NBSIR 74-629

Thermal Properties of Selected Plastic

Piping Used in Housing

Max Tryon

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D. C. 20234

April 1975

Report for Period

June 1973 through June 1974

Prepared for Office of Policy Development and Research

Department of Housing and Urban Development

Washington, D. C. 20410

NBSIR 74-629

THERMAL PROPERTIES OF SELECTED PLASTIC

PIPING USED IN HOUSING

Max Tryon

Center for Building Teclinology

Institute for Applied Technology

National Bureau of Standards

Washington. D, C. 20234

April 1975

Report for Period

June 1973 through June 1974

Prepared for Office of Policy Development and Research

Department of Housing and Urban Development

Washington, D. C. 20410

U.S. DEPARTMENT OF COMMERCE, Rogers C.B. Morton, Secretary

James A. Baker, III, Under Secretary

Dr. Betsy Ancker-Johnson, Assistant Secretary for Science arid Technology

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Acting Director

TABLE OF CONTENTS

Page

I. INTRODUCTION 1

A. Properties of Thermoplastic Materials 1

B. Properties Selected for Study 1

II. MATERIALS USED 2

III. RESULTS OF STUDIES 2

A. Thermomechanical Analysis (TMA) 2 6. Hardness 3 C. Oven Test 3

IV. DISCUSSION 3

A. TMA Results 3 B. Hardness Test Results 4

C. Oven Test Results 4

V. RECOMMENDATIONS FOR MATERIAL CRITERIA 5

VI. FUTURE NEEDS 5

VII. TABLES AND FIGURES 6

Table I - TMA Results 7 Table II - Hardness vs. Temperature and Time, Summary of Data 8

Table III - Impact Resistance Compared to Hardness 9 Table IV - Oven Heating of Plastic Pipe at 77 °C 10

Figure 1 - TMA Curves, 4" PVC-DWV Piping 11

Figure 2 - TMA Curves, 1/2" CPVC-DWV Piping 12

Figure 3 - TMA Curves, 4" ABS-DWV Piping 13

Figure 4 - TMA Curve, 3/4" PB-Pressure Tubing 14

VIII. REFERENCES 15

IX. APPENDIX 16

A. Test Methods for Plastic Pipe Materials 17

1. TMA Test Method 17 Figure Al TMA Curve for Tg Measurement 18

Figure A2 TMA Curve for Measurement of Coefficient of

Expansion (20-100°C) and for the Measurement of Percent

Residual Stress, RS (100-200°C) 18

2. Oven Test Method 19

3. Hardness Test Method 20

' Figure A3 Modified Hardness Apparatus 21

B. Suggested Criteria for Plastic Pipe 23

1. A. 1.2 Leak Resistance - Impact Loads 23

2. C.1.4 Criterion: Dimensional Stability - Glass Transition

Phenomenon 24

3. C.1.5 Criterion: Dimensional Stability—Creep/Permanent Set. 25

ill

Thermal Properties of Selected Plastic Piping

Used in Housing

Max Tryon

In a study of four thermoplastic piping materials, the following performancerelated properties were measured: coefficient of thermal expansion, glass

transition temperature, residual stress indicator, hardness, and hardnesstemperature coefficient. The purpose of the study was to determine typical

values of these properties for each of the piping materials. Results are given

with recommendations on the utilization of the test procedures as essential

elements in performance evaluation for thermoplastic piping materials.

Kejwords: Acrylonitrile-butadiene-styrene terpolymer (ABS) ; coefficient of

expansion; chlorinated polyvinyl chloride (CPVC) ; glass transition temperature;

hardness; polybutene (PB) ; polyvinyl chloride (PVC) ; residual stress; thermoplastic piping.

I. INTRODUCTION

The work described in this report is an extension of that described in the report

"Investigation of Procedures for Determination of Thermal Performance Characteristics of

Plastic Piping Used in Housing" (reference [1]). This earlier report dealt with the

problems associated with establishing the important materials performance characteristics

for the functional plumbing system. The state-of-the-art report [2] and the interim

report on performance criteria [3] revealed that certain important areas of performance

have not been considered in the usual approach to specifications and codes for plastic

plumbing piping materials. The results reported herein and in reference [1] are part of

the work undertaken to fill the gaps found in the state-of-the-art survey and in the

initial effort to develop performance criteria and test procedures.

A. Properties of Thermoplastic Materials

The basic properties of thermoplastic materials may be divided into two categories,

the physical properties and the chemical properties. Since less is known about the physical

properties required in building use, emphasis in this work is placed on the measurement of

selected physical properties of production samples of common plastic pipe materials.

B, Properties Selected for Study

The properties chosen for this study were selected as a result of the survey reported

in reference [1]. These properties include: the coefficient of thermal expansion, a ; the

glass transition temperature, Tg; residual stress indicator, RSI; hardness, H; and the

hardness-temperature coefficient, AH/AT. The residual stress indicator (RSI) and the

hardness-temperature coefficient (AH/AT) are not standard terms or measurements but resulted

from the analysis of the data collected in this study and are described herein. Of these

properties, the glass transition temperature, the coefficient of thermal expansion, and

hardness are materials properties, while the others are affected by the manufacturing process.

