozzles  have  been  tested  in  this  project,  such  as  the  Everloy  DNM0325, 
DNEX0833/1225  and  Lechler  HPS  6P3.567.  Only  the  DNM0325  and  0833  test  results  will  be 
presented here, with some additional results on the Lechler HPS nozzles as required.  

An extensive series of Al erosion tests were carried out for both new Everloy DNM0325 nozzles with 
short,  long  and  extra-long  filters  and  DNEX  series  (0833)  long  filters  (see  Figure  18).  In  this  report, 
only specific plots have been selected. Al tests were carried out using DoE approach presented in Task 
1.3 to assess influence of system pressure, standoff rake at fixed pitch and twist angle.   

37 
 
 
 
 
 
 Figure 17 Al erosion on DNEX 0833 nozzle 

Figure 18 Erosion rate 0833 and DNM0325 (DSP) nozzle function of system pressure and standoff-
Long filters. 

From  these  series  of  trials,  erosion  rate  can  be  determined  from  weight  loss  and  quantification  of 
impingement areas from image analysis. Also average erosion depth can be calculated from weight loss 
and imprint area and compared with Faro arm measurement.  

Figure 18 shows that erosion rate for 0833 is very low at low system pressure (115bars) and standoff of 
100mm and only establishes itself at longer time (2mins). Imprint is non-uniform with erosion starting 
from spray width centre before propagating to sides. No erosion (i.e. weight loss) at system pressure of 
90bars is visible. Erosion rate gradient is also very low. Only at a system pressure of 195bar that a full 
symmetrical and well developed imprint is established.  Harder Al plate reduces spray impact area and 
therefore  increases  IP,  however  similar  effect  to  the  softer  Al  erosion  tests  can  be  visible  with 
increasing impact from centre to edges as erosion time increases for the 0833 nozzle. This feature only 
characterises the 0833 nozzle. For the DNM0325, erosion for dual nozzle is similar to DNEX 0833 at 
195bar.  Influence  of  extra-long  filter  is  only  valid  at  the  highest  pressure.  In  view  of  the  spray 
interference, erosion is non-uniform between left and right spray. 

From the summary of the large matrix of tests carried out on the Everloy DNM0325 nozzle. 

38 
 
 
 
 
It can be concluded that for DNM0325 and Al impact time considered: 

•  No erosion at 130bar 
•  As SP decreases, erosion decreases. Erosion decreases as rake increases 
•  Erosion increases as standoff decreases 
•  Erosion decreases with short filter  
•  Erosion decreases as Al thickness reduces 
•  Min differences between long/extralong filter (f(header length) 
•  Uniformity of spray depth varies along the spray width with more uniformity on the right hand 
spray mostly as system pressure increases. This highlights the way stationary descaling operates 
with  pair  of  secondary  and  lead  nozzle  and  ways  that  water  flow  is  impinged,  deflected  and 
influenced  in  the  overlapping  area.  THIS  IS  A  KEY  ASPECT  when  comparing  with  hot 
shotblasting (stochastic/Gaussian type of imprint). Note also these effects will be influenced by 
the substrate (exacerbated by Al in view of low temperature and strength). 
Some variability does exist within the test mostly as erosion time decreases 

(cid:1) 

2.2.6.3. Impact force measurements 

Impact  force  measurements  Using  methodology  presented  in  Task  1.2  and  WP2,  impact  force 
measurements have been carried out to characterise the homogeneity and magnitude of the impact force 
distribution within the impact area. This is an excellent test to assess influence of nozzle technology, 
filter.  Usually  tests  are  conducted  under  single  nozzle  impact,  but  in  this  project  attempts  have  been 
made to measure impact force drop in the overlapping area. 

Almen  strip  deflection  tests  (impingement  energy)  Using  a  deflection  device  for  measuring  arc 
height  or curvature of specific test coupons submitted to a shot peening process (on one side only) (so 
called  an  Almen  strip),  shot  peening  energy  or  peening  intensity  can  be  assessed.  Almen  strips  are 
classified  into  3  types  (A,  N  and  C)  depending  on  thickness  and  peening  severity  but  have  all  same 
width  and  length.  Almen  adheres  to  a  SAE  standard  (Society  of  Automotive  Engineers)  and  is  a 
standard test for any shot peening manufacturers. Figure 19 shows WINOA Almen digital gauge which 
was used to assess HPW descaling energy and compare both processes using a common standard.  

Figure 19 Almen strip concept for application to HPW descaling 

Load cell 1 and 3mm measurements following extensive optimisation of experimental procedure have 
been carried out to characterise the impact force or impact pressure distribution across spray width and 
spray depth. These measurements take away the substrate and measure the true efficiency of the 
impact pressure delivered by the feed system and nozzle geometry. From these measurements not 
only  IP  can  be  measured  and  compared  to  theoretical  calculation  and  faro  arm/  image  analysis  Al 
erosion measurements but also spray width and spray depth can be obtained.  A statistical analysis of 
impact  load  distribution  according  to  a  given  threshold  (for  filtering  low  data  say  below  0.02kg)  has 
also been done.  
From this series of measurements and assessments, a comparison with theoretical analytical calculation 
will be made in task 2.7. 

39 
 
 
 
 
 
 
Everloy DNEX 0833 
(115bar) – 1mm pin 
Figure 20 Example of Load cell measurement for DNEX 0833, DNEX 1225 and DNM0325 at various 
pressures. 

Everloy 1225 (115bar) 
– 1mm pin 

DNM0325 200bar 75mm – 3mm pin 

2.2.6.4. Study of overlap with both Al testing and impact force measurement 

Extensive  series  of trials  have  been  carried  out to  study  influence  of  nozzle  geometry  to  overlap  and 
wash during descaling based on imposed pitch between two nozzles. This is a major parameter affecting 
non descaling area and likely tiger stripes. For this, Al erosion with dual nozzle configuration and 
impact force measurement with careful translation and incrementation of right hand nozzle has 
been carried out. 

Figure 21 Al erosion single DNM0325. Short filter showing overlap and wash- system pressure 180/280 
bar and influence of rake angle 0 and 15o 

Faro arm measurements for temporal erosion trial at 400bar for DSP DNM0325 were done.  The results 
of  the  faro  arm  measurement  showed  that  the  overlap  area  for  left  hand  side  nozzle  (preceding  or 
secondary nozzle) with the “destruction” of the impact force is clear visible. Several test were carried 
out at constant system pressure of 400-410 bar at different ramp up and holding time at 60s, ~120s and 
~30s. Reduced pressure ramp-up increases depth of profile slightly. 

The results were clear, as pressure decreases; left hand spray impact is becoming non uniform re. spray 
penetration  depth  and  ultimately  formation  of  wash  and  negative  overlap.  The  overlap  is  function  of 
pressure  and  has  to  compensate  for  the  pressure  drop  of  edge  of  a  given  nozzle  function  of  system 
pressure and nozzle geometry. In this case, descaling below 280bars will start destroying the left hand 
spray impact for Al testing. 

Al erosion testing in dual nozzle configuration has been backed up by impact load measurements 
for  one  test  case  at  280mm  bar,  93mm  standoff.  In  view  of  the  header  arrangement,  the  only 
possibility  was  to  increment  the  leading  jet  (right  hand  side  jet  by  0.5mm  each  time)  and  map  the 
impact force for a changing overlapping area.   

Figure 22 plots the change in impact force as the leading spray gets further away i.e. overlap reduces 
and become negative (i.e. towards no overlapping). It clearly shows that impact force increases in the 
secondary spray as overlap reduces from 0.2 to 0.8MPa by decreasing overlap by 3mm. 

40 
 
 
 
 
 
 
Figure 22 Mapping of impact force changes as overlap reduces- Impact force measurement experiment 
using 1mm pin load cell in overlap area by incrementing by 0.5mm right hand side leading jet 

2.2.7.  Task 2.7 Modelling 

Modelling of the descaling process has during this project addressed the following: 

•  Analytical  calculation  of  key  output  factors  from  descaling  theory  inc.  criteria  for  scale 
fracturing,  various  energy  concepts  (descaling,  evaporation)  and  influence  of  thermal  effects. 
Validation of some of these outputs has also been carried out against Al erosion, manufacturer 
data  and  impact  force  measurement.  All  equations  have  been  coded  to  Excel,  and  Excel 
spreadsheets run with a DoE environment to explore design space (see Task 1.3). 

•  Further development FEM based models for modelling the mechanical component of descaling 

allowing a cross comparison with shotblasting model predictions 

•  Development of more advanced Fluid based models within the FEM configuration using a CEL 
(Coupled  Eulerian  Lagrangian)  formulation  to  model  the  spray  and  impact  target  of  the 
descaling process. This goes towards further developing Fluid Structure Interaction formulation 
which will be required to model properly the complex interacting regimes during high pressure 
water descaling 

2.2.7.1. Analytical descaling theory 

All  equations  from  the  descaling  theory  presented  in  Table  4  are  incorporated  into  the  Excel 
spreadsheet. For a given descaling set-up and nozzle, all key outputs of Impact force, impact pressure, 
SWI, descaling energy, spray width/depth, fluid velocity can be calculated and output. 

In addition the spreadsheet proposes three ways of calculating these outputs based 1/ on pure geometry 
2/ on reverse calculation from manufacturer data of spray angle and spray depth or thickness angle and 
finally 3/ on calculated spray depth angle. 

The spreadsheet also enables to study influence of process set-ups on the following factors: 

•  Scale fracturing based on fracture  
• 

Influence  of  thermal  shock  on  scale  from  initial  scale  thickness  and  properties  of  scale  and 
descaling set-up (SWI) 
Influence  of  water  evaporation  and  calculation  of  evaporation  energy  (to  be  compared  with 
descaling energy) 

• 

•  Calculation of stresses inc. shear stress within the scale 

41 
 
 
 
STEP 1: Pressure-flow characteristics and fit for calculating pressure-flow constant 
Using  pressure  conversion  equations  based  on  Bernoulli,  the  coefficient  of  discharge  CD  linking 
pressure to flow rate and the coefficient CD* linking flow rate to pressure can be calculated (see Table 
14) 

STEP 2: Impact pressure - standoff relationship 

Figure 23 Manufacturer IP (MPA) v standoff distance (mm) for DNM0325 

STEP 3: Theoretical assessment of constants K and H describing influence of stand off 
Using  the  transformation/re-arrangement  of  IP  definition  3  (see  Table  4),  the  coefficients  K  and  H 
allowing prediction of IP function of standoff can be calculated (assuming 0o rake angle). By plotting IP 
function of A at various system pressures, K and H can be determined. 

These are needed input into the analytical spreadsheet. 

STEP 4: Optimisation of spray angle and depth angle based on form factor/fit from manufacturer 
nozzle description (if required) 
For the methods of calculating spray width and spray depth, ways to calculate spray angle (i.e. deviation 
from nominal) and spray depth were also added. 

(cid:1)  Spray width Angle Manufacturer catalogue usually expresses the spray angle as a unique 
angle, for example for the DNM0325 case, the spray angle a
 is 30o. However each nozzle 
will have a spray form which will gives deviation to the nominal angle, and directly impact 
on  the  calculated  impact  spray  width.  This  spray  form  becomes  more  significant  as 
standoff decreases leading to larger error compared to pure algebra. Another way is to 
express  the  spray  angle  function  of  stand-off  distance  and  system  pressure  or  flow  rate 
(independent factor).  

(cid:1)  Spray depth angle This angle directly affects the spray depth or thickness, i.e. the time 
under descaler for a given speed which will affect SWI (specific Water Impingement l/m2). 
The  spray  depth  angle  is  never  given  by  manufacturer  and  therefore  has  to  rely  on 
measured  spray  depth  (mm)  using  erosion  tests  or  impact  load  cell  measurement  for 
instance. Initial inverse calculation shows that spray angle for Everloy nozzle is small less 
than 20 (case of Everloy nozzles such as DNM0325/Everloy 0833) creating therefore small 
spread  depths  in  order  to  concentrate  impact  load.  The  spray  depth  angle  can  also  be 
calculated  by  considering  a  relationship  accounting  for  dependency  on  min  orifice 
diameter, standoff and system pressure.  

The analytical descaling spread sheet is shown below with an enhanced calculation of spray width and 
spray depth (i.e. spray area).  

42 
 
 
 
 
It could be observed that adopted the three definitions for geometric calculations, give us enveloped for 
IP, SWI, descaling energy as well as geometry of impact. 

2 

Spray 
angle 
correctio
n 
1.2 

0.95 

Scaling 
factor 
spray 
angle 

0.9 

Scaling 
factor 
spray 
depth 
angle 

Density kg/m³ 
Flow rate l/min 
Distance mm 
Atmospheric 
deceleration coef 

1000 
30.10 
93.00 
1 

Pressure head 1MPa 

102m 

Everloy DNM0325 
Nozzle Pitch E 
Nozzle constant K 
Nozzle constant X 
Flow-pressure CD 

System pressure SP at nozzle 
derived from flow rate 
G Flow rate l/min 
Alpha spray angle deg 

48.00 
2.0548089 
1.7320132 
0.31 

279.69 

30.10 
30.00 

Pressure bar 

279.69 

Pressure head m 

2852.87 

Flow rate constant C 

0.85 

Transverse spray angle 
imposed deg 
Fit spray angle constant a 
Fit spray angle constant b 
Fitted Alpha spray angle deg 

1.80 

31 
2.27E+26 
28.91 

Fluid velocity m/s 

201.0 

Fit transverse spray angle 
constant a 
Fit transverse spray angle 
constant b 
Fitted transverse spray depth 
angle deg 

Bernoulli impact 
force (definition 1) N 
Force of water jet 
(definition 2) N 

117.30 

Area mm² 

145.62 

100.8 

E smallest nozzle orifice mm 

Theoretical depth spray angle 
(definition 2) deg 
Gamma offset angle 
Lead angle beta 
Nozzle height or standoff H 
mm 
Speed (cm/s) 
D20 area mean diameter µm 

0.69 

1.80 

100 

1.68 

1.5 

2.35 

15.00 
15.00 
93.00 

30 
150 

Mean impact 
Pressure IP1 def1 
MPa 
Mean impact 
pressure IP def 2 
MPa 
Max Impact Pressure 
IP1 def 2 MPa 
Pressure in Pa 

Esurface 

Ekinetic 

(a) 

0.81 

D32 Souter mean diameter 

25 

Water surface tension N/m 
(room temperature) 

0.0729 

1.61 

2.797E+
07 
3.517E+
06 
2.818E+
09 

43 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Figure 24 Analytical HPW descaling spread sheet (main inputs in blue cell) and outputs in other 
colours based on three definitions adopted (algebra, manufacturer fit and calculated spray depth angle 
and fitted spray width) 

(b) 

2.2.7.2. Study of co-influence of rake and offset angle on spray distance and hence impact pressure  

The spray distance H can be increased H(+) or decreased H (-) depending on the lead (rake) and offset 
(or  twist)  angle.  Geometrically  the  standoff  decreases  at  left  of  nozzle  (assuming  positive  offset  and 
rake) and increases at right end side from nozzle orifice centre (or COG of imprint) with ever increasing 
rake and offset (or twist) angle. The spray width will also be affected from COG, and further stretched 
on one side compared to the other. 

Several  equations  have  been  input  into  a  Design  of  Experiment  (DoE)  within  the  Workbench  Isight-
FD®  to  compute  the  most  significant  parameters  influencing  standoff  distance  and  therefore  impact 
pressure (inversely proportional). 

The computed Pareto charts and main effect plots together with 2D response surfaces for varying the 
input factors were done. The main effects are shown in Figure 25 below. 

(a) decrease of standoff distance (left hand side of 

(b) increase of standoff distance (left hand side of 

44 
 
 
 
 
spray) main input factor effect 

spray) main input factor effect 

(c) 

(d)  

Figure 25 Main effect plots 

2.2.7.3. Study of scale fracturing 

From the calculation of the impact pressure (IP), the compressive stress can be easily calculated from 
which based on elastic theory the compressive strain deduced. Assuming that the pressure exerted by 
the jet is uniform over its entire area of impact, (not true), the following criterion for fracturing can be 
written:  

bbb b >

eeee

/

E

cos

IP
modulus of oxide scale. 

c

(Equation  1)  with  e c  being  the  critical  strain  for  fracturing  and  E:  average  young 

degC  W/mK  W/mK  W/mK  W/mK 
k FeO 
oxide 

ksteel 

T 

k 
Fe3O4 
oxide 
0.54 
0.52 
0.54 

k 
Fe2O3 
oxide 
0.2 
0.19 
0.20 

J/kgoC 
Cp 
steel 

657.03 
657.24 
657.04 

1050 
958 
1035 
degC 
T 

1.82 
1.75 
1.81 

29.36 
30.63 
29.55 
Kg/m³ 
Density 
ρ Fe2O3 
5101.93 

m²/s 
a steel 

m²/s 
a oxide 

GPa 
E FeO 
oxide 
124.38 

degC-1 
α steel 
(austenite) 
2.34E-05 

Cp 
oxide 

Density 
ρ FeO 

Density 
ρ steel 

J/kgoC  Kg/m³  Kg/m³  Kg/m³ 
Density 
ρ 
Fe3O4 
986.76  7747.05  5700.00  4997.36 
959.45  7764.17  5700.00  5015.09 
982.31  7794.95  5700.00  5000.25 
degC-1 
degC-1 
α Fe2O3  α Fe3O4 

degC-1 
α FeO 

958 

1050 

5120.03 

1.30E-
0.5 
1.30E-
0.5 
1.30E-
0.5 
Table 15 Thermal and mechanical properties of oxide scale. Properties of scale are taken from [26] 

5.77E-
06 
6.00E-
06 
5.80E-
06 

1.20E-
05 
1.20E-
05 
1.20E-
05 

3.24E-
07 
3.20E-
07 
3.23E-
07 

1.70E-
05 
1.70E-
05 
1.70E-
05 

2.24E-05 

2.33E-05 

5104.87 

134.75 

126.07 

1035 

Using theory of [12], and calculation of a roughness index ratio from [13] which accounts for geometric 
profile (roughness length and height of the interface) as well as the energy release rate of Wustite based 
on a smooth surface, one can calculate the critical strain as follows: 

  (Equation 2) 

45 
 
 
 
With c

 defined as follows  

The Figure 26 shows the Excel spread sheet calculation enhancing applicability of Figure 24. 

(Equation 3) 

Calculation of critical strain for fracture Robertson and 
Manning 

FeO Surface 
fracture 
J/m² 

3 
1 

Influence 
of IP on 
Scale 

Roughness 
height H 
µm 

Roughness 
length L µm 

Fe3O4 
Surface 
fracture 
J/m² 

4.5 
1.5 

Fe2O3 
Surface 
fracture 
J/m² 

1.95 

Scale compressive stress [MPa] 
Scale compressive strain 
Critical strain (1) from Manning 
Critical strain (2) from Manning 
Descale (Y/N) 

20 
(a) 

70 

1.40 
1.13E-05 
1.03E-05 
2.46E-04 
Yes 

From D. 
Tromans a, 
*, J.A. 
Meech 
Energy 
release rate 
smooth 
surface G10 
J/m² 
4.88 

1.51 
1.21E-05 
1.03E-05 
2.46E-04 
Yes 

Roughness 
index ratio 

14.56 

1.36 
1.09E-05 
1.03E-05 
2.46E-04 
Yes  

 (b) 
Figure 26 Calculation of critical strain and descalability based on IP calculated in Figure 24 

Changing the profile of the scale (related to interface) leads to non descalability by adopting same IP 
and descaling set-up as illustrated in Figure 27. 2D maps of roughness index ratio and critical strains are 
also shown in Figure 27c. 

Improvements  in  applicability  of  analytical  calculations  have  been  made  allowing  links  between 
process setup and oxide scale. 

Calculation of critical strain for fracture Robertson and 
Manning 

FeO Surface 
fracture 
J/m² 

Fe3O4 
Surface 
fracture 
J/m² 

Fe2O3 
Surface 
fracture 
J/m² 

Roughness 
height H 
µm 

Roughness 
length L µm 

3 
1 

4.5 
1.5 

1.95 
(a)  changes to roughness height and length (increase roughness) 

30 
(a) 

100 

From D. 
Tromans a, 
*, J.A. 
Meech 
Energy 
release rate 
smooth 
surface G10 
J/m² 
4.88 

Influence 
of IP on 
Scale 

1.51 
1.21E-05 
2.54E-05 
2.46E-04 
No 
(b) using same conditions with DNM0325 and 280bar, descalability is not ensure 

Scale compressive stress [MPa] 
Scale compressive strain 
Critical strain (1) from Manning 
Critical strain (2) from Manning 
Descale (Y/N) 

1.40 
1.13E-05 
2.54E-05 
2.46E-04 
No 

Roughness 
index ratio 

22.94 

1.36 
1.09E-05 
2.54E-05 
2.46E-04 
No 

Figure 27 Calculation of critical strain and descalability based on IP calculated in Figure 24 and 
changes in interface roughness 

46 
c
c
c
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
2.2.7.4. Study of influence of thermal effect 

Assuming  decoupling  between  thermal  effect  and  mechanical/fracturing  effect  (not  true),  analytically 
we can express the thermal elastic strain generated by the differential thermal contraction of both oxide 
scale (assuming 1 layer Wustite) and steel substrate.  

Two ways of calculating the thermal strain and hence thermal stresses, one is based on calculating the 
thermal stress but more correctly from the differential thermal contraction between scale and steel.  

Figure 28 shows two simulations using DM0325 set-up from results obtained Figure 24 changing only 
speed through the RSB descaler 

 is either calculated from the HTC function coded in the spreadsheet (as detailed later) or imposed 

by the spreadsheet (case here 15oC imposed). 

Influence 
of thermal 
shock on 
scale 

Thickness of scale affected by HPW descaling 
µm 
Maximum thickness affected by HPW µm 
Calculated DT degC 
Calculated thermal strain within affected scale 
Calculated thermal stress MPa 
Calculated mismatch strain between steel and 
scale 
Calculated mismatch thermal stresses between 
steel and scale 
Assumed DT degC 
Assumed thermal strain within affected scale 
Assumed thermal stress within scale MPa 
Assumed mismatch thermal strain between 
steel and scale 
Assumed mismatch thermal stress MPa 

57.16 

55.19 

65.33 

140.01 
91.97 
1.56E-03 
210.68 

135.18 
91.97 
1.56E-03 
210.68 

160.02 
91.97 
1.56E-03 
210.68 

5.92E-04 

5.92E-04 

5.92E-04 

79.72 

79.72 

79.72 

15.00 
2.55E-04 
31.72 

15.00 
2.55E-04 
31.72 

15.00 
2.55E-04 
31.72 

9.65E-05 

9.65E-05 

9.65E-05 

12.17 

12.17 

12.17 

(a)  case of speed set-up through RSB of 0.3m/s 280bar 93mm standoff with initial primary scale of 

1000microns 

Influence 
of thermal 
shock on 
scale 

Thickness of scale affected by HPW descaling 
µm 
Maximum thickness affected by HPW µm 
Calculated DT degC 
Calculated thermal strain within affected scale 
Calculated thermal stress MPa 
Calculated mismatch strain between steel and 
scale 
Calculated mismatch thermal stresses between 
steel and scale 
Assumed DT degC 
Assumed thermal strain within affected scale 
Assumed thermal stress within scale MPa 
Assumed mismatch thermal strain between 
steel and scale 
Assumed mismatch thermal stress MPa 

70.01 

67.59 

80.01 

171.48 
102.52 
1.74E-03 
236.93 

165.56 
102.52 
1.74E-03 
236.93 

195.99 
102.52 
1.74E-03 
236.93 

6.60E-04 

6.60E-04 

6.60E-04 

89.66 

89.66 

89.66 

15.00 
2.55E-04 
31.72 

15.00 
2.55E-04 
31.72 

15.00 
2.55E-04 
31.72 

9.65E-05 

9.65E-05 

9.65E-05 

12.17 

12.17 

12.17 

(b)  case of reduced speed set-up through RSB of 0.2m/s 280bar 93mm standoff with initial primary 

scale of 1000microns 

Figure 28 Effect of thermal effects based on calculated D T or imposed D T and fraction of thickness of 
scale affected by heat loss assuming decoupled thermal and mechanical effect 

47 
D
T
 
 
It can be observed that thermal stresses range from 12 to 236MPa depending on method of calculation 
for both the thermal strain and temperature drop. These stresses (assuming no initial fracturing) will be 
constrained  in  each  direction  (assuming  linear  differential  expansion  between  steel  and  scale).  If 
fracturing is induced, the remaining tensile stresses in the scale will introduce a shear stress which can 
be  estimated  by  multiplying  the  thermal  stress  calculated  by  a  factor  4  thickness  of  scale/distance  of 
scale fragment.  

