FINAL DRAFT UGANDA 
STANDARD  
  FDUS 945 -1 
First Edition  
2012-mm-dd 
 
 
 Reference number  
FDUS 945 -1: 201 2 
© UNBS 201 2  
  
Pre-insulat ed flexible pipe systems — Part 1: Classification, 
general requirements and methods  of test 
 FDUS 945 -1: 201 2 
ii © UNBS 201 2 – All rights reserved  
 Compliance with this standard does not, of itself confer immunity from legal obligations  
A Uganda Standard does not purport to include all necessary p rovisions of a contract. Users are 
responsible for its correct application  
© UNBS 2012   
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilised in any 
form or by any means, electronic or mechanical, includ ing photocopying and microfilm, without prior written 
permission from UNBS.  
Requests for permission to reproduce this document should be addressed to  
The Executive Director  
Uganda National Bureau of Standards  
P.O. Box 6329  
Kampala  
Uganda  
Tel: 256 41 4 505 9 95 
Fax: 256 41 4 286 123  
E-mail: unbs@infocom.co.ug  FDUS 945 -1:201 2 
© UNBS 201 2 – All rights reserved  iii 
 Contents  Page 
Foreword  ................................ ................................ ................................ ................................ .............................  v 
1 Scope  ................................ ................................ ................................ ................................ ......................  1 
2 Normative references  ................................ ................................ ................................ ............................  1 
3 Terms and definitions  ................................ ................................ ................................ ................................ ..... 2 
4 Classification  ................................ ................................ ................................ ................................ ...................  4 
5 Requirements  ................................ ................................ ................................ ................................ ...................  4 
5.1 Thermal insulation properties  ................................ ................................ ................................ .....................  4 
5.2 Flexibility  ................................ ................................ ................................ ................................ .......................  4 
5.3 Resistance to external actions  ................................ ................................ ................................ ....................  4 
5.4 Insulation Layer  ................................ ................................ ................................ ................................ ............  4 
5.4.1 Compressive creep  ................................ ................................ ................................ ................................ ... 4 
5.4.2 Water absorption at elevated temperatures  ................................ ................................ ...........................  5 
5.5 Casing  ................................ ................................ ................................ ................................ ............................  5 
5.5.1 UV stability  ................................ ................................ ................................ ................................ .................  5 
5.5.2 Thermal stability  ................................ ................................ ................................ ................................ ........  5 
5.5.3 Stress crack resistance  ................................ ................................ ................................ ............................  5 
5.5.4 Use of rework material  ................................ ................................ ................................ ..............................  5 
5.6 Surveillance systems  ................................ ................................ ................................ ................................ ... 5 
6 Test methods  ................................ ................................ ................................ ................................ ...................  5 
6.1 Flexibility  ................................ ................................ ................................ ................................ .......................  5 
6.2 Compressive creep  ................................ ................................ ................................ ................................ ...... 6 
6.2.1 General  ................................ ................................ ................................ ................................ .......................  6 
6.2.2 Principles of testing  ................................ ................................ ................................ ................................ .. 7 
6.2.3 Test apparatus  ................................ ................................ ................................ ................................ ...........  7 
6.2.4 Test sample  ................................ ................................ ................................ ................................ ................  9 
6.2.5 Test procedure  ................................ ................................ ................................ ................................ ...........  9 
6.2.6 Calculation and expression of results  ................................ ................................ ................................ .. 10 
7 Marking  ................................ ................................ ................................ ................................ ...........................  11 
7.1 General marking aspects  ................................ ................................ ................................ ...........................  11 
7.2 Minimum marking information  ................................ ................................ ................................ ..................  11 
8 Manufacturer's information  ................................ ................................ ................................ ..........................  11 
Annex A (normative) Measurement of linear thermal resistance and conductivity of the pipe  ...............  12 
A.1 General  ................................ ................................ ................................ ................................ ........................  12 
A.2 Apparatus  ................................ ................................ ................................ ................................ ...................  12 
A.3 Test sample  ................................ ................................ ................................ ................................ ................  12 
A.4 Test conditions and procedures  ................................ ................................ ................................ ..............  12 
A.5 Measurement  ................................ ................................ ................................ ................................ ..............  13 
A.5.1 Linear thermal resistance of the pipe system  ................................ ................................ .....................  13 
A.5.2 Thermal conductivit y of the pipe system  ................................ ................................ .............................  13 
A.6 Declared longitudinal thermal resistance and thermal conductivity  ................................ ...................  13 
Annex B (normative) Determination of the declared values of the radial thermal resistance of 
flexible pipe assembly  ................................ ................................ ................................ ........................  16 
B.1 Introduction  ................................ ................................ ................................ ................................ ................  16 
B.2 Selection of specimen  ................................ ................................ ................................ ...............................  16 
B.3 Determination of the declared values of the radial thermal resistance  ................................ ...............  16 
Annex C (normative) Determination of design values for the l ongitudinal thermal resistance  ...............  18 
Annex D (normative) Calculation of the heat flow from the medium to the ambient (heat loss)  .............  19 
D.1 G eneral  ................................ ................................ ................................ ................................ ........................  19 FDUS 945 -1: 201 2 
iv © UNBS 201 2 – All rights reserved  
 D.2 Calculations  ................................ ................................ ................................ ................................ ...............  19 
D.2.1 Single pipe system (SPS)  ................................ ................................ ................................ ......................  19 
D.2.2 Twi n pipe system (TPS)  ................................ ................................ ................................ .........................  19 
D.2.3 Longitudinal thermal resistance of the surrounding soil  ................................ ................................ .. 20 
D.3 Declared values of the longitudinal therma l resistance of buried pipe systems  ...............................  20 
Bibliography  ................................ ................................ ................................ ................................ .....................  24 
 