These properties are discussed in more detail in reference [1].

Factors not included in this study, but important for future consideration, are the

influence of common chemicals on the properties discussed here and the effect of long-term

aging on the system as a whole. Also, no studies of the joints between the fitting, the

piping, and the adhesive have been included in this work.

1
II. MATERIALS USED

At the present time, four types of thermoplastic materials are used in the U.S. for

plumbing piping in housing. The most widely used materials for drain, waste, and vent

(DWV) piping are ABS (acrylonitrile-butadiene-styrene terpolymer) and PVC (polyvinyl v chloride) . Pressure piping for potable water distribution is primarily CPVC (chlorinated

polyvinyl chloride) with limited use of PVC (cold water only) and a newcomer in the field,

PB (polybutene) , for both hot and cold water.

These thermoplastic materials can be formed with standard extrusion and injection

molding equipment. However, they differ from one another in many ways, both chemically

and physically. Chemically, polybutene (PB) is a hydrocarbon, composed of carbon and

hydrogen only; ABS is a more complex compound made from two hydrocarbons, butadiene and

styrene, and a compound containing nitrogen (acrylonitrile) . The other two materials are related to one another in that CPVC is made from PVC. Polyvinyl chloride (PVC), which is

made from vinyl chloride,' contains a large amount of chlorine (over 50% by weight)

•

Chlorinated polyvinyl chloride (CPVC) has additional chlorine added and may contain as much as 75% by weight total chlorine.

Competition between these materials for the piping market has been primarily based on initial cost, with little consideration being given to the effects on performance of their

widely differing chemical and physical properties. The different chemical properties make

some of these materials incompatible with one another, so care must be exercised in their

use. Unfortunately, the building industry is not fully aware of these differences and

tends to classify all "plastic pipe" as the same.

This study included samples of each of the four types of manufactured piping.

Following discussions with representatives of the Plastic Pipe Institute, piping manufacturers, and a plastics consultant, ABS and PVC-DWV in 4" and 1-1/2" sizes* from five

manufacturers, and CPVC tubing in 1/2" size from three manufacturers, were selected. PVC

and PB pressure pipe or tubing was not available from as many sources so only one sample

of PVC in 1/2" size and two samples of PB in 3/4" size were obtained for testing.

III. RESULTS OF STUDIES

A. Thermomechanical Analysis (TMA)

The apparatus us@d is described In ref@renc@ [1] and the test procedures are described

in appendix A of this report.

Typical TMA curves obtained on each of the materials are shown in figures 1 through 4. The curves in each figure were for specimens cut from the same sample of pipe. The

orientations of the specimens are designated as longitudinal, circumferential, and transverse.

Longitudinal is along the length of the pipe, circumferential is around the circumference

of the pipe, and transverse is through the wall of the pipe. As the figures show, there

are distinct differences in the behavior of the materials in the three directions. The

important features of these figures are the slopes of the linear portions of the curves from room temperature to the first bend, the temperatures at which the first bend occurs,

and the relative heights of the peak. The initial slope allows the calculation of the

coefficient of linear expansion (^) for the material as given in table I. The temperature

for the first bend in the curve is due to the glass transition of the material, and indicates

the maximum temperature, Tg, to which the material may be heated before irreversible

dimensional changes occur. The height of the curve, as shown in figure A2 in the appendix.

Section 1, is a measure of the amount of residual stress remaining in the pipe as a result of the manufacturing process. The higher this peak, the larger the permanent

deformation which will occur upon heating the sample above Tg. This deformation due to residual stress will be important if the temperature Tg is low enough to be in the range

of operating temperatures for the pipe. If Tg is well above the maximum operating temperature

of the system, or if the residual stress is very small, less importance need be attached

* These are the nominal sizes by which the plumbing industry designates the piping.

2
However, any factor which lowers Tg into the range of operating temperatures (e.g. certain

solvents or chemical compounds) may make this stress a critical factor in pipe performance.

An indicator of the relative importance of the combination of Tg and residual stress

for a particular sample may be labeled a Residual Stress Indicator (RSI) . This new concept

is proposed as a practical measure of the ability of a pipe material to function satisfactorily in the possible range of operating temperatures. These temperatures are considered

to be up to 100°C (212°F) , the boiling point of water. While this temperature is higher

than the usual operating temperature, such a temperature could be reached in the event of

failure of the water heater safety devices and may be considered a "worst case". The RSI

is defined as the ratio of the difference between the glass transition temperature and the

reference temperature, 100°C (212°F), to the residual stress calculated using the equation

given in the appendix. The RSI has the units of °F and is expressed mathematically as follows

:

.SI .

where: Tg is the glass transition of the material in 'F, and RS is the maximum change in

thickness of sample, %, in the temperature range from 25''C - 200*'C (ambient - 400°F) under

zero load in the TMA apparatus at 10°C per min. heating rate (see Appendix, Section Al)

.

