llillllllllillllilll REFERENCE

NBSIR 77-1261

Laboratory Tests of

Thermoplastic Piping

Assemblies Subjected to Water

Hammer and Intermittent Hot

Water Flow

Daniel E. Rorrer James R. Shaver

Robert S. Wyly

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D.C. 20234

August 1977

Final Report

Prepared for Division of Energy, Building Technology and Standards

Office of Policy Development and Research

Department of Housing and Urban Development

Washington, D.C. 20410

NBSIR 77-1261

LABORATORY TESTS OF

THERMOPLASTIC PIPING

ASSEMBLIES SUBJECTED TO WATER

HAMMER AND INTERMITTENT HOT

WATER FLOW

Daniel E. Rorrer

James R. Shaver

Robert S. Wyly

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

Washington, O.C. 20234

August 1977

Final Report

Prepared for Division of Energy, Building Technology and Standards

Office of Policy Development and Research

Department of Housing and Urban Development

Washington, D.C. 20410

U.S. DEPARTMENT OF COMMERCE, Juanita M. Kreps, Secretary

Dr. Sidney Harman. Under Secretary

Jordan J. Baruch. Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Acting Director

FOREWORD

This report describes the test methods used and the results of

testing chlorinated polyvinyl chloride (CPVC) thermoplastic pressure

piping assemblies for their resistance to water hammer (shock pressure)

and intermittent hot water flow (thermal cycling). Additionally, the

results of thermal cycling of two polyvinyl chloride (PVC) thermoplastic

drainage stack assemblies are reported.

The work described in this report was sponsored by the Department

of Housing and Urban Development and was conducted by the Center for

Building Technology, National Bureau of Standards, as part of a longrange research program with the goal of improving building standards.

This report, emphasizing thermoplastics, is one of several resulting

from this program concerning performance characteristics and criteria

for piping materials used in residential plumbing systems.

i
LABORATORY TESTS OF THERMOPLASTIC PIPING ASSEMBLIES SUBJECTED

TO WATER HAMMER AND INTERMITTENT HOT WATER FLOW

By

;, Daniel E. Rorrer

James R. Shaver

Robert S. Wyly

ABSTRACT

Evaluation procedures are described that were used at the National

Bureau of Standards (NBS) for simulating the long-term effects of water

hammer (shock pressure) and cyclic hot water flow (thermal cycling) on chlorinated polyvinyl chloride (CPVC) thermoplastic pressure piping

assemblies. Also included are the procedures used to study the effects

of thermal cycling of two (2) polyvinyl chloride (PVC) thermoplastic

drainage stack assemblies. The results obtained using these test

procedures are presented and, in addition, related work of other

investigators is briefly reviewed.

The shock pressure results show that a fatigue life curve can be

established for CPVC as a function of temperature and pressure. As the

temperature is decreased, the number of shock pressure applications

necessary to produce failure increases. An estimated use life of at

least 50 years was indicated at the maximum test temperature of 180° F

(82° C) with pressures of 150 psi (1034 kPa)

With intermittent hot water flow all test assemblies were performing

satisfactorily when the test was terminated after more than 1500 cycles

had been completed.

Key words: Intermittent hot water exposure tests of thermoplastic pipe;

pressure shock in thermoplastic pipe; water hammer in thermoplastic pipe.

ii
TABLE OF CONTENTS

Page

Foreword i

Abstract 11

List of Figures and Tables Iv

1. Introduction 1

1.1 Background 1

1.2 Objective 2 1.3 Scope and Approach 2

2. Shock Pressure Tests

2.1 Summary of Work by Other Investigators A 2.2 Apparatus and Procedure - NBS Test 8

2.3 Results and Discussion 13

3. Intermittent Hot Water Exposure Tests 19

3.1 Summary of Work by Other Investigators 19

3.2 Apparatus, Measurements and Procedure - NBS Test 21

3.3 Results and Discussion 27

4. Conclusions 35

A.l Intermittent Exposure to Hot Water 35

4.2 Internal Shock Pressure 36

4.3 Future Evaluation needs 36

5. References 38

6. Appendix 39

6.1 Definitions and Nomenclature 39

6.2 Units of Measure and S.I. Conversion Factors 42

6.3 Acknowledgements 43

iii
LIST OF FIGURES

Page

Figure 1 Schematic of Test Setup for Water Hammer 11

Figure 2 Photograph of Water Hammer Test Setup 12

Figure 3 Peak Pressure vs. Number of Cycles to

Failure at 75° F (2A° C) lA

Figure 4 Peak Pressure vs. Number of Cycles to

Failure at 120° F (49° C) 15

Figure 5 Peak Pressure vs. Number of Cycles to

Failure at 140° F (60° C) 16

Figure 6 Peak Pressure vs. Number of Cycles to

Failure at 180° F (82° C) 17

Figure 7 Photograph of Pin-Hole Leak in CPVC Elbow 18

Figure 8 Intermittent Hot Water Exposure Test 23

Schematic

Figure 9 CPVC Thermoplastic Test Loop 24

Figure 10 CPVC Thermoplastic Test Configurations 25

Figure 11 Hot Water Flow Stress Characteristics for

Different Mounting Configurations 30

Figure 12 ^ Hot Water Flow Stress Characteristics of

4-inch PVC (Thin-Wall) Drainage Pipe Fixed

at Both Ends 3^

LIST OF TABLES

Table 1 Typical 1/2-inch CPVC Water Pipe Test Data

for 5-Minute Flow of Hot Water 29

Table 2 Hot Water Flow Maximum Stress Characteristics

Summary for 1/2-inch CPVC Assemblies 31

Table 3 Typical 4-inch PVC DWV Water Pipe Test Data

For 5-Minute Flow of Hot Water 32

iv
1. INTRODUCTION

1.1 Background

The majority of the present standards for thermoplastic piping

materials (as well as for other piping materials) describe the physical

properties which are generally utilized for quality control purposes in

the manufacture of the materials. In general, these product-oriented

piping standards do not describe, under conditions of use, the functional

and durability performance requirements for assemblies of pipes and

fittings. It is generally understood that the product specification

approach has served its purpose when ample time has been available for

the accumulation of a sufficient body of satisfactory service history

for feedback purposes and proof of adequacy. As indicated in Section

1.2, the study described herein involved an effort to apply the performance approach, which places an emphasis on qualitative user needs under

service conditions, and on criteria and evaluation methodology for

measuring the probable adequacy of systems and components by calculation or by tests simulating end-use service conditions.

Two conditions of the end-use environment which are considered

to be of primary importance with respect to long-term durability of

thermoplastic piping assemblies are (1) shock pressure and (2) hot-water

cycling.

Shock pressure (water hammer) occurs whenever a pipin,g system is

subjected to a sudden change in flow rate and is most severe when flow

is quickly terminated by a fast-acting automatic valve such as found

in some water-using appliances using hot water.

The existing standards did not provide a generally-accepted performance test for evaluating the long-term effects of shock pressure

and thermal cycling on the durability of thermoplastic piping assemblies.