However  for  primary  scale,  thermal  effect  will  only  affect  maximum  20%  of  the  scale  thickness  and 
therefore alone cannot be the sole contributor for effective descalability. It only proves that conditioning 
the  scale  by  thermal  effect  can  help  pre-cracking  but  of  course  this  analysis  is  based  on  decoupling 
effect, which in real practice does not occur, as scale is fragmented from both mechanical and thermal.  

2.2.7.5. Study of evaporation effect, re. energy involved 

Water  impacting  the  oxide  scale  and  likely  cracks/pores  especially  when  reaching  the  scale/metal 
interface  will  be  evaporated  by  the  heat  of  the  steel  and  the  mechanical  impact  of  the  water  droplet,  
resulting  information  of  vapour  bubble  which  expended  by  further  heating  may  further  rupture  the 
scale. The energy available can be estimated from latent heat of vaporisation together with work done 
from expansion of water vapour bubble. 

E

Evaporatio

(

mkJn

/

=

]2

rrr r
Qx
.
.
vB
.

w

 +
L


RT
m




=

x

.

SWI

 +
L
.


RT
m




  (Equation 4) 

Where x: fraction of water evaporated, r w: water density (kg/m3), Q: flow rate (m3/s), B spray width, v 
feedstock velocity, L: latent heat of water evaporation (J/kg), m: molecular weight of water 18g/mol, R: 
universal gas constant. 

Assuming a given fraction x of water evaporated which is not in this formulation dependent on IP.  

SWI Volume of water/unit area of steel L/m² 
Fraction of water evaporated beta 

32.41 
0.05 

33.69 
0.05 

Influence 
of water 
evaporation 

Mass of water evaporated/unit area kg/m² 

Latent heat of water evaporation L kJ/kg 
Molecular weight of water m g/mol 
Calculated ∆T degC 
Energy/kg of water evaporated from calculated 
deltaT kJ/kg 
Total energy evaporation kj/m² based on 
calculated deltaT 
Assumed  ∆T degC 
Energy/kg of water evaporated from assumed 
delta T kJ/kg 
Total Energy evaporation kJ/m² assuming 
delta T 

1.62E+00  1.68E+00 
2270.00 
2270.00 
18.00 
18.00 
91.97 
91.97 

2.31E+03  2.31E+03 

30.29 
0.05 
1.51E+00 

2270.00 
18.00 
91.97 
2.31E+03 

3.75E+00  3.90E+00 

3.60E+00 

15 

15 

15 

2.28E+03  2.28E+03 

2.28E+03 

3.69E+00  3.84E+00 

3.45E+00 

Figure 29 estimation of energy for evaporation of water during HPW descaling (within scale) - assumed 
280 bar – travelling speed 0.3m/s 

It  can  be  concluded  that  the  descaling  conditions  can  lead  to  formation  of  steam  and  energies  of 
typically  2kJ/m2  (at  speed  of  0.6m/s),  to  ~5  kJ/m2  at  speed  of  0.2m/s  through  the  descaler. 
Comparing with the descaling energy estimated (between 20 to 55kJ/m2 within that speed envelope), 
steam/bubble  explosion  effect  cannot  be  the  sole  main  criteria  responsible  for  descaling  but  can 
contribute by formation of steam to further fracturing/fragmentation. This formulation and estimate is 
of course linearly dependent on the fraction of water evaporated which realistically should be function 
of IP / water droplet size. 

48 
 
 
 
 
2.2.7.6. Study of stresses developed 

A  brief  study  of  stress  distribution  using  either  the  approach  highlighted  by  YU  [15]  or  simply 
estimated  by  Herzian  theory  under  the  “contact  point”  of  the  spray  can  lead  to  the  following 
predictions:  

Assuming  280  bar  and  a  primary  scale  thickness  of  1000microns,  the  following  stresses  can  be 
estimated.  Validation  will  require  FEM  calculations,  and  at  this  stage  can  only  be  taken  as  first 
approximation. 

Mechanical 
stresses in scale 

Spray depth/scale thickness ratio 
Normal or vertical stress sigmax (MPa) 
Longitudinal stress sigmay (MPa) 
Fraction of momentum landa 
Shear stress (MPa) 

Mechanical stresses in scale from YU 
1.51 
-1.43 
-0.29 
0.50 
0.35 

Mechanical stresses in scale from Herzian theory 

Poisson ratio 
Spray depth/scale thickness ratio 
Sigmazz (normal) MPa 
Sigmaxx or sigmayy MPa 
Maximum shear stress MPa 
Maximum at z-0.49a 

0.3 
1.51 
-1.01 
-0.15 
0.43 
0.74 

0.3 
1.41 
-1.00 
-0.13 
0.44 
0.69 

1.41 
-1.44 
-0.27 
0.50 
0.35 

0.3 
1.98 
-1.08 
-0.24 
0.42 
0.97 

1.98 
-1.50 
-0.40 
0.50 
0.35 

a)  case of 280 bar – 93mm stand-off DNM0325 – 1000microns primary scale – IP~1.4MPa 

Mechanical 
stresses in scale 

Spray depth/scale thickness ratio 
Normal or vertical stress sigmax (MPa) 
Longitudinal stress sigmay (MPa) 
Fraction of momentum landa 
Shear stress (MPa) 

Mechanical stresses in scale from YU 
1.35 
-1.65 
-0.29 
0.50 
0.40 

1.27 
-1.66 
-0.27 
0.50 
0.41 

1.81 
-1.76 
-0.44 
0.50 
0.41 

Mechanical stresses in scale from Herzian theory 

Poisson ratio 
Spray depth/scale thickness ratio 
Sigmazz (normal) MPa 
Sigmaxx or sigmayy MPa 
Maximum shear stress MPa 
Maximum at z-0.49a 

0.3 
1.35 
-1.14 
-0.14 
0.50 
0.66 
b)  case of reduced stand-off to 83mm with IP ~ 1.7MPa 

0.3 
1.27 
-1.14 
-0.12 
0.51 
0.62 

0.3 
1.81 
-1.27 
-0.25 
0.51 
0.89 

Mechanical 
stresses in scale 

Spray depth/scale thickness ratio 
Normal or vertical stress sigmax (MPa) 
Longitudinal stress sigmay (MPa) 
Fraction of momentum landa 
Shear stress (MPa) 

Mechanical stresses in scale from YU 
2.70 
-2.15 
-0.77 
0.50 
0.47 

2.54 
-2.2 
-0.75 
0.50 
0.49 

3.63 
-2.15 
-0.94 
0.50 
0.45 

Mechanical stresses in scale from Herzian theory 

Poisson ratio 
Spray depth/scale thickness ratio 
Sigmazz (normal) MPa 
Sigmaxx or sigmayy MPa 
Maximum shear stress MPa 
Maximum at z-0.49a 

0.3 
2.70 
-1.56 
-0.57 
0.49 
0.66 

0.3 
2.54 
-1.59 
-0.56 
0.51 
0.62 

0.3 
3.63 
-1.54 
-0.66 
0.44 
0.89 

c)  same as b but with reduced thickness of scale 500microns  
Figure 30 Estimation of stress components within the scale from descaling set-up (IP) and scale 
thickness 

49 
 
 
 
 
 
 
It can be observed that estimation of shear stress component (from mechanical impact) can create shear 
stress values of 0.4 to 0.8 MPa depending on descaling pressure conditions, formulation, spray depth 
calculation and oxide scale thickness which appear realistic but which of course will require validation 
or  better  estimation  via  specific  mechanical  testing  (bending,  etc.).  This  type  of  approach  does  not 
account for interface description. 

2.2.7.7. Validation 

The  analytical  approach  has  been  cross  validated  for  the  DNM0325  nozzle  with  impact  force 
measurement and AL erosion as described in Task 2.6. 

(a) comparison impact pressure predictions from analytical calculation and impact force measurement 
function of standoff, system  pressure (up to 380bars) and stabilisers 

(b)  Comparison    of  overlap  analytical  calculation  with  Al  double  spray  erosion  and  predicted 
manufacturer calculation function of standoff, system pressure and stabilisers 
Figure 31 Validation of analytical predicted data of IP and overlap versus Al erosion and impact force 
measurements 

50 
 
 
 
In summary it can be observed that:  

• 

IP  is  overestimated  at  small  standoff  in  view  of  potential  error  in  spray  form.  The  mean  IP 
calculated via equation 1 (Bernouilli) as Table 4 gives better prediction for the short filter. Long 
and extra-long filter gives increased IP and that good agreement is reached at moderate to high 
pressure and standoff above 93mm. For the extra-long filter (> 150mm), the expected benefits 
were  not  realised  in  view  of  the  length  of  our  header  and  water  supply.  There  is  a  need  for 
additional head room to ensure that stabiliser/nozzle works efficiently. 

•  Analytical predictions of spray width are in good agreement with those measured from impact 

force and Al at the highest pressure. 

•  The  Al  imprint  is  affected  at  low  pressure  and  depends  on  time  for  erosion.    There  is  an 

influence between lead and secondary spray. 

•  Analytical predictions show a good agreement for spray thickness or depth but calculations do 
not  take  account  of  filter.  There  are  differences  a  low  stand  off  and  between  impact  force 
measurements and AL erosion tests at low pressure. Long filter calculations seem to be more 
consistent. 

•  Overlap  is  better  predicted  as  system  pressure  is  ramped  up  and  standoff  increases.  Over-

prediction can be observed at small system pressure. 

Variation  and  comparison  calculations  have  been  done  with  manufacturer  data  of  Al  imprints  width 
function of system pressure (up to 380bars), standoff, filter and rake. It was found that predictions by 
manufacturer calculation (Everloy) of spray width are in reasonable agreement withal measurements for 
leading nozzle (right) or secondary nozzle (left) at the highest pressure and low rake angle. Al overlap 
predictions do not show good agreements with manufacturer calculation.  

Figure 32 Overlap comparison between measured AL spray width and manufacturer overlap prediction 
on the assumption that left spray width measured by Al imprint is spray width occurring during real 
process with interacting nozzle 

51 
 
2.2.7.8. FEM HPW descaling 

FEM  modelling  addresses  both  the  thermal  and  mechanical  side  as  well  as  new  developments  for 
accounting for fluid-structure interaction (mechanical side only). 

•  Heat loss 

A  typical  heat  loss  pattern  assumes  full  descalability,  i.e.  no  effect  of  oxide  scale,  except  prior  to 
descaling jets.  The main uncertainties in this type of prediction come from the distribution of HTC to 
be applied as function of nozzle type, descaling time, descalability, saturation effect and IP. A range of 
HTC  can  be  found  in  [4,  56-60]  for  impact  pressures  varying  from  0.15  to  1.3MPa  [57].  Choi  [57] 
deduced a relation of convective heat transfer coefficient (HTC) (in the range of 310 to 430 kW/m2K) 
for one steel specimen (150x25mm), one speed (1m/s) and a range of impact pressures (IP) between 4 
and 8 bar. Other much lower values of HTC (3…5 kW/m2K) are reported by the researchers from Heat 
Transfer and Fluid Laboratory of Brno University for IP=1.4…13 bar and v=1m/s (on a 150 mm thick 
plate with residual scale) [42]. Work reported in paper [18] based on a design of experiment trial series 
of instrumented thermocouple steel block with/without secondary scale and with remaining presence of 
steam has allowed to express heat loss (average HTC) function of stock speed (SWI), IP and feedstock 
size effect. It uses a Gaussian distribution to simulate the shape of HTC within the descaling jet (spray 
depth). The shape of the HTC function takes also account of recovery as well as saturation due to SWI 
(40l/m2).  

All  the  functions  were  derived  from  secondary  scale  trials  and  work  is  to  reassess  thermal  effect 
during primary descaling. Figure 33 shows an example of estimated HTC for the billet and bloom size 
inc. processing conditions at SRM.  

Figure 33 Typical HTC predicted function of bloom and billet size, speed and spray depth studied in 
this project 

•  Mechanical  

The  mechanical  part  of  modelling  the  HPW  descaling  has  been  further  developed  with  the  aim  to 
compare with models of the shotblasting process, re. penetration depth/damage, etc. 

Modelling 
ABAQUS/CFD and the CEL formulation available within ABAQUS. 

is  also  considered  fluid  and  fluid-structure 

interaction  with  developments  using 

Two formulations are available: 

52 
 
 
 
 
 
• 

Implicit 2D formulation with single scale layer and explicit interface between oxide scale 
layer and steel substrate. 

The concept of scale removal relies on modelling (using ABAQUS® Standard) a scale fragment with 
two  interfaces  (scale-scale  and  scale–steel)  where  damage  is  expected.  Boundary  conditions  such  as 
surface traction (i.e., mechanical component of descaling) and film coefficient (i.e., thermal component) 
are applied on the top of the scale fragment. Speed is being considered via analysis step time. 

In  the  first  version  of  the  model,  the  interfaces  were  modelled  using  cohesive  elements.  Issues  with 
element aspect ratio and the inability of this type of elements to transmit heat led to a second version of 
the FE model, where these interfaces were modelled using one of the phenomenological ductile damage 
criterion available in ABAQUS® based on initiation (triaxiality-strain-strain rate based) and evolution 
(tensile  behaviour  based  on  stress-effective  plastic  displacement  following  onset  of  cracking).  The 
oxide  scale  is  ductile  at  high  temperature,  but  brittle  at  low  temperature  with  the  damage  evolution 
considered  almost  instantaneous  (based  on  exponential  softening,  using  Hillerborg’s  fracture  energy 
model)  [16]  to  reduce  mesh  dependency,  thus  reflecting  the  quick  transition  of  scale  to  brittle  state 
under HP water jet. The model integrates two steps, an initialisation where thermal boundary conditions 
are applied to top oxide scale surface, followed by a second step where both mechanical pressure and 
surface film are applied.  

The amount of scale removal predicted by the model is interpreted as a percentage of failed elements of 
the  two  augmented  interfaces.  Residual  scale  [%]  estimated  quantitatively  of  interfacial  elements 
around the fragment of scale under HP jet; brittle damage assumed due to fast water cooling. There is 
no element deletion procedure in this model. 

Calibration of the 2D FE model required determining the critical strain (i.e. damage criteria initiation in 
the  model)  for  the  type  of  oxide  scale  and  the  state  of  the  surface  feedstock  (i.e.,  as-cast/wrought) 
considered.  That  was  done  through  a  series  of  laboratory  trials  and  in  conjunction  with  the  scarcely 
available published data [12] (see Figure 34). 

(a)  ABAQUS  standard  oxide  scale  model  with  computation  of  residual  scale  changes  via 
DMICRT/MAXECRT parameter 

53 
 
 
 
 
 
 
(b) Tensile strain fitted to residual scale from [12]  (c) oxide scale interface delamination 

Figure 34 Three component oxide scale ABAQUS implicit model with ductile-brittle behaviour 
modelled at interface (delamination) 

•  Explicit Dynamics formulation with single scale layer and explicit interface between oxide 

scale layer and steel substrate. 

A  new  development  has  also  been  initiated  using  ABAQUS  Explicit  with  element  deletion  based  on 
damage  initiation  and  propagation.  The  model  has  an  outer  scale  continuous  interface,  an  explicit 
modelled interface and a substrate. The descaling operation is modelled by assigning a velocity to the 
stock  via  a  rigid  surface  (tray)  and  coupling.  A  node  based  surface  interaction  is  selected  to  allow 
removal of both surface and sub-surface layer as descaling progresses. Properties of oxide are assigned 
via elastic plastic with ductile damage based on triaxiality-strain data or damage traction separation law 
via Maxe (max strain criterion) with both normal and shear properties, and element deletion (e.g. for 
ductile  damage  outer  scale  max  UTS  25MPa  at strain  0.6,  ductile  damage  0.1  at  tensile triaxiality  of 
0.05, interface max UTS 70MPa at strain 0.6, ductile damage fracture strain 0.25 at tensile triaxiality of 
0.1,  Steel  UTS  100MPa  at  plastic  strain  of  0.6.  The  HPW  descaling  is  simulated  with  “rigid”  shot 
forming a continuous spray jet of the DNM0325 profile. The multiple 2D shots with mass property of 
water are assigned an initial velocity vector imposing their direction (angle) and intensity. No thermal 
effect is considered here. The aim of this model is to represent closer the conditions of the “mechanical” 
spray  and  the  kinematic  of  the  process.  2D  plane  strain  assumption  is  made  with  a  very  fine  mesh 
density (element size at contact ~24microns).  

This  model  is  used  to  study  interaction  between  interface properties  and  kinetic/momentum  of  spray. 
Although  oxide  scale  and  interface  are  geometrically  simplistic  and  continuous,  no  disintegration  of 
shot  is  modelled,  together  with  absence  of  thermal  effect  (which  can  be  significant  and  create  large 
shear  stresses),  the  model  once  calibrated  could  provide  a  valuable  insight  on  the  determination  of 
system pressure required to remove oxide scale/metal interface. See Figure 35.  

Figure 35 (a) Full detailed discrete model with water shots, outerscale, interface and steel substrate. 
Note refined meshing in partition for impact study. Model is driven via rigid surface boundary 
conditions (b) fracturing and attainment to interface 

a) 

b) 

•  Fluid-structure (FSI) approach based on Explicit Dynamics Formula 

Other developments are also being considered but have not yet reached any degree of maturity with the 
latest  formulation  of  ABAQUS.  ABAQUS/CFD  with  possible co-simulation (Fluid-solid  interaction), 
CEL  (Coupled  Eulerian  Lagrangian)  and  SPH  (smooth  Particle  Hydrodynamics)  are  interesting 
formulation  which  can  be  applied  to  model  more  accurately  the  HPW  descaling  process.  The  HPW 
descaling process ABAQUS/CFD is limited currently to incompressible fluids but has no free surface or 
mixing capability (single phase). In the CEL technique using ABAQUS Explicit,  the Eulerian domain 
represents  the  media  i.e.  air  or  water  (i.e.  the  fluid  structure)  which  material  flows  through  the  fixed 
mesh whilst the Lagrangian domain represents the target i.e. the steel which currently simulate a simple 
composite  steel  and  oxide  scale  layer  with  damage  initiation  using  a  deforming  mesh.  The  CEL 
approach  is  based  on  volume  of  fluid  method  and  uses  a  linear  equation  of  state  (EOS  using  a  Mie-
Grueneisen model for water where both the bulk modulus and viscosity of water is imposed) to model 
water  and  defines  relationship  between  density  and  pressure  and  the  fraction  of  fluid  which  will 
completely  or  partially  filled  the  Eulerian  mesh.  ABAQUS  provides  the  calculation  of  the  volume 

54 
 
 
fraction filling the Eulerian elements.  The model uses general contact to track fluid and target. Aim is 
to  predict  impact  force,  impact  area  from  the  modelling  and  tracking  of  the  water  flow.  Using  CEL 
FEM,  the  Eulerian  domain  will  transmit  the  impact  force  distribution  to  the  Lagrangian  structure 
through Eulerian-Lagrangian contact based on penalty method.  

Developments in the CEL descaling model have been carried out for both circular and flat jet nozzle.  

a 

Figure 36 Improved CEL model with better water spray representation. b) view of water impacting 
target with improved CEL model 

b 

2.2.8.  Task 2.8 Cross performance comparison of water-based technology 

In  view  of  Task  2.1  and  2.3  not  having  been  prioritised,  only  a  cross  performance  of  single/double 
descaling and descaling function of impact pressure will be made here.  

Performance will address regime of descaling energy function of grade, surface state and set-up. Entry 
temperature descaling is also important. In our tests surface temperatures between 880 to 1000oC with 
primary scale have been measured. 

55 
Grade 

Reheating 
Temperat
ure (oC) 
/time 
(mins) 

IP (MPa) 

SWI (l/m2) 

Descalin
g energy 
(kJ/m2) 

Rail 

1220/90 

~1 (200bar)  7.66 (1m/s) 

7-8 

Non uniform descaling for 
primary reheat 1220oC 
above fayalite formation 

Rail 

1220/90 

0.5-0.6 
(120bar) 

1.36 
(280bar) 

40* 
saturation 
(0.12m/s) 

22 

Full descaling 

32 (0.3m/s) 

44 

Descaling but not removal 
of interface 1160oC 

1160/60 

1160/90 

0.7 
(120bar) 

40*(0.12m/
s) 

28 

Not descaled properly 

1160/90 

1.15 (200 
bar) 

29 (0.3m/s) 

33 

Not fully decaled 1160oC 

1200/90 

1.7(300bar)  35 (0.3m/s) 

59 

Not fully descaled 

1160/60 

1.15 
(200bar) 

40*(0.12m/
s) 

1220/80 

0.7(120bar) 

40*(0.12m/
s) 

45 

28 

Table 16 Descaling set-up and performance 

Fully descaled 

Not descaled uniformly 

Electrical steel 
2213/2214/2215 
Machined prior 
tunnel 
Electrical steel 
UT23 B9S38 
Machined prior 
tunnel 
Electrical steel 
UT23 B9S38 
As-cast prior 
tunnel 
Electrical steel 
UT23 B9S38 
As-cast prior 
tunnel 
Electrical steel 
UT12 10BS4 
machined 
Valve spring 
B9S33 

The following conclusions can be made: 

•  As-cast reheat surface finish is more difficult to descaler than machined finish 
•  As-cast reheat post tunnel for electrical steel are the most difficult to descaler 
• 

Increasing  reheat  temperature  above  fayalite  formation  for  electrical  steel  and  valve  spring 
decreases descalability. 

•  The  descaling  energy  concept  is  a  reasonable  concept  for  assessing  cross  performance  of 

descaling 

•  Higher  pressure  and  hence  higher  flow  increases  descalability  but  improvement  is  linked  to 

coefficient of discharge of nozzle and constraints on heat losses. 

