A1110Q PUBLICATIONS

NBSIR 80-2045 (DoE)

ANALYSIS OF EROSION- RELATES FAILURE

INFORMATION FROM COAL GASIFICATION SYSTEMS

Metallurgy Division

Center for Materials Science

National Measurements Laboratory

National Bureau of Standards

Washington, DC 20234

A. W. Ruff

March 10, 1980

Final Report

HDO

100

,U56

80-2045

1980

c. 2

Prepared for:

Department of EnergyWashing ton, DC

Reproduction in

whole or in part is

permitted for any

purpose of the United

States Government
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National Bureau of Standards

library, E-01 Admin. Bldf. FEB 2 7 1981

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CoTABLE OF CONTENTS

I. Introduction

II. Particulate Erosion of Materials

III. Failure Report Trends

IV. Erosion Failure Information

V. Summary and Recommendations

References

i

ABSTRACT

Failure information reports concerning erosion that are contained

in the NBS-DOE Failure Information Center have been analyzed for

the purpose of identifying critical gasification applications.

Emphasis was placed on the components most frequently identified

in erosion failure reports - piping, valves, pumps, cyclones -

and on three of the principal processes. Recommendations are

presented on a minimum set of erosion-related information needed

to analyze erosion behavior. A brief review of solid particle

erosion and several bibliographic references are also included.

n

INTRODUCTION

The erosion of materials by surface impact of hard particles is one form

of material wear. It is understood that wear is, in general, a complex

phenomenon, consisting of simultaneous and interacting processes involving

mechanical and chemical effects as well as material parameters. In recent

years considerable progress has been made in gaining an appreciation of the

significant parameters of erosion and wear and in applying a materials

methodology to the problem. Technological improvements in erosion-resistant

performance of products should be possible now. It is well to keep in mind

that other wear processes, e.g., abrasive wear and corrosive wear, involve

many similar characteristics and perhaps mechanisms with erosion. Progress

in understanding any one of these processes may be applicable to the development of more erosion resistant materials ^nd systems.

This report will examine the problem of erosion-related failures of

components in coal gasification systems. It is hoped that an evaluation

of the existing data and information will assist in identifying common,

significant problems and solutions among different facilities and to some

extent among different system components. Emphasis will be placed on the

components most frequently identified in erosion failure reports and on three

of the coal gasification systems; Hygas, Synthane, and CO^ Acceptor processes.

A brief summary of particulate erosion will be given first in order to

indicate the significance of the many factors involved. This summary should

assist in assessing the erosion/corrosion problems reported in connection with

coal gasification equipment. Several reviews of solid particle erosion have

1-4

appeared recently. The state of earlier understanding has been adequately

5_8 reviewed in several additional articles which also can be consulted. While

these reviews emphasize basic erosion processes, many examples are provided

1
therein of practical problems (see ref. 1)

.

II. Particulate Erosion of Materials

Technological concern with the erosion of materials involves steady state

9 long term erosion. Consideration of the effects of a flux of particles

incident on a surface for some length of time suggests that many complex

aspects are present. These include a wide range of simultaneous attack

angles, particle fragmentation, surface shielding due to deposits, particle

embedding and particle/surface reaction effects, among others, all in addition

to the basic process of erosion impact.

Two basic types of equipment have been used in the laboratory to expose

solid specimens to a stream of erosive particles for the purpose of obtaining

erosion data on materials. In one design the specimen is moved at a controllable velocity, usually on a rotating arm fixture, through a slowly moving

erosive stream. The exposure may be intermittent but can continue for a

long time period. The relative particle-specimen velocity can be accurately

determined since the principal velocity component is that of the specimen

(in the laboratory system) . A variation on this design allows the erosive

particles to be spun from a rotating disk to strike a fixed specimen. The

alternative design involves propelling a stream of particles at a fixed

specimen. The specimen may be completely immersed in the stream, or perhaps

only a portion of the specimen exposed. In this scheme some method of

measuring or calculating particle velocity must be used. The particle concentration in the stream and the nature of the carrier gas (fluid) can be

chosen. Some type of nozzle or flight tube is involved in order to properly

„ 10-12 confine the erosive stream.