Neither was there sufficient measurement data on the service environment

for such systems to permit an accurate definition of representative

conditions for simulative service tests. Therefore, in order to

contribute to the development of systematic performance evaluation

methodology, a course was decided upon which involved a laboratory

investigation in combination with a review of related work by other

investigators. In this approach, tests were to be conducted on representative assemblies of thermoplastic piping for shock pressure

and thermal cycling durability, rather than on individual sections of

pipe and on fittings. This approach was thought to be necessary because

the system performance can be affected by interactions between the pipes,

fittings, supports and attachments, and by the quality of the assembled

joints.

Thermoplastic piping is lighter than its metallic counterpart.

This results in reduced structural loads and increased convenience in

fabrication and installation of the piping system. However, this lower

1
density as well as the greater thermal expansion of thermoplastics

contributes to greater physical movements under hydraulic and thermal

loadings. Because there is insufficient experience concerning the

effect of these movements on the performance of thermoplastic plumbing

systems, greater attention must be given to the installation details

when designing such a system; e.g. possible problem.s associated with

localized contact with the building structure and with the friction

between pipe hangers and supports must be considered. It is essential

that any comprehensive evaluation of thermoplastic piping assemblies

must include provisions for comparison of different installation methods

that might be used in the field.

1. 2 Obj ective

As a part of the Department of Housing and Urban Development (HUD)

long-range research program for improving building standards and performance evaluation methodology, a task for the National Bureau of

Standards (NBS) to develop performance criteria for piping materials for use in residential plumbing systems was sponsored. The scope of the

program was limited to laboratory evaluations of thermoplastic materials.

The topics of primary interest included: the long-term effects of

intermittent hot-water exposure (thermal cycling) on "thin wall"

poljrvinyl chloride (PVC) drain-waste-vent (DWV) systems and on chlorinated PVC (CPVC) water distribution piping; and the long-term

effects of water hammer (shock pressure) on CPVC water distribution

system piping.

The objective of the work on resistance of an assembly of pipe

and fittings to intermittent exposure of hot water was to examine the

effects of a simulated service exposure to this condition. The information of principal interest was the permanent change in dimensions

and the continuity of leak resistance. The objective of the work on shock pressure was to examine the effects of simulated "water hammer"

on an assembly of pipe and fittings, with particular attention to the

ability of the assembly to withstand, without leaking, repetitive

applications of shock pressure for a sufficient number of cycles to

represent anticipated exposure over the planned life of a residential

water distribution system.

1. 3 Scope and Approach

The constraints on the study reported herein limited the laboratory

investigation to selected thermoplastic materials. A review was made

of related work as reported by other investigations to supplement

the NBS study and to provide input to the design of the NBS experimentation. Because concern had been expressed as to the adequacy of "thinwall" schedule 30 PVC DWV pipe and of CPVC water tubing used in some of

the Operation BREAKTHROUGH housing systems, the NBS experimental work

was concentrated on these types of piping.

2
The approach adopted for the NBS hot water test involved the

exposure of representative assemblies of water piping and DWV piping

to a flow of hot water of approximately 8 gpm (0.5 1/s) for 5 minutes

at 1/2-hour intervals, at a temperature of about 140° F (60° C) . The

rationale for this was to simulate conditions produced by automatic

plumbing appliances such as dishwashers and clotheswashers. It has

been widely believed that the most severe exposure of residential

plumbing piping to hot water occurs in the water supply pipes leading

to automatic dishwashers and clotheswashers, and in the waste piping

serving these appliances. The test plan provided for different

techniques of attaching and supporting the piping to the building structure to simulate both good and bad installation practices. Essential

measurements made to indicate the level of performance were: evidence

of leaking, thermally induced deflections, and permanent changes in

dimensions of position. Such measurements are direct indicators of

capability of the system to maintain essential functions and characteristics, e.g. leak resistance, acoustical acceptability, and drainability.

The approach for the NBS pressure shock test involved the

repetitive application of a pressure pulse, at a frequency of 6 cycles

per second, on an assembly of water piping full of water at a normal

pressure and maintained at a selected temperature, and continuation

until either failure (leaking) occurred or for 350,000 repetitions. The

rationale for this was as follows: the most severe exposure to water

hammer in a residential water distribution system is assumed to occur under rapid closure of the solenoid valve in the hard-piped hot-water

supply to appliances such as the automatic dishwasher. It was estimated

that as many as 350,000 operations of the hot-water supply solenoid

in a dishwasher could occur over the life of a plumbing system.

Review of the work of other investigators, plus some preliminary tests,

showed that a frequency of as much as 6 Hz (desirable to shorten the

required length of the test as much as feasible) yielded a number of

cycles-to-fallure essentially the same as for the much lower frequencies

believed typical. Tests were made at different pressures and temperatures to gain some idea of the effects of these parameters.

3
2. SHOCK PRESSURE TESTS

2.1 Summary of Work by Other Investigators

Three studies have been reviewed. One of the investigations [1] was concerned with the prediction of the magnitude of shock pressure

and the sizing of air chambers to reduce shock pressure. The other

two [2,3] were concerned with the possible effect of shock pressure on

the burst strength of PVC water pipe. The three studies are discussed

in the following sections.

2.1.1 Water-Hammer Theory

The classical theory estimates that maximum over-pressure (pres- sure rise above static line pressure) (AP) caused by the rapid closure

of a valve in a pipe line is given by the expression

AP = a AV

(3^) 2.31 g

in which

^ T'%e + KDC^)

where:

AP = pressure rise due to valve closure, psi

a = shock wave velocity in pipe, ^t/s

g = acceleration of gravity, ft/s

V = flow velocity in pipe before valve closure, ft/s

AV = change in flow velocity due to valve closure, ft/s

K = Bulk modulus of elasticity of water, psi

E = modulus of elasticity of the pipe material, psi

e = pipe wall thickness, in

^

p = mass density of water, slugs/ft

D = inside diameter of pipe, in

= a function that depends on Poisson's ratio for the pipe material

and on the physical restraint of the pipe.

The maximum shock pressure will occur only if the valve closure

occurs within the time period which is less than 2L/a seconds. When

this closure time is greater than lOL/a seconds, destructive waterhammer pressures will not be produced. The term L represents the

length of pipe in which velocity V exists before valve closure.

4
2.1.2 Wat er-Hammer Control

There are two generally accepted methods of water hammer control:

(1) Rapid closure of valves should be prevented, particularly

during the last 15% of the movement.

(2) If method (1) is not practicable, shock-absorbing devices

such as air chambers may be used. A chart for sizing pipe

air chambers has been provided by Dawson and Kalinske [1],

and manufacturers of sealed air chambers (shock arrestors)

have provided sizing criteria for their products [4, 5, 6].

2.1.3 Effect of Water Hammer on PVC Pipe

(a) Tests at Johns Manville [2]. Laboratory data for PVC 1120

pipe which was pressurized for up to two years at twice its

rated pressure showed greater short-time (60 to 70 seconds)

rupture (burst) strength than that of new pipe as determined

in accordance with ASTM D 1599. The test was planned to

provide for future verifications of this effect for pressurization up through 10 years.

Cyclic pressure surge tests for nominal 2-in and 4-in PVC

pipes were made at a rate of 0.38Hz from a base pressure of

50 psi (344.7 kPa). Other tests at 0.17, .017 and .0017 Hz

indicated that the frequency of the pressure surges (over

this frequency range) did not significantly affect the total

number of surges that the pipe could withstand at a given

pressure.