 FDUS 945 -1:201 2 
© UNBS 201 2 – All rights reserved  v 
 Foreword  
Uganda National Bureau of Standards (UNBS) is a parastatal under the Ministry of Tourism, Trade a nd 
Industry established by the Act of Parliament of 1983, of the Laws of Uganda.  UNBS is mandated to co -
ordinate the elaboration of standards and is  
(a) a member of International Organisation for Standardisation (ISO) and  
(b) a contact point for the WHO/FAO Cod ex Alimentarius Commission on Food Standards, and  
(c) the National Enquiry Point on TBT/SPS Agreements of the World Trade Organisation (WTO).  
The work of preparing Uganda Standards is carried out through Technical Committees. A Technical 
Committee is establis hed to deliberate on standards in a given field or area and consists of representatives of 
consumers, traders, academicians, manufacturers, government and other stakeholders.  
Draft Uganda Standards adopted by the Technical Committee are widely circulated t o stakeholders and the 
general public for comments. The committee reviews the comments before recommending the draft standards 
for approval and declaration as Uganda Standards by the National Standards Council.  
Committee membership  
The following organizati ons were represented on the Building and civil engineering standards Technical 
Committee (UNBS/TC 3), during the development of this standard:  
 Institution of Surveyors of Uganda  
 Department of Geological Mines and Surveys  
 Kyambogo University  
 East African Di stributors Ltd  
 Multiple Industries  
 Uganda National Association of Building and Civil Engineering Contractors  
 Uganda National Bureau of Standards  
 Uganda National Plumbers Association  
 FINAL DRAFT UGANDA STANDARD  FDUS 945 -1: 201 2 
 
© UNBS 201 2 – All rights reserved  1 
 Pre-insulated flexible pipe systems — Part.1: Classification, 
general r equirements and methods  of test 
1 Scope  
This Final Draft Uganda S tandard specifies the  classification, general requirements and methods of test for 
flexible, pre -insulated,  directly buried district heating pipe systems.  Depending on the pipe assem bly (see 
Table 4), this standard can be used  for maximum operating  temperatures of 95 °C to 140 °C and operating 
pressures of 6 bar to 25 bar.  
The pipe systems are designed for a lifetime of 30 years. For pipe systems with plastic service pipes, the  
respective temp erature profiles are defined in FDUS 945 -2. 
NOTE  For the transport of other liquids, for example potable water, additional requirements may be applicable.  
2 Normative references  
The following referenced documents are indispensable for the application of th is document. For dated  
references, only the edition cited applies. For undated references, the latest edition of the referenced  
document (including any amendments) applies.  
IEC 60811 - 4, Assessment of carbon black dispersion in polyethylene using a  microsc ope 
ISO 6964, Polyolefin pipes and fittings — Determination of carbon black content by calcination and pyrolysis 
— Test method and basic specification  
ISO 8497, Thermal insulation — Determination of steady -state thermal transmission properties of thermal  
insulation for circular pipes  
ISO 9967, Thermoplastics pipes — Determination of creep ratio  
ISO 9969, Thermoplastics pipes — Determination of ring stiffness  
ISO 10508;  Plastics piping systems for hot and cold water installations — Guidance for classifica tion and 
design   
ISO 16770, Plastics — Determination of environmental stress cracking (ESC) of polyethylene — Full-notch 
creep test (FNCT)  
ISO 16871, Plastics piping and ducting systems — Plastics pipes and fittings — Method for exposure to  direct 
(natural ) weathering   
ISO 21003 -1; Multilayer piping systems for hot and cold water installations inside buildings — Part 1: General    
ISO 23993 , Thermal insulation products for building equipment and industrial installations — Determination of 
design thermal cond uctivity  
US 482 -1, High Density Polyethylene (PE -HD) pipes  — Part 1: General quality requirements  
US 482 -2, High Density Polyethylene (PE -HD) pipes  — Part 2: Dimensions  FDUS 945 -1: 201 2 
2 © UNBS 201 2 – All rights reserved  
 3 Terms and definitions  
For the purposes of this standard , the following terms and defi nitions apply.  
3.1 
lifetime  
time during which the flexible pipe system operates without failure at the designated operating  temperature  
3.2 
continuous operating temperature  
temperature of the heat medium for which the system has been designed to operate co ntinuously  (sSee Table 
4) 
3.3 
maximum operating temperature  
exceptionally high operating temperature occurring for short periods only  
3.4 
operating pressure  
pressure at which the hot water network is designed to operate continuously  
3.5 
service pipe  
medium  carrying pipe which is in contact with warm water  
3.6 
outer casing  
separately applied outer layer of the pipe assembly, protecting the construction during installation and         
protecting the construction against external influences (after installation)  
3.7 
insulation layer  
layer which provides the designated thermal characteristics of the pipe assembly  
3.8 
pipe assembly  
assembled product, consisting of at least one service pipe, insulating material and casing  
3.9 
pipe system  
pipe assembly, plus service pipe fittings, casing joints, and other components like surveillance  elements  
3.10 
single pipe system  (SPS) 
pipe system with one service pipe  
3.11 
twin pipe system  (TPS) 
pipe system with two service pipes  
3.12 
bonded system  
service pipe, insulating materia l and casing which are bonded by the insulating material  
3.13 
non bonded system  
service pipe, insulating material and casing which are not bonded by the insulating material  FDUS  945-1: 201 2 
© UNBS 201 2 – All rights reserved  3 
 3.14 
casing joint assembly  
casing joint  assembled product, consisting of at least i nsulating material and casing, designed to protect and      
thermally  insulate a service pipe joint  
3.15 
ageing factor , fa 
factor without a dimension which expresses the ageing of the insulating layer in relation to the expected  
lifetime  
3.16 
moisture fact or, fm 
factor without a dimension for the influence of moisture on the insulating layer in relation to the expected  
lifetime  
NOTE  The term 'moisture' as it is used here is not identical with the term 'moisture' as it is used in  ISO 10508  and 
ISO 21003 -1. 
3.17 
ovality  
difference between the maximum and minimum diameter at a cross section expressed as a percentage of the  
minimum diameter  FDUS 945 -1: 201 2 
4 © UNBS 201 2 – All rights reserved  
 4 Classification  
The field of application for the different designs of pipe assembly is defined  in Table 4,  
Table 1 — Clas sification system  
Service pipe  
material  Pipe assembly  
design  Field of application  
Operating  
pressure , 
bar Continuous  
operating 
temperature , 
°C Maximum  
operating 
temperature , 
°C 
plastics  bonded  6, 8 or 10  80 95 
plastics  non bonded  6, 8 or 10 80 95 
metal  bonded  16 or 25  120 140 
 