2
Quantitative measurements of erosion rate require careful attention to

the experimental system and the parameters of exposure. For example, wear

of the abrasive delivery nozzle can greatly alter the stream shape and velocity

profile. Turbulance within a flight tube or caused by the presence of the

specimen itself in the stream can significantly affect particle flux and

particle velocity as experienced by the test specimen, particularly for small

particle sizes. Consideration of the particle trajectories within the incident

13

stream, particularly near the specimen, are important. Since the erosion

rate can vary as high as the third power of the particle velocity, accurate

knowledge of particle impact velocity is essential. All these considerations

are essential if the laboratory data are to be useful to designers of practical

systems

The variation of erosion, usually measured in mass or volume loss- from

the specimen per unit mass of impacting abrasive, as a function of angle of

attack of the particles is shown schematically in Fig. 1 for brittle and for

ductile materials. For ductile materials the peak erosion loss occurs at

around 20°. For brittle materials the peak erosion loss occurs at around

90° (normal incidence). Thus, designers should avoid these erosion angles

for the materials involved. The dependence of erosion rate on particle

velocity has been measured for many materials over typically two or three

2 orders of magnitude in velocity. The erosion rate is found to increase as v

3 . 6,14

to v in most cases. The velocity exponent has been reported not to

depend on the type of material (Fig. 2 ); however, detailed studies have shown

some dependence of the velocity exponent on the temperature of erosion (Fig.

3) . A reduction in particle or flow velocity can drastically reduce erosion

rate and may be the most effective design approach.

3
The dependence of erosion on particle size has also been studied by

several workers. Goodwin et ad..^ have examined the erosion of steel by

quartz particles over a large size range. As shown in Fig. 4, an increase

in erosion with increasing particle size was found up to a limiting size,

above which the erosion remained constant and then increased for particle

sizes greater than about 500ym. A theory explaining this result has been

proposed.^ Much interest has been centered on the erosion effects of

very small particles e.g., less than 5ym in diameter. There have been conflicting reports in the literature, for such small particles. Recent studies,

however, have shown significant erosion of metals by particles as small as 2ym.^ The effect of particle size as measured using flat test specimens

may not be applicable in all geometries as shown by the recent work of Mills

and Mason.^In studying erosion in 90° tube bends due to the conveying

of abrasive sands, they reported that depth of penetration for 70um particles

was much greater than for 230ym particles. Further a different surface

morphology resulted and a different angle of maximum penetration was found.

The effects of increasing temperature on erosion have been studied in

more detail in the last few years. The environment in which high temperature

erosion takes place usually has a significant effect on erosion rate. Depending

on the material being eroded, the temperature range, and the environment,

different effects due to temperature have been reported. The results in one

instance"^ revealed a large increase in erosion of type 310 stainless steel

on going from 25°C to 975°C. A recent study^ of erosion of aluminum and type

310 stainless steel also reported increased erosion for increased temperature.

In work on other alloys, however, decreases in erosion with increasing temper18

ature have been reported. It is believed that temperature effects must be

studied using the specific exposure conditions expected in the application.

4
20

One material parameter that has been of particular interest in connection with the understanding of ductile material erosion is indentation

hardness. Numerous correlation studies have been attempted to determine the

relation of hardness to erosion rate. In Fig. 5 some results are shown.

There the erosion rate of different metals decreases with increasing

value of material hardness. However, the effect of hardness variation for

one alloy (varied through thermal treatments of a tool steel) was found to

produce little effect on erosion rate. The influence of other erosion

parameters such as particle concentration in the erosive stream, particle

hardness, and particle strength, have only been examined in a few instances.

In the case of particle concentration, divergent findings have been reported

It would seem that relative erosion (specimen mass loss divided by impacting

erosive mass) should be independent of particle concentration so long as each

particle event is equally effective. At higher concentrations, where particle

interference (shielding) effects occur at the specimen surface, the relative

erosion should be expected to decrease and this has been reported . ^

At

elevated temperatures, the hot hardness and high temperature toughness of

both the specimen and the eroding materials would be important parameters to

consider

.

In ceramic materials the main parameter that controls the rate of erosion

is the particle velocity. A number of studies indicate that the erosion rate

can be expressed as a power function of the particle velocity. As with metals,

21 22 velocity exponents generally range ’ from ^2 to ^3. Higher values have been

reported. The value obtained for the velocity exponent of a given ceramic

material apparently bears little relation to composition or microstructure of

that material. Thus, castable refractories, which are ^30 percent porous and

5
have a multiphase structure, exhibit the same range of velocity exponents

(2.3 to 3.9) as dense, relatively homogeneous ceramics such as hot-pressed

silicon nitride, and high-density aluminum oxide. In dense ceramic materials,

grain size also has little apparent effect on the velocity exponent, even

though it has a significant influence on the absolute rate of erosion.