•  Double descaling has been covered in Task 2.4. Evidence of efficiency is grade dependent (so 
far High Si will benefit) but more work is required, re. Influence of process set-up (pressure, 
speed)  and  analysis  of  constraints  (temperature,  timing).  Key  aim  is  whether  oxide  scale 
interface is drastically changed prior linear regrowth of secondary oxide scale.  Consideration 
of heat losses should be made mostly at the highest system pressure or impact pressure which 
minimises effect of scale (see Task 4.3). at 300bar +, heat losses of  the order of 70 to 100oC at 
0.12m/s 300 bar (SWI ~40l/m2) per pass is important and therefore recommendation of double 
descaling should primarily involve pre-cracking of scale using low pressure sprays followed by 
high  pressure  descaling.  In  certain  installation,  double  descaling  with  two  passes  through  a 
rolling mill using a primary descaling unit could also be required mostly if secondary descaling 
is weak. 

56 
 
 
Additional data of Al erosion as presented, characterisation of imprint via hardness measurement and 
application of simulation material to approximate scale strength is also added in this section to provide 
additional elements to the performance of water based technology.  

(cid:2)  Oxide scale properties : In addition to the properties highlighted in Table 15, re. thermal 
and  some  mechanical  properties,  with  regard  to  high-temperature  hardness,  little  data  are 
available for magnetite and hematite. In [20] is measured the degree of softening of Wustite as 
a  function  of  temperature  and  reported  a  typical  hardness  of  about  10  HV.  Similarly  in  [21] 
measured tensile strength at high temperature with values for Wustite dependent on strain rate 
in the temperature range of 500–700 °C but independent of strain rate at 1000 °C, and found a 
typical value of around 3 MPa compared with 0.4 MPa at room temperature. By comparison, 
tensile  strength  for  magnetite  and  hematite  at  room  temperature  is  of  the  order  of  40  and  10 
MPa, respectively. The relatively low values of oxide tensile strength at room temperature are 
due  to  extreme  brittleness.  For  primary  scale,  created  during  high  oxidation  temperature, 
significant  plastic  flow  can  occur  without  cracking,  leading  to  the  relaxation  of  the  growth 
stress and retention of contact despite the increased thickness.  

This section on oxide scale properties has to be put into the context of stresses calculated in task 2.7 
whereby shear stresses of ~0.6, 0.7MPa have been calculated and which might not be enough to fully 
descale the interface. 

(cid:2)  Al  erosion  (see  description  in  task  2.5-2.6  and  above).    Key  is  to  assess  nozzle  efficiency 
function of erosion rate and impact area/volume. Best nozzle efficiency is measured in relation 
to maximum erosion rate at minimum time. Currently erosion rate is used as weight loss over 
imprint area.  
It was demonstrated that Al erosion tests can be used to assess nozzle efficiency and that for 
getting maximum out of new nozzle either system pressure had to increase (even at lower flow) 
or  standoff  to  decrease.  Good  agreement  of  spray  width  and  depth  with  impact  force 
measurement and analytical calculation is providing the basis for increasing the confidence of 
the analytical tool developed and hence the performance of descaling. Al erosion is not ideal 
technique for overlap (at least up to 230bar) and therefore only hot tests or test on simulation 
material  approaching  the  strength  of  oxide  can  be  used.  Further  work  should  also  look  at 
deriving quantity such as impulse of force and also link erosion with IP or over concept such 
integral of IP or power of descaling. 

(cid:2)  Simulation material Cross performance of HPW decaling has also been assessed using 

simulation material.  A range of simulation materials has been investigated to replicate oxide 
scale at room temperature. Although Al is the preferred material for static erosion test and 
has been used by nozzle manufacturer as a simulation material for high temperature steel 
descaling, its intrinsic strength is minimum 90MPa for the 1050 quality which is on average 
higher than the steel strength at 1200oC but far greater than the outerscale strength of oxide [4-
20MPa]. 
Therefore in this section a range of simulation material has been investigated: 

- Al 1050 H14 quality and Al H22 5251 series (66HV ~ 200MPa) at two gauges (3 and 
5mm) in both static, dynamic conditions 
-  AL  in  hot  conditions  (500oC)  and  dynamic  descaling  with  strength  of  around  max 
40MPa 
- Lead (Pb) with strength between 15-30MPa 
- HDPE material with strength of ~20-30MPa 
- Plasterboard with strength between 6-12MPa 
- Teflon  

It can be concluded that in dynamic mode (descaling under velocity), the Al at both room temperature 
and high temperature is not affected by the HPW descaling. At 500bar, only lead, HPDE and Teflon are 
affected  forming  typical  descaling  “dimple”  pattern  (water  disintegration),  and  for  the  plaster  board 
(lowest strength), 150 bar has created a deep erosion /descaled channel which depth could be related to 
IP  and  SWI,  i.e.  descaling  impact  energy  or  power.  Plasterboard  and  Teflon  will  be  used  to  cross 
correlate HPW descaling with hot shot blasting, see task 5.2. 

57(cid:2)  Hardness measurement Analysis of imprint nozzle profile on Al erosion (normal to mid spray 
width)  along  the  spray  depth  with  four  “micro”  hardness  profiles  (HV0.5kg    load)  has  been 
done. It can be concluded that no plasticity (at that load) has been imparted to sub-layers of 
the erosion  impact  area (aligned  to  high  pressure  water  cutting  theory). This  highlights  that 
the process does not involve plasticity. So the HPW descaling is purely a damage-cavitation –
erosion process where no in depth plasticity is created even at the highest system pressure (400 
bar in this case). 

58 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
2.3.  WP3: Water-free descaling process - high temperature shot blasting 

This  work  package  aims  to  test  new  water-free  descaling  processes.  Several  different  descaling 
conditions will be investigated in order to improve descaling performance.  

2.3.1.  Task 3.1: Development and test of heat-resistant blasting media grade 

2.3.1.1. Criteria for blasting media selection 

The blasting media (steel abrasive) is characterized by several criteria such as shape, size, hardness and 
a distribution called operating mix due the wear during blasting service. 

•  Shape  is  defined  by  the  SAE  J444  standard  designation  (Society  of  Automotive  Engineers). 
According  to  this  standard  there  are  2  types  of  shapes:  shot  or  round  particles  and  grit  or 
angular particles. 

Figure 37 Pictures of shots (a) and grits (b) 

 a)

 b)      

•  Size is also defined in the SAE J444 standard designation. For shots, size is characterized by 
the nominal dimension in 1/10 000 inch (for example the shot S550 corresponds to 550/10 000 
inch = 1.40 mm aperture), and for grits the number of  screen mesh in ASTM E11-95 standard 
corresponding to nominal dimension (#18 = 1.00 mm aperture). Detailed tables of shot and grit 
size granding according to SAE J444 standard are presented in the Mid-term report [R] 

•  According to the blasting application (shot peening, descaling…), WINOA has developed his 

own specification in terms of hardness range (Figure 38). 

Figure 38 Internal hardness specification 

Operating  mix  is  a  mixture  of  particles  used  in  a  blasting  machine.  It  is  characterized  by  its  size 
distribution,  stabilized  according  to  the  abrasive  type  and  quality  as  well  as  blasting  parameters 
(throwing  speed,  material  and  hardness  of  blasted  articles,  elimination  size).  After  several  blasting 
cycles, the operating mix has a very different size distribution from that of new abrasive although it has 
the same nominal size (Figure 39). 

59 
 
 
Figure 39 Sieve analysis curves (a) of new abrasives (b) and operating mix (c) 

2.3.1.2. Development of heat-resistant blasting media grade 

WINOA and CRM worked on the development of an appropriate blasting media grade for descaling at 
high temperature. It was expected that compared to standard conditions (close to ambient temperature) 
steel abrasive media will show lower efficiency and higher consumption. WINOA initially thought that 
media  temperature  would  rise  significantly  during  operation  (up  to  around  500°C).  So  the  first 
investigation was performed between WINOA and CRM on “heat-resistant” grade which would be able 
to  keep  its  hardness  at  high  temperature.  To  avoid  this  problem,  we  defined  three  steps  which  are  a 
preliminary  study  of  potential  resistant  grades  (alloyed  steels),  achievement  of  laboratory  samples  of 
selected grades and finally characterization and tests in simple blasting conditions.  

In  case  the  standard  metallurgy  is  not  adapted  to  hot  shot  blasting,  the  following  metallurgical 
composition of the shots can be adapted:  

S170 
S230 

HRB01  HRB02  HRB03  HRB04 

C 

0,85 

Si 

0,8 

0,6 

0,4 

0,6 

0,4 

0,5 

0,4 

0,5 

0,6 

)

%

(
n
o
i
t
i
s
o
p
m
o
C

Mn  0,8 

0,9 

0,9 

0,9 

0,6 

Cr 

Ni 

Mo 

V 

- 

- 

- 

- 

1,5 

1,8 

1,2 

1,8 

0,55 

0,55 

0,15 

0,15 

1,2 

1,3 

0,5 

0,2 

3 

0,1 

1,55 

0,3 

=> to reduce the number of precipitates and the 
fragility 
=> necessary to adapt it to have a good shape 

to 

improve  hardness  and  mechanical 

=> 
resistance (compensation of the C decrease) 
+ deoxidiser (similar effect to Ni) 
=>  to  improve  corrosion/oxidation  resistance 
and the quenchability (for heat treatment) 
=> 
improve 
corrosion/oxidation resistance 
=> 
improve 
to 
temperature 
=> 
to 
temperature 

resistance  at  high 

resistance  at  high 

ductility 

improve 

and 

the 

the 

to 

Table 17 Metallurgical composition of shots possible to use at high temperature 

However with the tests carried out in task 3.2 and some simulation from task 3.5, it was showed that 
media  temperature  rise  can  be  limited  due  to  the  very  short  contact  time.  It  was  estimated  that  the 
blasting media temperature will not exceed 150 °C. Moreover, with the experiments in task 3.2, it was 
also showed that a higher hardness is not really required to have an efficient oxide removal. In addition, 
higher  hardness  could  be  detrimental  and  lead  to  shot  inlaying  phenomenon.  Regarding  standard 
product  consumption,  WINOA  showed  that  there  is  a  compromise  between  hardness  and  lifetime  in 
blasting standard conditions (Figure 40).   

60 
 
 
 
 
 
 
 
 
Figure 40 Relative consumption of high-carbon abrasive depending on its hardness 

As  it  mentioned  above;  laboratory  test,  numerical  simulations  and  slow  motion  videos  show  that  the 
abrasive-to-substrate contact time is very short. Heat transfer from the substrate to the abrasive is very 
low and abrasive temperature increase due to the contact time is negligible.  To confirm this calculation, 
the  temperature  of  the  abrasive  has  been  measured  after  blasting  trials  in  Tata  Steel  industrial  pilot. 
Temperature of the shots increase during the blasting of one hot sample at 1200°C  from 11°C to 18 - 
22  °C.  This  temperature  increase  has  been  measured  using  an  infrared  camera  and  a  thermocouple 
(Figure 41).  

Figure 41 IR picture of abrasive after hot blasting test with blocks at 1200°C 

Industrial shot blasting machines are equipped with dynamic air separator. The aim of these separators 
is to remove small particles (broken shots, dust, oxide scales) from the operating mix. A side effect of 
using  a  dynamic  separator  is  that  the  abrasive  is  air-cooled  during  the  process.  If  the  standard  air 
separator  is  not  efficient  enough  for  hot  blasting  operations,  it  is  possible  to  implement  an  extra  air 
cooling device on the abrasive flow.  

Standard shot are thermally stable up to: 

200 °C – start of stress relief (which will increase service life).  

~400-450°C – tempered temperature for 48 HRc shots.  

Therefore,  it  was  not  necessary  to  continue  the  development  of  a  specific  heat-resistant  shots  for  hot 
descaling application.  

61 
 
 
 
Air curtain 
already acting  as 
a cooling device

1 = dusts output 
2 = flow regulator 
3 = blasting media + dusts + scale input 
4 = scale + broken media 
5 = security sieve 
6 = flap gate 
7 = operating mix  

Figure 42 Industrial air separator scheme 

2.3.2.  Task 3.2: Preliminary trials of hot temperature blasting operations 

2.3.2.1. Shot blasting parameters 

Shot  blasting  can  be  described  as  a  mechanical  process  for  removing  surface  material  such  as  oxide 
scale with one of many types of shots, but it is also carried out to impart a specific roughness to the 
object being shot blasted. In standard descaling with brittle oxide scale, the media usually used is steel 
grits or an operating  mix  of  grits and shots.   By  changing  parameters  other  than  the  media, it  is  also 
possible  to  improve  the  efficiency  of  the  process  i.e.  to  remove  different types  of  oxides  or  different 
oxide layer  thickness.  In  previous  studies,  steel  shot blasting  showed  good  results in  removing  oxide 
layer after hot rolling [4-7].  

The aim of this section is to identify the key parameters of shot blasting at high temperatures and assess 
the effects of each one on the descaling efficiency. 

Coverage  rate:  In  the  shot  blasting  field,  the  descaling  efficiency  is  associated  to  the  coverage  rate. 
The coverage rate is defined as the ratio of the area covered by hits and the complete surface treated by 
shot blasting expressed as a percentage.  

This criterion will also be coupled with surface analysis to assess the amount of residual oxides and to 
check that there is not shot embedded. 

The coverage rate is given by the following function:  
Cn = 1 - (1 - C1)n   (%)  (Equation 5) 

C1 = coverage as % after one pass 
Cn = coverage as a % after n passes 
n = number of passes 

Figure 43 Example of a coverage curve after one pass at 40% 

From  this  equation  it  is  possible  to  draw  a  chart  to  assess  level  of  coverage  rate  (Figure  44a).  The 
coverage rate of a work piece has to be determined directly on the component to be treated. Therefore 
visual  inspection  is  the  standard  method  to  assess  the  coverage  level.  With  the  help  of  a  magnifying 
glass  (x30)  (Figure  44b),  the  treated  surface  may  be  assessed  in  comparison  with  the  internal  chart 
(Figure 44c).   

62 
 
 
 
 
 
 
 
Figure 44 (a) Coverage rate chart, (b) Different coverage levels 

Factors  influencing  the  coverage  rate:  As  described  before,  the  coverage  rate  is  correlated  to  the 
surface deformation.  According to the Figure 45, the Ekin1, one of the most important parameters is 
part of the kinetic energy before impact, which is converted into deformation of the work piece (Edp). 
Indeed  the  kinetic  energy,  which  is  the  product  of  the  media  velocity  and  the  mass  of  the  media 
transformed  into  the  deformation  energy  transferred  to  the  work  piece,  the  deformation  energy 
transferred  to  the  media,  the  heat  energy  (caused  by  friction)  and  the  resilient  energy.  Therefore  the 
mechanical  properties  such  as  the  elastic-plastic  deformation  behavior  of  the  work  piece  and  media 
hardness are mainly responsible for this energy conversion. 

Kinetic energy before impact          Ekin1 = ½ mv² 
Ekin2 = ½ mv² 
Kinetic energy after impact  
Edp 
Deformation energy part 
Etherm 
Deformation energy shot 

Ekin1= Edp + Eds + Etherm + Ekin2  
Edp = Ekin1- Eds – Etherm – Ekin2 (Equation 6) 

Figure 45 Energy relations and energy conversion during the impact of the media 

The following additional factors affect energy transfer and hence the coverage rate: 

•  Types of blasting systems 

In wheel blasting system (Figure 46), the media is propelled by a bladed wheel rotating thanks to a 
motor. This operation is categorized as an airless blasting operation because there is no propellant (gas 
or liquid). In the industrial field, there are several kinds of wheel blasting machine with different size, 
number and power of the wheels depending on the parts to be blasted as well as on the expected result 
and efficiency. The wheel method of propulsion has a lot of advantages such as an easy control of the 
shot  velocity,  a  high  production  capacity,  and  a  high-efficiency  blasting  operation  with  recyclable 
media.  In  our  context,  the  best  configuration  for  descaling  long  and  strip  products  is  a  Pass  through 
machine (Figure 47). 

63 
 
 
 
 
 
 
 
1 = feed spout 
2 = impeller 
3 = control cage 
4 = centering plate 
5 = spacer 
6 = blade 
7 = bare wheel assembly  

(a) 

(b) 

Figure 46 (a) Wheel blasting system, (b) Wheel components 

Figure 47 Passthrough machine adapted for descaling long products 

Air  blasting  systems  introduce  the  shot  either  by  direct  pressure  or  by  gravity  (Figure  48),  into  a 
stream  of  compressed  air  directed  through  a  nozzle  onto  the  work  piece.  In  the  case  of  pressurized 
projection system, the compressed air is used to put both abrasive pot and mixing chamber under the 
same  pressure  which  sweeps  abrasive  along  in  the  blast  hose.  In  the  other  case  (suction  projection 
system), the compressed air is injected in the gun through a nozzle and creates partial vacuum in the 
chamber  that  sucks  a  mix  of  abrasive  and  air.  The  main  advantages  of  air  blasting  systems  are  the 
flexibility and the easiness; however it is not possible to control easily the shot velocity. 

(a) 

(b) 

Figure 48  (a) Pressurized projection system, (b) Suction projection system 

•  Media velocity The media velocity has a direct effect on the kinetic energy (see Figure 45). 

64 
 
 
 
 
 
•  Type of media Besides the shape of media (shots or grits), their size, mass and hardness affect 

the coverage rate. 

According to the calculation of WINOA about the number of grains per kilogram of media (Figure 49), 
it  is  easily  understandable  that  by  increasing  the  number  of  grains  (size  reduction),  the  number  of 
impact  will  be  higher  which  will  tend  to  increase  the  coverage.  Moreover  the  average  particle 
dimension in the operating mix being lower than in new products (Figure 39), the number of particles 
per kg and therefore number of impacts per minute and coverage will be higher. 

Figure 49 Number of grains in WINOA´s media 

The simulations made show that to achieve the same coverage rate, the fact of reducing the size of the 
media  will  greatly  increase  the  impact  and  reduce  the  coverage  time  but  reduce  each  other  impact´s 
energy. 

•  Mass flow rate The mass flow rate defines how much mass of the media is accelerated per time 

• 

unit, and also determines the time required to obtain the specified coverage rate 
Impact angle theoretically an impact angle of 90° results in maximum energy transfer onto the 
work piece. In practice, especially in wheel blasting system where the media flow is very high, 
impact angles between 75° and 85° are proven to allow the media rebound and the recyclability. 
See Figure 50.  

2.3.2.2. Pre-selection of blasting parameters 

Figure 50 Effect of impact angle  

First  an  air  blasting  system  was  selected  and  used to  perform  the  first tests  of  descaling  at  very  high 
temperatures. The aim of the first test was to check the efficiency of the treatment and select the right 
shot blasting parameters, to implement those shot blasting conditions afterwards to the wheel blasting 
machine (industrial size equipment) of WINOA to go back to velocity and then to be able to compare 

65 
 
 
 
 
each  descaling  process  (Shot  blasting  and  HPW)  on  the  same  kind  of  samples  at  room  temperature 
through several criteria such as impact, topography, coverage, and micro hardness. 

For this part of project four main blasting parameters were screened: 
Shot size : WS 170 (0.425mm) vs WS 230 (0.6 mm)  
Pressure : Low pressure vs High pressure 
Flow : Low flow vs High flow 
Hardness : Soft media vs Standard media 

The shot size is an important parameter to get efficient descaling but also on the economic side. For our 
first  trials  we  worked  with  two  standard  shot  sizes,  WS  170  (0.425  mm)  and  WS  230  (0.6  mm). 
Normally,  shot  blasting  with  small  size  leads  to  numerous  impacts  which  enables  higher  coverage 
speed.  For this reason it is very interesting to use this size of shot to have a good productivity for an 
industrial line. However the production capacity of this shot size could be limited.  That’s why it was 
also decided to study the effect of bigger shot size. Moreover the kinetic energy of larger particles is 
higher  which  will  have  a  significant  effect  in  terms  of  cleanliness.  We  have  to  find  thus  the  best 
compromise between shot blasting efficiency and productivity of industrial line. 

For this demonstration pilot, the shot velocity increases with the pressure. In this case we have to find a 
compromise between the kinetic energy (depending on shot velocity) for an efficient descaling and the 
possible risk of shot inlaying. 

Regarding the flow, this parameter will have an impact on two points. The first one is the dimension of 
industrial equipment. Indeed the fact of working at low flow involves fewer turbines which enables a 
more compact installation.  The second point is the productivity of treated parts. A high flow enables a 
shorter blasting time. 

Finally  shot  hardness  is  supposed  to  have  an  effect  on  the  descaling  efficiency  but  also  on  the  shot 
consumption and on the final quality of the surface treated (shot inlaying, roughness).  

2.3.2.3. Trials air blasting system without controlled reheating atmosphere 

The first sets of trials had as objective to check the scale removal efficiency through the coverage rate 
with a first pre-selection of working blasting parameters. To get first indications about relative blasting 
time for efficient descaling and to compare 2 shots hardness’s on descaling efficiency.  

All experiments were carried out with a specially modified blasting pilot Figure 51 to test the blasting 
of  hot  products  in  simplified  conditions.  The  tests  were  realized  in  static  conditions  without  media 
recirculation.  The  CRM  electrical  furnace  (Figure  51)  was  used  to  heat  up  the  specimen  at  high 
temperature (1200°C) during 1 hour before the descaling. The reheating atmosphere was not controlled 
for the first trials. Water cooling was used in the first test but was then changed to nitrogen cooling to 
avoid oxidation and cracking phenomena, in this report only the main results are mentioned.  

66 
 
 
Figure 51 Shot blasting device designed by WINOA to perform test at CRM Lab 

Figure 52 Liquid nitrogen cooling system 

Parameter 
Shot 

Test1 
WS 170 
(d = 0.425 mm) 

Pressure 
Quantity of shot 
Hardness 

Distance nozzle-target 
Samples composition 

4 bars and 7.5 bars 
1kg and 3kg 
48  HRC  (483  HV)  and 
39 HRC (388 HV 
300 mm 
1.2 to 1.7% of Si 

Atmosphere  
Sample temperature 
Cooling 

20 % O2 
> 1000°C 
Water quenching 

Test2  
WS 170 
(d = 0.425 mm) and 
WS 230 
(d = 0.600 mm) 
4 bars and 7.5 bars 
1kg, 3kg and 6kg 
48 HRC (483 HV) 

300 mm 
1.2 to 1.7% of Si 

20 % O2 
> 1000°C 
Liquid nitrogen cooling 
(-120°C) 

Test3 
WS 170 (d = 0.425 mm) 
and WS 230 
(d = 0.600 mm) 

4 bars and 7 bars 
3 kg and 6 kg 
48 HRC (483 HV) 

300 mm 
0.22% C-1.50% Mn-1.75% 
Si-0.03% Al 
0 % O2 and 9 % humidity 
1200 0C 
Liquid  nitrogen  cooling 
(atmosphere temperature: -
120 0C) 

Table 18 Summary of parameters of the preliminary test without control of atmosphere 

67 
 
 
 
Summary of main conclusion of preliminary test 

•  The most favourable blasting parameters were high pressure (higher shot velocity), numerous 
impacts  (shot  blasted  quantity  and  numbers  of  particles  per  kg),  and  standard  products  (48 
HRC) 

•  The quantity of blasted shot is an important parameter for optimizing the coverage rate. 
•  According to the quantity of shot blasted (1 to 6kg), the coverage rate achieved is between 80 

and 98% with small shots, and between 70 and 95% with larger shots.  