The effect of prolonged exposure to high static pressure before the imposition of cyclic pressure was studied,

as well as exposure first to cyclic pressure and then to

prolonged static pressure. These tests showed that static

pressure life and cyclic pressure life were essentially

independent.

Pipe that had been subjected to cyclic pressure to near

predicted failure and then subjected to the quick-burst

test (ASTM D 1599) showed a strength just below that expected

of new, uncycled pipe, according to the investigator [2].

Tests were made of the effect of longitudinal scratches on

the external surface of 1 1/2-in 160-psi (nominal) pressurerated PVC 1120 pipe. Scratch depths of 0.005 and 0.010 inch

were milled on the test specimens. Although the static pressure life was not adversely affected, there was a significant

decrease in cyclic pressure life due to the scratches. This

notch effect was greater than that attributable only to the

reduction of the wall thickness at the scratch.

5
Field measurements on operating water systems containing PVC

pipe were made under normal operating conditions and with

pressure variations deliberately introduced by the manipulation

of fire hydrants. The pressure surges introduced by the fire

hydrant manipulation resulted in pressure rises ranging up to

a maximum of about 100 psi (689.5 kPa) above line pressure.

Long-term pressure measurements were also made on one system

over a period of 2 months. Pressure surges up to 225 psi

(1551.3 kPa) were recorded 12 times, and over 228 surges to

160-169 psi (1103.2 - 1165.2 kPa) occurred. High-frequency

"noise" pressure observed on the records was attributed to

the operation of pressure-reducing valves in the system.

Average static pressure in this system was given as 112 psi

(772.2 kPa).

It was concluded that resistance to pressure surge is an important design criterion for PVC pipe, and that PVC 1120

pipe rated for 160 psig may be expected to have a life of

250,000 to one million cycles of pressure surges up to 110

psi (758.2 kPa) . Surface scratches significantly reduced

cyclic pressure life.

The study showed that the magnitude of water hammer surges

could be estimated for PVC pipe using the traditional

equations (1) and (2) with constants appropriate to the

material and its mode of restraint [2].

The author [2] recommended a similar testing program for

plastic pipe of other materials prior to determination of

a design basis for taking surge pressure into account.

The essence of the recommended approach was as follows:

(1) A cyclic hydrostatic design stress (CDS) should be

established by testing samples. CDS is defined as the extrapolated hoop stress to which the pipe can be cycled an infinite number of times. (This was stated as 1500 psi (10.3mPa)

for CPVC 1120).

(2) A cyclic hydrostatic design basis (CDB) should be

calculated by multiplying the CDS by a service factor.

(3) The cyclic hydrostatic design stress (CDS) should be

used in the same manner as the hydrostatic design stress

(HDS) in determining wall thickness required to provide a desired pressure rating for a particular pipe.

(b) Tests at B. F. Goodrich [3].

Three test arrangements were used. Tests were made on 1-inch schedule 40 PVC, 2-inch SDR 17.6 PVC and 1-inch

schedule 40 stainless steel piping. An air-operated ball

6
valve, located at the downstream end of the test piping, was used to stop the flow. A pressure transducer immediately

upstream of the ball valve was used to measure the pressure.

In two of the test arrangements a closed system containing

a pump was used, with the desired test flow velocity determined by an appropriate orifice in the line located downstream of the ball valve. In the third test arrangement,

the water was taken from the building water-distribution

system and flow rate was controlled by adjustment of a ball

valve upstream of the test piping. Records of pressure versus

time were made by means of both a recording oscillograph and an oscilloscope with a photographic attachment.

Measured shock pressures were compared with theory; the

agreement was best in the closed system. Possibly the

greater scatter in the data from the system connected to the

building supply was caused by variations in the building

supply pressure during the flow period. In all three tests,

a theoretical overpressure equation which was similar to

equations (1) and (2) , was shown to be a satisfactory means

of predicting the maximum over-pressure (providing the flow

velocity, the pipe diameter and wall thickness, and the pipe

material are known) . Analysis of sample records in the report

Indicated a frequency of reflected surge pressure ranging,

in most cases, from 2 to 5 Hz and a frequency of the "Noise"

superimposed on the primary surge ranging from 30 to 50 Hz.

Statements and recommendations concerning limiting water

velocities in thermoplastic piping systems included the

following [3]:

1. The maximum safe water velocity in a thermoplastic

piping system depends on the specific details of the system

and the operating conditions. In general, 5 feet per second

is considered to be safe. Higher velocities may be used

in cases where the operating characteristics of valves and

pumps are known to be such that sudden changes in flow

velocity will be controlled to yield overpressures less than

the theoretical maximum. The total pressure in the system at

any time (static pressure during flow plus the overpressure

from surge or water hammer) should not exceed 150 percent of

the pressure rating of the system.

2. The pressure rating of PVC pipe should be 1.4 times the

maximum operating pressure. This provides a safety factor

of 2.8 based on long-term hydrostatic strength, which is

adequate to account for water hammer and surges for velocities

of 5 ft/s or less.

3. The factors recommended for PVC may not be appropriate

for other materials.

7
4. Long-term hydrostatic strength was not decreased by

exposure to 2000 cycles of water hammer or 2000 cycles of

surge pressure.

5. Surge pressures in PVC pipe computed from theory were

less than 50% of the values computed for cast iron or asbestos cement pipe.

2.2 Apparatus and Procedure - NBS Test

2.2.1 Introduction

This section describes the test procedure used in the NBS

experimental study on the resistance of chlorinated polyvinyl chloride

(CPVC) thermoplastic piping to pressure shock similar to that produced

in a domestic water-distribution system. The review described in Section

2.1 was helpful in establishing the frequency of the cyclic pressure

applications, and in establishing the need for reproducible, programmed

pressure pattern.

Currently, the design method for thermoplastic piping systems

is based on using a hydrostatic design stress obtained by applying a service factor to the long-term hydrostatic strength. The hydrostatic

design stress is intended to provide a service life under a continuously

applied internal hydrostatic pressure with a high degree of certainty

that the pipe will not fail. This method provides only the service

factor as the means for assuring that the system will withstand the

action of water hammer, which produces high internal pressure for very

short time periods. Although no standard method of testing for water

hammer strength currently exists, water hammer can occur in many systems

during their service life, and this phenomenon should be considered in

the design of the system.

In a residential potable water distribution system, the most

severe water hammer occurs in the hard-piped hot water supply pipe to

the dishwasher when the solenoid valve in the dishwasher suddenly stops

the flow of hot water. At the instant when this occurs, the hot water

supply line is subjected to a momentary overpressure. This pressure

"spike" will then propagate through the line and may recur as repetitive

"reflected shocks" with successively decreasing intensity until

stabilizing at the prevailing static pressure. The severity and

frequency of these shock waves will depend upon the mechanical action of

the solenoid in the particular dishwasher (or other automatic appliance)

,

on the length of the affected piping, the pipe material, and on the use

of the machine. Other pressure spikes, probably not as severe as those

caused by the dishwasher, may occur elsewhere in the distribution

system from the clotheswasher and from the rapid closure of faucets.