In general, the larger the RSI value, the better the performance of the material is likely

to be from the point of view of freedom from thermal stress relief with time. A material

with a glass transition temperature of 100°C (212°F) will have a zero residual stress

indicator meaning that it is just acceptable. Experimental results and derived RSI values

are given in table I.

B. Hardness

The hardness test was conducted using the apparatus described in the earlier report

[1] and shown in the photograph in Section 3 of appendix A. While there is no direct

relationship between hardness and strength factors (such as burst strength for pipe), it

is believed there may be a relationship between the temperature coefficient of hardness

and the effect of temperature on the resistance of the material to failure under impact.

Generally, the softer the material, the more resistant it is to impact fracture [4].

Also, the smaller the change in hardness with temperature, the smaller the effect of

temperature on the impact resistance is likely to be. Hence, the magnitude of hardness

and its temperature coefficient may predict the relative resistance of materials to impact

fracture under different temperature conditions.

Data obtained on the materials investigated in this study are given in table II.

The rate of change of hardness with time of measurement is an indication of the flow

of the material under load and is related to its molecular weight. The lower the average

molecular weight of the plastic, the greater the change in hardness reading over the time

interval used.

C. Oven Test

Evidence from the TMA studies that some of the piping samples exhibited permanent

length changes on heating led to the development of a sample oven test on 3 ft long specimens

for determination of the predicted permanent shortening. The test is described in Appendix

A. Only specimens of DWV pipe were tested this way. Previous work with CFVC described in

reference [1] indicated that no measurable change occurred with this material under the

conditions of this test. The PB samples were not tested because they were coiled samples

and length measurements of the required precision were not possible under these conditions.

The results are given in table IV.

IV. DISCUSSION

A. TMA Results

Table I shows that, of the four materials studied, only PVC shows a glass transition

below the boiling point of water. Hence, the residual stress Indicator for this material

3
la negative and PVC Is considered unsuitable for long-term use in eomplete DWV systems

where very hot water or other hot liquids may be discharged. Design details incorporated

into the plumbing system, such as metal pipe sections at the immediate drain point to allow precooling of waste, could resolve part or all of this potential problem. However,

these considerations are beyond the scope of this report. The other materials all appear

satisfactory and similar to one another in this regard.

Both ABS and PB have higher coefficients of linear expansion than either CPVC or PVC,

with the PB coefficient being at least twice as great as that for PVC. However, PB is

amuch softer, more pliable material and its large expansion coefficient could be compensated

for by attention to installation procedures, while the more rigid ABS requires stricter

design and installation techniques.

The results indicate that potential problems may be anticipated with PVC in the DWV

system where waste water temperatures approaching the boiling point are anticipated for

significant periods of time. For the same reason, if it is used in the water service or distribution system, it should be limited to the conveyance of cold water only.

Because of its higher glass transition temperature, it may be anticipated that ABS

would be less subject to permanent dimensional change than PVC when used for the drainage

of water at elevated temperatures. However, caution should be exercised where solvents

(e.g. paint solvents and similar substances) may be discharged into the drainage system,

as these materials can lower the Tg value of the ABS.

The results obtained indicate satisfactory long-term dimensional stability of both

CPVC and PB when used in hot or cold water supply systems. But because of their relatively

high coefficients of thermal expansion (particularly in the case of PB) , care must be

exercised in design and installation to provide for compatible methods for attaching and

supporting the piping, and for connecting it to fixtures, appliances, and other piping

materials.

B. Hardness Test Results

Table II shows the results of the hardness measurements and gives three basic kinds

of information, First, the hardness itself; seco-nd, hardness change as a function of

temperature; and, third, hardness change with time of measurement. The three factors are interrelated and important in evaluating the material. The harder the material, the less

its impact resistance; the smaller the change in hardness with time of measurement, the more resistant is the material to flow or creep; the smaller the change in hardness with

temperature, the less the change in impact or flow properties with temperature.

One way of interrelating two of these parameters of hardness (type D hardness and

change in hardness with temperature) for the various m.aterials is shown in table III. This table shows the temperature at which each material would have a hardness of 100 on

the Durometer D scale as calculated from the equations given for each material in Section

3 of the Appendix. The values are extrapolations and should only be considered meaningful

in the order they rank the materials rather than as quantitative measures. The good

correlation between the Izod impact resistance [5] and the Tj^qq values indicates that a more certain relationship between hardness and impact resistance may be developed with

further work.

PVC and CPVC both show hardness values higher than ABS or PB, with PB the lowest of

all. This data indicates that PVC and CPVC would tend to have lower impact resistance

than either ABS or PB. However, PB has such a high hardness temperature coefficient that

at about 0°C (32''F) it would have the same hardness as PVC at 23°C (73°F) and presumably

similar Impact resistance. Further, PB is more susceptible to flow or creep than the

others as the temperature increases, as indicated by the larger change in hardness with

time of test.