•  The impacts on the surface of the sample shot blasted under 7 bar are larger and deeper due to 

the higher velocity 

•  The size of the impacts is larger by increasing the shot size. 
•  Reheating atmosphere has an influence on surface aspect after descaling on those lower alloyed 

steel composition 

From cross section analysis the conclusions are:  

•  Assuming that the duration of the process is similar, it seems that the bigger shots have a better 

descalability than the smaller ones.  

•  The  scale  thickness  is  quite  similar  in  all  samples  and  no  significant  effect  of  the  blasting 

parameters on the oxide layer is observed.  
•  Higher pressure remove more oxide scale  

Standard shot media product: 

•  After the blasting operation (only one pass) no variation of micro- or macrostructure of shots 

was observed. 

2.3.2.4. Hot temperature blasting with controlled reheating atmosphere  

CRM developed a new controlled reheating atmosphere setup corresponding to the industrial reheating 
conditions. The validation of the new controlled reheating atmosphere setup has been done in relation 
with WP 2 and WP4. 

A selection of favourable blasting parameters has been obtained during the first trials. Nevertheless, all 
tests  weren’t  performed  in  industrial  reheating  conditions  which  led  to  a  non-representative  scale  in 
terms of adherence. Thereby, after the development of a reheating setup to work in industrial reheating 
conditions a new round of test were done on laboratory materials (from CRM) and industrial materials 
(from Tata Steel).  

The  reheating  and  atmosphere  control  device  displayed  in  Figure  53  allow  the  precise  control  of  the 
reheating atmosphere (N2 + O2 + humidity) during reheating. The principle is to use a closed box in the 
furnace to heat up samples in smallest volume. The device in Figure 53a allows adapting the oxygen 
level by changing the nitrogen pressure into the atmosphere and changing the dew point at the entrance 
of the furnace controls the humidity in the atmosphere. At the exit of the furnace, water cools down the 
air to extract the humidity (Figure 53c) and its oxygen level is measured (Figure 53d) and adapted by 
adjusting N2 flow rate if necessary. During the trials, a dew point of 57 °C was set corresponding to 17 
%  humidity.  A  multi-step  setting  adapted  the  set  point  of  nitrogen  flow  to  control  the  oxygen  level 
range between 1.6 % and 2.4 % (similar to atmosphere in Tata Steel furnace see WP2). Exact control of 
the  oxygen  level  at  a  constant  2  %  is  difficult,  because  at  high  temperature  the  blocks  consume  the 
oxygen to form scales and thus some feedback control is required. 

After descaling the block are cooled down with nitrogen till 400 °C within 15 min freezing the surface 
scale.  

68 
 
 
Figure 53 Reheating device developed in CRM Gent(a) Controlled atmosphere setup (b) closed box (c) 
water cooling device (d) oxygen analyzer. 

Tests have been performed with the CRM lab cast samples (see WP1).  

The  main  objectives  of  this  campaign  were  to  check  the  descaling  efficiency  in  industrial  reheating 
conditions  of  shot  blasting  with  the  selected  parameters  on  different  steels  and  compare  the 
descalability by shot blasting of each grade. In parallel, the surface temperature close to the oxide layer 
was also investigated thanks to a thermocouple to assess the heat loss during the shot blasting (see task 
4.3). 

The  same  descaling  devices  were  used  as  previously.  A  test  matrix  was  made  including  different 
parameters  such  as  shot  medium,  blasting  time.  A  thermocouple  was  used  to  monitor  the  surface 
temperature loss of the blocks during the shot blasting. 

Based on the earlier results it was decided to use the maximum reachable pressure with the pilot and 
increase the shot quantity to maximize the impact energy and to increase the coverage rate.  

WS  170  (d = 0.425 mm)  and  WS  230 
(d = 0.600 mm) 
7.5 bars 
300 mm 

Shot 

Pressure 
Distance 
nozzle-
target 

Samples 
See WP1 

Laboratory materials (CRM):  

•  2213, 2214, 2215, 2216, 2217 

Industrial materials (Tata Steel):  

Quantity  of 
shot 
Hardness 
Reheating 
conditions 

Cooling  

6 kg and 9 kg 

48 HRC (483 HV) 
1150°C  –  75  min  (2%  02, 
17% humidity) 
1200°C  –  60  min  (2%  02, 
17% humidity) 
Liquid  nitrogen  cooling 
(atmosphere temperature: -
50 0C). 

•  34  (298Q-B/9/S/34/1-2),  32  (UT23-
B/9/S/32/1), 38 (UT23-B/9/38/1)  

Shot 
velocity 
Table 19 Summary test parameters 

~70m/s 

For  each  test  condition,  different  analyses  were  performed  to  determine  the  descaling  efficiency 
(coverage  rate),  the  roughness  and  the  surface  temperate  evolution  during  shot  blasting.  The  main 
conclusions are: 

•  Results and discussions (see Figure 66):  

Electrical steels (CRM 2213, CRM 2214, CRM 2215, Grade 32, Grade 38) 

69 
 
 
•  All  of  the  blocks  show  a  clear  impacted  zone,  some  of  which  is  slightly  concave  due  to  the 

nozzle position and high pressure. 

•  The  impact  area  of  the  electrical  steel  compositions  reheated  at  1150  0C  and  1200°C  varies 

between 50 % and 90 %.  

•  The  increase  of  shot  blasting  quantity  improves  the  descaling  efficiency.  However  no 

significant effect of shot size is observed for these steel compositions. 
. 

Rail steels (CRM 2216, CRM 2217, Grade 34) 

•  Both  laboratory  and  industrial  materials  are  100%  impacted  but  at  first  view  without  being 
descaled (descaling efficiency estimated between 0 to 10%). The steel composition could have 
a strong effect on the oxide adherence especially at this range of temperature. 

•  The  results  based  on  surface  inspection  seem  degraded  in  terms  of  descaling  efficiency.  The 
shot  blasted  samples  are  100%  impacted  by  shot  but,  depending  on  the  steel  composition, 
several samples seem only partially descaled.  

•  The heated samples at 1150°C are more descaled than the samples at 1200°C.  
•  Air blasting pilot used in CRM has as limit flow rate (9 kg/min) and shot velocity (~70 m/s). 

Hardness tests have been performed:  

•  The shots impact doesn’t influence the surface hardness/ microstructure.  
•  The decreased hardness below the surface of the rail steel is caused by the decarburized 

layer (see also TGA analysis)  

The  roughness  of  the  interface  scale/steel  of  reheated  samples  and  reheated+  blasted  has  been 
measured using image analysis. By comparison the roughness of the samples before and after blasting 
shows little difference. The roughness at the interface after reheating and blasting is directly related to 
the  shots  size  but  the  shots  do  not  penetrate  enough  the  interface  to  produce  a  big  difference  in 
roughness with the interface before blasting.  

2.3.2.5. Implementation on a wheel blasting system 
Test under blasting conditions in a wheel have been done in a first phase at room temperature in order 
to check shot velocity and the influence of shot blasting on the material (Aluminuim plates from Tata 
Steel) in terms of impact energy, topography, coverage, etc.   

The  trials  in  the  wheel  blasting  machine  will  give  information  of  parameters  like  shot  velocity  and 
blasting  conditions  closer  to  the  industrial  application  (flow  rate,  conveyor  speed…)  which  are  high 
interest for WP5 and WP6. These parameters are difficult to obtain from the shot blasting device used 
in the CRM test.  

Intensity at saturation 

The  intensity  measurement  is  standardized  (SAE  AMS J443  standard).  Intensity  is  the impact energy 
level  of  a  shot  stream.  The  kinetic  energy  transferred  by  the  shot  stream  is  referred  as  “saturation 
intensity”. The measurement of blasting intensity is achieved by determining its effect on standard tests 
strips (Almen strips). Almen test are performed with the device in the Figure 19. Almen strips, gage and 
holder  are  needed.  Saturation  curve  is  constructed  from  the  Almen  results.  To  compare  or  transpose 
several shot blasting conditions the intensity at saturation in needed.  
Saturation point is defined as the earliest point of the saturation curve that, if the exposure time (or the 
shot quantity thrown) is doubled, the arc height increases by 10% or less. 
Factors influencing intensity are media size, velocity, hardness and flow rate. 

Main parameter 
Media size 

velocity 

Media 
and hardness 
Media flow rate 

Influence on saturation curve 
Increasing  media  size  –  higher  intensity  and  longer  exposure  time  due  to  lower 
particles number 
Saturation point is effected but only a marginal effect on exposure time 

Increasing media flow rate – reduction in time before saturation 
Table 20 Parameters influencing saturation curve 

70 
 
 
 
Shot blasting trials 

Almen and Aluminium test test 

Almen tests have been performed in the shot blasting machine in CRM (Figure 51) in order to get the 
saturation  intensity  with  both  shot  sizes  tested  in  the  previous  experiments.  Aluminium  tests  were 
performed to analyse the surface after the treatment in terms of roughness and surface quality and to 
compare with HPW impacts, see WP2.  

Parameters 
Shot 
Pressure 
Quantity of shots 
Hardness  
Distance nozzle target 
Temperature 
Saturation curve results 

Microscopic  and  macroscopic 
results 

Coverage rate 

Almen (from WINOA) 
WS170 - WS230 
7.5 bars 
0.25kg to 8kg 
48HRC (483HV) 
300mm 
Room temp 
WS 170: F31A: f = 0.310 mm 
WS 230: F35A: f = 0.350 mm 
Shot  size  and  quantity  increase 
the saturation intensity 
Quantity 0.61kg for WS170 and 
0.82kg for WS230 
No  significant  difference  on 
surface of the Almen strips 
Shots are not embedded  

Aluminium (from Tata Steel) 
WS170 - WS230 
7.5 bars 
6kg 
48HRC (483HV) 
300mm 
Room temp 

in 

roughness 
No  difference 
when  using  different  shot  sizes 
and quantity.  
98%  for  WS170  and  95%  for 
WS230 

Figure 54: Microscopic investigation of the Almen and Aluminium surface after shot blasting under 
air pressure of 7,5bar for shot WS170  

Table 21 Test performed at CRM Shot blasting device 

Test on the wheel blasting machine 

The shot blasting conditions from the air blast pilot were implemented to the wheel blasting machine 
(industrial size equipment) of WINOA (Figure 55). 

71 
 
 
•  1 wheel Rutten, 22kW 
•  Variable motor speed throwing speed 30-140 m/s 
•  Variable conveyor speed: 1-14 m/min 
•  Max dimensions of test parts: - 1200 mm length x 

500 mm width; pipes 400 mm in diameter 

•  Load capacity: 500kg 

Figure 55 Wheel blasting machine of WINOA 

For  each  shot  size  (WS  170  and  WS  230),  the  wheel  blasting  system  was  calibrated  to  obtain  the 
intensity  at  saturation  similar  to  those  measured  by  the  pilot.  The  purpose  of  the  calibration  was 
therefore  to  find  the  shot  velocity  in  order  to  get  the  right  intensity  at  saturation.  To  do  so,  we  have 
tested several shot velocities and for each one, the saturation curves were performed. For wheel blasting 
tests, the measurement of deflection is a function of the number of passes in opposition to blasting pilot 
where the deflection was a function of the quantity of thrown shot.  

Parameters 
Shot 
Flow rate 
Convoyor speed 
Hardness  
Distance nozzle target 
Pass number 
Almen saturation 

Coverage rate 

Almen (from WINOA) 
WS170 - WS230 
50kg/min 
14 m/min 
48HRC (483HV) 
500mm 
12 
WS 170: F31A 
WS 230: F35A 

Results from Almen test 
Shot velocity 
Shot velocity used in aluminium test 

WS170: 78m/s 
WS230: 72m/s 

Conclusions:  

Aluminium (from Tata Steel) 
WS170 - WS230 
50kg/min 
14 m/min 
48HRC (483HV) 
500mm 
10 
WS 170: F31A 
WS 230: F35A 
99%  for  WS170  and  99%  for 
WS230 

WS170: 78m/s 
WS230: 72m/s 

•  The roughness profiles and surface state are very similar for both air- and wheel- blasting devices 
•  No real impact of shot size on roughness 
•  The blasting transposition of parameters was achieved with success 
•  Test done with new abrasives in order to be repetitive which means that there is a very low difference 
in  terms  of  distribution  size  between  the  WS  170  and  the  WS  230.  Even  if  in  one  case  the  impact 
number is higher, the fact to work with similar shot velocities will not change the topography. 

•  The coverage rate seems to be similar in both processes. 
•  No significant difference on the impacted surface is visible on the microscopic investigation 
•  No embedded shot in the surface can be observed for all investigated blasting parameters. 

Table 22 Test performed at WINOA wheel blasting device 

72 
 
 
 
 
2.3.3.  Task 3.3: Definition of an experimental procedure to assess the high temperature 

resistance of the blasting media 

Abrasive high temperature life tool 

The  design  of  this  new  tool  (Figure  56)  is  based  on  an  air  blasting  system  due  to  the  flexibility  and 
easier  use  in  an  R&D  context  than  a  wheel,  which  would  not  be  pertinent  on  a  too  small  scale.  The 
target simulating hot parts were heated up with an electrical resistance. 

Heated target 

Heat 
evacuation 

Figure 56 Pictures of the abrasive life tool 

Several  trials  have  been  performed  with  the  abrasive  life  tool,  heating  test  was  done  with  heating 
resistances with a capacity of 3.6kW and an optical pyrometer. Several technical problems were found 
during the test: 

•  Test with resistance of 220 V – 3,6 kW: the heating resistance broke very quickly due to the 

high temperature created and the low energy dissipation.  

•  Test  with  a  second  electrical  resistance  380V–  3,6  kW  and  with  adhesive  spots  to  hold  the 
resistance:  saturation  of  temperature  around  650-700°C  after  45-60min.  After  temperature 
stabilisation the air blasting is open but the tube temperature dropped to 200°C.  

WINOA has tried to get information about the evolution of the blasting during temperature service with 
an  abrasive  life  tool.  A  lot  of  effort  was  put  in  the  development  of  the  tool  and  procedure  to  have  a 
better idea of the media evolution and consumption. But after several trials the heating system did not 
allow to simulate a hot part blasting. It was decided to move to industrial wheel blast equipment where 
the  abrasive  was in  direct contact to the hot sample. This  equipment  is used during  the  pilot  trials  at 
Tata Steel in WP6. The consumption was then evaluated under real conditions.  

2.3.4.  Task 3.4: Validation of the water-free descaling process in online conditions 

2.3.4.1. Recycling of abrasive 

Samples from abrasive WS230 were taken after several trials at CRM with the shot blasting device and 
sent to WINOA for further analysis. Measurements with the sieve and hardness analysis were done on 
abrasive sample before and after hot sample blasting, the results did not show a significant difference, 
as seen in the following table. 

73 
 
 
W. 49 / Hides Trials

Hardness (HV0.5)

Sieve analysis

SAE J444 : 
may 1993
S230
All pass
10 % max

85% min
97% min

Sieve size (mm) New S230 Used S230

1,000
0,850
0,710
0,600
0,500
0,425
0,355

Voids

0,1
4
67
90
94
96
99

0,1
7
79
96
98
99
100

S230
15%

Used S230
17%

SAE J827: 
Sept 1996
< 10%

Shot N° New S230 Used S230
459
447
433
440
421
415
451
478
401
414
427
377
477
429
471
421
475
447
459
473
441

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Average

501
491
472
473
461
442
463
518
470
470
378
478
499
497
474
510
432
448
472
420
468

Table 23 Winoa’s laboratory comparison of new and used S230 sample 

During use, shot wears or breaks. Shots diameter will be reduced by wear. Shots breaking at the impact 
will divide their diameter. Shots wear or breakage can be measured by checking diameter distribution 
before and after use.  

Voids  are  production  defects.  The  voids  act  as  breaking  starting  points.  Abrasive  with  voids  used  in 
extreme conditions will break very fast. We can see from the analysis that the voids quantity has not 
changed  between  the  new  and  used  sample.  Hot  shot  blasting  cannot  be  considered  as  extreme 
conditions for metallic abrasive.  

We  can  see  on  the  previous  table  that  the  size  distribution  is  very  similar  between  new  and  used 
abrasive. This first result shows that the abrasive has been worn neither broken during the blasting tests 
on hot samples.  

Another  wear  factor  using  metallic  abrasives  on  hot  parts  is  linked  to  heat  treatment  induced  by  the 
contact  between  the  abrasive  and  the  substrates.  Heat  treatment  will  affect  the  abrasive  hardness. 
Hardness measurement on a sample of 20 shots showed no significant difference between new and used 
abrasives.  

Based on these 3 measures and the hot shot blasting tests done, we can conclude that hot shot blasting 
induced a normal wear of the abrasive. It is not necessary to use and develop a specific abrasive for this 
application.  

2.3.4.2. On-line blasting pilot 

The  possibility  of  trials  in  the  Continuous  hot  rolling  trials  on  baby-coil  with  in-line  shot  blasting  in 
CRM was studied but the air blasting pilot available in CRM cannot achieve the desired flow rates and 
has not been designed for dynamic tests. And the trials in the pilot hot rolling mill seem no to be the 
best  solution  as  we  target  primary  decaling.  Indeed  sample  thickness  (4  to  8  mm)  is  far  from  the 
industrial practice and the creation of the right oxide layer prior to descaling is not assured. Moreover, 
based  on  the  outcome  of  a  basic  engineering  study  and  taking  into  account  the  available  space  to 
implement  the  blasting  machine  in  the  CRM  line,  we  need  to  consider  the  shot  recuperation  and 
transport  to  container  on  the  top  of  the  pilot.  This  adds  an  additional  complexity  to  the  blasting 

74 
 
 
machine. Therefore this option is likely not to be further considered for these reasons it was decided to 
move to install a wheel blasting machine in the pilot plate mill of Tata Steel (see task 6.3).  

2.3.5.  Task 3.5 Modelling of high temperature shot blasting 

The  objective  of  this  task  is  to  develop  a  finite  element  model  for  the  numerical  simulation  of  shot 
blasting at elevated temperatures with the goal of descaling a steel slab using ABAQUS/explicit.  

2.3.5.1. Simulation model 

The  first  simulations  that  were  performed  did  prove  that  the  concept,  which  was  developed  for 
simulating abrasive shot blasting at elevated temperatures, works. However, improvement still had to be 
done to the models since the results did not correlate well with the experiments. The main cause for the 
difference  was  assumed  to  be  the  chosen  damage  model.  The  Johnson-Holmquist-Beissel  model  that 
was used at first could not be fitted to show plausible results regarding scale damage. While very thin 
scale layers in comparison to shot diameter could be simulated with good results, thick scale layers in 
comparison to shot diameter could show results that were not comparable to experiments. Changing the 
damage model to brittle and tensile, respectively, and calibrating the material parameters with data from 
Tata Steel allowed much better simulations and results. In this report we present the latest results that 
show good correlation with the experiments. Unfortunately the validation of the results can just be done 
through rating the plausibility as no parameters could be found that can be compared to experimental 
indications for the high temperatures during shot blasting. 

The model has been finished and can be used to analyze the shot blasting process at high temperatures. 
It  consists  of  the  bulk  material  with  a  layered  oxide  scale  and  a  number  of  shots  that  impact  on  the 
surface.  The  layered  oxide  scale  allows  the  assignment  different  material  properties.  It  takes  into 
account the findings in this project. For the simulation, the commercial software ABAQUS/explicit is 
used.  Some  simplifications  and  abstractions  had  to  be  made  for  the  simulation  model:  only  a  small 
section of the work piece can be simulated, no symmetry is present in the model and the shots are taken 
as rigid bodies. Half infinite elements are attached to the sides of the model in order to damp the stress 
waves since they are reflected at the edges. Since only a small part of the bulk is simulated the reflected 
stress  waves  would  cause  problems  (compare  Figure  57).  This  simulation  concept  has  already  been 
successfully used for shot peening simulations at room temperature [28]. 

Figure 57 Simulation model with scale layer (blue), half infinite elements (white) as well as shots 
(white half-spheres). The bulk material is not visible. 

2.3.5.2. Material model and parameters 

The  bulk  material  is  modeled  with  elastic-plastic  material  behavior.  For  the  oxide  layer  different 
material definitions have been investigated. The results can be summarized as follows: 

•  The models published by Holmquist and Johnson [29] were developed for the evaluation of the 
behaviour  of  silicon  carbide  during  the  high  velocity impact  of  a  projectile. Theoretically  the 
model could be used for any brittle material. The required experiments however are not suitable 
for  iron  oxide  scales.  Test  with  this  material  model  have  shown,  that  the  damage  does  not 
correlate to the damage which was found in experiments. Holes are punched into the oxide by 
the  shots  without  causing  any  damage  beyond  the  shot  path.  In  the  simulations,  this 

75 
 
 
 
phenomenon  however  can  only  be  observed  for  very  small  shots  impacting  on  a  thick  scale 
layer. 

•  Tensile  and  shear  failure  models  are  targeted  towards  materials  that  show  elastic-plastic 
behaviour.  According  to  [30],  iron  oxide  can  show  ductile  behaviour  with  a  narrow  plastic 
strain range of εp < 1 % at temperatures above 700 °C and appropriate strain rate. 

•  The  brittle  failure  and  damage  models  have  also  been  used  for  simulating  the  effects  of  an 
impact on the oxide scale [31]. The required parameters can be taken from literature [24, 32] or 
are attainable through experiments in an easier way than for the Holmquist-Johnson model. 
•  Simulations using the tensile failure model and brittle failure model have shown good results 

which do not show a significant difference. 

The simulation model does not feature an interface or adhesive contact between bulk material and scale 
layer. The scale  layer  is attached  directly  to the bulk  material. The  layered design  already  mentioned 
can  be  used  to  assign  special  properties  to  the  first  scale  layer,  which  can  act  as  an  interfacial  layer. 
Implementation of an adhesive contact between bulk and scale is possible but has not been implemented 
at that time because of problems with the contact definitions between the shots and the scale layer when 
using an adhesive contact between scale layer and bulk have been encountered that could not be solved 
in an appropriate amount of time. With no adhesive contact the simulation itself is very stable, although 
no parallelisation is possible due to the contact definitions. In contrast to that, the XFEM indentation 
simulations that have been developed at the start of the project took several days up to weeks until they 
usually aborted. Although the model is designed for multiple impacts, the first simulations were carried 
out with a limited number of shots in order to speed up the simulations. The fastest case, of course, is 
having only one shot. A script for the generation of arbitrary shot patterns with the desired number of 
shots, shot speed and impact angle is being used to create the corresponding input file data. The first 
results however were taken from simulations where only one shot was present. Later, simulations with a 
4-shot ordered pattern have been used. Different shot speeds and scale strengths have been investigated, 
as well as different shot sizes and scale thicknesses. 