 
5 Requirements  
5.1 Thermal insulation properties  
The manufacturer shall submit values for the heat loss of buried pipe assemblies for  all pipe dimensions in  
accordance with Annex D, rounded to 0 .001 W/mK.  
NOTE  Annex A specifies how to measure thermal properties, Annex B specifies how to calculate declared values for  
thermal properties of all pipe dimensions, and Annex C specifies how to  include ageing effects.  
5.2 Flexibility  
The flexibility of the pipe assembly is verified by testing at the minimum bending radius. The manufacturer of  
the pipe assembly shall declare the minimum installation bending radii for all dimensions produced, rela ted to  
the central axis of the pipe assembly.  
The minimum declared installation bending radius of the pipe assembly according to this standard  shall not 
exceed thirty times the outer diameter of the casing.  
When bending to the minimum radius, the service p ipe and the casing of the pipe assembly shall not break,  
and the ovality of the outer casing shall not exceed 30 % when tested according to 6.1.  
5.3 Resistance to external actions  
When tested in accordance with  ISO 9969 the ring stiffness of the pipe assem bly shall be at least 4 kN/m² and  
the ring stiffness divided by the creep ratio according to ISO 9967 shall be at least 0 .8. 
When tested in accordance with  ISO 10508  the outer casing of pipe assemblies and casing joints shall show 
no cracks  when exposed to  an impact of 4 J.  
5.4 Insulation layer 
5.4.1 Compressive creep  
When tested according to 6.2, the insulation shall not be compressed by more than 10  %. FDUS  945-1: 201 2 
© UNBS 201 2 – All rights reserved  5 
 5.4.2 Water absorption at elevated temperatures  
When tested in accordance with  ISO 21003 -1, the water ab sorption shall not exceed the limits of one of the 
test options defined in Table 2. 
Table 2 — Test option for water absorption  
Test option  Test temperature , 
°C Water absorption (by volume) , 
% 
A 100 10 
B 80 1 
 
5.5 Casing  
5.5.1 UV stability  
Casings shall be made of a material containing at least 2 % by mass of carbon black (determined in  
accordance with ISO 6964).  
The requirements of 5.2 and 5.3 sh all still be fulfilled after an exposure to an energy of ≥ 3 .5 GJ/m² in 
accordance with ISO 16871.  
5.5.2 Thermal stability  
The oxidation induction time of the material to be used for the casing shall be at least 20 min at 210 °C  when 
tested in accordance w ith ISO 21003 -1. 
5.5.3 Stress crack resistance  
The time for the stress crack resistance of PE -HD materials used for the casing shall be at least 100 h  when 
tested at 4 MPa and 80 °C in accordance to ISO 16770.  
NOTE  The test may be carried out on samples pr epared by compression moulding, injection moulding or extrusion  
from the same raw material as being used for the production of the casing.  
PE-LD materials used for the casing shall not exceed a failure rate F20 when tested for 1  000 h in  accordance 
with US 482-1 and US 482 -2. 
5.5.4 Use of rework material  
If rework material is used, only clean, not degraded, rework material generated from the manufacturer's own  
production of pipes  shall be used.  
5.6 Surveillance systems  
If measuring elements for surveillance  systems are being installed in flexible pipe systems, all elements  
installed and the installation in pipe systems shall comply with the requirements of  ISO 21003 -1. 
6 Test methods  
6.1 Flexibility  
The pipe assembly shall be conditioned for 24 h at the mini mum temperature according to the  manufacturer's 
installation instructions. Afterwards the pipe assembly shall be fixed onto a bending rig  according to Figure 1 
within 10 min. After 30 min the ovality shall be measured at the position  shown in Figure 1.  FDUS 945 -1: 201 2 
6 © UNBS 201 2 – All rights reserved  
 