C. Oven Test Results

The data in table IV show a practical measure of the effect of residual stress in a thermoplastic piping material whose glass transition temperature is near the maximum service
water temperature in use. PVC showed a permanent shortening on the order of 17c of its

length after a few hours to a few days at a temperature of approximately 77°C (170°F)

.

Concomitant changes occur in its diameter with a pronounced increase in wall thickness.

Similar changes occur at lower temperatures, but at a slower rate. This property of

thermal distortion due to relaxation of internal stress is not restricted to PVC. All the

thermoplastic materials exhibit a similar behavior to a degree dependent on the method of

processing of the product. However, this behavior is only significant for PVC piping used

for drain or pressure water use because its glass transition temperature is near the

maximum operating temperature of the system. The other materials included in this study

all have glass transition temperatures well above the maximum operating temperature and so are not subject to this type of failure in the same usage.

Changes in the manufacturing process could probably relieve the residual stress and

so reduce the effect shown in this study. Whether such changes are economically practical

is not known.

V. RECOMMENDATIONS FOR MATERIAL CRITERIA

The results of the thermal studies given in this report were used to update three of

the performance criteria initially considered in reference [3]. These updated, presently

suggested versions are given in their entirety in Appendix B along with specific test

procedures developed during the course of this study.

VI. FUTURE NEEDS

Areas of importance in establishing performance criteria and specifications for

thermoplastic piping, which are not covered by this report, include chemical resistance,

weatherability and resistance to aging.

Chemical resistance includes the resistance of the system to slow degradation of

necessary properties and environmental stress cracking, sometimes referred to as "stresscorrosion". The first of these should be investigated in a study of the changes in Tg,

RSI, and dimensions with representative chemical exposures as a function of time. A

second study is needed to establish whether stress cracking is a serious potential problem

and, if so, to relate it to composition and internal structure of the piping material.

Such studies of chemical resistance would aid the development of test procedures needed in

the establishment of acceptance criteria.

Weatherability and resistance to aging studies require the development of appropriate

procedures for the accelerated weathering or aging of cylindrical specimens. Such procedures, combined with the measurement of changes in basic properties (such as reported

here) would contribute significantly to the establishment of adequate criteria for the

resistance of thermoplastic piping to weathering and aging.

Another important broad area of future need is recognized as that of realistic

correlation between test conditions and service conditions, particularly as to temperature,

chemical composition, concentration, and time of exposure. This may require emphasis on

the collection of relevant field data and on needed correlation between tests on specimens

taken from pipe and fittings and tests on assemblies of pipe and fittings subjected to simulated service conditions in the laboratory.

5
VI I. TABLES AND FIGURES

Th© tables and figures discuastd in the text are presented in a group for the convenience

of the reader. Their numbers and titles are as follows:

Table I - TMA Results '

Table II - Hardness vs. Temperature and Time, Summary of Data

Table III - Impact Resistance Compared to Hardness

Table IV - Oven Heating of Plastic Pipe at 77°C

Figure 1 - TMA Curves, 4" PVC-DWV Piping

Figure 2 - TMA Curves, 1/2" CPVC-DWV Piping

Figure 3 - TMA Curves, 4" ABS-DWV Piping

Figure 4 - TMA Curve, 3/4" PB-Pressure Tubing.

6
TABLE I TMA RESULTS

a X 10

MATERIAL* Tg RS R.S.I.

% "F/'/o °C~-^ "f"-*-

CPVC, Press. 122.7 252.8 14.2 +2.8 7.4 4.3

CPVC, Press. 123.0 253.4 22.4 +1.8 9.8 5.4

PVC, Press. 78. 7 173.7 12. 7 -3.0 8.6 4.8

PVC, DWV 85. 7 186.2 26.7 -1.0 7.2 4.0

PVC, DWV 83.3 182.0 22.0 -1.4 6.8 3.8

PVC, DWV 85.3 185.6 26.7 -1.0 6.0 3.3

rVC, UWV 83.3 182.0 37.6 A Q -U . O 0 . o

Q "7

PB, Press. 119.0 246.2 18.7 +1.8 19.2 10.7

r D , rreSS. 111.3 232.4 21.3 0 9 Q.y 10 7

ABS, DWV 108.3 227.0 12.7 +1.2 10.9 6.1

ABS, DWV 105.0 221.0 26.3 +0.3 13.7 7.6

ABS, DWV 109.3 228.8 26.4 +0.6 10.9 6.1

ABS, DWV 109.0 228.2 24.8 +0.7 9.3 5.2

* Each listing in. each plastic represents material supplied by a different

manufacturer

.