However, the shock pressure produced by the valve action in the clotheswasher is reduced, since the clotheswasher generally is connected to

the system by means of a rubber hose which can flex with the shock

waves. Because of differences in elasticity in the basic materials,

8
the maximum pressure for a given set of initial conditions (such as flow velocity and rate of valve closure) will be less in thermoplastic

pipe than that produced in copper or steel pipe of the same length.

The particular design of a solenoid valve can affect the effective rate

of closure and hence the maximum pressure produced. The service life

of a domestic water distribution system subjected to water hammer is

based on the system's ability to withstand a large number of pressure

spikes at a representative hot water temperature and on its ability to

withstand a normal hydrostatic pressure for a long time period. Assuming

a maximum of six primary pressure surges (peak spikes) per dishwasher

cycle and a maximum use of the dishwasher of three times a day, the

distribution system could see as many as 328,500 primary pressure surges

in a 50-year period.

2.2.2 Water Hammer Evaluation Test

(a) Scope

Because no standard test method existed for the evaluation of

water hammer resistance in pressure piping systems , a procedure

was developed by which water hammer could be simulated in a representative system.

The primary element in this simulation is the loading program.

Since the procedure required the generation of several different

pre-selected magnitudes of peak pressure, a critical parameter

is the duration (or period) of the pressure spike. Based on test data from another study of water hammer performed on polyvinyl chloride (PVC) pipe [3], a close relative of CPVC,

the duration for the NBS test was selected as 0.16 seconds.

As previously mentioned, under normal service conditions the

initial spike is the most severe, as subsequent, reflected spikes

are reduced in magnitude (with an increased time duration) due to

the inherent damping in the pipe system.

The time between pressure pulses (or frequency) is also important.

Under actual service conditions this can vary considerably.

Initial testing of a specimen using a rapid cyclic pulse

produced failure at a very low number of cycles. The frequency

was then decreased to one pulse every half-second. This

produced an increase in the number of pulses to failure by

several orders of magnitude. A subsequent decrease in frequency

to one pulse per second did not produce any noticeable change in

the number of pulses required to produce failure. Therefore, in

order to achieve a large number of pulses in a reasonable length

of time, the frequency of pulse was chosen as 2 per second. The

limiting number of primary pulses was taken to be 350,000, since

this is a conservative estimate of the maximum number of severe

pulses that might occur in a 50-year time span in residential

water-distribution piping systems.

9
(b) Test Specimens

The test specimens were fabricated by joining together two 7-foot

10 1/2-lnch sections (2.4m) of nominal 1/2-inch CPVC pipe (tubing)

with a 90° elbow to form an L-shaped section. Transition fittings

and couplings were then cemented to each open end of the two

pipes. The final resulting length of each leg was 8 feet (2.44m)

(see figure 1). A solvent cement jointing technique was used as recommended by the manufacturer of the materials. A total of

sixty-five specimens were fabricated in two sets, consisting of one group of five and six groups of ten, and were air-cured in the

laboratory for a minimum of seven days prior to testing. The

specimens were then divided into four test sets and each set was

tested at a different temperature over a range of different peak

pressures

(c) Test Procedure

The thermoplastic pipe specimens were tested in a thermal chamber

constructed specifically for these tests and shown in figures 1

and 2. The chamber was an L-shaped box with internal dimensions

of 15 X 27 X 108 inches (38 x 68.6 x 274 cm) in each leg. The

faces of the chamber consisted of 1/2-inch (1.3 cm) plywood

covered with 3-inch (7.6 cm)-thick sheets of foam insulation.

Access to the interior was provided by attaching the facings on

the inside of the L to the box with "suit case" type latches.

Six nominal 2 x 4-inch timbers (2 x 4) were nailed to the sides

of the chamber in each leg with a spacing of 16 inches (40.6 cm).

The specimens were attached to the 2x4 every 32 inches (81.3 cm)

starting from the elbow, as recommended by the manufacturer.

Heating of each leg within the chamber was provided by wrapping

an electric heating element around an eight-foot section of

nominal 6-inch-diameter cast iron pipe. The cast iron pipe was attached to the 2 x 4 on the side away from the specimens.

Pressure was supplied to the specimens by means of a single-stroke

piston pump connected to one end of the specimen. The pump was

controlled by a closed-loop electro-hydraulic test machine. A

pressure transducer was connected to the other end of the specimen

for pressure monitoring. Three thermocouples were used during

the test to monitor the temperature of the specimen. One was attached to the elbow fitting and the other two were attached to

the pipe in the center of each leg. Thermostats connected to the

heating elements maintained the required test temperature. The

test temperatures were 75°, 120°, 140°, and 180° F (24°, 49°,

60°, and 82° C, respectively).

The closed-loop electro-hydraulic test machine was programmed to

generate a predetermined maximum pressure "spike" having the

appropriate magnitude, duration, and frequency. Since the volume

of water in the specimen was essentially a constant before failure,

a significant change in this volume was used to indicate that

10
11
12
failure had occurred. This change in volume occurred when water

was lost due to change in order to maintain the programmed maximum

pressure. The position of the piston was monitored to determine

when the volume of water had changed, and to indicate when a specimen had failed. This sudden change in position was programmed

to stop the test. The specimen was initially filled with water

from the NBS hot water supply and the flow was maintained through

the test specimen as the thermal chamber was heated until the

temperature stabilized, as indicated by the thermocouples. The

flow was then terminated and the surface temperature of the pipe

was monitored until it stabilized at the required test temperature.

The test temperature was maintained with +5° F (+2.8° C) during

the test. Next the programmed pressure in the specimen was increased to the maximum test pressure for that specimen. The

loading program was then initiated and the number of pulses

counted until either failure occurred or 350,000 pulses occurred

without failure.

2.3 Results and Discussion

The results of the NBS simulated water hammer test to ascertain

the effect of water hammer on chlorinated polyvinyl chloride for the

four test temperatures are presented in figures 3, 4, 5, and 6. Because

of variability factors in the specimens, a range in the number of pulses

to failure was obtained for a given test pressure. This range was fairly

narrow at high pressures and broadened as the pressure decreased. This

is illustrated in the figures, where the solid circles represent the

minimum and maximum number of pulses for failure at a given pressure

level. The triangle represents the average. The region of the curve

to the right, where a large number of pulses were necessary for failure,

is not well defined, as a very large number of tests would have been

required. Hence, the curves shown in the figures represent estimates in

this region, based on the limited number of test results. Most failures

in the destructive tests, with the exception of those at zero pulse

(failure with one application of the indicated pressure) , were due to

fatigue of the elbow. This fatigue produced a small pin hole in the

throat of the elbow, as shown in figure 7.

13
14
15
O o O O Q O O O O •O CO CN •—

'3linSS3iid >IV3d

16
17

3. INTERMITTENT HOT WATER EXPOSURE TESTS

3.1 Summary of Work by Other Investigators

A report [7] on tests of deflection of horizontal thermoplastic

pipe from alternate hot-and-cold water loading was reviewed. Also, an elevated temperature cycling test for a vertical assembly of DWV pipe

and fittings (British Standard BSS 4514 [8]) was reviewed. These reports

provided ideas useful in deciding upon the experimental design for the

NBS test and provided meaningful supplemental Information.