 
Key 
1 pipe assembly  
2 bending rig  
3 straps or clamps  
4 measuring points for ovality  
Figure 1 — Flexibility test  
After measuring the ovality the outer casing shall be opened in the axial direction and visual inspection of the  
insulation material of the whole  bend section shall be carried out.  
6.2 Compressive creep  
6.2.1 General  
The test procedure for the compressive creep at elevated temperatures of the insulation material shall be  
carried out in a similar way to  ISO 21003 -1. In addition to these tests the fo llowing  changes/additions in testing 
are standardised in order to reflect the special situation of insulation procedures  for flexible pipe systems.  
NOTE  Table 2 and the test are based on the "Findley equation" (see  ISO 21003 -1). The traceability of the log arithmic 
coherence and the adequate verification of the test should be shown by calculation (with the squared factor for accuracy of 
determination larger than 0 .9). FDUS  945-1: 201 2 
© UNBS 201 2 – All rights reserved  7 
 6.2.2 Principles of testing  
The creep behaviour of samples under pressure is tested by meas uring the increase of deformation of a test 
sample under a constant pressure load and defined conditions respectively temperature, humidity and time.  
6.2.3 Test apparatus  
6.2.3.1  Plate for heating purposes  (for heating up one side of the test samples formi ng part of the 
pressure apparatus ). The heated plate shall provide an equally distributed temperature at the surface of the 
heating plate and produce a heat flow vertical to the plate. The temperature shall be measured with an 
accuracy of +/ -0.5 K. 
6.2.3.2  Pressure apparatus , consists of two horizontal plates with one being able to tilt in the plane in 
order to apply an even compressive load on the entire surface of the sample in a vertical direction. It shall be 
assured that the plates are able to withstan d the test loads without deformation, so that the load during the 
test can vary by not more than +/ - 5 %. 
6.2.3.3  Measuring equipment , instrument for measuring the distance between both plates, that is,  the 
deformation of the sample measured to within 0 .01 mm 
The apparatus is shown in Figure 2.  FDUS 945 -1: 201 2 
8 © UNBS 201 2 – All rights reserved  
 Dimensions in millimeters  
 
b) Test apparatus with cover gas  
Key 
1 measuring device for thickness  
2 test specimen  
3 pressing plate  
4 side insulation  
5 heating panel  
6 thermostat  
7 gap 
8 test load  
9 hood for cover ga s       
Figure 2 —Test apparatus  FDUS  945-1: 201 2 
© UNBS 201 2 – All rights reserved  9 
 6.2.4 Test sample  
The dimensions of the sample should be related to the minimum thickness of the insulation used in the type of 
district heating pipe assembly tested, the maximum temperature of the heat medium used, and at or near to 
the maximum diameter produced. The form of the samples should be rectangular or cylindrical with 
dimensions of the base  at 50 mm up to 100 mm or an equivalent diameter.  The length should be equal to or 
greater than the thickness.  
The samples are  preferably taken from the insulation material of the pipe assembly. In case the samples 
become too small using this procedure they can also be taken from a square formed of the material having the 
same consistency and properties. Alternatively, the sample s can be assembled from more than one layer. 
This comparative sample shall be taken from the same production machine used for manufacture of the 
insulation material normally. The specification values, especially density and cell -structure, shall be 
compara ble with the insulation material used for pipe assembly production.  
The minimum number of test samples is three for each test condition.  
During preparation of the samples , the samples shall be taken from the insulation in such a way that the 
direction of t he test load is equal to the direction in which the load lasts on the pipe assemblies installed. The 
samples shall be conditioned for a minimum of 6 h at 23 °C ±3 °C and at a relative humidity of 50 % ± 5 %. 
6.2.5 Test procedure  
The length and width of the sample are measured in accordance with US 482 -2 to an accuracy of at least 0 .5 
%. With this data the initial area of the cross section of the sample can be ca lculated for determination of the 
maximum load.  
The preliminary load of the test sample shall be less than 10 % of the lowest amount of load chosen for the 
test. The thickness shall be measured with an accuracy of 0 .1 mm. The test samples shall have an add itional 
side insulation (see Figure 2) during the test. However, it shall give free movement to the test sample itself.  
During the test phase the first thermal test should last for two hours on the heated plate in order to 
compensate effects of expansion d ue to gas production of the sample and first appearance of additional cross 
linking processes. Therefore the sample has to be put on the heating plate under the test load and heated up 
to the test temperature. The first test value is taken after two hours.  This is declared then as the zero -value of 
the test series.  
The relevant test methods shall be selected for the product to be tested in accordance with Table 3. The tests  
are done in two test sequences, A and B in parallel.  
Table 3 — Test conditions for t esting stability of dimensions  
No.  System  Test load, 
Pa Test A  Test B  
Test temperature , 
° C Test time, 
h Test 
temperature , 
° C Test time , 
h 
1 Metal service pipe  Ptest continuous operating  
temperature  1 000 maximal 
operating  
temperature  300 
2 Plastic  service  pipe Ptest continuous operating  
temperature minus 2 
K 1 000 maximal 
operating  
temperature 
minus 2  K 300 
 