** Coefficient of linear expansion over temperature range of 20--60°C (68-140°F),

Tg = glass transition

RS = residual stress

R.S.I. = residual stress indicator

a = coefficient of linear expansion

7
TABLE II HARDNESS VS. TEMPERATURE AND TIME

SUMMARY DATA

Material Time

(mlns)

HARDNESS*

73»F 140 °F

TEMP COEFF (°F"'^)

AHardness/AT

0 1

PVC

(AH/At)**

ABS

(AH/At)

CPVC

(AH/At)

PB

(AH/At)

84.5 81.1

-3.4

78.8 76.1

-2.7

86.9 83.7

-3.2

63.6 59.5

-4.1

79.2

75.6

82.9

52.1

-2.8

-2.2

-3.3

-7.4

76.4

73.4

79.6

44.7

-0.079 -0.070

-0.049 -0.040

-0.060 -0.062

-0.172 -0.220

* Hardness; durometer, type D., average of all data for Indicated material - each sample

measured 10 times.

** Change in durometer reading from t=0 to t=l minute.

8
TABLE III IMPACT RESISTANCE COMPARED TO HARDNESS

Material Izod Impact

ASTM D256

[5] Hardness

,

type D at 73°F (H73)

Hardness/ °F

(AH/AT)

T ^

1 on

PVC 0.3-1.0 84.5 -0.079 -123

PB 0.5-2.0 63.6 -0.172 -139

CPVC 1.0-5.6 86.9 -0.060 -145

AfiS 2.0-4.5^^ 78.8 -0.049 -360

a) T = 100 - H73 + 73

(AH/At)

represents the extrapolated intercept of the hardness temperature relationship for ; hardness value of 100.

b) No data is available for PB but the values given for PP (polypropylene) should be of

the same order since they are paraffinic homologs.

Izod data for all samples measured on 1/2 x 1/2 inch specimens except for ABS where

1/8 X 1/2 inch specimens were used. Hence, these impact values for ABS indicate high

impact resistance.

9
TABLE IV

OVEN HEATING OF PLASTIC PIPE AT

77'C (170. 6°F)

SAMPLE* AVERAGE LENGTH**, inches

t=0 t=lhr. t=2hr. t= 120 hr. % change

in 120 hr.

PVC, 4" 35.94 35.70 35.66 35.65 -0.81

PVC, 4" 35.99 35.75 35.70 35.65 -0.94

PVC, 1-1/2" 35.98 35.63 35.60 35.57 -1.14

PVC, 1-1/2" 35.51 35.51 35.48 35.44 -1.06

ABS, 4" 35.92 35.91 35.91 35.92 0

ABS, 4" 35.91 35.88 35.89 35.83 -0.22

ABS, 1-1/2" 35.90 35.94 , 35.94 35.91 +0.03

ABS, 1-1/2" 35.90 35.88 35.88 35.91 -0.08

Each sample is a single length of pipe.

Average of 4 readings made at different points around the circumference of each sample.

10
LONGITUDINAL

"C 20 40 60 80 100 120 140 160 ISO 200

TElviPERATURE

Figure I - TMA Curves for 4" PVC-DWV Piping. Probe displacemeats from an arbitrary zero are in units of 0.01 inch.

11
TRANSVERSE

TEMPERATURE

Figure 2 - TMA Curves for 1/2" CPVC - Pressure Piping. Probe displacements

from an arbitrary zero are in units of 0.01 inch.

n
LONGITUDINAL

CIRCUMFERENTIAL

TRANSVERSE

68 104 I4C 20 40 60

TEMPERATURE

Figure

fro.

3 - THA Curves for 4" ABS-DWV Piping Prob. an arbitrary zero are in units of 0 Clinch

'^^P'"""'^"^

13
I I I

'

I ' »I

I I L_J I I I I I 1 •F 68 104 140 176 212 248 284 320 356 392

•C 20 40 60 80 100 120 140 160 ISO 200

. TEMPERATURE

Figure 4 - TMA Curve, 3/4" PB - Pressure Tubing. Probe displacements

from an arbitrary zero are in units of 0.01 inch. (Curves

not obtainable on longitudinal and circumferential orientations

due to the low hardness and thin wall of the piping).

14
VIII. REFERENCES

1. Tryon, M. , "Investigation of Procedures for Determination of Thermal Performance

Characteristics of Plastic Piping Used in Housing", NBSIR 74-610, November 1974.

2. Wyly, R.S., Parker, W.J., Rorrer, D.E., Shaver, J.R,, Sherlin, G.S., Tryon, M.

,

"Review of Performance Characteristics, Standards, and Regulatory Restrictions

Relating to the Use of Thermoplastic Piping in Residential Plumbing", NBSIR 74-531,

March, 1975.

3. Wyly, R.S., Beausoliel, R.W. , Parker, W.J., Pierce, E.T., Rorrer, D.E., Shaver, J.R.,

Sherlin, G.C., Tryon, M. , "Interim Report on Criteria for Thermoplastic Piping

Materials for Above-Ground Use in Water Supply and Drainage for Residential Buildings",

NBSIR (in review)

.