3.1.1 The Deflection of Thermoplastic Pipe Resulting from Thermal

Cycling [7].

The significant features of the testing procedure used and the

important findings [7] are as follows:

An apparatus was used that provided for alternating exposure

of nominally horizontal 20-foot lengths of pipe to hot and cold

water. Supports were placed at 3- and 4-foot intervals. A

slope of 1/4 in/ft was provided in the test pipes. The following

thermal loading cycle was provided:

2 min with 180° F water at 7 1/2 gpm

2 min with no flow

6 min with 60° - 75° F water at 15 gpm

2 min with no flow (Deflection measurements were made during

this time. Preliminary tests with measurements made at one- minute intervals during the first 10 minutes of the cycle

showed that the most meaningful deflection was that remaining

after completion of each cycle)

Tests results were shown from 1 1/2-inch sch 40 GEON 85092 PVC;

1 1/2-inch sch 40 ABS; 1 1/2-inch SDR 17, 21 and 26 GEON PVC; and

1 1/2-inch sch 40 PVC of compounds with hydrostatic design temperature

values of 158°, 160° and 169° F.

The method compared deflection as affected by the heat deflection

temperature of the material (ASTM D 648), by the material's flexural

modulus (ASTM D 790), by the pipe-wall thickness, and by the support

spacing. It was suggested that by projection of the test results, the

probable deflection at 73,000 cycles (which was considered equivalent to

50 years of service at 4 cycles per day) could be predicted.

For the purposes of the study [7], a deflection between supports

(at mid-span) after 73,000 cycles not exceeding d/4 inches was considered

permissible, where the elevation difference between adjacent supports is

"d" inches. This limit provided assurance against the development of

"zero" or "negative" slope.

19
Transient temperature profiles were computed across the wall of

1 1/2-inch sch 40 PVC pipe for various times of exposure of the inside

surface temperatures and were compared with experimental measurements,

with good agreement [7]. The outside surface temperatures at 2-min and

5-min exposure were shown as approximately 142° and 148° F, respectively.

The results showed that the principal factors affecting the deflection

of PVC pipe were heat deflection temperature (as defined by ASTM D 648)

,

support-spacing, and wall thickness; deflection was. less with the greater

wall thicknesses and higher heat deflection temperatures, and more with

the greater support spacings. It was concluded that PVC DWV pipe made

from material with a high heat deflection temperature will withstand

long-term exposure to thermal cycling without excessive deflection. ABS

pipe showed slightly less deflection than PVC.

3.1.2 Elevated Temperature Cycling Test for Vertical Assembly of DWV

Pipe and Fittings

British Standard BS4514: 1969 [8] contains a requirement and a test for "elevated temperature cycling" of hot and cold water through a vertical assembly of PVC DWV pipe and fittings.

BS4514 requires that there be no leaks during the test, that

after 2500 cycles the assembly shall withstand being filled with water

to 150 mm (5.9 in) above the waste inlet without leaking, and that the

assembly accept the passage of a ball with a diameter 6 mm (1/4 in)

less than the nominal diameter of the system being tested.

The test installation consists of a horizontal waste pipe branch

and a soil pipe, fittings, and an expansion joint. Alternately hot and

cold water is passed into the assembly through a 0.6 m (23.6 in)

minimum length of straight waste pipe branch according to the following

schedule for 2500 cycles:

(1) 35+3 litres (7 1/2 gallons) water at a temperature

of 91 + 9° C (160 + 2° F) over a period of 90 s to 95 s. The water temperature shall be measured at the point

of entry into the stack.

(2) Rest and drain period of 60 s to 70 s. (3) 35+3 litres (7 1/2 gallons) of cold water (no

temperature specified) over a period of 90 s to 95 s. (4) Rest and drain period of not less than 60 s. During the test the ambient temperatures shall be

17 + 5° C (63 +9° F).

It was stated in BS4514 that the test* is to be carried out for

each formulation used and when any change is made in compositon or method

of manufacture of pipe or fittings.

* A test to be made for each specified "type" or category of product,

but not required subsequently in routine production of the same

product. If significant variations are introduced, another type

test is required.

20
3.2 Apparatus, Measurements and Procedure - NBS Test

The design of the apparatus and of the procedure for the NBS

intermittent hot water exposure tests benefitted from the review of

codes, trade information and References 7 and 8.

3.2.1 Test Specimens

The piping materials subject to the intermittent thermal loading

test were of PVC and CPVC thermoplastics. The fixture traps, trap arms

and drainage stacks were of PVC. Trap arms were nominal 1 1/2-inch

Schedule 40, and drainage stacks were nominal 4-inch Schedule 30. The

water piping was of nominal 1/2-inch CPVC (tubing size).

Two methods of attachment of the PVC drainage stacks were utilized:

1. Longitudinal motion restrained at both ends.

2. Longitudinal motion not restrained (through the use

of an expansion joint).

The length of the 1 1/2-inch trap arms in the drainage system

test was on the order of 3 feet, 6 inch (1.07 m) , the maximum allowed

by many codes for hydraulic and pneumatic reasons. The drainage piping

components of the test assembly were designed in a fashion similar to

that described in BS 4514-1969 [8].

Four different methods of attachment of the simple water pressure

piping specimen to the simulated building construction (floor joists at

right angles to the pipe) were utilized:

1. One end restrained and the other end not restrained, and

supported with non-restraining clamps at 32-inch (81cm) centers.

2. Both ends restrained and supported with restraining clamps

at 32-inch (81cm) centers.

3. Both ends restrained and supported with non-restraining

clamps at 32-inch centers.

4. Both ends restrained and supported with non-restraining

clamps at 32-inch (81cm) centers. Additionally, a nominal

1-foot (30.5cm) 90° offset was provided at the mid-point.

According to industry recommendations, methods 2 and 3 are improper

and methods 1 and 4 are acceptable methods of installation.

All piping test systems were installed by qualified practicing

plumbers, following the industry-recommended procedures for making

joints.

21
3.2.2 Test Apparatus

The general configuration of the intermittent hot-water exposure

test system is depicted schematically in Figure 8. During flow, water

was pumped from a holding tank of approximately 30-gallon (114 liters)

capacity to a nominal 52-gallon (197-liter) capacity household-type

electric water heater forcing hot water through a CPVC thermoplastic

pressure piping test loop which discharged into one of two PVC thermoplastic trap arms. Then, the water was returned to the holding tank

through the PVC test drainage stack which received the trap arm discharge.

The nominal flow rate of 8 gpm (0.51 l/s) for 5 minutes produced a volume of discharge less than the rated capacity of the water heater

during any one flow cycle. Each flow cycle was controlled through a set

of electrical solenoid valves so that the water flow direction could be

reversed in the CPVC test loop with discharge into a different PVC trap arm and drainage stack. The relatively short distances between the

water heater and the solenoid valves made it necessary to install a small thermal expansion tank of 2 1/4-gallon (8 1/2 -L) capacity in order

to limit excessive pressure buildup during the "no flow" condition wnen

thermal expansion of the water occurred during heating. Flow rate was controlled by a throttle valve and a 1-inch circuit setter (a calibrated

flow rate measurement device with provisions for flow restriction)

installed between the pump and water heater, and was measured through

the use of a 1 1/2-inch venturi. Although the thermal expansion tank

served the secondary function of limiting water hammer, additonal water

hammer control was achieved through the use of a vertically piped air

chamber (see figure 8) . Pressure regulation was maintained with a pressure reducing valve.