Simulations were carried out to investigate the influence of scale strength and scale thickness as well as 
the influence of shot size and shot speed. Different scale strengths and three shot speeds (10, 40 and 75 
m/s) have been simulated. The scale strengths have been described in the tensile damage model as well 
as the brittle damage model in ABAQUS/explicit. The critical strain for failure was set to 2,5x10-05 - 
1,25x10-04  to  represent the  scale  strength  of  4  to  20 MPa  for  the  brittle  damage  model.  These  values 
were provided by CRM. The elastic constants for scale were set to Young’s Modulus E = 159 GPa and 
Poisson Ratio n
 = 0,36 [5]. The bulk has ideal elastic-plastic material behaviour with a yield stress of 
Ryield = 50 - 120 MPa according to Tata Steel. Unfortunately, there exist only a few publications with 
material  data  for  oxide  scales.  In  addition  to  that,  the  scale  behavior  depends  on  many  influencing 
factors, so only generalized material parameters were used. 

For the simulations different damage models were used in order to compare and evaluate the results in a 
more appropriate way. Compare Table 24 for a complete list of all simulation parameters that have been 
investigated. Not all parameter variations and combinations will be discussed in this final report. 

76 
Parameter 
Young’s modulus bulk 
Yield stress bulk 
Poisson ratio bulk 
Bulk density 

Young’s modulus scale 
Poisson ratio scale 
Scale density 
Critical strain 
Scale strength 
Scale thickness 

Young’s modulus shots 
Shot density 
Shot size 
Shot speed 

2.3.5.3. Results 

Value 
EBulk = 115 GPa 
Rvied = 50-120 MPa 
νBulk = 0,33 
ρBulk = 7,85 g/cm3 

EScale = 159 GPa 
νScale = 0,36 
ρScale = 5,7 g/cm3 
εcrit = 2,5*10-5 – 1,25*10-4 
4-20 MPa 
250 – 1000 µm 

EShots = ∞ (rigid body) 
ρShots = 7,85 g/cm3 
0,4 mm and 0,6 mm (S170 and S230) 
10 – 75 m/s 

Table 24 Simulation parameters 

The influence of shot size as well as scale strength and scale thickness has been investigated. Here, also 
the different  damage  formulations  are  presented  (brittle  and  tensile).  Bigger  shots usually  have  fewer 
impacts  per  area,  due  to  a  constant  mass  flow.  Coverage  effects  like  that,  however,  have  not  been 
investigated.  For  the  shot  size,  two  commercially  available  shot  sizes  (S170  and  S230)  have  been 
simulated  with  their respective  diameters.  Scale  thickness  was  varied from  250 µm  to  1000  µm  with 
respect  to  data  from  CRM.  The  simulated  shot  speed  was  75  m/s,  which  is  the  average  shot  speed 
according to WA. 

At first, the simulations using the brittle damage model are presented. Later, some results for the tensile 
damage model are shown for comparison. 

Figure 58 Result of four impacts of S170 on a 250 µm scale layer (brittle damage formulation) with a 
strength of 4 MPa (top) and 20 MPa (bottom). 

77 
 
 
 
 
 
 
 
Comparing  the  results  for  a  small  shot  and  different  strengths  in  Figure  58  clearly  shows  a  different 
amount of damage to the scale. While there are crack networks as well as ablation outside of the impact 
area for the low strength scale (top), only the direct impact area has been damaged for the high scale 
strength of 20 MPa (bottom). The scale with a strength of 20 MPa is showing stresses of around 10 – 15 
MPa in the remaining scale layer after the impact. This cannot be found for the 4 MPa scale layer, since 
this  would  be  above  the  limit.  Instead  the  scale  is  damaged  to  compensate  the  stresses  that  would 
otherwise occur. 

The  stresses  result  from  plastic  deformation  of  the  substrate  material,  which  is  caused  by  the  shot 
impact after breaking the scale layer. 

Figure 59 Result of four impacts of S230 on a 250 µm scale layer (brittle damage formulation) with a 
strength of 4 MPa (top) and 20 MPa (bottom). 

Using S230 instead of S170 (Figure 59) also leads to a full penetration of the scale layer for the low 
scale  strength  as  well as  the  high  scale strength.  It  is  interesting  that  the  4 MPa  scale layer  seems  to 
have taken less damage than being impacted by S170. The damage here is concentrated in the area of 
impact and cracks have formed starting at the impact area. The damage of S230 shots on high strength 
scale is comparable to the damage from S170. The S230 shots have more kinetic energy and thus the 
cracks are longer and the bulk material has undergone more plastic deformation. 

For the influence of scale thickness, only S170 shots will be considered. Of course, thicker scales are 
harder  to  penetrate.  This  can  be  clearly  seen  from  the  results  of  the  brittle  damage  simulations. 
Comparing Figure 60 to the results for 250 µm (Figure 58) shows that for the low scale strength, fewer 
cracks  have  formed.  For  the  higher  scale  strength  no  cracks  have  formed  at  all  and  the  damage  is 
limited to the immediate impact area. In addition to that, most kinetic energy is used to break the scale 
so only little plastic deformation of the bulk material occurs. That is the reason why no stresses can be 
found in the 500 µm scale layer for the high strength scale in contrast to the 250 µm scale layer. 

78 
 
 
Figure 60 Result of four impacts of S170 on a 500 µm scale layer (brittle damage formulation) with a 
strength of 4 MPa (top) and 20 MPa (bottom). 

Further  increasing  the  thickness  of  the  scale  layer  to750  µm  and  1000  µm  (Figure  61)  leads  to  a 
configuration where the scale layer could not be penetrated fully by the S170 shots on the first impact. 
The  scale  is  partially  destroyed,  but  there  is  still  scale  remaining  on  the  bulk  material.  Subsequent 
impacts would be necessary to further remove the scale. Unfortunately, the simulations are not stable if 
shots  impact  on  an  already  damaged  area,  thus  it  was  not  possible  to  simulate  coverage  effects  with 
multiple impacts on the same area. It is obvious, that successive impacts will damage the scale further 
and eventually remove it. 

79 
 
 
Figure 61 Result of four impacts of S170 on a 750 µm (top) and 1000µm (bottom) scale layer (brittle 
damage formulation) with a strength of 4 MPa. 

Comparing  the  different  damage  formulations  for  the  low  scale  strength  with  a  thickness  of  250  µm 
being impacted by four S170 shots shows some difference (Figure 62 (top) and Figure 58 (top)). In both 
cases, the scale is fully penetrated and crack networks have formed. The damage that occurs when using 
the brittle damage formulation seems to be higher than the damage using the tensile formulation. The 
same  tendency  can  be  seen  for  the  500  µm  scale  (Figure  62  (bottom)  and  Figure  60  (top)). 
Unfortunately, simulation with 750 µm and 1000 µm scale layers were not stable for the tensile damage 
formulation and aborted.  

It could be shown that the simulation of abrasive shot blasting is possible using ABAQUS/explicit and 
the approach that is presented here. The simulations are in accordance with the experiments in terms of 
scale removal. Both brittle and tensile damage formulations can be used for the oxide scale. The brittle 
formulation  is  more  stable,  however,  and  therefore  favored.  One  interesting  aspect  that  should  be 
investigated further is the influence of a particular shot size and scale thickness. There seems to be an 
ideal shot size for a specific scale thickness, in terms of maximizing the damage done by a single shot. 
In  addition to  that,  it  should  be  noted that  faster  shots  do  not  automatically  cause  more  damage  than 
slower shots. While it is obvious that faster shots carry more kinetic energy that can be used to damage 
the scale, the damaged area can be much smaller due to a hole-punching effect, where only very little 
energy is used to damage the scale layer. 

80 
 
 
 
Figure 62 Result of four impacts of S170 on a 250 µm (top) and 500 µm scale layer (tensile damage 
formulation) with a strength of 4 MPa. 

Figure 63 Amount of total deleted (failed) scale elements for selected simulations 

In Figure 63 it can be seen that the number of scale elements that fail due to the shot impact is increased 
with  the  thickness  of  the  scale layer.  Please  note,  that  there  are  more  elements available  as  the  scale 
thickness increases, since the element size was not changed. Most damage is done by the S230 shots 
because  of  the  higher  kinetic  energy.  With  increasing  thickness  of  the  scale  layer,  there  are  more 
elements in the shot path. Thus, the total failed elements are increased if the shot is able to penetrate the 
oxide layer. There is also damage from the deformation of the bulk material which also has an influence 
on the total failed elements. Only for the low scale strength of 4 MPa in combination with the impact of 
S170 shots no clear tendency can be seen. A scale layer of 250 µm and strength of 4 MPa receives more 
damage  from  S170  shots  than  from  S230  shots.  For  a  scale  thickness  of  750 µm  it  is  noticeable  that 

81 
 
 
 
 
there are more damaged elements for the scale layer with a strength of 20 MPa than for the scale layer 
with a strength of 4 MPa. Unfortunately, the simulation with a scale layer thickness of 1000 µm and a 
strength of 20 MPa impacted by S170 shots aborted after a few steps and did not complete. 

The  S230  shots  are  causing  more  damage  in  terms  of  deleted  elements  than  the  S170  shots  for  scale 
layers of 500 µm and above because the S230 shots are causing a lot of damage at the interface between 
bulk  and  scale  due  to  the  plastic  deformation  of  the  bulk  material  (see  Figure  64).  Damaging  the 
interface is beneficial in terms of descaling, since this leads to ablation of the scale layer. 

Figure 64 1000 µm scale layer (brittle damage formulation) with a strength of 4 MPa impacted by S230. 
Damage at the interface (white arrows) 

The main results can be summed up as follows: 

•  Abrasive shot blasting can be simulated using ABAQUS/explicit. 
•  Brittle damage formulation is more stable than tensile formulation, although both are possible. 
•  Coverage effects cannot be simulated because of stability issues. 
•  Shot size (and speed) should be chosen depending on scale thickness and strength. If the shot 
has too much energy, damage to the scale can be reduced and damage to the bulk material can 
be increased. 

82 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
2.4.  WP4: Characterization of surface state and properties 

2.4.1.  Task 4.1 Characterisation oxide/surface/sub-surface and Task 4.2 Analyse of the 

primary/secondary scale growth and adhesion.  

2.4.1.1. Primary scale 

This task is primarily associated with the TGA analyses (see main results of the TGA test in WP1) and 
reheating  test  done  under  industrial  and  lab  conditions  carried  out  on  all  the  steels  studied  in  this 
project, the analysis was completed by Tata Steel and CRM. Oxide layer composition not affected by 
surface state.  

Samples 

(2213)0.044% C-
2.57% Si-0.48% 
Al-11500C 

(2216):0.65% C-
0.35% Si - 0.12% 
Al-11500C 

(2216):0.65% C-
0.35% Si- 0.12% 
Al-12000C 

(2217):0.65% C-
1.23% Si - 0.05% Al-
12000C 

Thickness(µm) 

650 

500 

550 

1050 

Table 25 Scale thickness in reheating conditions 

Figure 65 Comparison reheated scale CRM lab reheating vs HPW descaler 

The main conclusions of this task are the following:  

•  The  primary  scale  is  non-uniform  and  already  fairly  porous  with  spallation  and  through 

thickness cracks.  

83 
 
 
 
 
 
 
•  The thickness of 0.65% C-1.23% Si-0.05% Al rail steel is 1050 µm, almost matching with the 
scale  thickness  of  940  µm  formed  under  industrial  reheating  atmosphere.  This  validates  the 
working procedure for reheating the samples in both CRM and Tata Steel device.  

•  The comparison of the primary oxide layer achieved on lab steels 2214 and 2215 in Tata Steel 
furnace  (see  WP2)  and  in  CRM  reheating  furnace  show  a  similar  morphology  and  scale 
thickness. See Figure 65.  

2.4.1.2. Impact of surface finishing 

Trials  have  been  performed  on  industrial  rail  materials  for  oxide  scale  characterization  to  check  the 
impact  of  surface  states  (as  cast reheated,  machined and  polished  surface). The  production  298Q  rail 
steels are reheated under controlled atmosphere with an operating temperature of 1200 0C.  

The main conclusions of the results already reported in Annual report [R] are here summarised:  

•  Surface state do not have an effect on the scale formed during reheating, no difference in scale 

thickness between as-cast and polished samples  

•  After  shot  blasting  the  polised  sample  shows  lower roughness  and  best  descalability  than the 

samples with surface state as-cast. 

2.4.1.3. Surface after shot blasting 

Cross section of the samples shot blasted and described in the WP3 have been analysed in detail. Figure 
66 displays the cross section view for different shot size and the quantity of the media’s for both lab 
cast and industrial materials.  

•  For the low Al electrical steels (2213, 2214 and industrial electrical steels, shot blasted with 6 
kg to 9 kg), the oxide layer is mostly removed at 7.5 bars. No significant effect of the blasting 
parameters on the oxide layer is observed. The liquid phase of FeO-Fe2SiO4 forms at 1178  0C 
and penetrates into the steel, appears especially at the grain boundaries. Al also in combination 
with  Si  reduces  the  eutectic  Fayalite  temperature  to  below  1178  0C  (~1148  0C)  therefore 
increasing liquid oxides penetration. 

•  For the high Al electrical steel (2215), aluminum (Al) is enriched at the scale/ metal interface. 
Strong enrichments, at higher Al levels, lead to Fe-Al spinel formation (FeAl2O4) at the scale/ 
metal.  

•  The longer the duration of the shot blasting, the less oxide layer remains on the metal surface. It 

• 

seems that bigger shots have a better descalabiliy than the smaller ones. 
In order to ensure descaling effect and reduce descaling time higher flow rate (200-500 kg/min) 
and higher shot velocity will be necessary. But the pilot shot blasting machine currently used in 
CRM  is  close  to  its  maximum  flow  rate  9kg/min.  New  wheel  blasting  machine  will  be 
implemented in Tata Steel to continue the industrial testing. 

Settings parameters 

WS230 

9 kg 

6 kg 

WS170 
9 kg 

CRM 
2213(Electri
cal steel) 

CRM 
2214(Electri
cal steel) 

84 
 
 
 
 
 
 
 
 
 
 
CRM 
2215(Electri
cal steel) 

Industrial 
32(Electrical 
steel) 

Industrial 
34(Rail 
steel) 

Figure 66 Surface of specimen shot blasted 7.5 bar of air with controlled reheating atmosphere at 1150 
°C 

2.4.1.4. High speed camera test 

During trials performed at Tata Steel UK with the wheel blasting machine (described in the WP6) tests 
using a high speed camera were performed. The objective of the test was to observe the behaviour of 
the  oxide  during  water-free  descaling  process  at  high  temperature.    Tests  are  done  in  static  way. 
Following pictures show the full removal of the oxide during shot blasting.  

Figure 67 Tata Steel UK high speed camera test.  

85 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
2.4.2.  Task 4.3 Surface temperature during descaling 

2.4.2.1. Hydraulic descaling 

Trials  were  carried  out  to  study  influence  of  heat  losses  during  single  and  double  descaling.  A  new 
concept/shield was used to protect the thermocouples and a selective number of trials at 200, 300 and 
400 bars have been conducted for both primary and secondary scale. Sampling rate was 700samples/s.  

a)  400bar primary scale 1040 to 981oC i.e. 60oC loss 

at 0.12m/s - 100mm standoff 

b)  797oC  to  750oC  or  47oC  at  lower  temperature  – 
secondary scale from initially chilled surface 

Figure 68 Assessment of surface temperature during descaling - water based descaling 

The  descaling  trials  using  a  modified  and  more  robust  design  has  led  to  interesting  data  of  heat 
loss/HTC measurements of typically 60 to 80°C loss at 0.12m/s in the range of 300 to 400 bars with 
reduced heat losses on secondary scale but initially chilled surfaces of the order of 50oC. Test done in 
dynamic mode.  

2.4.2.2. Water-free descaling – shot blasting 

By means of thermocouple measurements, the temperature was also assessed during hot shot blasting 
processes, to be able to compare with the heat loss during hydraulic descaling.  

A  thermocouple  was  used  to  follow  the  surface  temperature  of  the  blocks  during  the  shot  blasting 
process mentioned in Task 3.2. The curve corresponds to static shot blasting tests with 6 to 9kg of shots, 
corresponding respectively to 40s and 60s blasting time. Such long blasting times are not compatible 
with the industrial practice but are due to the limits of the current blasting unit (limited flow rate and 
shot velocity).  

In Figure 69a it is observed that the different blocks exhibit the same cooling rate during shot blasting 
which is about 5 0C/s, (the thermocouple was fixed 2 mm below the surface). The different shots types 
have  no  influence  on  the  cooling  rate,  and  the  shots  temperature  increased  little  after  shot  blasting 
process. In the Figure 69b, it is shown also the sample rolled during pilot trial at Tata Steel, see WP6, 
the  sample  was  descaled  on  both  faces,  top  water  descaling  and  bottom  shot  blasting  descaling,  the 
upper side has a lower temperature due to the water cooling higher than the cooling from shot blasting.  

86 
 
 
 
 
 
 
 
Figure 69 Assessment of surface temperature during descaling - water free descaling a) on static test, b) 
on dynamic test, HPW and Shot blasting combined in one sample 

 a) 

b) 

87 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
2.5.  WP5: Process efficiency comparison and implications 

2.5.1.  Task 5.1 Assessment of optimum descaling techniques 

2.5.1.1. Water based descaling 

See methodology of Task 2.8 and regime maps of Task 6.1.  

Optimum descaling methodology requires: 

•  Appropriate  level  of  descaling  energies  based  on  grade  and  pump/water  supply  from  17  to 
above 50kJ/m2 for electrical steels. Depending on mill layout, feedstock speed can be adjusted 
and potentially reduced above  minimum speed to increase descaling energies. This is key for 
primary descaling. 

•  Optimum  selection  of  nozzle  with  maximum  spray  angle  of  30o  assuming  coverage  can  be 

achieved 
standoff within 90 to 120mm again based on minimum pitch (45mm) and overlap/wash 

• 
•  Careful control of overlap to avoid overcooling (see HTC measurements) with overlap tailored 

to impact pressure edge drop + allowance, i.e. between 7 to 15% spray width. 
•  For difficult to descaler grade, the rotary descaling should be the preferred method. 
•  Pre-descaling, scale can be pre-conditioned via low pressure spray but more trials are required. 
•  Post-descaling, secondary scale growth can be controlled via coating or other inhibitor. 

2.5.1.2. Water free descaling 

From results obtained from WP3 optimal parameters to test during trials in the pilot mill at Tata steel 
were selected: 

•  Line speed 0.1 to 1m/s 
•  Test duration 10sec 
•  Sample dimension max 700-900mm length  
•  Shots: WS170 and WS230 
•  Speed: 61m/s (50Hz) or 76m/s (60Hz) 
•  Conveyor speed: 2.9m/min (25Hz), 4.7 m/min (40Hz), 5.8m/min (50Hz); 7 m/min (60Hz) 
•  Turbine angle: 90°C (perpendicular to the movement) and 37° (optimal coverage)  
•  5.5kW blasting wheel 
•  Max flow rate 90kg/min 
•  Covered width 0.6-1m 

2.5.2.  Task 5.2 Detailed comparison water-based / water free descaling on selected grade  

The comparison of the two processes has involved the following methodology: 

1.  Modelling to compare energy involved, penetration, contact areas, etc. as well as ability to scale 
the two processes together as to reach based on differences in density between water and shot 
similar velocity 

2.  Experimental  and  characterisation  technique  based  on  micro-hardness  measurement,  Al 

erosion, plasterboard erosion 

3.  Water-free and water-based descaling tests including hot rolling process at lab scale.  
4.  detailed surface characterisation (LOM, SEM/EDA and Elcometer residual scale thickness) and 

identification of key performance indicators 

2.5.2.1. Modelling 

In  view  of  the  complexity  of  both  processes  as  well  as  the  need  to  determine  a  set  of  common 
parameters or conditions under which both processes can be compared, a range of modelling activities 
complementary  to  the  work  in  Task  3.5  has  been  undertaken.  This  dealt  with  analytical  and  FEM 
modelling  to  get  estimate of  penetration  function of initial shot  velocity  and  relative  strength, typical 
impact pressure/force and energy and typical contact area and influence of set-up 

89 
 
 
 
 
The full factorial DoE encompassing WINOA conditions was based on the following input and range: 

 Shot density [1000,4000,7800] (kg/m3) representing both water and steel 

•  R Shot radius[0.25,0.5,1] (mm) 
• 
•  Vo Shot Velocity [1,10,100] (m/s) 
• 

p (yield strength pressure equal to 3Ys) [1,10,100] (MPa)  

The density was varied to integrate water and steel. The Pareto chart and main effects are shown below. 

(a) 

(b) 

(c) 2D map showing penetration depth z function 
of shot velocity and yield strength of material 

(d) 2D map showing penetration depth z function 
of shot density and shot radius 

Figure 70 DoE Analytical study of penetration depth z [mm] 

It can be clearly observed that depth of 1200microns or greater can be obtained for substrate less than 
20MPa irrespective of shot density and within shot radius of max 0.4mm which is at the upper limit of 
mean  diameter  of  water  droplet.    Of  course  as  shot  density  increases,  greater  penetration  can  be 
sustained.  

shot/r water)0.5 is therefore the ratio to scale down (:2.79) the velocity of the shot function of 
A ratio of (r
water velocity from the HPW descaling (derived from Bernoulli principle). Typical Fluid velocities for 
DSP DNM0325 are shown below with likely correspondence for the shot blasting process (Table 26). 

90 
r
 
 
 
 
 
 
 
 
 
 
Flow rate (l/min) 

Pressure (bar) 

Water velocity 
(m/s) 

Shot velocity 
(m/s) 

HPW descaling 
IP [Mpa] 
@93mm standoff 
0.6 
0.94 
1.36 
1.6 
1.85 
2.4 

20 
25 
30 
32.5 
35 
40 

133 
167 
200 
217 
233 
267 
Table 26 Analytical equivalence between mechanical descaling and shotblasting (no thermal effect and 
static impact) 

47.6 
59.8 
71.6 
78 
83.4 
95.6 

124 
193 
278 
326 
378 
493 

It can be observed that the top end of shot blasting process (~80m/s) considered corresponds to a HPW 
descaling of max 320bar for this particular nozzle (DNM0325) giving theoretical HPW descaling IP of 
the order of 1.5 - 1.8 MPa. The estimated analytical penetration depth is 0.1 to 0.3mm using water or 
metallic shot for 0.4mm diameter particulate.  

Further  comparison  between  the  HPW  descaling  and hot  shot  blasting  has  considered fixing  the  max 
line speed of ~0.12m/s of the WINOA prototype and calculating for two system pressures the various 
energies involved during HPW descaling using the analytical method presented in Table 4 and Figure 
24.  Further  calculation  of  impact  energies  involved  during  hot  shot  blasting  has  been  made  using 
penetration  depth  and  calculated  surface  area  in  impacting  zone  using  Knud  Thomsen’s  method  [27] 
surface area calculation of an ellipsoid and estimated kinetic energy of shot. 

Figure 71 shows typical energies at both 120 and 200bar HPW descaling at 0.12m/s using DNM0325 
nozzle. 

Parameters which have been fixed are standoff 88mm and rake angle of 5o which simulated most of all 
experimental trials to compare two methods. 

It  can  be  observed  that  at  low  speed  descaling,  accounting  for  both  effect  of  IP  and  water  (as  these 
cannot be decoupled), the descaling energies at lowest system pressure is typically ~28kJ/m2 compared 
to 8kJ/m2 for a single martensitic shot 0.4mm diameter travelling at 78m/s on a oxide-steel surface of 
10MPa strength. 