4. Doan, G.E. , Principles of Physical Metallurgy, 3rd Edition, McGraw-Hill, Inc.,

New York, N.Y.

5. Modern Plastics Encyclopedia, Vol. 47, No. lOA, October 1970, McGraw-Hill, Inc.,

New York, N.Y.

15
IX. APPENDIX: Test Methods and Suggested Criteria

This Appendix treats the test methods and criteria indicated in the following outline:

A. Test Methods for Plastic Pipe Materials

1. TMA Test Method 3^

2. Oven Test Method * -

3. Hardness Test Method

B, Suggested Criteria for Plastic Pipe . h .

1. A. 1.2 Leak Resistance - Impact Loads

2. C.1.4 Dimensional Stability - Glass Transition Phenomenon

3. C.1.5 Dimensional Stability - Creep/Permanent Set
A. Test Methods for Plastic Pipe Materials

1. TMA Test Method

This method is used to determine the glass transition temperature, Tg, the residual

stress indicator, RSI, and the coefficient of linear expansion, a , for thermoplastic

piping materials.

Apparatus: A Dupont^ TMA apparatus or equivalent with a hemispherical tip probe.

The apparatus must be calibrated so that sample dimensions can be calculated from the

recorder chart.

Sample Preparation: 1/4" square samples are cut from the piping using a method that

does not elevate the temperature of the materials. Slow hand cutting with a sharp hacksaw

or jewelers saw or cleaving with a sharp blade and hammer impact are examples. The samples

should be of a size to readily fit into the apparatus in a stable manner so that the

sample will not tip or slide during the test.

Procedure: The sample thickness is measured to the nearest .0025 mm (0.1 mil) with a micrometer equipped with a spherical anvil to compensate for the curved shape of the pipe.

The sample is placed in the TMA apparatus so that the rounded tip of the probe rests on

inner surface of the piping sample. The instrument conditions for Tg determination

(illustration Al) are preset as follows:

The temperature scale: 0 to 200°C

Probe displacement scale: 5-10 mil/inch chart

Loading on Tray: 10 g

Heating Rate: 10°C/min

The instrument conditions for determining residual stress and the coefficient of

linear expansion (illustration A2) are as follows:

Temperature Scale: 0 to 200''C

Probe displacement scale: 0.1 - 0.2 mil/inch chart for temperature range 20-80°C,

10-20 mil/inch chart for temperature range 8^0-200°C

Load on Tray: 0 g

Heating Rate: lO'C/min

Two separate samples are measured for each determination, one sample under each of

the two conditions. Tg is determined for the first set of conditions by drawing two tangents to the curve as shown in figure Al below and reporting the temperature indicated

by the intersection of these lines.

The coefficient of expansion, a , is calculated from the linear part of the 25-80"'C

portion of the second run (a typical example is attached)

.

The percent residual stress, RS, is calculated from the second part of this same run

as illustrated in figure A2.

Certain commercial instruments are identified in this paper in order to accurately specify

the experimental procedure. In no case does such identification imply recommendation or endorsement by the NBS, nor does it imply that the equipment identified is necessarily the

best available for the purpose.

17
F 68 104 140 176 212 248 ' 284 320 356 3S2

C 20 40 ' 60 80 100 120 140 . 160 180 . 200

TEMPERATURE .

Figure Al - TMA Curve for Tg Measurement. Probe displacements from an arbitrary zero are in units of 0.01 inch.

18
Calculations: Slope = £

T - T

2 1 RS = h X instrument calibration factor x 100

original sample thickness

Coeff . of linear expansion, a = slope x instrument calibration factor

original sample thickness

Residual Stress Indicator, RSI = Tg - 212 , where Tg is in °F RS

2. Oven Test Method

This is a test procedure to determine the permanent deformation, i.e., change in

length, of thermoplastic piping at temperatures in the region of the expected maximum in

normal use.

Apparatus: Constant temperature oven capable of containing piping samples approximately

3 ft. long in a horizontal position and controlling the internal temperature at 77°C ± 0.5°C (171 ± 1°F) for at least 120 hours. Three ft (or 1 meter) rigid rule graduated in

0.01 inch (or 0.1 mm) units.

Sample Preparation: Samples of pipe approximately 3 ft. long are cut and marked

along the length so that repeat measurements of length may be made at the same point on

the sample. These marks should be made at 4 points around the circumference of the samples.

Procedure: The length of each sample is measured to the nearest 0.01 inch or 0.1 mm

at each of the 4 points around its circumference.

The measured samples are then placed in the oven which has been preheated to 11° C.

The measurements are repeated by removing the samples from the oven and allowing them

to cool to the original room temperature and then measuring at all 4 positions. The

samples are then returned to the oven. This procedure is repeated following the time

schedule given below.

t, orig. measurement = L

o

t. 1 hour (oven) measurement = \

t. 2 hour (oven) measurement =

t. 120 hour (oven) measurement = ^120

Calculations

:

The permanent deformation, P.D., is calculated by subtracting the average of the 4 readings at each time interval from the average of the original 4 readings.