A detailed layout of the CPVC test loop is presented in figure 9

with the individual CPVC tests outlined in further detail in figures 10a,

10b, 10c, and lOd. The capped stubs shown in (a) and (b) of figure 9

served the purpose of simulating the fittings and branch piping which

would normally be installed in water-distributing systems. These stubs

were omitted from figure 10a for clarity.

3.2.3 Measurements

All measurements of water pressure, water temperature, and pipe

displacement were made using manual reading methods with standard

pressure and temperature gages, mercury-in-glass thermometers, rulers,

calipers, and scales. Surface temperatures were recorded by direct

reading of standard bi-metallic maximum/minimum surface thermometers.

The load cell measurement data were automatically recorded on magnetic

tape for subsequent data reduction, calculation, and plotting by the use of computerized techniques.

22
.CONTROL ELECTRICAL

SOLENOID VALVES

2nd FLOOR

CEILING

LOAD CELL

/2in CPVC TEST LOOP

(FIXED)

2nd FLOOR

12ft P7 M)

^/iin METALLIC

PIPING -

1/210 PVC TRAP ARM

THERAAAL

EXPANSION

TANK

'4in PVC DWV

DRAIN STACK

HOT

WATER

HEATER

PRESSURE

RELIEF

^/iin METALLIC

PIPING -

.EXPANSION JOINT

1st FLOOR

n CIRCUIT

SETTER

VENTURI

CHECK

VALVE

%\n METALLIC

PIPING

Figure 8. Intermittent Hot Water Exposure Test Schematic.

23
24
[o]

Z^LOAD CELL

fIXED)

(b)

"

T

LOAD CELL fIXED) (c)

^ FIXED

J 1 „

^

,J_

(d)

LOAD CELL (FIXED)

LEGEND:

SLIP CLAMP

FIXED CLAMP

-H H" DISPLACEMENT MEASUREMENT

ZZZ FINAL POSITION AFTER FLOW

Figure 10. CPVC Thermoplastic Test Configurations.

25
3.2.4 Test Procedure

The apparatus provided for intermittent repetitive thermal

loading of the water tubing and the drainage piping. The loading

cycle is described as follows:

a. Hot water flow at 8 gpm (0.5 l/s) average for 5 minutes

clockwise through the water loop at 120° to 144° F

(49° to 62° C) with discharge into the first drain stack.

b. 25 minute dwell or cooling pause with no water flow.

c. Hot water flow at 8 gpm (0.5 L/s) average for 5 minutes

counterclockwise through the water loop at 120° to 144° F

(29° to 62° C) with discharge into the second drain stack.

d. 25 minute dwell or cooling pause with no water flow.

e. Repeat of a, b, c, and d above for a total of over 1500

exposures to hot water flow in the water loop, and over 750

exposures to hot water flow in each drain stack. The

reason for twice as many exposures of the water loop as of the drain stacks was that alternately each drain

stack was idle as the other was exposed to the hot water

discharged from the water loop.

The above loading cycle was chosen as a compromise between the

normal homeowner appliance hot water usage cycle and the necessity to

subject the test system to as many cycles as reasonable in a short time

period. It was felt that the 5-minute hot water flow followed by a 25-

minute pause was reasonably representative of the conditions in the hot

water supply line serving a clothes washer or a dishwasher. The 25-

minute pause allowed for some cooling, but not down to ambient temperature.

The flow direction in the water loop was reversed with each cycle in

order to subject each of the four pressure-pipe test components to the

same temperature and pressure conditions, on the average. In addition,

this arrangement provided for the test of two drainage systems during

the same period—one with expansion device and the other with rigid

attachment

It should be noted that the water in the pressure pipe assembly

did not cool completely to the normal ambient temperature of 78° F

(26° C) but did cool to an average temperature of 125° F (52° C) . Also,

although the water heater thermostat was adjusted to a temperature of

180° F (82° C) due to the control limitations of the thermostat and the

time required to reheat the water returned to the heater after passing

through the test system, the actual water temperature delivered to the

test pipes was in the range of 144° F (62° C) . This water temperature

is near to the 140° F (60° C) which is normally experienced in the home

and specified as the upper limit in the HUD Minimum Property Standards.

The significance of the relatively small amount of cooling down

is that this test did not simulate conditions of thermal cycling , but

rather Intermittent hot water exposure with limited cool-down (at least

in the water loop). Had the constraints permitted, the test could have

been extended to include alternating hot and cold-water exposure of the

26
drainage stack, and greater cool-down of the hot-water loop between hotwater flows.

Locations of key measurement stations are shown in figures 8, 9,

and 10.

Measurements or observations were made of the following parameters:

° Water and pipe-surface temperatures at a number of points.

° Internal pressures at the entrance and exit of the water

pipe testing loop.

" Longitudinal forces generated by the pipes at their restraint

points. (Reported as the compressive stresses in the pipes).

° Longitudinal movements at unrestrained ends.

° Lateral movements at midpoint between points of attachment of

pipes restrained at ends or intermediate points.

° Leakage

The measurements were classified as either static or dynamic. The

general operating procedure for making the tests is described as follows:

1. Within one minute of the beginning of hot water flow, all

selected static readings were manually recorded on data log

sheets

2. Within one minute of the end of hot water flow, the readings

taken in (1.) above were repeated, but these readings were

classified as the dynamic set.

3. All measurement readings were typed in to a computer for

placement on magnetic tape and for subsequent data reduction

and display.

Because of the length of time required to make a complete set of

measurements in the manner described, only partial sets of data could be

taken at any one selected "cycle time"; however, 35 sets of partial data

were recorded over the duration of the test. Additionally, a full set

of "before test" data and a full set of "end-of-test" data were recorded.

3.3 Results and Discussion

The relatively small number of exposure cycles (1500 for the

water piping and 750 for the DWV) made before the test was stopped

probably does not represent a sufficiently long period of service

exposure. Also, the inadequate capacity of the water heater resulted in

poor control of the temperature of the water in contact with the test

piping and in the necessity to average successive measurements obtained

at significantly different exposure temperatures for the purposes of the

analysis. For these reasons, there is not a satisfactory degree of

confidence in conclusions that might be drawn from the data.

27
3.3.1 Water Piping

Table 1 summarizes the average of the longitudinal and lateral

motions, pressure drops and temperatures measured in the water piping

during several "typical" cycles. These typical cycles were chosen based

on the availability of required data from the partial data sets.

For the pressure pipe assembly that was fixed at one end only

(figure 10a) the typical dynamic elongation was +.24* in (6mm) or + 0.18%. If a numerical approximation is applied to the assembly which

was fixed at both ends and slip-clamped (figure 10c) , a typical dynamic

elongation of + .1 in (2.5mm) or + 0.08% is indicated. Indicated

permanent elongation for the two assemblies (figures 10a and 10c) varied

between -.2% to +.11% respectively and +.6% to +.05% respectively, with

the final values at the end of the test of -.01% and +.05% respectively.