Everloy DNM0325 

Nozzle pitch E 
Nozzle constant K 
Nozzle constant x 
Flow pressure CD 
System pressure SP at nozzle derived from Flow rate 
G flow rate L/min 
Alpha spray angle deg 
Transverse spray angle imposed deg 
Fit spray angle constant a 
Fit spray angle constant b 
Fitted Alpha spray angle deg 
Fit transverse spray angle constant a 
Fit transverse spray angle constant b 
Fitted transverse spray depth angle deg 
E smallest nozzle orifice mm 
Theoretical depth spray angle definition 2 deg 
Gamma offset angle 
Lead angle beta 
Nozzle height or standoff H mm 
Speed (cm/s) 

HPW 
descaling 
120bar 
48.00 
2.0548089 
1.7320132 
0.31 
119.81 
19.70 
30.00 
1.80 
31 
2.27E+26 
30.16 
1.80 
100 
1.74 
1.5 
2.71 
15.00 
5.00 
88.00 
12 

HPW 
descaling 
200bar 
48.00 
2.0548089 
1.7320132 
0.31 
202.32 
25.60 
30.00 
1.80 
31 
2.27E+26 
29.38 
1.80 
100 
1.71 
1.5 
2.54 
15.00 
5.00 
88.00 
12 

91Impact descaling Energy [Kj/m²] 
Total energy evaporation [kJ/m²] based on calculated delta T 

28.25 
4.61E+00 

47.70 
4.64E+00 

HPW descaling 120 bar and 200 bar -0.12m.s and corresponding energies 

Figure 71 Comparison of estimated energies between HPW descaling and shot blasting 

From the characterisation of impacted metal-oxide interface by shot blasting (see description of trials in 
this section), one can use the approach above to impose penetration measured and by imposing typical 
energies similar to the HPW descaling check the magnitude of the strength of the material which will 
have given this measured penetration as a check of the overall approach.  

Shot 
dia 
mm 
4.00E
-01 

Shot 
dia 
mm 

4.00E
-01 

Shot 
radius 
mm 

Shot volume 
mm³ 

Shot 
volume m³ 

Density 
kg/m³ 

Shot mass 
kg 

Shot 
speed 
m/s 

2.00E-01 

3.35E-02 

3.35E-11 

7.80E+03 

2.61E-07 

72 

Kinetic 
E  
j 
6.77E-
04 

Shot area 
m² 

Min energy 
kJ/m² 

Penetration 
mm 

Knud 
Thomsen´
s surface 
area mm² 

Knud 
Thomsen´
s ellipsoid 
surface 
area m² 

5.03E-07 

1.35E+00 

1.095E-01 

2.59E02 

2.59E-08 

Max 
Energy 
kj/m² 

2.61E+0
1 

Figure 72 Typical reverse calculation by fitting the material strength to give penetration ~100µm close 
to measured values and estimate shot blasting energy 

 Using this approach which is similar to a 200bar impact pressure, typical energies are close to half of 
the  HPW  descaling  when  considering  similar  travelling  speed  of  0.12m/s  (lower  range  of  HPW 
descaling,  upper  range  of  WINOA  prototype  shot  blasting  unit).  To  equate  energies  between  HPW 
descaling and shotblasting, speed through HPW descaling has to be increased to 0.4m/s. 

This  approach  is  interesting  as  it  tries  to  compare  two  different  processes  one  involving  only 
mechanical  impact  with  the  HPW  descaling  coupling  both  effect  of  impact  and  water.  Faro  arm 
technology, image analysis and micro-hardness 

Faro  arm  technology  is  being  used  to  cross  compare  HPW  descaling  erosion  impacts  with  impacts 
from  shot  blasting  process  within  imposed  masked  area  (simulating  impingement  area  of  HPW 
descaling). 

WINOA in collaboration with Tata Steel carry out at CRM the a range of Al shot blasting experiments 
varying time, standoff, rake, shot quantity and blasting or erosion time.  

Faro  arm  measurements  have  been  carried  out  on  the  aluminium  blasted  samples,  the results  showed 
that no erosion has occurred only material displacement (plasticity) Figure 73 under shot impact. For 
that reason plasterboard and teflon shot blasting erosion tests were also carried out. 

Hardness 
plasticity under spray impact HPW 

showing 

imprint 

little 

Hardness 
/plasticity below the shot blasted area 

imprint  showing  Hardening 

Figure 73 Shot blast imprints on masked Al plate 

92 
 
 
 
 
 
2.5.2.2. Plasterboard and Teflon wheel blasting test 

Shotblasting  onto  plasterboard  and  Teflon  were  also  carried  out  to  get  additional  comparative 
information  of  efficiency  and  coverage  of  process  in  relation  to  the  HPW  descaling.  This  was  done 
using  appropriate  masking  in  a  dynamic  mode  at  a  given  turbine  rate  and  speed.  This  was  then 
compared with HPW descaling keeping line speed constant (0.12m/s).  Table 26 gives speed conversion 
which  for  60Hz  (76m/s)  should  statically  be  equal  to  330bar  (~215m/s  fluid  velocity).  Using  a 
simulation material in dynamic mode, to achieve similar erosion depth, the descaler had to be ramped 
down  to  120bar.  This  gave  120  bar  system  pressure  to  give  same  erosion  depth  as  shot  blasting  or 
~0.7MPa and a descaling energy of 40kJ/m2. So similar to HPW descaler, both turbine speed (i.e. shot 
velocity) and line speed are key factors affecting descalability.  Therefore Table 26 detailing conversion 
factor in a static mode between HPW decaling (fluid velocity) and shot blasting (shot velocity) based 
only on density ratios need to be scaled accounting for line speed. Fixing line speed means that same 
descalability between the two processes should be reached at 120bar for the HPW descaling and 60Hz 
turbine speed, therefore a decrease ratio of 2.75 on system pressure. 

plasterboard 

(a) 
dynamic 
shotblasting  line  speed  0.12m/s 
60Hz (76m/s)   

plasterboard 

(b) 
HPW 
descaling  same  line  speed 
0.12m/s 120bar (DNM0325) 

(c)  shotblasting  on  Teflon  at  both 
speed 

Figure 74 Imprint on simulation material (plasterboard and Teflon)  

2.5.2.3. Descaling efficiency comparison lab scale 

Figure 75 displays the cross section obtained after respectibely high pressure water descaling (double 
descaling see task 2.4) and shot blasting (task 3.2) for the steels 2214 and 2215. Although a small scale 
layer can still be observed, it can be concluded that on lab scale test static hot shot blasting is at least as 
efficient as double high pressure water descaling in removing the primary scale.  

93 
 
 
 
 
Figure 75 Comparison descaled samples shot blasting vs HPW descaling 

2.5.2.4. Water-free and water-based descaling comparison including hot rolling process at lab scale.  

CRM  has  performed  a  series  of  trials  using  water  descaling  and  shot  blasting  descaling  in  order  to 
compare the surface evolution of the samples after the descaling and rolling process for both processes.  

Water descaling + hot rolling test 

A new device has been designed in CRM to improve the removal of oxide from the samples using water 
descaling after reheating and before rolling. In the new descaler box the standoff, the inclination angle 
and the distance between nozzles are easy to adjust. The speed of the block and the temperature before 
and  after  descaling  can  also  be  measured  during  the  test.  The  samples  used  for  this  test  are 
100x100x30mm.  

94 
 
 
 
Descaler Box Nozzles 

Nozzles number 
Nozzle spray angle (α) 
Pressure 
Flow rate 
Inclination angle (β)  
Offset angle (γ) 
Vertical spray height (h2) 
Spray width (B) 
Spray depth  
Total force 
Max impact 
Total flow rate  

642.537 
30° 
130bar 
17.10l/min 
20° 
15° 
60mm 
46mm 
2.73mm 
47N 
0.45N/m² 
34.2l/min 

Figure 76 New descaler box CRM Gent 

The  objective  of  the  hot  rolling  after  water  descaling  is  to  follow  the  scale  evolution  and  compare  it 
with the shot blasting descaling process. For the test two industrial materials are used 298Q (34) and 
UT23  (32).  See  composition  in  Table  3.    Parameters  are  shown  in  the  Table  27.  After  reheating  in 
controlled atmosphere (described in WP3) the samples are descaled and then rolled in the rolling stand 
with a maximum rolling force of 400Ton and a maximum roll speed of 0.66m/s. the rolling reduction 
was 20%. After rolling the samples were taken inside a cooling nitrogen device during 30min at -50°C.  

Reheating condition 

Rolling 

Water descaling 

Cooling 

Material 

c
o
l
B

.
f
e
R

e
c
a
n
r
u
F

)

C
°
(
e
r
u
t
a
r
e
p
m
e
T

e
m

i
t
g
n
i
t
a
e
h
e
R

)
n
i
m

(

C
°

t
n
i
o
P
w
e
D

)

%

(

l
e
v
e
l

n
e
g
y
x
O

%
n
o
i
t
c
u
d
e
R

s
s
e
n
k
c
i
h
t

l
a
n
i

F

d
e
e
p
s

t
e
g
r
a
t
-
e
l
z
z
o
N

)

m
m

(

e
c
n
a
t
s
i
d

)
s
r
a
b
(

e
r
u
s
s
e
r
P

e
l
g
n
A
n
o
i
t
a
n
i
l
c
n
I

e
l
z
z
o
n

34 

7837  1160  60  57  2 

20 

23.2 

0.4m/s 

34 

32 

32 

7838  1160  60  57  2 

20 

23.2 

0.4m/s 

7839  1160  60  57  2 

20 

23.2 

0.4m/s 

7840  1160  60  57  2 

20 

23.2 

0.4m/s 

60 

60 

60 

60 

130 

15 

130 

130 

0 

0 

130 

15 

Table 27 Hot rolling parameters water descaling trials 

e
r
u
t
a
r
e
p
m
e
t

g
n
i
l
o
o
C

)

C
°
(

-50 

-50 

-50 

-50 

e
m

i
t
g
n
i
t
i
a
w

0 

0 

0 

0 

)
n
i
m

(

e
m

i
t

g
n
i
l
o
o
C

30 

30 

30 

30 

After descaling and hot rolling for material 32, still present some entanglement and internal oxidation, 
the  water  descaler  could  not  remove  completely  the  scale  formed  in  the  reheating  furnace.  For  the 
material 34 the entanglement is less pronounced but the oxide is not completely removed with the water 
descaling. After hot rolling still a remaining oxide layer of around 20µm is present in both materials.  

95 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Cross section material 34 after water descaling and hot rolling  

Cross  section  material 
32  after  water  descaling 
and hot rolling 

Figure 77 Cross section material 32 and 34 after water descaling and hot rolling with reheating 
temperature of 1160°C 

Shot blasting descaling + hot rolling test 

The objective of hot rolling after descaling by shot blasting is to follow the scale evolution. Many tests 
have been performed with the descaling by shot blasting in this project with successful results. But it is 
important to follow the scale growth during rolling and check what will be the effect of the shots impact 
on the material surface. Using the same parameters of atmosphere control the samples are descaled by 
shot  blasting  and  then  rolled  in  the  rolling  stand  with  a  maximum  rolling  force  of  400Ton  and  a 
maximum roll speed of 0.66m/s. the rolling reduction was of 20%. After rolling the samples were taken 
inside  a  cooling  nitrogen  device  during  30min  at  -50°C.  The  samples  used  for  the  rolling  are 
100x70x30mm.  samples  used  for  reference  and  shot  blasting  descaling  only  are  70x70x30mm  The 
parameters used during the trial are in the following table: 

Reheating condition 

Shot 

Rolling 

Shot 

Cooling 

e
l
p
m
a
s

s
s
e
n
k
c
i
h
T

29 
29 

l
a
i
r
e
t
a
M

c
o
l
B

.
f
e
R

e
c
a
n
r
u
F

e
r
u
t
a
r
e
p
m
e
T

)

C
°
(

g
n
i
t
a
e
h
e
R

)
n
i
m

(

e
m

i
t

t
n
i
o
P
w
e
D

C
°

l
e
v
e
l
n
e
g
y
x
O

)

%

(

t
c
u
d
o
r
P

s
s
e
n
d
r
a
H

)
v
H

(

%
n
o
i
t
c
u
d
e
R

l
a
n
i
F

s
s
e
n
k
c
i
h
t

e
r
u
s
s
e
r
P

)
s
r
a
b
(

y
t
i
t
n
a
u
Q

)
g
K

(

34  7790  1200 
34  7797  1200 

7795  1200 

34 

7799  1200 

34 
32  7789  1200 
32  7796  1200 

7798  1200 

32 
32  7800  1200 

60 
60 

60 

60 

60 
60 

60 

60 

57 
57 

57 

57 

57 
57 

57 

2 
2  WS230  450 

REF 
0 

29 

7.5 

2  WS230  450 

10  26.1  29 

7.5 

2  WS230  450 

20  23.2  29 

7.5 

2 
2  WS230  450 

REF 
0 

29 

29 
29 

7.5 

2  WS230  450 

20  23.2  29 

7.5 

9 

9 

9 

9 

9 

2  WS230  450 

0 
57 
Table 28 Hot rolling parameters second set of trials 

7.5 

29 

29 

9 

g
n
i
l
o
o
C

e
r
u
t
a
r
e
p
m
e
t

)

C
°
(

-50 
-50 

-50 

e
m

i
t

g
n
i
l
o
o
C

)
n
i
m

(

30 
30 

30 

-50 

30 

-50 

-50 

-50 

30 

30 

30 

Ref 
Ref Shot 
hot rolling 
10% 
hot rolling 
20% 
Ref 
Ref Shot 
hot rolling 
20% 
7796 

The  samples  have  been  observed  right  after  the  reheating,  shot  blasting  and  rolling  reduction.  In  the 
following table the aspect of the surface after each process is shown for the two materials. The sample 
after hot rolling of 20% shows a very smooth surface, no cracks are visible or shots inclusions on the 
surface.  

96 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Reference 

Shot blasting 

Shot blasting + hot rolling 20% 

Figure 78 Surface aspect and cross section of samples after reheating, shot blasting and hot rolling at 
20%. Material 34 

Reference 

Shot blasting 

Shot blasting + hot rolling 20% 

Figure 79 Surface aspect and cross section of samples after reheating, shot blasting and hot rolling at 
20%. Material 32 

Samples were taken for cross section analysis; the surface after shot blasting shows a wavy aspect but 
after hot rolling the oxide and substrate is deformed to a smooth surface and homogenous oxide layer. 
Entanglements, internal oxidation or cracks are not visible.  

In  summary  at  lab  scale  the  static  shot  blasting  descaling  shows  a  better  descaling  performance, 
entanglement and internal inclusion observed after water descaling and even after water descaling and 
rolling are completely removed by shot blasting process.  

97 
 
 
 
 
 
 
 
 
 
 
 
 
 
2.6.  WP6: Regime maps, sensitivities and industrial validation for optimum descaling  

2.6.1.  Task 6.1 Regimes maps of innovative mechanical descaling techniques 

Task  6.1  summarises  all  work  carried  out  in  this  project  and  is  based  on  an  extensive  Design  of 
Experiment  exploring  the  design  space  of  input  factors  highlighted  in  Table  5  for  primarily  the  DSP 
nozzle DNM0325. Optimization of the SRM was also done. 

2.6.1.1. DoE and sensitivity HPW descaling parameters 

The revised analytical Excel spread sheet of Figure 24 has been wrapped into the Workbench Isight-
FD®  for  deriving  sensitivities  and  most  significant  input  factors  to  key  responses  such  as  IP,  SWI, 
Impact Energy and cooling.  

•  DSP 

A 9-factor full factorial (13122 runs) Hybrid quadratic-linear DoE has been developed and run across 
the following “tighter” design space than the one reported in [1], i.e. closer to DSP production level 
and in-line with AL erosion and impact force testing. 
Figure 80 shows an example of Pareto charts of the range of IP and SWI calculated within the design 
space  (13122  runs).  Note  that  SWI  was  capped  at  the  saturation  value  of  40l/m2.  These  graphs  are 
useful in highlighting regions of interest, i.e. high IP- low SWI. In Annex 2 initially Pareto charts show 
sensitivities/influence of input factors on a given selected output (e.g. IP, etc.). Any bar coloured in blue 
indicates a positive effect whilst in red negative (i.e. any decrease of a given variable will be related to 
an increase in the output).  

Figure  80  an  example  of  the  2D  regime  maps  is  shown;  details  of  the  typical  2D  regime  maps  of 
descalability, IP as well as isolines of descaling energy at 20, 30 and 44kJ/m2 are in the Appendix 2.  

Impact pressure IP (only linear 
effect plotted) 

(equation 
energy 
Impact 
IP*SWI)  (only  linear  effect 
plotted) 

2D regime maps descaling energy 
function  of  flow  rate  and  speed 
(DSP  –  DNM0325)  @  93mm 
standoff  ,  15deg  offset,  15deg 
rake, 30deg spray angle 

Figure 80 Example Pareto charts and 2D regime maps, line of iso-descaling energy together with 
avenues for optimisation (DNM0325) 

99 
 
 
 
 
a)

b) 
Figure 81 regime maps, line of iso-descaling energy together with avenues for optimisation 
(DNM0325) 

Plots of impact energy versus SWI are also of interest in order to maintain a minimum value of impact 
energy (e.g. ~17kJ/m2 for CMn steel). It shows that at 60cm/s a minimum flow rate of 25l/min will be 
required to reach this threshold. 

For DSP, it can be concluded that a minimum of 30l/min is required per nozzle in order to be able to 
descale uniformly and even higher flow-pressure for reaching the descaling energies required for very 
difficult  grades.  Relations  between  IP  and  SWI  have  been  derived  (see  Figure  81f)  and  should  be 
implemented. Overlap is more difficult to predict and should be tested more thoroughly using hot tests 
but for this spray angle and regime map of Figure 81c operating between 88 and 93mm standoff should 
create correct overlap. 

A DoE Analysis for hot HPW descaling was used using EISME concept [8] inc. theoretical calculation 
based  on  analytical  approach  of  Figure  24.  Three  input  parameters  have  been  varied  to  study  and 
validate the required descaling  energies  for  electrical steel  UT23  as  well  as  overlap as  derived  by  Al 
erosion testing. Typical reheating conditions of 1160oC 60 min soak, 2%excess O2 have been applied as 

100 
 
utilised previously. In total 11 tests were carried out on UT23 B9S38 (prior tunnel) on 70x70x100mm 
block with descaling across the 100mm  width of the samples.  Best descaling results are Samples 61 
(400bar, 0.1m/s, 90mm), 70 (400bar, 0.2m/s, 100mm) and then 71(400bar, 0.5m/s, 85mm). 

Figure 83 plots regime maps of IP v SWI v velocities and surface state post descaling. 

(a)  DoE  1  –  400bar  0.1m/s 
90mm 

(i)  DoE  10  –  400bar  0.2m/s 
100mm  –  note  an  overlap 
bands can be observed 

(j)  DoE  11  –  400bar  0.5m/s 
85mm 

Figure 82 surface state post descaling 

(a) IP v SWI 

101 
 
 
 
 
(b) IP v V (independent variables) 

(c) IF (calculated by IP * contact area) v V 

Figure 83 Regime maps UT23 

It can be observed that from Figure 83a, that assuming a saturation point of 40l/m2 on SWI, IP v SWI 
shows good trend between IP and SWI as previously adopted concept with typical 2MPa – 1.7MPa at 
30-35l/m2  for  effective  uniform  descalability  of  UT23.  IP  v  V  (velocity  through  descaler)  is  also  a 
useful concept as using two independent concepts not sharing flowrate. (Figure 83b). Impact force v V 
shows a reasonable trend except at high pressure where no differentiation can be made at large Impact 
force  owing  to  in  one  case  reduced  IP  and  larger  impact  area  which  generates  large  impact  forces, 
therefore concept of impact area cannot be accounted for. 

Figure  Figure  83d  shows  descaling  energies  plotting  versus  residual  scale  measured,  which  is  also  a 
concept worth exploring, although when linked to detailed measurements of scale thicknesses does not 
seem  to  show  clear  correlation  as  various  points  of  very  high  descaling  energies  above  60kJ/m2  can 
produce different descalability index.  

A  concept  worth  exploring  is  Impact  Force  per  unit of  mm  (either  from  spray  width  or  indeed  spray 
depth).    This  concept  seems  to  differentiate  very  well  the  all  output  results  and  descalability  status 
(residual scale). 

Figure 84 Independent variables of Impact force/unit mm v Velocity V (m/s) 

102 
 
 
 
In summary, optimised regime  maps have been output and validated up to 400bar for DSP and SRM 
grades.  Further  work  is  required  with  lower  gauge  hot  samples  to  assess  HTC  and  effect  of  system 
pressure and velocity in overlap areas. 

2.6.2.  Task 6.3 Industrial testing of selected techniques 

Large experimental trials inc. descaling/rolling trials with large scale hot shot blasting prototype 
developed by WINOA/CRM at STC against HPW descaling 

A series of industrial pilot trials to compare HPW descaling and hot shot blasting inc. effect on rolling 
was  carried  out  in  December  2012  after  careful  planning  by  the  Consortium  members.  A  large  scale 
shot blasting unit was refurbished and improved by WINOA and CRM and delivered to STC G block 
plate mill area. The idea was to perform a large series of controlled “heavy” trials as close to production 
to  compare  efficiency  of  both  processes.  A  series  of  ~50  trials  was  carried  out  on  the  range  of 
composition highlighted in Table 3, i.e. from rail to valve spring and electrical steels. All steel blocks 
were  prepared  by  Tata  Steel  integrating  small  blocks  (70x70x100) to  medium  blocks  (120x90c50)  to 
large  rolling  blocks  (up  to  460mm  in  length).  Thermal  imaging  and  pyrometer  temperature 
measurements were made during this campaign of trials inc. attempt to measure shot temperature post 
shot blasting.  

A  standard  wheel  blasting  machine  was  adapted  to  perform  these  tests.  To  be  able  to  work  with  hot 
samples  >1000°C  all  rubber  parts  were  removed,  inlet  and  outlet  curtains  were  custom  built  out  of 
metallic chains.  

On  the  top  of  the  blasting  cabinet  a  blasting  wheel  was  positioned.  To  access  comparable  angles  to 
HPW, the turbine could be adjusted in 3 dimensions. Hot spot (highest abrasive density) adjustment is a 
standard in wheel turbine. The rake angle of the wheel has been custom-made  designed and built for 
this application. A blasting wheel of 5.5kW with capability of 90kg/min in term of flow rate should be 
enough to ensure a good efficiency and productivity. Blasting speed and blasting flow were monitored 
through  an  automation  system.  The  tests  were  realized  in  dynamic  conditions.  Media  was  reused  for 
each sample.  

Figure 85 3D adjustment of wheel turbine 

The parameters of the test are:  

•  5.5kW blasting wheel 
•  Max flow rate 90kg/min 
•  Shot speed ~80m/s 
•  Sample speed 0.12m/s 
•  Covered width 0.6-1m 

103 
 
Figure 86 Hot shot blasting prototype at STC G block Plate mill top level chute for WINOA shot 
(~60kg shot) 

Several initial surface finishes were considered, machined sawn, machined smooth and as-cast.  