% P.D. = o^j^Vj^

L

o where = original length

L = length measured at time, t.

19
3. Hardnggi Test Msthpd

This method Is used to determine the hardness and hardness-temperature eoeffielent for

thermoplastic piping materials.

Apparatus: A modified hardness apparatus is used. Some means for supporting a cylindrical specimen so that the hardness instrument can be properly applied to it must be

provided. One such means is illustrated in the attached photograph.

A constant temperature bath and circulating pump provide heated water at a constant

rate through the specimen.

A contact thermometer, thermistor, or thermocouple, capable of measuring the surface

temperature of this sample to the nearest 0.2°C is used.

Means must be provided for sealing the ends of the sample and provide constant temperature water circulation through sample. The photograph also indicates one means of achieving

this.

Sample Preparation: Samples are cut approximately 1 foot long and the plates are attached and leaks sealed.

Procedure: The sample is placed in the apparatus and water circulated through the

sample at room temperature until temperature equilibrium is reached as determined from the

surface thermometer. Ten hardness measurements are made on different spots on the sample

and the temperature of the bath changed to 71°C (160°F) . After the temperature equilibration

is reached and recorded, 10 more hardness measurements are made. With care, hardness

measurements to within 0.2 units are achieved.

The hardness measurements may be recorded in a table having the following format:

Hardness, Durometer D.

Room Temp (R.T.), °F Elevated Surface Temperature

(E.T.) , °F

'^o ^(1 rain) ^0

1

2 .

'

'

34

5

6

7 V . :

'

8

9

' '

10

Calculations: Averages of each set of 10 values are calculated. The hardness-temperature

coefficient is calculated for t and t,

:

o 1 AH/AT = ^R.T. ~ ^E.T.

T - T R.T. E.T.

*^(1 min)

20
The hardness for exactly 73°F and 140"? is then calculated from the R.T. hardness as follows for t = 0 and t = 1 min.

= (AH/AT) X - 73) + H^^^^

\,0 = ^ ^"r.T. - 1^°) + »R.T.

The change in hardness with time is calculated for each temperature.

AH^= H^^o- H^^l

At

^»140 = "14$°- ^14^1

At

The temperature at which the material reaches a hardness of 100 is calculated.

"lOO = - »73 +

AH/AT

21
Figure A3. Modified Hardness Apparatus

B - circulating, constant temperature bath

C - timer

G - hardness gage

P - scaling plates with tubing connections

S - sample

T - thermocouple

V - support V-block

22
B. Suggested Criteria for Plastic Pipe

1. Attribute: FUNCTIONAL ADEQUACY A. 1.2

A.l Requirement: LEAK/BURST RESISTANCE

A. 1.2 Criterion; Leak Resistance—Impact Loads

Pipe, fittings, and joints shall withstand impact loads over the temperature ranges

encountered in service without rupture or leakage of fluids from the system. The hardness

temperature coefficient shall be -0.8 or less; the hardness at 73°F shall be 75 or more

and the hardness at 140°F shall be 70 or more; the change in hardness with time shall be

-3.5 or less; and the temperature for a hardness of 100 shall be -120''F or lower.

Method of Evaluation for A. 1.2

Review of service history data and test data for functional reliability/suff iciency.

Hardness Test described in appendix A.

Commentary on A. 1.2

Impact Loads are caused internally by water hammer in water supply piping and externally

by blows inflicted in handling, installation, and use. Impact behavior presents a more

intractable situation because it is extremely difficult to express it in any quantitative

terms that have real significance (for plastics) . Experience shows that when plastics

break in service under impact conditions, they invariably do so in a brittle manner; the

strains are small and signs of gross yielding are rare. To give the most satisfactory

performance under impact conditions a material should behave in a tough manner even in the

widest range of conditions. Many factors can affect the behavior of a plastic material

under impact, but the most important in determining any change from a tough tj brittle

behavior are changes in temperature and the presence of stress concentration.

The Hardness Test is not a dynamic test for water hammer loads or impacts but is a newly developed static test that may serve to rate materials until more specific test methods are developed. The values chosen for acceptance were based on limited testing of

typical pipe products but have not been service correlated. The actual values chosen may

be changed as more service data and hardness data are collected and compared.

Paper 2, Thermoplastics as Engineering Materials, by R.D. Bacon, BSc, ARCS, ICI Plastics

Division, Plastics Pipe Symposium (University of Southampton, England, Sept. 14, 15, 16,

1970) . Sponsored by the pipe group of the British Plastics Federation in association with

the University of Southampton.