If the test is carried out under cover gas conditions the test apparatus shall comply with Figure 2.b) and the 
pressure of the cover gas shal l be 5 mbar ±3 mbar above ambient pressure.  FDUS 945 -1: 201 2 
10 © UNBS 201 2 – All rights reserved  
 6.2.6 Calculation and expression of results  
The area related load Pweight resulting from load on the cross section of the test specimen of the insulation  
material shall be calculated as follows:  
Pweight = Fweigh t/A in Pa  
where  
Pweight  is the area related load on the cross section of the test specimen of the insulation material . 
Fweight =Mg; in N  
where  
M is the mass of the pipe including the water inside in k ilggrams;  
A is the projected area of the service pipe ( length width) in m2, 
g is the gravity in m2. 
The area related load Pexp on the insulation resulting from heat expansion of the service pipe is calculated as 
follows:  
Pexp = 2 × Fexp/(πr.d2) in Pa  
where  
Fexp is the force resulting from heat extension in N ewtons , 
r is the bending radius in the axis of the pipe in m etres , 
d2 is the diameter of the service pipe.  
The test load Ptest shall be the maximum value of Pweight and Pexp. 
NOTE  The stability of dimensions of the insulation can be negatively influenced i n the vertical direction by the mass 
of the service pipe filled with water and in the horizontal direction by the extension forces caused by heating up.  
It is sufficient to test the stability of dimensions for each pipe assembly in accordance with the maxi mum value  
of the forces appearing because in the first approach these forces act independently from each other. The test  
shall always be done with the largest dimension of the pipe assembly and with the smallest thickness of  
insulation.  
In case of corrugat ed service pipes (compensation for the thermal related change of the length by the  
corrugated contour) and in case of plastic service pipes (axial stresses relax under operating temperatures  
relatively fast) the area related force Pweight has to be used fo r the calculation.  
The testing temperatures and testing times are selected in accordance with Table 3 in relation to each system.  
The test results as a percentage (compression ∑) shall be documented for each test and each test piece shall  
be rounded to thr ee digits in percent:  
∑= (s - sSTB)/s × 100;  
where  
∑is the compression in % ; FDUS  945-1: 201 2 
© UNBS 201 2 – All rights reserved  11 
 s is the thickness of the test piece before applying the load in m illimetres ; 
sSTB is the thickness of the test piece after load testing and temperature testing in m illimetres . 
7 Marking  
7.1 General  
The marking shall be printed, formed or labelled directly on the outer surface of the pipe assembly.  
7.2 Minimum marking information  
At least every 3 m of the outer casing shall be marked with the following information:  
a) manufacturer 's/supplier's name or registered brand name;  
b) number of this Uganda Standard including the relevant part; 
c) number;  diameter and wall thickness of the service pipe(s) and the diameter of the casing in 
millimetres ; 
d) material or material code (according to the r elevant Uganda n standard) of the service pipe;  
e) maximum operating temperature and pressure;  and 
f) production date (possibly by a code).  
8 Manufacturer's information  
The manufacturer shall provide in his technical documentation information on at least the foll owing:  
a) minimum bending radius;  
b) the heat loss of the pipe assembly in accordance with Annex D;  
c) classification in accordance with Table 4;  
d) precautions for transport;  
e) storage conditions;  
f) embedding prescriptions;  
g) documentation in accordance with ISO 21003 -1, if surveillance elements are installed;  
h) allowable traffic loads;  
i) length -compensation -fixpoints;  
j) wall entries;  
k) ageing of the insulation;  
l) precautions against ingress of moisture/water into the insulation material through the pipe ends;  
m) instructions for instal lation and operation in ground water.  FDUS 945 -1: 201 2 
12 © UNBS 201 2 – All rights reserved  
 Annex A  
(normative)  
 
Measurement of linear thermal resistance and conductivity of the pipe  
A.1 General  
This annex describes benchmarks and procedures for measuring the linear thermal resistance of flexible pipe 
systems  in accordance with  ISO 8497.  
A.2 Apparatus  
For testing purposes heated test pipes (compensation heating) and test pipes with calibrated or calculated 
pipe ends according to ISO 8497 shall be used.  
A.3 Test sample  
The test sample is of the same length as t he test pipe, including compensation heating if being used. The 
sample shall be conditioned for one week at room temperature conditions. Pipe systems with cell gases in the 
insulation material other than air shall be tested not earlier than six weeks after  production.  
A.4 Test conditions and procedures  
The thermal parameters shall b e measured in accordance with  ISO 8497 under the following conditions:  
a) ambient air temperature at 23 °C ±2 °C;  
b) for the determination of a thermal conductivity at 50 °C a minimum of three measurements are 
necessary,  the spacing of which shall be 10  K ±2 K and the temperature range shall include 50 °C;  
c) the measured values are to be related to the arithmetic a verage value of the temperature 
1  at the 
inner  diameter of the service pipe d1 and 
4 , at the outer diameter of the casing d4 (see Figure A.1);  
d) for pipe systems with metal service pipes the temperature value 
1  of the service pipe can be taken 
as for  the temperature value 
2  measured at the outer diameter d2 of the service pipe;  
e) for pipe systems with plastic service pipes the temperature value 
1  of the serv ice pipe shall be 
measured  directly at the inner side of the service pipe;  
f) the temperature 
4  is the temperature directly at the outside of the casing pipe;  
g) for pipe systems with corrugated casing pipes the temperature 
4  is the average value of the  
temperature  measured at the highest and lowest point of the wave (see Figure A.2).  
For pipe systems with corrugated medium or casing pipes an average value for the maximum and minimum  
diameter shall be taken for the therma l calculation purposes (see Figure A.2).  
 