These trials were split into two strands 

(cid:2)  HPW descaling (pilot descaling rig) vs hot shot blasting for all grades followed by cooling in 

Argon using the two argon boxes available 

(cid:2)  HPW descaling vs hot shot blasting inc. effect of rolling in plate mill STC (1 & 3 rolling 

passes) followed by Argon cooling (after 1 pass rolling) or DQ cooling on hot rolled material 
after 3 passes.  

For  each  block  two  faces  were  either  shot  blasted  or  HPW  water  descaled  to  enlarge  the  matrix  of 
testing conditions. 

2.6.2.1. HPW descaling (pilot descaling rig) vs hot shot blasting 

Figure 87 Small block in and out (before and after descaling) of shot blasting cabinet 

Preliminary test has been done to adjust the industrial wheel blasting machine, the test were done with 
small blocks as shown in the Figure 87. It can be seen that block enters the wheel blasting machine with 
a heterogeneous layer of scale and at the exit the block showed a homogenous surface where the scale is 
removed after the blasting process.  

HSB 

Figure 88 Electrical steels UT12 and UT23 (see Table A2.1) Left hand side: Hot shotblasting (right) 
HPW descaling 200bar 0.12m/s 

104 
 
 
 
 
Tests  with  bigger  blocks  were  after  performed.  From  visual  observation  it  can  be  said  that  at  the 
exception  of  UT  23  post  tunnel  furnace  being  submitted  to  worse  conditions (high  temperature)  than 
potentially production, hot shot blasting seems a promising way to water free descale samples. As O2 
content  increases  (i.e.  oxidation)  and  initial  as-cast  surface  are  considered  (mostly  for  electrical  steel 
post tunnel furnace), reduced descalability is observed for both processes.  

500µm    -   50µm 
Rail sawn face HPW descaling 120 bar -  0.12m/s 
- 1220°C - 900min 2%O2 - 88mm standoff 
Good  descalability  owing  to  large  descaling 
energy: >20kJ/m² 

500µm    -   50µm 
Rail sawn face HPW descaling 200 bar -  1m/s - 
1220°C - 900min 2%O2 - 88mm standoff 
Poor  descalability  owing 
energy: <8kJ/m² 

low  descaling 

to 

HPW descaling 200 bar – 1m/s 

500µm 
Scaled area 

500µm    -   50µm 

Descaled area 

Shot blasting – WS230 

250µm 
Scaled area 

250µm    -    50µm 

Descaled area 

Figure 89 Rail sawn descaling HPW and shot blasting – 1220°C - 90min – 2%O2 

105 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
HPW descaling 120 bar  - 0.12m/s 

250µm    -    50µm 
Scaled area 

Shot blasting – WS230 

50µm 

Descaled area 

250µm    -    50µm 
Scaled area 

50µm 
Descaled area 

Figure 90 B9S33 valve spring  - Smooth machined descaling HPW and shot blasting - 1220°C - 80min 
– 2%O2 
HPW descaling 120 bar  - 0.12m/s 

250µm    -    50µm 
Scaled area 

Shot blasting – WS230 

50µm 

Descaled area 

250µm    -    50µm 
Scaled area 

50µm 

Descaled area 

Figure 91 B9S33 valve spring  - As-cast - descaling HPW and shot blasting - 1220°C - 80min – 2%O2 

106 
 
 
 
 
 
 
 
 
 
 
 
 
250µm 

250µm 

Primary scale 

Descaled area - HPW descaling 200 
bar  - 0.12m/s 
Figure 92 Electrical steel UT12 - descaling HPW and shot blasting - 1160°C - 60min – 2%O2 

250µm 
Descaled area Shot blasting – 
WS230 

HPW descaling 120 bar  - 0.12m/s 

250µm   –    50µm 
Scaled area 

50µm 
Descaled area 

Shot blasting – WS230 

250µm   –    50µm 
Scaled area 

50µm 
Descaled area 

Figure 93 DSP – Electrical steel UT23 as-cast - descaling HPW and shot blasting - 1160°C - 60min – 2%O2 

HPW descaling 300 bar  - 0.3m/s 

50µm 
Primary scale 

500µm                             250µm                            50µm 
Descaled area 

Shot blasting – WS230 

50µm 
Primary scale 
Figure 94 DSP – Electrical steel UT23 - descaling HPW and shot blasting - 1200°C - 90min – 2%O2 

Descaled area 

500µm                             250µm                            50µm 

107 
 
 
 
 
 
 
 
 
 
 
 
 
 
From  cross  section  analysis  it  can  be  confirmed  HPW  descaling  for  pressure  considered  200bar  and 
high speed (low descaling energies see Table 16) resulted in poor descalability as compared to lower 
system pressure and low speed. A speed of 0.12m/s corresponded to a similar speed between the HPW 
descaling and hot shot blasting using the WINOA pilot prototype. The HSB shot blasting process for 
WS230 shot at 60HZ turbine speed created shot indentation to the steel surface. Prior as-cast surfaces 
gave the worse surface finish for the two processes. 

2.6.2.2. HPW descaling vs hot shot blasting inc. effect of rolling 

A  detailed  experimental  plan  was  conceived  to  allow  on  one  single  large  block  of  typically 
100x70x430mm to be hot shotblasted (initial top surface) until exit of shotblasting machine, then flip by 
180o and then craned to the roller table of the plate mill for being HPW descaled and then rolled in 1 to 
3 passes, all within safe operating conditions and timing (max 5mins). A total of 6 large blocks were 
rolled  encompassing  UT23,  UT12  and  Rail  steel  grades.  All  these  large  blocks  were  reheated  with 
dummy bars (for initial primary scale morphology) in the large gas furnace of the G block plate mill 
(~6-8%  excess  O2).  Post  rolling,  these  large  blocks  were  either  air  cooled  in  the  large  Argon  box 
(following single pass rolling) or direct quenched in the AC_DQ unit. 

Scale  thickness  profile  was  determined  with  Elcometer  probe  455.  Next  figure  shows  2D  maps  of 
residual  scale thickness  on  as-rolled  HPW  descaled  (HPW)  and  hot  shot  blasted  (HSB)  blocks in  the 
steady state area.  

(a)  HPW  and  rolled  10BS4  UT12  electrical  steel 
machined surface- 1 pass rolling 10mm reduction 

(b)  HSB  and  rolled  10BS4  UT12  electrical  steel 
machined surface- 1 pass rolling 10mm reduction 

Figure 95 Residual scale measurement maps for HPW and HSB surfaces post rolling, Electrical steel 
UT12 

It can be observed that UT12 steady state residual scale thickness maps are fairly uniform with average 
rolled residual scale below 20microns achieved after one rolling pass. For the two other grades rail and 
UT23,  the  UT23  has  the  worse  “descaling”  behaviour  with  remnant  patch  scale  and  non-uniform 
surface state. Reheating conditions would have worsen descalability.  

50µm 

50µm 

108 
 
 
 
 
 
10µm 
HPW160bar 

5µm 
Shot blasting 60Hz 

Figure 96 Electrical steel UT23 B9S38 – 1160°C - Descaled HPW and shot blasting + Rolling – 3pass 

500µm 

200µm 

20µm 

HPW 160bar 

20µm 
Shot blasting 60Hz 

Figure 97 LOM/SEM characterisation of rolled surfaces Electrical steel UT12 

From LOM/SEM characterisation it can be said that regions of good descaling are regions of minimum 
internal oxidation  or  entanglement  especially  for the electrical  steel  UT23.  Irrespective  of  the turbine 
set-up, the profile seems to possess a smoother and less wavy interface (due to shot impact) except in 
areas where scale remains. It should be stated that HPW descaling was carried out in the primary plate 
mill  descaler  which  is  less  controlled  and  was  not  set-up  with  DNM0325  nozzle  (instead  Lechler 
dovetail 666.648.12 series, 40o spray angle).  

In  conclusions  it  can  be  said  that  the  water  based  and  water  free  descaling  tried  during  the  pilot 
industrial trials show a similar efficiency in terms of scale removal. Similar amount of scale remaining 
and similar morphology of scale after both processes is visible.  

2.6.3.  Task 6.2 comparative assessment of upscaling new descaling techniques and guidelines 

Using the heavy pilot prototype and work by WINOA to scale shot blasting unit to an industrial unit for 
use at two extreme plants and products (SRM rod mill 283 bloom and Heavy Plate Mill Scunthorpe on 
slab), the following calculation have been made. 

2.6.3.1. Upscaling new descaling techniques and guidelines 

Wheel  blasting  pilot  was  able  to  run  at  0.08  -  0.12m/s.  Blasting  pattern  width  was  adjusted  between 
600mm and 1m. To calculate the upscaling of this equipment to an industrial line, we have to keep the 
coverage rate and adjust the abrasive flow. If necessary, the number of turbines can be adjusted.  

109 
 
 
 
 
 
 
 
Shot size is fixed by the experiments. Shot speed is given by turbine diameter and rotating speed. These 
2 parameters must not be changed.  

Finally, upscaling tests have to be run to make sure hypothesis are good. These tests can be done with 
similar or representative equipment. This test will aim at finding the best abrasive size, shape, hardness, 
flow  and  projection  speed.  We  have  only  drafted  possible  parameters  with  Hides  project.  These 
parameters could be optimised. According to the results found obtained from the industrial test and the 
size of the industrial parts, we were able to estimate upscaled equipment as follow:  

3 different needs are investigated:  

•  SRM bloom, primary descaling (283x230 Lg 9400, 0,2m/s) 
•  SRM bloom, secondary descaling (283x230 Lg 9400, 1m/s) 
•  HPM slab (1900x228 Lg 3600, 0,5m/s) 

Upscale equipment sizing 

As  seen  previously,  the  upscalling  calculation  is  made  on  increase  abrasive  flow  to  the  parts.  The 
projection  speed  and  abrasive  properties  will  stay  the  same.  There  are  2  ways  of  increasing  abrasive 
flow: increasing the number of turbines or increasing the flow through each turbine. A combination of 
more turbines with higher flow is also possible. The more turbines we input, the longer the line has to 
be, to avoid having facing turbines. The more turbines we input, the more flexible the line can be (ex. 
4x11kW  or  2x22kW  turbines  can  blast  as  much  as  1x45kW).  Figure  98  show  possible  wheel 
arrangement for blasting the 2 sides of a plate.  

Face 
A 

(a)  1  turbine,  sheet  returned  to 
blast both sides 

(b)  2  turbines,  1  on 
each side 

(c) 2 turbines per face 

(d)  3  turbines  per 
face 

Figure 98 Possible wheel arrangements 

The size of the blasting cabinet will be impacted by the number of turbines. We can estimate the length 
of a blasting cabinet as 2 to 4m + 0.5 to 1m per turbine. Semi industrial pilot had a 5,5 kW turbine and 
an abrasive flow of 90 kg/min.  

•  SRM bloom, primary descaling: 

To  increase  speed  from  0.12  m/s  to  0.2  m/s,  abrasive  flow  has  to  be  increased  by  1.67.  To  increase 
impacted surface from 600mm to [283+230+283+230]mm, abrasive flow has to be increased by 1.71 
For SRM bloom, we would need 90 kg/min x 1.67 x 1.71 = 260 kg/min abrasive flow 
2 x 11 kW or 4 x 5,5 kW turbines could be enough.   

•  SRM bloom, secondary descaling: 

To increase speed from 0.12 m/s to 1 m/s, abrasive flow has to be increased by 8.33.  
To  increase  impacted  surface  from  600mm  to  [283+230+283+230]mm,  abrasive  flow  has  to  be 
increased by 1.71 
For SRM bloom, we would need 90 kg/min x 8.33 x 1.71 = 1300 kg/min abrasive flow 
4 x 22 kW turbines are necessary. 

•  HPM slab 

To increase speed from 0.12 m/s to 0.5 m/s, abrasive flow has to be increased by 4.17.  
To increase impacted surface from 600mm to 2x 1900mm, abrasive flow has to be increased by 6.33 
For HPM slab, we would need 90 kg/min x 4.17 x 6.33 = 2400 kg/min abrasive flow  
4 x 37 kW or 6 x 30 kW or 8 x 18,5 kW turbines could be used.  

110 
 
 
 
 
 
 
 
 
Recycling 

The abrasive is recovered at the bottom of the cabinet (screw conveyor, vibrating floor or belt conveyor 
system) and delivered to the elevator that carries it to the separator.  
The  media  is  reused  hundreds  of  times,  only  a  small  portion  of  the  abrasives  will  break  upon  each 
impact, it is measured that 450g are broken/eliminated when one ton of abrasives is projected.  

2.6.3.2. Cost estimation 

The  cost  estimation  considers  cost  of  energy,  water  and  shot,  type  of  product  for  full  descaling 
coverage, variable line speed, pump type and power and descaling time inc. idle time. It also accounts 
for wear rate of nozzle via an increase of the coefficient of discharge CD.  It however simplifies cost for 
water  discharge,  any  water  treatments,  accumulators/  (case  of  plate  mill),  maintenance  and  operator 
cost, etc.  

Electricity rate (0.065 £/kWh or 0.076 €/kWh) was rather low. This is due to increase in the next years 
and  impacts  a  lot  more  the  HPW,  less  the  HSB.Cost  is  based  on  24/7,  47w/year  running  for  water 
descaling the calculations are based on 8064h/year and for blasting only when needed by the process. 
Standby energy is estimated at 30% of running energy. The £ to euros exchange rate (average over 5 
year) is 1.17 £/Euro. The investment cost is not included, but the value is similar for both systems. 

Calculations of WINOA for Water-free descaling 

Taking into account the number of turbines needed for each plant (see upscaling calculations), the flow 
rate,  the  production  and  blasting  period,  the  size  of  shots  and  size  of  bloom,  the  amount  of  blasting 
media consumed per year is calculated (the abrasive has a price of 1000euro/ton).  
To estimate the annual process cost, the standby energy, spare parts, wear parts and energy cost are also 
calculated. For this estimation the cost was calculated for two feed frequencies in the same way as for 
the HPW descaling in order to be able to compare the cost of the two processes. The total annual cost 
for the SRM bloom primary descaling is in the Figure 104, for the SRM bloom secondary descaling is 
in the Figure 101 and for the HPM slab is in the Figure 107.  

•  SRM Secondary:  

Feed frequency 20s: 

Figure 99 Cost estimation SRM secondary 20s feed frequency 

Feed frequency 30s: 

Figure 100 Cost estimation SRM secondary 30s feed frequency 

111 
 
 
 
 
 
 
Figure 101 Annual process cost estimation SRM secondary  

•  SRM Primary:  

Feed frequency 20s 

Figure 102 cost estimation SRM primary 20s feed frequency 

Feed frequency 30s 

Figure 103 Cost estimation SRM primary 30s feed frequency 

112 
 
 
 
 
Figure 104 Annual process cost estimation SRM primary 

•  HPM slab:  
Feed frequency 180s 

Figure 105 cost estimation HPM slab 180s feed frequency 

Feed frequency 360s 

Figure 106 Cost estimation HPM slab 360s feed frequency 

113 
 
 
 
 
 
Figure 107 Annual process cost estimation HPM slab 

Calculations of Tata Steel for Water based descaling  

The  annual  cost  estimation  for  HPW  was  done  based  on  pumps  and  descaling  header/nozzles 
parameters,  feedstock  dimensions,  rolling  parameters,  descaling  parameters,  electricity  and  water 
consumed. Two feed frequency are estimated, for SRM bloom 30 and 20s and for HPM 180 and 360s. 
The cost of electricity is calculated based in cost when descaling is used and when standby (30%) and 
water cost is based in water consumption per bloom or slab.  

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Rolling and descaling factors 

Electricity 

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HPW total 
annual cost 

Wheel blasting cost 
calculated 

351 
351 
351 
351 

6 318 € 
6 318 € 
6 318 € 
6 318 € 

48 707 € 
48 429 € 
75 716 € 
73 437 € 

(3) 
(3) 

39 321 € 
37 330 € 
28 529 € 
26 716 € 

4 
4 

351 
351 

4 648 € 
6 972 € 

1173 
23 166 € 
1173 
23 166 € 
(1) exclude all accumulator etc. to supply additional flow . Therefore not realistic. 
(2) not realistic see difference in energy cost from quick estimate.  - Quick estimate taken into account
(3) based on speed and primary descalling tests. To be confirmed for secondary descalling. 
(4) number of pumps adjusted to fit required flow . 
Wear exclude labour, accumulators, flow increase and header 

294 293 € 
296 617 € 

40 800 € 
44 641 € 

Table 29 Economical calculations comparing HPW and blasting descaling 

Results show a higher annual cost for HPW compared to HSB.  All neglected costs are known to be 
higher  with  HPW  than  for  shot  blasting.  Both  cost calculations  are  based  on the  test  done  during 
this  project,  it  is  an  estimation  and  not  all  the  industrial  values  and  conditions  are  taken  into 
account, more test should be done to have a more real estimation cost.  

115 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
 
 
 
 
 
  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
  
  
  
  
  
  
  
 
 
3.  CONCLUSIONS  

On the axis high pressure hydraulic descaling, methodologies for erosion assessment and developments 
of simulation material are innovative and have been used to cross validate model prediction of descaling 
as well as providing a basis of cross-comparison between HPW and hot shot blasting. Good progress 
has been made related to modelling of the descaling process with development of a detailed analytical 
spread sheet which has been the basis for DoE analysis and optimisation (case of DNM0325). Iso-lines 
of descaling energies have been computed based on experimental trials and modelling. A range of steel 
grades  was  studied  with  the  most  difficult  descalability  being  provided  by  UT23  electrical  steel  post 
tunnel. New nozzles were tested such as the Lechler HPS, series Everloy DNEX 08 and 12 as well as 
the DNM range.  

Shot blasting descaling technique has been studied in detail; parameters and conditions to work at high 
temperature were selected and tested with static and dynamic test, at small and heavy samples and with 
lab and industrial equipment. The media grade evolution when working at high descaling temperature 
was also analysed, the need of a development of heat-resistance blasting media grade was not found, lab 
and  pilot  trials  showed  that  the  abrasive  /substrate  contact  time  is  very  short,  during  trials  the  shots 
heated up to 22°C.  

The  modelling  of  abrasive  shot  blasting  was  also  performed  using  ABAQUS/explicit  simulating  one 
shot and multi shots (4-shots).  The simulations were in accordance with the experiments in terms of 
scale  removal.  The  influence  of  a  particular  shot  size  on  scale  thickness  should  be  studied  further 
because it seems that exists an ideal shot size for a specific scale thickness  

Shot blasting descaling trials have proven that the technique can be used at high temperature to remove 
primary scale and within the constraints of the prototype developed by WINOA and tested at Tata Steel 
should be cost effective although more work is required. 

For  cross  comparison  of  HPW  with  HSB  was  necessary  to  fix  the  line  speed  to  have  the  same 
descalability,  it  means  60Hz  turbine  speed  for  HSB  and pressure  of  120bar for  HPW (decreasing  the 
HPW  system  pressure  of  ratio  of  2.75).    The  cross  comparison  between  HPW  and  shot  blasting 
technique, done with lab and pilot trials, show that the descaling efficiency is similar even for difficult 
to descale steels.  

One  of  the  main  problems  of  the  HPW  is  that  it  depends  on  many  parameters  that  could  reduce  the 
descaling efficiency if not good controlled and difficult to solve, like overlap, overcooling, banding, etc, 
problems  that  shot  blasting  technique  does  not  present.    For  HSB  the  main  problem  founded  in  this 
project  was  line  speed,  which  is  lower  than  HPW,  but  further  development  for  application  at  high 
temperature needs to be done.  

A cost benefit analysis was done for both processes, the results show that HPW annual cost is higher 
than HSB, but both cost calculations are based on the test done during this project, it is an estimation 
and not all the industrial values and conditions are taken into account, more test should be done to have 
a more real estimation of cost. 

117 
 
 
 
 
 
 
4.  EXPLOITATION, IMPACT AND TRANSFERABILITY OF THE RESEARCH 

RESULTS 

Main findings per WP have been highlighted in Final Summary. A cost benefit analysis is covered in 
WP6.  
Already exploited and transferable 

•  Optimisation of overlap and HPW descaling theory and set-up function of steel grade 
•  Regimes maps for HPW descaling 
•  Modelling of HPW descaling and hot shot blasting 
•  Approach for cross comparing processes and influence of dynamics (speed of process) 

To explore in the future: 

•  Upscaling  of  hot  shot  blasting  to  production  units  and  to  secondary/tertiary  or  late  descaling 

(via pilot and demonstration project) 

•  Transferability of descaling theory and approach 
•  Consideration and costing of environmental consideration and better costing of both processes 
•  Further  development  and  targeting  of  technology  (HPW  descaling  and  hot  shot  blasting) 

through the steel manufacturing process 

Recommendations and future work 

Influence of hot shot blasting on downstream rollability (tribology) and oxide growth 

•  Development and access of oxide scale properties (thermal-mechanical) 
•  Optimisation of hot shot blasting with composite shot and pre/post treatments of scale 
•  Study of shot recyclability and property 
• 
•  Better understanding of regimes acting and influencing scale-metal interface 
•  Develop database and regime maps for hot shot blasting 
•  Study influence of hot shot blasting on yield and throughput 
•  Enhanced  instrumentation  and  capability  for  more  in-situ  characterisation  of  oxide  scale  and 

surface state (e.g. raman spectroscopy, etc.) 

•  Further  development  of  modelling 

accounting 

for  multiple 

interactions, 

scale 

fracturing/spallation, real scale morphology and composition, fluid-solid interaction 

119 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
5.  CONFORMITY WITH THE PLAN 

The work is conform the new work plan as presented in the bar chart Table 30 and as explained in the 
document addressed the project officer and to the experts in December of 2011.  
Due to initial delays tasks have been rescheduled but over the duration of the project they have been 
addressed except task 2.1 and 2.3. Priority has been given in comparing HPW descaling with hot shot 
blasting,  which  is  one  of the  main  objectives  of  this project  with  detail  calculations,  extensive  heavy 
pilot trials and sample characterisation.  
Dynamic  shot  blasting  trials  have  been  finished  at  the  end  of  2012;  a  lot  of  effort  was  put  in  the 
modification of the industrial wheel blasting machine to use in the pilot mill of Tata Steel and the pilot 
semi-industrial  trials.  Preliminary  trials,  heavy  trials,  hot  rolling  trials  and  the  respectively  sample 
characterisation of all the materials was performed.  
Modelling shot blasting has been extended to the end of the project due to required change in modelling 
approach; the modelling is finished and here presented.  