Brittle ceramic materials exhibit a maximum in erosion rate at an angle

of 90° (Fig. 6) . This type of behavior has been used to classify materials

as either brittle or ductile with regard to erosion. Actually, most ceramic

materials exhibit behavior that is neither completely ductile nor completely

brittle.

21

In a study of the effect of temperature on erosion, Hockey et_ al . ,

demonstrated that plastic flow occurs during the erosion of brittle materials.

The erosion rate of glass, silicon nitride, and aluminum oxide was measured

as a function of temperature and impingement angle using ^150ym silicon carbide

particles as the erosion agent. Although a low angle maximum in the erosion

rate characteristic of ductile materials was not observed, there did seem to

be a significant enhancement of the erosion rate at low angles of impingement.

It was concluded that wear generally occurs by a mixed mode of erosion, with

the ductile processes becoming increasingly more important with decreasing

angle of impingement.

Theories have been developed for the erosion rates of both ductile and

brittle materials. In 1960 Finnie considered a micro-machining mechanism

as a model^ for ductile materials. He determined the erosion rate (W) to be

dependent on the flow stress as follows:

tt - mV

W = o a

f Kd g (a)

where m is the particle mass, the impact velocity, K the ratio of vertical

6
1

force to horizontal force on the particle, and d the depth of cut. g(a) is a

function describing the effect of attack angle a. This approach was quite

successful in explaining many features of solid particle erosion. Recent

4 refinements of the original analysis have led to velocity exponents of

about 2.5, which are more closely those found by experiment. Several other

theories have been proposed, and recent reviews can be consulted for details.

Two basic models of erosion have been developed for brittle materials:

one is based on the assumption that erosion occurs entirely by crack prop24 agation and chipping ; the other is based on the asumption that plastic

deformation contributes to the process of crack formation and surface chipping.

Erosion rates are predicted in terms of both target (fracture toughness, hardness, flaw density, etc.) and particle (velocity, density, size, etc.)

properties. The models assume that particle impact is normal to the target

24 4 surface. The model proposed by Sheldon and Finnie gives the erosion rate, W,

in terms of the particle size, r, the particle velocity, V

q

, and two constants.

25

a and b:

W = k. rV3 1 o 25 The erosion model developed by Evans _et_ al. assumes that the erosion

rate is proportional to the amount of material removed by each impact event.

The erosion rate (W) is given by:

TT 19/6 11/3 19/12 -4/3 u-l/4

W V K H

o r p c

where p is the density, the stress intensity factor, and H the hardness.

Although the erosion theories summarized above are supported to some extent

by erosion data from the various laboratory studies, the functional dependence

of these theories on material properties differ significantly. Additional

experimental testing is still required to clarify some uncertainties.

7
A recent conference on corrosion and erosion of materials for coal

conversion applications included several papers addressing specific problems

of erosion in laboratory studies as well as practical applications. ^he pro- Hi 2 6 ceedings^ of that conference provides a very valuable source of information

in this field.

III. Failure Report Trends

The MBS /DOE Failure Information System receives and evaluates failure

reports from field installations that identify many specific causes for the

failure problems. The emphasis in this report will be on failures classified

as erosion. Table I summarizes the distribution of failure causes reported

through December, 1978. It is seen that erosion accounts for about 21% of

all failures reported, and that same proportion is experienced at two specific

gasification facilities, the Synthane facility and the Hygas facility. In view

of the nature of this process; namely, the processing of coal particles, steam

and gases at elevated temperatures, pressures and flow rates, it is not

unexpected that solid particle erosion constitutes one of the principal, lifelimiting processes for the equipment involved. Further analysis of the failure

information data base provides the results in Table II concerning the components

involved in erosion failures. It is seen that three principal classes of

components, pumps, valves and piping, account for about 90% of reported erosionrelated failures. On this basis it should be useful to carefully examine the erosic.

reports on those classes to identify common problems in materials, design and

operation. Further, concentration of this analysis on three gasification

systems; Synthane, Hygas, and C0o Acceptor, is also indicated since these

failure reports account for (1) 55% of all reported failures, (2) 53% of all

erosion failures reported, and (3) 50% of erosion reports on pumps, valves and

8
piping. Records for those systems seem the most detailed.

The scope of this report will be limited to the erosion failures reported

for those three processes. Emphasis will be placed on the three classes of

components identified above. It is thought that conclusions from this study

can properly be extended to other systems and components using similar

considerations. The NBS Failure Information System has the available details

on all reported failures and can provide the resources needed for any additional

study

.