The sensors have to be fixed firmly at the surface of the medium and casing pipes in order to ensure proper 
thermal contact  FDUS  945-1: 201 2 
© UNBS 201 2 – All rights reserved  13 
 A. Measurement  
A.5.1 Linear thermal resistance of the pipe system  
The average temperature for single pipes as shown in Figure A.1 shall be calculated in accordance with 
equation A.1.  
av
 =
24 1  in °C  … (A1) 
The average temperature of twin pipes shall be calculated in accordance with equation A.2 . 
av
 = 

24 1/2r1, 1,f    in °C  … (A2) 
The radial thermal resistance R of the pipe system at any average temperature 
av  can be calculated with the 
measured value of the radial heat flow rate q and the length L of the tested pi pe and the temperatures 
measured at the relevant surfaces d1 and d4 with equation A.3; equation A.4 shall be used for twin pipe 
systems.  
R
av   =
qL ) (4 1  in (m.K)/ W … (A3) 
RTPS
av  = 

r fr1, 1,f 41/2
qqL
  in (m.K)/W  … (A4) 
 
A.5.2 Thermal conductivity of the pipe system  
The thermal conductivity of a pipe system at any average temperature 
av  shall be calculated from  
av
= 
 2πln
.14
1 4dd
Lq
  in (m.K)/W  … (A5) 
The therm al conductivity of a twin pipe system at any average temperature 
 av shall be calculated from  
av TPS,
 = 
   2ln
.2/1) (14
4 ,1 ,1dd
Lq q
r fr f
  in (m.K)/W  ...(A6) 
A.6 Declared longitudinal thermal resistance and thermal conductivity  
The relation of the thermal values and the average temperatures can be obtained by an analysis (regression 
curve) of the minimum of three temperature measuring points at various average temperatures.  
For other temperatures than those which have been measured, the thermal resistance and conductivity shall 
be obtained from this regression curve.  FDUS 945 -1: 201 2 
14 © UNBS 201 2 – All rights reserved  
 The declared values for the longitudinal thermal resistance of the pipe system Rdecl and of the longitudinal 
thermal conductivity 
declλ  shall be calculat ed for an average temperature of 50 °C.  
 
 
Figure A.1 — Diameter designations  FDUS  945-1: 201 2 
© UNBS 201 2 – All rights reserved  15 
 
 
Figure A.2 — Diameters of corrugated pipes  
 
 
 
 
 
 
 
 
 
 
 FDUS 945 -1: 201 2 
16 © UNBS 201 2 – All rights reserved  
 Annex B  
(normative)  
 
Determination of the declared values of the radial thermal resistance of  
flexible pipe assembly  
B.1 Introduction  
The manufacturer of the flexible district heating pipes is responsible for providing the declared values and 
respective traceable information about the radial thermal resistance of the pipe assembly.  
Information about the long -term performance of the thermal resistance is given in Annex C.  
B.2 Selection of specimen  
The pipe system shall be tested at least for one of the two the smallest and one of the two largest nominal  
dimensions of the production variety of the pipe system according to Annex A. 
Additionally the value for the thermal conductivity 
 I of the insulation shall be determined according to  US 
482-1 from a test sample taken from the same batch.  
B.3 Determination of the declared values of the radial thermal resistan ce 
All calculations shall be based on an average temperature of 50  °C. 
Any differences between calculated thermal resistance of a pipe assembly based on declared thermal 
resistance values of the pipe components and the measured test results according to An nex A are to be 
expressed by a corrective factor fcor: 
fcor = 
Iλ
2334
c 42
s
ln
2π1.ln
2π1.ln
2π1
dddd
ddR
    … (B1) 
where  
R is the value of the radial thermal resistance determined according to Annex A; in m K/W; 
λ
I is the thermal conductivity of the insulation material acc ording to US 482 -1 in W/(mK); 
λ
S is the thermal conductivity of the service pipe in W/(m K); 
λ
c is the thermal conductivity o f the casing pipe; in W/(m K); 
dx is the diameter according to Figure A.1 or Figure A.2 in m etres.  
For nominal dimensions, for which no radial thermal resistance has been determined, the respective 
corrective factor , fcor shall be interpolated or extrapola ted from corrective factors determined using equation 
B.1. 
The declared value of the radial thermal resistance Rdecl at average temperature 
λ av = 50 °C for each  nominal 
dimension shall be calculated with equation  FDUS  945-1: 201 2 
© UNBS 201 2 – All rights reserved  17 
 
av decl, R = 
34
c 23
Icor
12
s.ln1.ln
λ.ln12π
dd
λ dd f
dd
λ   in mK/W ... (B.2)  
and the declared value of the thermal conductivity with  
 
av decl,λ
 = 
2πdd.ln1.ln .ln1
34
c 23
Icor
12
Sλ dd
λf
dd
λ   in W/(mK)  …(B.3)  
 
In case no values for the radial thermal conductivities are given by the manufacturer, the following values shall 
be taken:  
 mild steel (C -steel ):   50 W/(mK) 
 stainless steel (CrNi steel ):  15 W/(mK) 
 copper :      384 W/(m K) 
 polyethylene (PE, PE -X):  0.4 W/(mK) FDUS 945 -1: 201 2 
18 © UNBS 201 2 – All rights reserved  
 Annex C  
(normative)  
 