Figure 11 illustrates the compressive stress** buildup and decay

within the three noted assemblies of 1/2-inch nominal CPVC pressure

piping which were subjected to an 8 gpm (0.5 L/s) flow of 150° F (60° C)

water for 5 minutes. The conditions of each test assembly at the time

of maximum stress are summarized in table 2. The data used in the

development of figure 11 and table 2 were obtained by averaging the

information attained from four individual tests using automatic recording

techniques for the stress information and manual recording for other data.

3.3.2 Drain-Waste-Vent Piping

Table 3 summarizes the average of the longitudinal and lateral

motions (see figure 8), water temperatures, and flow rate, and pipe

surface temperatures measured during several hot water flow cycles of

5-minute duration through 1 1/2-in nominal Schedule 40 PVC trap arms

and 4-in nominal Schedule 30 PVC DWV stacks. The particular cycles

chosen for use in the development of table 3 were based on the availability of the required data from the partial data sets.

Because of uncertainty in the accuracy of the surface temperature

measurements, caution should be exercised in making precise comparisons

of absolute values, particularly of values taken at different points.

The data indicated lower maximum surface temperatures at the branch than

at the mid-point of the stack. This seeming inconsistency may be

attributable in part to (a) difference in diameter and wall thickness of

branch and stack, and (b) possible difference in proximity of flowing

water to temperature sensor for the branch (horizontal) and the stack

(vertical)

* A (-) sign indicates a shortening and a (+) sign indicates a lengthening of the test pipe.

** The stress was calculated as an average obtained by dividing the

measured longitudinal force by the cross-sectional area of the

stack pipe wall.

28
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29
350 I—

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SLIP CLAMPS ONLY

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to

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300

150°F (66°C)

- WATER FLOW - AT 8 GPM (.5 L/S)

400 500 600

TIME (SECONDS)

COOLING

- FLOW TERMINATION

1000

INITIAL TEMPERATURE = 80°F (27°C)

Figure 11. Hot Water Flow Stress Characteristics for Different Mounting

Configurations of 1/2 Inch CPVC Pressure Pipe.

30
TABLE 2. SUMMAEY OF TYPICAL COMPRESSIVE STRESSES AND

DEFLECTIONS FOR l/2-INCH CPVC ASSEMBLIES DURING

5-MINUTE FLOW OF HOT WATER (66° C) AT A RATE OF

8.1 gpm (0.51 L/s)

ASSEMBLY TIME OF

MAXIMUM

STRESS

(seconds)

MAXIMUM

STRESS

MAXIMUM

LONGITUDINAL

LOAD DEFLECTION

FIXED

CLAMP

(FIGURE 10b)

80 sec 340.7 PSI

(2.35 MPa)

45.7 lb

(20.7 kg.)

0.63 in

(16nim)

SLIP

CLAMP

ONLY

(FIGURE 10c)

40 sec 88.6 PSI

(0.61 MPa)

11.9 lb

(5.4 Kg.)

0.56 in

(14.2Tran)

SLIP

CLAMP

WITH

OFFSET

(FIGURE lOd)

270 sec 61.1 PSI

(0.42 MPa)

8.2 lb

(3.7 Kg.)

0.10 in (2.5inin)

LONGITUDINAL

0.11 in (2.8inni)

LATERAL

31
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32
The longitudinal expansion measured in the stack with the

expansion joint was only 0.06 in (1.5 nun). This indicates that the

average temperature within the wall of the stack pipe did not rise

to a value anjrwhere near the temperature of the hot water. This is

also indicated by the fact that the measured maximum surface temperatures

were significantly below the temperature of the hot water.

The lateral change in position measured at the mid-point of the

stack was less for the stack with the expansion joint than for the stack

fixed at both ends, as expected (0.08 in/2.0 mm and 0.16 in/4.0 mm,

respectively). The small deflection of the stack with the expansion

joint, in combination with a non-uniform temperature gradient through

the pipe wall results in deflections of those small magnitudes. The

small disturbances would not significantly affect the functional performance of drainage stacks.

The lateral deflections measured in the branches (0,16 in/4.0 mm

and 0.12 in/3.0 mm) were not sufficiently large to affect essential

functional capability of the branches.

Figure 12 illustrates the stress buildup and decay within a 12-

foot (3.66mm) length of nominal 4-inch Schedule 30 PVC drainage pipe

fixed at both ends and subjected to an 8 gpm (.5l/s) flow of 145° F

(63° C) water for 5 minutes. The initial pipe surface temperature was

75° F (24° C) , and the maximum surface temperature reached was in the

range of 125° to 130° F (52° to 55° C) . The maximum stress occurred

about 250 seconds after the beginning of hot water flow and was equal

to 71.7 psi (0.49MPa). This corresponds to a maximum longitudinal load

of 145.2 pounds (65.9kg) which was transmitted to the restraint devices,

one of which was the load cell attached to the test frame. The maximum

lateral pipe deflection in this run was 0.14 in (3.6mm) at the mid-point;

however, the pipe returned to its original position after cooling.

The data on permanent change in length of the stack with the

expansion joint are not considered reliable. Values corresponding to

a shortening of 0.05 to 0.20% were obtained, but consistency between

successive measurements was lacking. The reason for this is not clear.

In any event, the measured values do not indicate a change of more than

1/4 in (6.1 mm) per 10-ft story. Permanent changes in length of this

magnitude could be accommodated by generally accepted good practice in

design and installation.

33
75 r- -1.5

- .4

300 400 500 600 700

TIME (SECONDS)

900 1000

145°F {63°C) - WATER FLOW

AT 8 GPM p.5 L/S)

a.

CO

.3 to

CO

o.o

COOLING

FLOW TERMINATION (TIME AT WHICH VALVES WERE CLOSED)

INITIAL TEMPERATURE = 75°F (24°C)

Figure 12. Hot Water Flow Stress Characteristics of 4 -Inch PVC (Thin -Wall)

Drainage Pipe Fixed at Both Ends.

34
4. CONCLUSIONS

4.1 Intermittent Exposure to Hot Water

The Intermittent hot water flow tests were terminated after

approximately 1500 cycles (pressure pipe) and 750 cycles (drainage

pipe). Because of the relatively small number of cycles. It Is not

clear whether long-term dimensional stability had been fully attained,

nor could realistic extrapolations be made. The conclusions presented

here are, therefore, based on the state of the test assemblies when the

test was terminated and do not necessarily reflect conditions which

might have occurred with a completely representative life-cycle test.

Based on the data obtained, thermal expansion and associated

lateral deflections, as well as permanent dimensional changes, were not

considered excessive. Changes of these magnitudes can be accommodated

by generally accepted good practice in design and installation, and do

not imply any significant effects on essential hydraulic performance.

4.1.1 CPVC Pressure Piping

The following statements and conclusions can be made from the

analysis in terms of leak resistance, thermal deflections and permanent

dimensional changes

1. The performance of the CPVC hot water supply piping was satisfactory from the standpoint of thermal deflection and

permanent change in length. The typical lateral deflection

observed for the improper installation, fixed at both ends, was 0.37 in (9.5 mm) in a span of 36 in. This might be

considered excessive. However, with recommended installation

methods, the comparable lateral deflection did not exceed

0.04 in (1.0 mm), an Insignificant amount. Longitudinal

movement at the unrestrained ends of the recommended installations was typically about 1/4 in. The amount of movement

can readily be accommodated in generally accepted good

installation practice.