IV. Erosion Failure Information

27 28

A. Synthane Facility ’

1. Piping

The Failure Information System contains 10 reports concerned with erosionrelated failures of piping components. The summary of that information is

shown in Table III (using a format that will be followed in this report) . The

basic information taken from the failure report concerned with each component

is shown. Information concerned with erosion parameters such as erosion

velocity, erosion depth, temperature, etc., are also listed where available.

The piping failures due to erosion involved both plain carbon steel

material as well as stainless steel (304, 316). Two nickel-based alloys, 1800

and 1825 were also involved in two instances. Temperatures of service

ranged from 300 to 900°F depending on the location of the component. The local

environment involved either coal dust or coal char as the particulate material,

carried in water, steam, coal gas or other gases, or a mixture of these.

Unfortunately little information was provided on the solids concentration

and the erosion velocity, both of which are controlling of erosion rate. Six

*1800 (Incoloy 800); 1825 (Incoloy 825)

9
of the components experienced erosion penetration through the wall thickness

in the region where the directed flow of steam, particulates, and gases impacted

the surface. Several sketches provided in the reports indicated that erosion

was maximum at a low angle impact, consistant with the peak erosion angle

of 20-30° usually found for metals. Several actions to reduce this erosion

problem were carried out. These included redesign of the flow, the use of a

blocked tee in place of an elbow (so the incident stream impacts principally

on a deposit of coal or char) , reduction of flow velocity, addition of wear

pads to critical locations by welding, and in one case substitution of a ceramic

sleeve for the original metal sleeve. One report concerned the internal

cyclone used to remove fines from the gas prior to water scrubbing. As in

other piping problems, the directed gas/particle flow eroded the wall of the

impact site. A wear plate was installed to provide greater material thickness at

the impact site.

It is difficult to draw conclusions concerning the comparative erosion

rates of these piping components since in all cases essential data are missing.

Measurements of erosion depth were only reported in three cases. Even in

those cases, the time in service under erosion conditions was not clearly

given. Further, the solids concentration and flow velocity were not provided

in these reports (with one exception) . Since erosion loss is generally proportional to amount of impacting solids and to the square or cube power of

flow velocity, in the absence of those data it is not possible to quantitatively

compare the three cases. Future failure analysis report activities should

emphasize the need to obtain such data from field service.

2. Valves

There were 12 reports concerning valve failures in this group. In most

cases (see Table III)the materials involved were specialty steels and alloys

10
indicating the recognition of the difficult service expected. Most of the

valves were in pressure letdown service, with pressure drops of 600 psi to

1000 psi. The failures generally involved erosion of valve seats and internal

liners designed to properly direct the flow down the piping axis. Three

of the reports concerned Willis choke valve designs utilizing ceramic or

tungsten carbide orifice plates. These hard materials were not sufficiently

resistant to particulate erosion under the conditions present. In other

reports, there was indication that solids became lodged at the valve seats

preventing complete closure. The continuing leak of gases and particulates

through the gap would quickly produce considerable erosion. Reaction to

several of the failures involved replacement of metal parts with harder

materials, such as tungsten carbide. However, it was not clear from the

reports the degree of improvement in durability that resulted.

It was not possible to compare the erosion rates of the various valve

materials and designs. None of the reports provided erosion depth data,

erosion velocity data, or solids concentration data. Service time ranged

upward from 37 hrs. although the duty cycles were not described to any detail.

Temperatures as high as 1400°F were involved. Conditions such as those

involving pressure letdown are very difficult for conventional valve designs.

Several reports have become available on valve material and valve design

28-31

programs, containing some very promising findings; these reports should

be consulted for further details in this area. It is suggested that combinations of improved design (for example, several stages of pressure letdown

rather than one; minimizing pressure drops across conventional valves) and

improved erosion resistant materials could lead to improved valve service.

11
should be consulted for

29-31

Recent reports on the erosion of valve materials

some results on hard surfaced materials for valve seats and other intervals.

3. Pumps

A total of 8 reports concerned with pump failures were examined. Severe

particle erosion of the cast iron casings was a common finding. The other

materials employed included high Cr irons principally in the centrifugal

impellers. While the temperature of service was not particularly t'-igh,

the solids concentration (gasifier fines in water) was reported as large as

20%. At the impeller tip speeds involved, this solids concentration provided

considerable potential for rapid erosion of the casing as well as the impellers.