Determination of design values for the longitudinal thermal resistance  
The design val ue for the longitudinal thermal resistance R should be calculated in accordance with US 482 -1 
taking into account the conditions relevant to the expected lifetime.  
Rdesign  = 
34
s 23
designcor
12
s.ln1.ln .ln12π
dd
λ dd
λf
dd
λ 
  in (m.K)/W  … C1 
with 
designλ
am decl.ffλ
 in W(m.K)  … C2 
where 
λ
design  is the calculated value of the thermal conductivity of the insulation material in W/(m K); 
fcor   is the correction factor for existing open splits, thermal bridges or change of the factor for shape  
caused by influence of laying in the ground and the relevant factors set up by ISO 21003 -1; 
fm  for the influence of moisture;  
fa  for the infl uence of ageing.  
NOTE  In case fm or fa are not known , the following values should be taken:  
fm  = 1 for metal service pipe;  
 = 1.1 for plastic service pipes if no other information is available and if not laid in ground water and the 
 operating  temperatur e is not higher than 80 °C up to 85  °C; 
fa  = 1 for insulation material with air as cell gas only ; 
fa  = 1 for diffusion tight encapsulation of the insulation ; 
fa  = 1.25 for insulation materials with other cell gases unless other values are supported by t est results.   FDUS  945-1: 201 2 
© UNBS 201 2 – All rights reserved  19 
 Annex D  
(normative)  
 
Calculation of the heat flow from the medium to the ambient (heat loss)  
D.1 General  
This annex provides methods and recommended bench marks for the calculation of the heat flow of the heat  
medium for single pipe systems i n the earth without a heat influence between the flow and return pipes and for  
a twin pipe system.  
D.2 Calculations  
D.2.1 Single pipe system (SPS)  
The longitudinal heat flow density for a buried single pipe system to the ambient condition is given by the 
following equations:  
Flow pipe:  
amb ff f(Uq  in W/m  …(D.1) 
where 
U is the coefficient of heat loss,  
f
 and 
amb  are the flow and ambient temperatures.  
 
  qf =

f samb f
R R  in  W/m   …(D.2) 
where  
Rs is the longitudinal thermal resistance of the soil.  
Return pipe:  
qr  = 
amb rr U  in W/m   …(D.3) 
qf = 

r sambr
R R  in  W/m   …(D.4)  
The longitudinal heat flow density for buried flow and return single pipe systems to the ambient condit ion 
without a heat interaction between flow and return pipes is given as follows:  
r f rfqq q
 in  W/m   …(D.5)  
When the flow and return pipes are laid near together the longitudinal density of heat loss of the flow or return 
pipe can influence th e longitudinal density of heat loss of the return and flow pipe, so that the total longitudinal 
density of heat loss of a pair of pipes can be reduced (see  ISO 21003 -1). 
D.2.2 Twin pipe system (TPS)  
The longitudinal heat flow density for twin pipe systems shall be calculated with the equations D.6 and D.7:  FDUS 945 -1: 201 2 
20 © UNBS 201 2 – All rights reserved  
 qTPS = 

sr f
2  in W/m   …(D.6)  
qTPS = 





TPS ssr f
2
RR  in W/m   …(D.7)  
D.2.3 Longitudinal thermal resistance of the surrounding soil  
Rs = 
4c
s4.ln
2π1
dZ
λ  in (m.K)/W   …(D.8)  
where  
Zc  is a corrected value for the soil coverage  in metres.  
Zc = 
so.λRZ   …(D.9)  
Z is the soil coverage above the center line of the pipe  in metres . 
Z = 
Hd
24   …(D.10)  
λs is the thermal conductivity of the soil in W/(m K); 
R0 is the thermal transmittance factor of earth surface to ambient air in (m2K)/W ; 
H is the soil covering in m etres . 
D.3 Declared values of the longitudinal thermal resistance of buried pipe systems  
If the manufacturer declares general values for the longitudinal thermal resistance (or conductivity) of buried  
pipes, the respective calculation shall be based on:  

s = 1.0  W/(mK) 
R0 = 0.0685 m2K/W 
H = 0.8 m (other values may be give n additionally)  
 FDUS  945-1: 201 2 
© UNBS 201 2 – All rights reserved  21 
 Annex E  
(informative)  
 