23
2. Attribute; ADEQUACY FOR DURABILITY /MAINTAINABILITY C.1.4

C.l Requirement: RETENTION OF PROPERTIES FOR ESSENTIAL FUNCTIONAL CAPABILITY

C.1.4 Criterion; Dimensional Stability - Glass Transition Phenomenon

The glass transition temperature of the materials used in the piping shall be above

the maximum expected service temperature. The Residual Stress Indicator value shall be

greater than zero.

Method of Evaluation for C.1.4

The TMA test method is given in appendix A.

Commentary on C.1.4

The glass transition temperature must be above the service temperature in order to prevent possible excessive permanent dimensional change due to relaxation of internal

stress in the piping components produced in the manufacture of pipe and fittings. Service

temperatures of not over 140°F are probably typical in residential plumbing; however,

plumbing appliances may produce greater temperatures under some circumstances, and temperatures

approaching the boiling point for water may occur occasionally for short periods upon

failure of water-heater temperature control devices. Softening point tests are not adequately

precise or accurate as a method of evaluation for this criterion.

This criterion can become Important in connection with long-term use, through the

possible imposition of excessive thermal loads resulting in stress on joints and fittings,

distortion of cross section, excessive lateral deflection, separation of expansion fittings,

etc.

The test method indicated is new and should be considered as tentative.

24
3. Attribute; ADEQUACY FOR DURABILITY /MAINTAINABILITY C.1.5

C.l Requirement; RETENTION OF PROPERTIES FOR ESSENTIAL FUNCTIONAL CAPABILITY

C.1.5 Criterion; Dimensional Stability—Creep/Permanent Set

The piping materials shall maintain dimensional stability over the range of temperatures

and structural loads encountered in the service environment, such that, taken together

with fixings/supports the essential functional performance of the system is maintained.

Permanent changes in length after exposure of piping to the maximum expected service

temperature shall not exceed 1/4%.

Method of Evaluation for C.1.5

The BRAB test S-3 Concentrated Load Test [1]. Oven Test as described In appendix A.

Commentary on C.1.5

Further study for an applicable test is needed. The oven test Is a newly developed

test and is considered tentative. The BRAB test is also not a standard test.

A limited amount of dimensional change in a piping material can be accommodated by

design and installation, but excessive changes and permanent differential changes can lead

to the development of rupture, leaking, acoustical problems, etc. Dimensional changes may

occur from long-term effects of the thermal environment in combination with the structural

loads induced by thermal, hydraulic, and installation parameters. "Creep data for plastic

piping now being obtained is based almost entirely on measurements of uniaxial creep in

tension. At the present time, no theory exists for predicting longterm deformation

arising from complicated stress patterns."

Building Research Advisory Board, Federal Construction Council, Technical Report No. 61,

Thermoplastic Piping for Potable Water Distribution Systems, 1971.

2Paper 2, Thermoplastics as Engineering Materials , by R.D. Bacon, BSc, ARCS, ICI Plastics

Division, Plastics Pipes Symposium (University of Southampton, England, Sept. 14, 15, 16,

1970) . Sponsored by the pipe group of the British Plastics Federation in association with

the University of Southampton.

USCOMM-NBS-DC 25
NBS.114A (Hsv. 7.73)

U.S. BiPT. OP eOMM.

BliUIOGRAPHIC DATA

SHEET

1. PUHLIC.ATION OR RKPORT NO.

NBSIR 74-629

2. Gev'f Aeeessien

No.

3. Recipient's Acct'Hsien Ne.

4. TITLE AND SUBTITLlv

Thermal Properties of Selected Plastic Piping Used In Housing

5. Publication Date

6. Performing Organization Code

7. AUTHOR(S)

Max Tryon

8. Performine Orean. Report No. NBSIR 74-629

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No.

11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

Office of Policy Development and Research

Department of Housing and Urban Development

Washington, D.C. 20410

13. Type of Report & Period

Covered

7/73 through 6/74

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less factual summary of most si^ificant information. If document includes a significant

bibliography or literature survey, mention it here.)

In a study of four thermoplastic piping materials, the following performance-related

properties were measured: coefficient of thermal expansion, glass transition

temperature, residual stress, hardness, and hardness^temperature coefficient. The

purpose of the study was to determine typical values of these properties for each

of the piping materials. Results are given with recommendations for performance

tests and changes in previously-proposed interim performance criteria.

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)

ABS; coefficient of expansion; CPVC; glass transition temperature; hardness;

polybutene; PB; polyvinyl chloride; PVC; residual stress; thermoplastic piping.

18. AVAILABILITY

^

Unlimited

1

' For Official Distribution. Do Not Release to NTIS

Q"! Order From Sup. of Doc, U.S. Government Printing Office WashinEton. D.C. 20402. SD Cat. No. C13

pC] Order From National Technical Information Service (NTIS)

Springfield, Virginia 22151

19. SECURITY CLASS

(THIS REPORT)

UNCL ASSIFIED

21. NO. OF PAGES

28

20. SECURITY CLASS

(THIS PAGE)

UNCLASSIFIED

22. Price

* 3.75

USCOMM-DC 29042-P74