Hard-face coatings were applied by welding in some cases to extend erosion

life. Erosion depths on the casings ranged from 1/32 in. - 3/16 in. ^he

service time reported varied from 4 hrs. to 1400 hrs. although the solids

concentration was not noted and may have varied from less than 1% to as high

as 20% due to process upsets. The high erosion rates appear to have involved

erosion conditions considerably more severe than were originally anticipated.

Several of the failures involved abrasive wear (rather than erosion) of the

shaft seals due to solids trapped in the pump. Modifications in seal design

to better accomodate higher-than-normal solids concentrations may be possible.

There were not sufficient data concerning service values of velocity,

solids concentration, and erosion depth to permit quantitative conclusions to

be drawn about specific materials or components of the pumps involved in the

reported failures.

32

B . Hygas Facility

1. Piping

There are 12 failure reports (see Table IIl)concerned with erosion of piping

12
components in the Hygas low BTU Ash Agglomerating Gasifier system. Two reports

were concerned with transfer lines. In one case a blocked cross was severely

eroded after 4 years of residence in the system transporting a 10% char in

water slurry. Measurements of the eroded depth were not provided; however,

this performance appears reasonable based on the indicated service. Clearly

some regular replacement schedule is called for in char transport service;

perhaps more erosion data on this example could provide quantitative input

to assist in forecasting expected service life. Programs to ultrasonically

monitor wall thickness during operation would be one approach. The second

report concerned the erosion of an inner liner and subsequent erosion of a

connection bellows. Few details are provided in the report; however, the

potential always exists for misalignment or improperly fabricated joint

structure. It is expected that joint discontinuities may sharply increase

erosion over that expected for ideal conditions; hence, alignment is critical

where erosion must be expected.

Two failure reports were concerned with pipe structures in or near the

fluid bed in the gasifier. One report involved a carbon steel cooling pipe/

heat exchanger system operating at 800°F. Over a period of 1350 hours erosion

reduced the pipe wall thickness sufficiently to permit the pressure to exceed

the ultimate wall strength and burst the wall. Relatively few details were

provided to permit further analysis.

Five reports were concerned with erosion within the internal cyclone

33 separator. A summary of these experiences has been published. The original

design involved a single wall 310 stainless steel structure. After about 20

days, this wall (1/4 inch thick) was penetrated at the location of the entry

stream impact. Upon repair, an erosion shield of RA330 stainless alloy (thickness 1/4 inch) was placed within the cyclone at the entrance flow impact site.

13
After 288 hours of further service, erosion penetrated the shield and wall

(1/2 inch total) . The erosion conditions were about 1000 lb/hr at a nominal

velocity of about 90 ft/sec. The next modification involved welding onto the

shell a liner of RA330 alloy that had been coated with a cobalt

hardfacing. After 32 hours this liner failed near the weld joint ; however, it

was reported that this coated liner was considerably more erosion resistant

than the uncoated liner. It was also noted that corrosion and the influence

of corrosion scale on the erosion problem did not appear significant. The

final disposition of this cyclone separator modification scheme is not

known; however, proper installation (and positioning) of a suitable erosionresistant liner would seem an appropriate strategy. Modest design changes to

reduce the particle density in the flow by a larger impact area and to reduce

the flow velocity by staging could also have a significant beneficial effect.

9 One additional failure involved fracture of the cyclone-dipleg assembly due

to stress caused by operation of the fluid bed at a raised level. Erosion of

the dipleg occurred subsequent to the loss of proper position in the gasifier.

Three failures reported were concerned with a pressure tap tube and a 34 thermowell tube located near and within the fluid bed. The high exposure

temperature (1700 to 2100°F) appeared to cause rapid (61 hrs) erosion/corrosion

attack of the 310 stainless steel tubes even though the erosion velocity was

relatively low, about 5 ft/sec.

2 . Valves

There were no reported failures in valves due to erosion causes.

3. Pumps

One erosion report concerned a slurry pump that experienced rapid casing

erosion in service that involved solids concentrations as high as 45%. Low

pressure centrifugal pumps were employed that were of cast steel construction

14
with a plasma-sprayed hard coating. It was found that the coating rapidly

flaked off under the erosive conditions present. Weld overlay of the critical

parts with Stellite 12 coupled with a reduction in pump velocity by 50%

was found to produce acceptable performance in this service.