Symbols, definitions and dimensions  
Table A.1  
Symbol  Description  Unit 
A projected area of the service pipe  m2 
d1 inner diameter of the service pipe  m 
d1,c inner diameter of the service pipe at the crest of a corru gation  m 
d1,t inner diameter of the service pipe at the trough of a corrugation  m 
d2 outer diameter of the service pipe  m 
d2,c outer diameter of the service pipe at the crest of a corrugation  m 
d2,t outer diameter of the service pipe at the trough of a  corrugation  m 
d3 inner diameter of the casing  m 
d3,c inner diameter of the casing at the crest of a corrugation  m 
d3,t inner diameter of the casing at the trough of a corrugation  m 
d4 outer diameter of the casing  m 
d4,c outer diameter of the casing a t the crest of a corrugation  m 
d4,t outer diameter of the casing at the trough of a corrugation  m 
F force  N 
fa ageing factor  / 
fcor corrective factor for differences between calculated and measured thermal  
conductivities  / 
Fexp force resulting from he at expansion  N 
fm moisture factor  / 
Fweight  weight force  N 
g acceleration due to gravity  m/s2 
H earth covering  m 
L length of the test  m 
M mass of the pipe inclusively the water inside  Kg 
Pexp area related load on the insulation resulting from heat e xpansion of the service pipe  Pa 
Ptest test load  Pa 
Pweight  area related load on the cross section of the test specimen of the insulation material  Pa 
q Heat flow rate  W 
qf radial heat flow rate for buried single pipe system in the flow pipe  W 
qf+r radial heat flow rate for buried single pipe system in the flow and return pipe  W 
qr radial heat flow rate for buried single pipe system in the return pipe  W 
qTPS radial heat flow rate for buried twin pipe system  W 
r bending radius in the axis of the pipe  m 
R radial thermal resistance  mK/W  
R,av radial thermal resistance of a twin pipe system at any average temperature  mK/W  
R0 thermal transmittance factor from earth surface to ambient air  m2K/W FDUS 945 -1: 201 2 
22 © UNBS 201 2 – All rights reserved  
 Table 1 (cont’d)  
Symbol  Description  Unit 
Rdecl declared value of radial thermal resistance  mK/W  
Rdecl,av declared value of thermal resistance at average temperature  mK/W  
Rdesign  design value for the radial resistance  mK/W  
Rf radial thermal resistance of the flow pipe  mK/W  
Rr radial thermal resistance of the return pipe  mK/W  
Rs radial thermal re sistance of the soil  mK/W  
RTPS radial thermal resistance of a twin pipe system  mK/W  
RTPS,av radial thermal resistance of a twin pipe system at any average temperature  mK/W  
s thickness  mm 
SDR  ratio of nominal outer diameter and nominal wall thickness  / 
smin minimum wall thickness  mm 
sSTB thickness of test piece after load testing and temperature testing  mm 
ax shear stress  N/m 2 
U coefficient of heat loss  W/(mK)  
Uf coefficient of heat loss for buried single pipe system  W/(mK)  
Ur coefficient of heat  loss for buried single pipe system in the return pipe  W/(mK)  
UTPS coefficient of heat loss in a twin pipe system  W/(mK)  
Z depth of laying distance from the center line of the pipe to the surface  m 
Zcor corrected minimum value for thermal transmittance on the surface of the earth  m 
av thermal conductivity of a pipe system at any average temperature  W/(mK)  
λC thermal conductivity of the casing  W/(mK)  
λdecl declared thermal conductivity of a pipe system  W/(mK)  
decl,av declared value of thermal cond uctivity at average temperature  W/(mK)  
λdesign  calculation value of the thermal conductivity of the insulation material  W/(mK)  
λI thermal conductivity of the insulation  W/(mK)  
λs thermal conductivity of the soil  W/(mK)  
λS thermal conductivity of the se rvice pipe  W/(mK)  
TPS,av thermal conductivity of a twin pipe system at any average temperature  W/(mK)  
1 temperature at the inner diameter of the service pipe  K 
1,f temperature at the inner diameter of the service flow pipe  K 
1,r temperature at the  inner diameter of the service return pipe  K 
2 temperature at the outer diameter of the service pipe  K 
4 temperature at the outer diameter of the casing  K 
amb ambient temperature  K 
av average temperature  K 
f flow temperature  K 
r return temperat ure K 
s temperature of the soil  K 
Σ compression  mm 
Table 1 (completed)  FDUS  945-1: 201 2 
© UNBS 201 2 – All rights reserved  23 
 Table A.2 – Indices  
Symbol  Definition  
0 thermal transmittance (from earth surface to ambient air)  
1 position at the inner diameter of the service pipe  
2 position at the outer dia meter of the service pipe  
3 position at the inner diameter of the casing  
4 position at the outer diameter of the casing  
a ageing  
amb ambient  
av average  
ax axial 
c crest of a corrugation  
C casing bzw. casing pipe  
cor corrective  
decl declared  
design design  
exp expansion  
f flow 
I Insulation  
m moisture  
min minimal  
r return  
s soil 
S service pipe  
STB stability  
t trough of a corrugation  
test test 
TPS twin Pipe System  
weight  weight  
x placeholder for 1,2,3 or 4  
av average temperature  
 
Table A.3 — Abbreviations  
Abbreviation  Name  
PB polybutylene  
PE-HD high density polyethylene  
PE-LD low density polyethylene  
PE-X cross linked polyethylene  
PE-Xb silane cross linked polyethylene  FDUS 945 -1: 201 2 
24 © UNBS 201 2 – All rights reserved  
 Bibliography  
 EN 1295 -1, Struct ural design of buried pipelines under various conditions of loading — Part 1: General  
requirements  
 
 
 
 
 
 FDUS 945 -1: 201 2 
© UNBS 201 2 – All rights reserved  25 
 Certification marking  
Products that conform to Uganda standards may be marked with Uganda National Bureau of Standards 
(UNBS) Certification Mark shown  in the figure below.  
The use of the UNBS Certification Mark is governed by the Standards Act, and the Regulations made 
thereunder. This mark can be used only by those licensed under the certification mark scheme operated by 
the Uganda National Bureau of Standards and in conjunction with the relevant Uganda Standard. The 
presence of this mark on a product or in relation to a product is an assurance that the goods comply with the 
requirements of that standard under a system of supervision, control and testi ng in accordance with the 
certification mark scheme of the Uganda National Bureau of Standards. UNBS marked products are 
continually checked by UNBS for conformity to that standard.  
Further particulars of the terms and conditions of licensing may be obtai ned from the Director, Uganda 
National Bureau of Standards.  
 
 FDUS 945 -1: 20 12   
 
ICS 23 .040.20  
Price based on nn pages  
© UNBS 201 2 – All rights reserved