121WP 

Tasks 

1.1 

1.2 

1.3 

2.1 
2.2 
2.3 
2.4 
2.5 
2.6 

 2.7 

2.8 

3.1 

 3.2 

2 

3 

3.3 

 3.4 

 3.5 

4.1 

4 

4.2 

5 

6 

4.3 

5.1 

5.2 

6.1 

6.2 

6.3 

2009 

2010 

2011 

2012 

III  IV  I 

II  III  IV  I 

II  III  IV  I 

II  III 

I
V 

6 

5 

4 

2 

3 

1 

descaling 

of  HPW 

Steel composition 
Envelope 
processing conditions 
Sample  preparation,  trial  matrix, 
etc. 
Pulsating/fluctuating water jet 
High pressure/low flow rate 
Particular water jet 
Double descaling 
Latest descaling nozzle 
Effect of nozzle geometry 
Modelling  of  mechanical  HPW 
descaling 
Cross  performance  comparison  of 
water-based technology 
Development of heat-resistant 
blasting media grades 
Preliminary trials of hot 
temperature blasting operations 
Definition of an experimental 
procedure to assess the high 
temperature resistance of the 
blasting media 
Validation of the water-free 
descaling in online conditions 
Modelling of high temperature shot 
blasting 
Characterisation oxide/surface/sub-
surface  
Analyse of the primary/secondary 
scale growth and adhesion 
Surface temperature evolution 
during descaling 
Assessment of optimum descaling 
techniques 
Detailed comparison water-
based/water-free descaling on 
selected agreed steel grade  
Regime maps of innovative 
mechanical descaling techniques 

Comparative assessment of 
upscaling new descaling techniques 
and guidelines 
Industrial testing of the selected 
techniques 

Initial 
New planning (mid term & 
document Dec’11) 

Table 30 Bar chart 

122 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Partner Collaboration 
The technical collaboration between partners has been excellent and covered: 
•  Steel quality and supply via lab and production cast 
•  Prototyping of shot blasting techniques from 
•  Development of a heavy pilot facility co-developed by WINOA and CRM and installed at Tata Steel 

who provided all source materials and ability to benchmark against HPW descaling 

•  Process costing comparison and details of installation 
•  Oxide scale properties for HPW descaling and hot shot blasting 
•  Web portal for storing and exchanging information 
•  Face to face meetings and web conferences. 

123 
 
6.  LIST OF FIGURES  

Figure 1 Diagram illustrating interaction between work packages .................................................... 5 
Figure 2 Comparison static versus rotary descaling ...................................................................... 16 
Figure 3 Example of SWI function of IP for a SI-steel .................................................................. 17 
Figure  4  Flat  jet  spray  nozzle  characteristics  and  significant  parameters  affecting  descalability  in 
stationary descaling rigs (DR: Rolling Direction) ......................................................................... 20 
Figure 5 CRM Lab cast – Effect of Si (%weight 1.23 versus 0.23) content on rail steel oxidation ...... 27 
Figure 6 SEM/EPA analysis CRM lab cast rail steel variant 2217 (a) 5% CMEG TGA analysis (b) 45% 
CMEG TGA analysis ............................................................................................................... 27 
Figure 7 (a) Pulsating nozzle (b) normal water jet spray (c) shock wave front theory [9] ................... 29 
Figure 8 High pressure – low flow testing validation with Erosion tests on Al function of pressure and 
time [150 to 400bar] DNM0325 Everloy nozzle inc. faro arm correlation see Task 2.6 ..................... 30 
Figure 9 Micros on reheated, single and double descaled samples – 2213 (DSP grade) ..................... 32 
Figure 10 Micros on reheated, single and double descaled samples – 2214 High Si (DSP grade) ....... 32 
Figure 11 Micros on reheated, single and double descaled samples – 2215 high Al (DSP grade)........ 32 
Figure 12 Comparison reheated scale HPW descaler v TGA analysis (see Task 1.3) ........................ 33 
Figure 13 New Lechler HPS series (in particular 6P3.606.27) ....................................................... 34 
Figure 14 Influence of nozzle filters (a) nozzle components (b) effect of filter in straightening flow (c) 
Influence of filter (short, long) on impingement area .................................................................... 36 
Figure 15 Overlap effect schematic inc. from reference [11] ......................................................... 37 
Figure 16 Typical Al imprints from erosion test ........................................................................... 37 
Figure 17 Al erosion on DNEX 0833 nozzle ............................................................................... 38 
Figure  18  Erosion  rate  0833  and  DNM0325  (DSP)  nozzle  function  of  system  pressure  and  standoff-
Long filters. ............................................................................................................................ 38 
Figure 19 Almen strip concept for application to HPW descaling ................................................... 39 
Figure 20 Example of Load cell measurement for DNEX 0833, DNEX 1225 and DNM0325 at various 
pressures. ................................................................................................................................ 40 
Figure 21 Al erosion single DNM0325. Short filter showing overlap and wash- system pressure 180/280 
bar and influence of rake angle 0 and 15o ................................................................................... 40 
Figure 22 Mapping of impact force changes as overlap reduces- Impact force measurement experiment 
using 1mm pin load cell in overlap area by incrementing by 0.5mm right hand side leading jet ......... 41 
Figure 23 Manufacturer IP (MPA) v standoff distance (mm) for DNM0325 .................................... 42 
Figure 24 Analytical HPW descaling spread sheet (main inputs in blue cell) and outputs in other colours 
based on three definitions adopted (algebra, manufacturer fit and calculated spray depth angle and fitted 
spray width) ............................................................................................................................ 44 
Figure 25 Main effect plots ....................................................................................................... 45 
Figure 26 Calculation of critical strain and descalability based on IP calculated in Figure 24 ............ 46 
Figure  27  Calculation  of  critical  strain  and  descalability  based  on  IP  calculated  in  Figure  24  and 
changes in interface roughness .................................................................................................. 46 
Figure 28 Effect of thermal effects based on calculated D T or imposed D T and fraction of thickness of 
scale affected by heat loss assuming decoupled thermal and mechanical effect ................................ 47 
Figure 29 estimation of energy for evaporation of water during HPW descaling (within scale) - assumed 
280 bar – travelling speed 0.3m/s ............................................................................................... 48 
Figure  30  Estimation  of  stress  components  within  the  scale  from  descaling  set-up  (IP)  and  scale 
thickness ................................................................................................................................. 49 
Figure 31 Validation of analytical predicted data of IP and overlap versus Al erosion and impact force 
measurements .......................................................................................................................... 50 
Figure 32 Overlap comparison between measured AL spray width and manufacturer overlap prediction 
on  the  assumption  that  left  spray  width  measured  by  Al  imprint  is  spray  width  occurring  during  real 
process with interacting nozzle .................................................................................................. 51 
Figure 33 Typical HTC predicted function of bloom and billet size, speed and spray depth studied in 
this project .............................................................................................................................. 52 
Figure  34  Three  component  oxide  scale  ABAQUS  implicit  model  with  ductile-brittle  behaviour 
modelled at interface (delamination) .......................................................................................... 54 

125Figure  35  (a)  Full  detailed  discrete  model  with  water  shots,  outerscale,  interface  and  steel  substrate. 
Note  refined  meshing  in  partition  for  impact  study.  Model  is  driven  via  rigid  surface  boundary 
conditions (b) fracturing and attainment to interface ..................................................................... 54 
Figure  36  Improved  CEL  model  with  better  water  spray  representation.  b)  view  of  water  impacting 
target with improved CEL model ............................................................................................... 55 
Figure 37 Pictures of shots (a) and grits (b) ................................................................................. 59 
Figure 38 Internal hardness specification .................................................................................... 59 
Figure 39 Sieve analysis curves (a) of new abrasives (b) and operating mix (c) ............................... 60 
Figure 40 Relative consumption of high-carbon abrasive depending on its hardness ......................... 61 
Figure 41 IR picture of abrasive after hot blasting test with blocks at 1200°C .................................. 61 
Figure 42 Industrial air separator scheme .................................................................................... 62 
Figure 43 Example of a coverage curve after one pass at 40% ....................................................... 62 
Figure 44 (a) Coverage rate chart, (b) Different coverage levels .................................................... 63 
Figure 45 Energy relations and energy conversion during the impact of the media ........................... 63 
Figure 46 (a) Wheel blasting system, (b) Wheel components ......................................................... 64 
Figure 47 Passthrough machine adapted for descaling long products .............................................. 64 
Figure 48  (a) Pressurized projection system, (b) Suction projection system .................................... 64 
Figure 49 Number of grains in WINOA´s media .......................................................................... 65 
Figure 50 Effect of impact angle ................................................................................................ 65 
Figure 51 Shot blasting device designed by WINOA to perform test at CRM Lab ............................ 67 
Figure 52 Liquid nitrogen cooling system ................................................................................... 67 
Figure 53 Reheating device developed in CRM Gent(a) Controlled atmosphere setup (b) closed box (c) 
water cooling device (d) oxygen analyzer. .................................................................................. 69 
Figure 54: Microscopic investigation of the Almen and Aluminium surface after shot blasting under air 
pressure of 7,5bar for shot WS170 ............................................................................................. 71 
Figure 55 Wheel blasting machine of WINOA ............................................................................ 72 
Figure 56 Pictures of the abrasive life tool .................................................................................. 73 
Figure  57  Simulation  model  with  scale  layer  (blue),  half  infinite  elements  (white)  as  well  as  shots 
(white half-spheres). The bulk material is not visible. ................................................................... 75 
Figure 58 Result of four impacts of S170 on a 250 µm scale layer (brittle damage formulation) with a 
strength of 4 MPa (top) and 20 MPa (bottom). ............................................................................. 77 
Figure 59 Result of four impacts of S230 on a 250 µm scale layer (brittle damage formulation) with a 
strength of 4 MPa (top) and 20 MPa (bottom). ............................................................................. 78 
Figure 60 Result of four impacts of S170 on a 500 µm scale layer (brittle damage formulation) with a 
strength of 4 MPa (top) and 20 MPa (bottom). ............................................................................. 79 
Figure 61 Result of four impacts of S170 on a 750 µm (top) and 1000µm (bottom) scale layer (brittle 
damage formulation) with a strength of 4 MPa. ........................................................................... 80 
Figure 62 Result of four impacts of S170 on a 250 µm (top) and 500 µm scale layer (tensile damage 
formulation) with a strength of 4 MPa. ....................................................................................... 81 
Figure 63 Amount of total deleted (failed) scale elements for selected simulations ........................... 81 
Figure 64 1000 µm scale layer (brittle damage formulation) with a strength of 4 MPa impacted by S230. 
Damage at the interface (white arrows) ....................................................................................... 82 
Figure 65 Comparison reheated scale CRM lab reheating vs HPW descaler .................................... 83 
Figure 66 Surface of specimen shot blasted 7.5 bar of air with controlled reheating atmosphere at 1150 
°C .......................................................................................................................................... 85 
Figure 67 Tata Steel UK high speed camera test. ......................................................................... 85 
Figure 68 Assessment of surface temperature during descaling - water based descaling .................... 86 
Figure 69 Assessment of surface temperature during descaling - water free descaling a) on static test, b) 
on dynamic test, HPW and Shot blasting combined in one sample ................................................. 87 
Figure 70 DoE Analytical study of penetration depth z [mm] ........................................................ 90 
Figure 71 Comparison of estimated energies between HPW descaling and shot blasting ................... 92 
Figure 72 Typical reverse calculation by fitting the material strength to give penetration ~100µm close 
to measured values and estimate shot blasting energy ................................................................... 92 
Figure 73 Shot blast imprints on masked Al plate ........................................................................ 92 
Figure 74 Imprint on simulation material (plasterboard and Teflon) ............................................... 93 
Figure 75 Comparison descaled samples shot blasting vs HPW descaling ....................................... 94 
Figure 76 New descaler box CRM Gent ..................................................................................... 95 

126 
Figure  77  Cross  section  material  32  and  34  after  water  descaling  and  hot  rolling  with  reheating 
temperature of 1160°C ............................................................................................................. 96 
Figure 78 Surface aspect and cross section of samples after reheating, shot blasting and hot rolling at 
20%. Material 34 ..................................................................................................................... 97 
Figure 79 Surface aspect and cross section of samples after reheating, shot blasting and hot rolling at 
20%. Material 32 ..................................................................................................................... 97 
Figure  80  Example  Pareto  charts  and  2D  regime  maps,  line  of  iso-descaling  energy  together  with 
avenues for optimisation (DNM0325) ........................................................................................ 99 
Figure  81  regime  maps,  line  of  iso-descaling  energy  together  with  avenues  for  optimisation 
(DNM0325) .......................................................................................................................... 100 
Figure 82 surface state post descaling ....................................................................................... 101 
Figure 83 Regime maps UT23 ................................................................................................. 102 
Figure 84 Independent variables of Impact force/unit mm v Velocity V (m/s) ............................... 102 
Figure 85 3D adjustment of wheel turbine ................................................................................. 103 
Figure  86  Hot  shot  blasting  prototype  at  STC  G  block  Plate  mill  top  level  chute  for  WINOA  shot 
(~60kg shot) .......................................................................................................................... 104 
Figure 87 Small block in and out (before and after descaling) of shot blasting cabinet .................... 104 
Figure  88  Electrical  steels UT12  and  UT23  (see Table  A2.1)  Left hand side:  Hot  shotblasting  (right) 
HPW descaling 200bar 0.12m/s ............................................................................................... 104 
Figure 89 Rail sawn descaling HPW and shot blasting – 1220°C - 90min – 2%O2 ......................... 105 
Figure 90 B9S33 valve spring  - Smooth machined descaling HPW and shot blasting - 1220°C - 80min 
– 2%O2 ................................................................................................................................ 106 
Figure 91 B9S33 valve spring  - As-cast - descaling HPW and shot blasting - 1220°C - 80min – 2%O2
 ............................................................................................................................................ 106 
Figure 92 Electrical steel UT12 - descaling HPW and shot blasting - 1160°C - 60min – 2%O2 ....... 107 
Figure 93 DSP – Electrical steel UT23 as-cast - descaling HPW and shot blasting - 1160°C - 60min – 
2%O2 ................................................................................................................................... 107 
Figure 94 DSP – Electrical steel UT23 - descaling HPW and shot blasting - 1200°C - 90min – 2%O2
 ............................................................................................................................................ 107 
Figure 95 Residual scale measurement maps for HPW and HSB surfaces post rolling, Electrical steel 
UT12 ................................................................................................................................... 108 
Figure 96 Electrical steel UT23 B9S38 – 1160°C - Descaled HPW and shot blasting + Rolling – 3pass
 ............................................................................................................................................ 109 
Figure 97 LOM/SEM characterisation of rolled surfaces Electrical steel UT12 .............................. 109 
Figure 98 Possible wheel arrangements .................................................................................... 110 
Figure 99 Cost estimation SRM secondary 20s feed frequency .................................................... 111 
Figure 100 Cost estimation SRM secondary 30s feed frequency .................................................. 111 
Figure 101 Annual process cost estimation SRM secondary ........................................................ 112 
Figure 102 cost estimation SRM primary 20s feed frequency ...................................................... 112 
Figure 103 Cost estimation SRM primary 30s feed frequency ..................................................... 112 
Figure 104 Annual process cost estimation SRM primary ........................................................... 113 
Figure 105 cost estimation HPM slab 180s feed frequency .......................................................... 113 
Figure 106 Cost estimation HPM slab 360s feed frequency ......................................................... 113 
Figure 107 Annual process cost estimation HPM slab ................................................................ 114 

127 
7.  LIST OF TABLES 

Table 1 Up-scaling blasting descaling for industrial application ..................................................... 13 
Table 2 Economical calculations comparing HPW and blasting descaling for three plants ................ 14 
Table 3 Chemical composition of Industrial steels and laboratory cast melts ................................... 15 
Table 4 Dependencies of main HPW descaling ............................................................................ 18 
Table 5 Descalability output parameters ..................................................................................... 21 
Table 6 HPW descaling input parameters (controlled) .................................................................. 22 
Table 7 HPW descaling input parameters (uncontrolled) ............................................................... 22 
Table 8 Summary of envelope of processing conditions ................................................................ 26 
Table 9 TGA Analysis:  Rail steel (298Q) – QA code B9S34 (Table 3) .......................................... 27 
Table 10 TGA analysis: Modified CRM Rail steel (2217) (Table 3) ............................................... 27 
Table 11 TGA Analysis:  Modified DSP electrical steel composition (Table 3) ............................... 28 
Table 12 TGA Analysis:  LFCS 209/1  (Table 3) ......................................................................... 28 
Table 13 TGA Analysis:  VS56 SRM (B9S33)  (Table 3) ............................................................. 28 
Table 14 DNM0325 flow-pressure ............................................................................................. 30 
Table 15 Thermal and mechanical properties of oxide scale. Properties of scale are taken from [26] .. 45 
Table 16 Descaling set-up and performance ................................................................................ 56 
Table 17 Metallurgical composition of shots possible to use at high temperature ............................. 60 
Table 18 Summary of parameters of the preliminary test without control of atmosphere ................... 67 
Table 19 Summary test parameters ............................................................................................. 69 
Table 20 Parameters influencing saturation curve ........................................................................ 70 
Table 21 Test performed at CRM Shot blasting device ................................................................. 71 
Table 22 Test performed at WINOA wheel blasting device ........................................................... 72 
Table 23 Winoa’s laboratory comparison of new and used S230 sample ......................................... 74 
Table 24 Simulation parameters ................................................................................................. 77 
Table 25 Scale thickness in reheating conditions .......................................................................... 83 
Table 26 Analytical equivalence between mechanical descaling and shotblasting (no thermal effect and 
static impact) ........................................................................................................................... 91 
Table 27 Hot rolling parameters water descaling trials .................................................................. 95 
Table 28 Hot rolling parameters second set of trials ..................................................................... 96 
Table 29 Economical calculations comparing HPW and blasting descaling ................................... 115 
Table 30 Bar chart ................................................................................................................. 122 

129  
8.  LIST OF ACRONYMS AND ABBREVIATIONS 

Expected Integrated Mean Square Error 

AC_DQ: Accelerated- direct quench        
AMEG: Anchor  Mixed enriched gas (works arising gas) 
CEL:   Coupled Eulerian Lagrangian  
CMEG: Central mixed enriched gas (works arising gas) 
DNEX: new Everloy type nozzle 
DNM:  Everloy type nozzle 
DoE:   Design of Experimentsµ 
DSP:   Direct Sheet Mill 
EISME: 
FEM:  Finite Element Modelling  
HPDE:  High Density Polyethylene 
HPM:   Heavy Plate Mill 
HPS:   High Performance Scalemaster (Lechler nozzles) 
HPW:   High Pressure Water 
HSB:   Hot Shot Blasting 
MEG:   Mixed Enriched Gas 
MSM:  Medium Section Mill 
RSB:  Roughing scale breaker 
SRM:   Scunthorpe Rod Mill  
SRSM:  Scunthorpe Medium Section Mill 
STC:  Swinden Technology Centre 
TCM:  Thrydberg combination mill 
TGA:   Thermo Gravimetric Analysis 
WS#:  Winoa shot number 

velocity 

Atmospheric 

Spray lenght 
Spray width 
Flow rate coefficient 

A:  
B:  
C: 
CD:   Coefficient of Discharge   
Cv: 
deceleration coefficient 
D:  
Overlap 
DR:   Rolling Direction 
Descaling energy 
E: 
gravitational constant 
g: 
Spray Distance 
H:  
 Rockwell hardness 
HRC: 
HTC:   Heat Transfer Coefficient  
HV:  Vickers Hardness 
IF: 
IP:  
Q:  
SP: 
SWI:   Specific Water Impingement  
V: 
Vf: 
α:  
β:  
γ:  
ρ:  

Impact Force from Fig 84 
Impact Pressure 
Flow rate 
system pressure 

Velocity 
fluid velocity 
Spray angle 
Rake angle 
Twist angle 
fluid density 

131 
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1 
2  
3 
4 
5 
6 
7 
8  

9  

10  

11  

12  

13  

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87 

88 
89 

90 

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Files%5C2778%5Carticles%5C12836%5Carticle8.pdf 

- 

136 
 
APPENDIX 1: DESCALING BASIC FORMULA 

Simple trigonometric relationships (all angles in degree) can be derived as follows: 

Spray width B (mm) 

Spray width C (normal rolling 
direction) (mm) 

B =

.2

H

.

aaa a
tan(

).2/

1
bbb b
cos(

)

C = cosg. g. 

g. g. B              

Overlap D (mm) 

D = C-E   

Spray depth d (mm) 

d =

.2

H

.

fff f
tan(

).2/

1
bbb b
cos(

)

a) 

b) 

c) 

d) 

Now although nozzle spray angles are reported in nominal form in manufacturer catalogues, the flow 
departs  from  normal  trigonometry  and  for  improved  accuracy  should  be  characterised.  Usually  form 
factors have to be applied to account for the spray bell shape, although recently more straightened flow 
and reduced wear rate has been obtained by nozzle tip design optimisation. 

d1 (depth) = d – b1.H – c1.P 
B1 (width) = B + b2.H 

With 
pressure 

P: 

system 

From [76]: 

e) 

Other more complex forms (see Lechler for instance) exist for instance for spray depth d 

f) 

137 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Another approach is to take a tolerance function of nozzle, usually for a spray angle of 30o, 2 to 3o can 
be added (see For instance Lechler nozzle catalogue) 

Regarding Impact pressure (IP): 

Several definitions of the force of water exist from gravimetric Bernoulli’s law consideration of flow 
rate  times  water  jet  velocity  (equations  g-l)  to  equations  derived  experimentally  from  pin  load  cell 
measurement of impact force (equation m) as follows: 

VfCvQ

.

Fi

Vf

.rrr r=
.
.2.=
C

.
SPg

Cv = -0.0005.H + 1.1 

IP =1

Fi
A
A = d.B 

[MPa] 

A = 

4

H

2

aaa a
tan(
2

).

fff f
tan(

2

)

IP =
2

SPK
.(

)

5.0

Q
.

.

bbb b
cos(

2

(

xH
.)

aaa a
tan(

2

)

h) 

i) 

j) 

k) 

l) 

)

m) 

g)  With Fi: impact force [N] 

r:  Density of fluid (water, 1000kg/m3) 
Q: system Flow rate m3/s 
Vf: Fluid flow velocity at nozzle exit m/s 
Cv: atmospheric velocity deceleration coefficient  (Cv=1 at 
distance H of 200mm, Cv= 0.85 at H = 500mm)  
C: Flow rate coefficient (0.85) 
g: gravitational constant 9.8m/s2 
SP: System Pressure (pressure head 1MPa = 102m) 
with  A:  impingement  area  calculated  from  nozzle  angle 
geometry, i.e. spray width (B) and spray depth (d) (in mm). 

:  nominal  spray  angle  (deg)  and  fff f :  nominal  depth 

with  a
angle (deg) 

Note  that  form  factor  for  both  spray  and  depth  angles  are 
required to get accurate predictions of impingement area. 
Where: 
K:  nozzle  constant  (to  be  determined  based  on  Pressure-
flow relationship 
X:  nozzle  constant  (Function  of  nozzle  height  generally  ~ 
2) 

The term K/Hx  is similar to an impact density IDD. 

All other parameters as defined above. 

IP decreases as lead angle increases 

It  should  be  noted  that  differences  exist  between  these  two  IP  equations  and  therefore  with  the 
implementation  in  the  new  STC  rig  of  a  1mm  high  resolution  impact  force  measurement  device, 
calibration of IP equations will need to be reviewed. Force/pressure impact equation g-j relies on the 
knowledge or detailed characterisation of the nozzle geometry both in terms of width and depth as well 
as the assumption that force is constant over impingement area which is not true mostly along the depth 
direction. Simple application of basic trigonometry to calculate width and depth may not be sufficient 
due to form factor of nozzle jet and sensitivity to stand-off distance H 

138 
 
 
 
 
 
 
 
 
 
 
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141 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
European Commission

EUR 26177 —  Innovative high temperature and mechanical descaling (HIDES)

Luxembourg: Publications Office of the European Union

2013 — 142 pp. — 21 × 29.7 cm

ISBN 978-92-79-33229-6
doi:10.2777/4304

143