35

C. C0 9 Acceptor Facility

1. Piping

The Failure Information System contains 6 reports concerned with erosion

failures of piping and related components (see Table III) . A range of materials

were involved including stainless steel alloys, nickel-based alloys, coatings

and refractories . Two reports were concerned with acceptor lift line pipe

experiencing excessive erosion at slip joints. The service involved temperatures of about 1400°F, erosion velocities of 55 ft/sec and an atmosphere

of dolomite and gas. It was concluded that improper alignment of the pipe

and the slip joint components can lead to increased erosion of the metallic

liners. Design or installation procedure improvements should avoid such

problems

.

Two reports concerned an internal cyclone separator designed to remove

fine particulates from the process gas. The wall material, type 316 stainless

steel, eroded and in one report was penetrated at the location of flow impact

from the inlet pipe. An erosion-resistant liner was noted as a recommended

design change. In addition, it is suggested that the question of servicability

should be examined so that cyclone maintenance can be routinely carried out

by schedule.

Refractory liner erosion was experienced in one report concerned with the

regenerator vessel. The impact area of gas, char and dolomite from an inlet

line caused extensive erosion (about 13 in. deep) in the vessel wall refractory

15
liner. The importance of proper flow direction and the need to avoid limited

areas of impingement are illustrated in this example.

2. Valves

One failure report was examined concerning valve erosion. The valve

was used to handle dolomite and recycled gas at velocities of about 100 ft/sec.

Severe erosion of an 1800 alloy inner liner was found (a 1 inch by 3 inch section)

The liner was apparently misaligned when installed leading to an unexpectedly

rapid erosion situation. Neither the solids concentration nor the eroded

depth were reported, preventing any quantitative conclusions concerning erosion

rates in this situation.

3 . Pumps

There were no erosion-related failures reported for pumps.

4. Other Information

An extensive review of the operating records of this facility has been

35 36 carried out and reported. ’ A number of erosion problems were identified

through this records study that did not appear in the Failure Information

System. Relatively little detailed information on erosion parameters was

available, however, so further analysis would be difficult. It was noted that

significant problems faced during plant operation fell into five catagories:

plugs, failures of materials and components, process related problems, coal

preparation, and off site problems. Failures accounted for about 20% of

total problems. Erosion was specifically mentioned in 24 instances of problems

35 36

in this report. A study of maintenance and operability records included

examination of pump and valve components performance. Further details beyond

failure report information can be found in that source.

16
V. Summary and Recommendations

The purpose of this study was to examine the failure information available

concerning erosion-related failures of selected components in three principal

coal gasification systems. Examination of these records and other sources of

information indicated that erosion was a serious problem in these systems.

However, adjustments in response to those problems involving material design,

components and system changes were for the most part successful and can

probably be applied in future instances of related problems.

Many common problems were identified in spite of obvious differences

in system characteristics.

• Piping components were prone to problems at joints and bends. Very

careful alignment to avoid flow disturbances and low angle flow impact

on metal walls is necessary. Reductions in solids concentration and

flow velocity can be very effective in reducing erosion rates. These

findings also apply to cyclone separator components where erosion

opposite the inlet pipe was frequently a problem. Improved flow

patterns within the cyclone should be an effective strategy, for example,

exposing a larger area to first impacts (reduces particle density)

.

Velocity reductions through the use of two or more stages can greatly

2 3 reduce erosion due to the velocity dependence (V to V ) relation -

although at a cost in separation efficiency.

• Valve components exhibited characteristic problems of liner erosion

and closure failure leading to erosion. The existence of large pressure

drops across valves (up to 1000 psig) placed a severe burden on most

designs. It appears that other design approaches should be followed

17
for pressure letdown service (e.g. chokes). Hard facing materials

application to valve seats and other internals is effective, although

design changes and operating practices (with respect to solids

contamination of the valve area) may be equally or more effective.

• Pump components also responded well to the use of hard coatings and

overlays. It was noted that process upsets causing a significant

increase in solids concentration presented to the pumps invariably

led to serious problems. The tolerance of pump systems to 5 or 10

fold increases in solids concentrations is not large, particularly

where seal and bearing wear enter as well as erosion. Pump speed

reductions are an effective strategy in view of the power law

velocity effect on erosion mentioned previously.

As indicated in Table III a minimum set of erosion-related information is

needed to analyse erosion behavior. In all cases examined here, some critical

information items were missing and prevented quantitative problem analysis.

While it is appreciated that great difficulty exists in gathering such details

"on the spot" in field situations, some improvements in information access

can probably be accomplished in the future. The listing that follows is one

suggestion of the needed items in priority order, i.e. the earlier listed

items provide the most significant impact to subsequent problem analysis in

quantitative terms.

1. Component description (geometry, sizes, etc.)

2. Material identification (alloy, coating, etc.)

3. Time in service (duty cycle, time of erosion, etc.)

4. Erosion velocity (maximum, average)

5. Erosion depth (maximum, area of erosion)

6. Solids concentration (maximum, average)

18
7. Environment (chemical, temperature)

8. Narative description of sequence of events

Even a partially complete set of information in each instance following

these guidelines could permit a productive analysis of material erosion

rates in service and provide valuable input to future materials, applications

and component design developments.

Acknowledgments

Considerable assistance in obtaining the necessary information for this

study was provided by W. Willard and R. Dobbyn of NBS . Their help and

contributions through numerous discussions is gratefully acknowledged.

Comments on this report received from S. Dapkunus of DOE are also appreciated.
Table I. Failures due to Erosion and Other Causes

All Causes:

Process

:

Erosion:

Process

:

CO^ Acceptor

Synthane

Hygas

Others

C0

? Acceptor

Synthane

Hygas

Others

Number of Items

485

53

148

63

221

102 (21% all causes)

7 ( 13%)

34 ( 23%)

13 ( 21%)

48 ( 22 %)

20
Table II. Erosion-related Failure of System Components

Number of Items

All Causes: 485

Erosion:

Pumps

Valves

Piping

Other

102

29

32

39

13

(Note: Some reports involve more than one component)

21
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27

Fig.

1.

Schematic

representation

of

erosion

rate

vs

attack

angle.
Fig. 2. Influence of velocity on erosion for different materials.

15

28
Fig. 3. Velocity dependence of erosion of stainless steel at 975 C and 25 C

11

29
x o & 90° impact

Fig. 4. Influence of particle size on erosion of an 11 percent chromium steel

15

30
Fig. 5 . Volume removal as a function of hardness (VHN) for metals eroded at a=20

deg and velocities of 250 and 450 ft/sec. (No data were taken for

nickel at 450 ft/sec.) All metals except cadmium were in annealed

. 6

condition

.

31
9

ANGLE OF IMPINGEMENT, a

A k

Fig. 6. Erosive wear of hot-pressed silicon nitride as a function of

impingement angle. Curves represent erosion dependence for

purely brittle behavior.

32
REFERENCES

1. Erosion , ed. C. Preece, Treatise on Material Science and Technology ,

vol. 16 (Academic Press, 1979). See in particular chapters by Evans,

Ruff and Wiederhorn, Vyas, and Summers.

2. Preece, C. M. and Macmillan, N. H., Ann. Review of Materials Science

(1977).

3. Hutchings, I. M. , Proceedings of the ASTM Symposium "Erosion: Prevention and Useful Application ," STP 664 (1979).

4. Finnie, I. , Levy, A. and MccFadden, Proceedings of the ASTM Symposium

"Erosion: Prevention and Useful Applications ," STP 664 (1979).

5. Finnie, I., Wear 3, 87-103 (1960).

6. Finnie, I., Wolak, J. and Kabil, Y. , J. of Materials 2, 682-700 (1967)

7. Bitter, J. G. A., Wear 6, 5-21, and _6, 169-190 (1963).

8. Neilson, J. H. and Gilchrist, A., Wear 11 , 111-122 (1968).

9. National Research Council, Erosion Control in Energy Systems , pp . 228

(1977).

10. Young, J. P. and Ruff, A. W. , J. Engrg. Matls . and Tech, Trans ASME ,

_99, 121-125 (1977).

11. Ives, L. K. , J. Engrg. Matls. and Teen ., Trans ASME 99 , 126-132 (1977)

12. Grant, G. and Tabakoff, W. , J. Aircraft 12 , 471-478 (1975).

13. Tilly, G. P., Wear 14, 63-79 (1969).

14. Sheldon, G. L, and Kanhere, A., Wear 21 , 195-208 (1972).

15. Goodwin, J. E., Sage, W. , and Tilly, G. P., Proc. Inst. Mech. Engrs .

184 , 279-292 (1969).

16. Tilly, G. P., Wear 23, 87-96 (1973).

33
17. Barkalow, R. H. and Pettit, F. S. and Spriggs, D. R. , NACE Conference

on Corrosion/Erosion , p. 139 (1979).

18. Mills, D. and Mason, J. S., Wear 44, 311-328 (1977).

19. Smeltzer, C. E., Gulden, M. E. , and Compton, W. A., J. Basic Engrg .,

Trans ASME 92, 639-654 (1970).

20. Uuemois, H. and Kleis, I. Wear 31 , 359-371 (1975).

21. Hockey, B. J., Wiederhorn, S. M. and Johnson, H. , Fracture Mechanics

of Ceramics - 3, Flaws and Testing , Plenum Press (New York, 1978) .

22. Sheldon, G. L.

,

Trans. ASME: J . Basic Engr . , 92

,

619-26 (1970)

23. Wierderhom, S, M. , Fuller, E. R. , Jr., Bukowski, J. M. , and Robbins

,

C. R. , Trans ASME Journal of Engineering Materials and Technology , 99 ,

143-46 (1977).

24. Sheldon, G. L., and Finnie, I., Trans ASME: Journal of Engineering

for Industry , 88 , 387-92 (1966)

25. Evans, A. G. , Gulden, M. E. , and Rosenblatt, M. E., Proc . Roy . Soc .

,

in press.

26. NACE Conference on Corrosion/Erosion of Coal Conversion System Materials,

ed. A. V. Levy (NACE, Houston, TX, 1979).

27. Lewis, R. , Haynes, W. P., Strakey, J. P., and Santore, R. R. , Synthane

Process Update - Mid '78 , Fifth International Conference on Coal

Gasification, Liquif ication and Conversion to Electricity, (Pittsburgh,

PA, August, 1978).

28. Lewis, R. , Strakey, J. P. , and Haynes, W. P., Update of Synthane Pilot

Plant Status , Ninth Synthetic Pipeline Gas Symposium, (Chicago, IL, October,

1977)

34
29. Dubis, D., Santore, R. R. , and Lewis, R. , Valve Experiences in the

Synthane Pilot Plant , Workshop on Valves for Solids Handling

Service in Coal Conversion, (Morgantown, WV, November, 1977)

.

30. Carson, S. E. , and Runnels, 0. D. , Valve Applications at the Synthane

Plant in Mixed Phase Erosion Service , Report to USDOE,(June, 1978).

31. Performance of Valve Materials Under Erosion Conditions , DOE Materials

and Components Newsletter, #22 (1979)

.

32 . Experience with Materials in Hygas Coal Gasification Pilot Plant ,

Youngblut, K. C., Corrosion 1973 (Natl. Assoc. Corrosion Engineers, Houston,

TX, 1973).

33. Cyclone Erosion in Hygas Ash Agglomerating Unit , DOE Materials and

Components Newsletter, #14 (1978).

34. Component Failures in Hygas Ash Agglomerating Gasifier , DOE Materials

and Components Newsletter, #20 (1979).

35 . An Evaluation of the Performance of Materials and Components used

in the Conoco Lignite Gasification Pilot Plant, C0 o Acceptor Process ,

Dobbyn, R. C. et al. , NBS report (1979).

36 . Review and Evaluation of Failures, Maintenance and Operability Data

for C0 o Acceptor Plant Mechanical Equipment , MTI P^eport #78TR.3 (1977).
NBS-114A (REV. 9-781

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. 2. Gov't Accession No, I. Recietent' s Accession No*' dHT r -Mm. 4. TITLE AND SUBTITLE

ANALYSIS OF EROISON- RELATED FAILURE

INFORMATION FROM COAL GASIFICATION SYSTEMS

5. Publication Date

6. Performing Organization Code

7. AUTHOR(S)

A. W. Ruff

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, DC 20234

28. Project/Task/WorK Unit No.

.

11. Contract/Grant No.

12. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City, state, ZIP)

Department of Energy

Washington, DC

13. Type of Report & Period Covered

14. Sponsoring Agency Code

’

15. SUPPLEMENTARY NOTES

Document describes a computer program; SF-185, FIPS Software Summary, is attached.

16. ABSTRACT (A 200-ivord or less tactual summary of most significant information. If document includes a s i gni ficant bibliography or literature survey, mention it here.)

Failure information reports concerning erosion that are contained in the

NBS-DOE Failure Information Center have been analyzed for the purpose A

identifying critical and common factors associated with erosion in coal

gasification applications. Emphasis was placed on the components most frequently identified in erosion failure reports - piping, valves, pumps, cyclones - and on three of the principal processes. Recommendations are presented on a minimum set of erosion-related information needed to analyze erosion behavior.

A brief review of solid particle erosion and several bibliographic references

are also included.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name;

separated by semicolons)

Cyclones; energy; erosion; metals; pumps; valves; wear.

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(THIS REPORT)

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