However, because the average temperatures in the pipe wall

were considerably lower than the water temperature, thermal

expansion was correspondingly lower than if the pipe wall had

been heated to the temperature of the water.

2. No leaks occurred in any of the CPVC test assemblies.

3. Lateral motion of all CPVC supply piping was essentially

limited to a plane which was parallel to the structure against which it was mounted. No apparent negative slope was observed

in any of the CPVC test assemblies. This would be anticipated

for the methods commonly used for attaching pipe to horizontal

surfaces such as the lower faces of floor joists. However,

35
lateral deflections of the piping could produce appreciable

slope changes where attached in contact with vertical or leaning surfaces.

4. The maximum compressive stresses recorded in the CPVC test

assemblies are considered to be within acceptable limits

(much lower than the 2,P00-psi design hydrostatic (tensile),

stress levels used by the industry for PVC and CPVC pipe of

the type and grade tested in the present study.

4.1.2 PVC Drainage Piping

The following statements and conclusions can be made from the

data analysis in terms of leaks, thermal deflections and permanent

dimensional changes:

1. The performance of both PVC test assemblies was satisfactory

from the standpoint of thermal deflection and permanent change

in length.

2. The maximum compressive stress recorded was considered to be

within acceptable limits (much lower than 2,000-psi design

hydrostatic (tensile) stress levels used by the industry for

PVC and CPVC pipe of the type and grade tested in the present

study.

4.2 Internal Shock Pressure

The following statements can be made from the water hammer test

results:

1. A fatigue life curve can be established for a given test

temperature.

2. As the temperature increases, the number of pulses necessary

to produce failure at a given peak pressure decreases (from

approximately 160,000 pulses at 500 psi and 75° F to less than

25,000 pulses at 5000 psi and 120° F).

3. At the maximum temperature rating of 180° F (82° C) specified

for this material by the manufacturer, a very large number

(in excess of 350,000) of pressure surges to 150 psi (1.03

MPa) were withstood without failure.

4.3 Future Evaluation needs:

1. Performance acceptance criteria are needed for the evaluation

of the long-term durability of new piping materials when

subjected to pressure shock and/or the intermittent cyclic

flow of hot water. Experience to date with CPVC residential

hot water piping has been encouraging when the industry

36
recommendations on the design and installation of the piping

system have been followed. A DE Journal* survey conducted in

1976 indicated that approximately 25% of the local codes now

allow CPVC for hot and cold water piping.

2. Standard performance test methods are needed for evaluating

the ability of new piping materials to meet essential requirements in relation to shock pressure (water hammer) and

intermittent transport of hot water. The most important needs

relate to methods for estimating the long-term effects of

these phenomena on the ability of new piping materials to

maintain essential functional performance capability.

It is believed that test methods patterned after those

described herein would be applicable as performance tests,

and that the work described in this report provides a meaningful

basis for development of the needed Standard Methods. In order

to achieve this, the following steps should be taken:

A. The experimental techniques, methods of measurement

and statistical treatment of the data should be

improved for simplicity, reproducibility and accuracy.

B. The procedures should be tried on a wider range of

materials than were used in the present study. This

could be the basis for the accomplishment of the

objectives of A.

C. The results of the present study plus the results of

steps A and B should be offered to the national

standardizing organizations having an interest in

developing performance evaluation methodology.

3. Since the series of tests described in this report was conducted,

additional field service history of thermoplastic piping

materials (e.g. CPVC, PB, ABS, PVC) has been accumulated and

there have been changes in code acceptance of thermoplastic

piping. This information should be identified and examined

periodically. It would be beneficial to coordinate this

systematic updating of service history and code acceptance

with acceptance surveys conducted by the DE Journal.

Published monthly by the Construction Industry Press, Inc., 522 North

State Rd., Briarcliff Manor, N.Y. 10510

37
5. REFERENCES

[1] Water Hammer and Noises in Water-Piping Systems - Chapter VIII

of Water- Supply Piping for the Plumbing System, F. M. Dawson and

A. A. Kalinske, Technical Bulletin No. 3, National Association

of Master Plumbers, 1942.

[2] Performance of PVC Pipe in Water Distribution Systems; R. T. Hucks,

Jr.; Modern Plastics, September, 1972.

[3] Special Report to AWWA Relative to PVC Pipe, Plastics Pipe

Institute.

[4] *Water Hammer Arrestors Standard PDI-WH201, Plumbing and Drainage

Institute, September, 1974.

[5] Engineered Mechanical Water Hammer Arrestors. Jay R. Smith Mfg.

Co. Catalog J-70, Piscataway, New Jersey.

[6] Theory of Water Hammer and Shockstop Sizing. Wade Specification

Manual 1976, Wade Division - Tyler Pipe Industries, Tyler, Texas.

[7] The Deflection of Thermoplastic Pipe Resulting from Thermal Cycling;

Robert C. Wilging, paper presented at Engineered Plumbing Exposition,

American Society of Plumbing Engineers, Chicago, 111., September,

1970.

[8] Elevated Temperature Cycling Test, Appendix G of British Standard

4514: 1969, Specification for UPVC Soil and Ventilating Pipe,

Fittings and Accessories, British Standards Institution, London.

* See also: Water Hammer Arrestors. ANSI A112.26.1 - 1969 (Reaffirmed)

1975), American Society of Sanitary Engineering and the American

Society of Mechanical Engineers.

38
6. APPENDIX

6.1 Definitions and Nomenclature

ABS: Acrylontrile-butadiene-styrene, a thermoplastic material

used in drain, waste and vent piping systems and also for

shallow-well water piping and for gas distribution. The

minimum content of each component is: acrylontrile , 13

percent; butadiene, 5 percent; and styrene and/or substituted

styrene, 15 percent.

Aging : The effect on materials of exposure to an environment for an interval of time; also, the process of exposing materials

to an environment for an interval of time. (ASTM)

Code ; As related to plumbing work, usually an ordinance, with any

subsequent amendment thereto, or any emergency rules or regulations which a city or a governing body may adopt to

control the plumbing work within its jurisdiction.

CPVC : Chlorinated poly (vinyl chloride), a thermoplastic

material used for piping in hot and cold water distribution

systems.

DWV System; All the sanitary drainage and vent piping inside a building or relevant portion thereof, Including the building

drain to its point of connection with the building sewer.

Fitting ; A device used to join or to terminate sections of pipe.

Horizontal Branch ; A drain pipe extending laterally from a soil

or waste stack or building drain with or without vertical

sections or branches, which receives the discharge from

one or more fixture drains and conducts it to the soil or waste stack or to the building drain.

Pipe : A term applied generally to tubular products and materials

commonly used to conduct or transport fluids or gases. In

this specific nomenclature, "pipe" usually has greater wall

thickness than similar products called "tube" or "tubing."

Plastic Pipe : A hollow cylinder of plastic material in which the

wall thickness is usually small when compared to the diameter

and in which the inside and outside walls are essentially

concentric. See plastic tubing. (ASTM)

Piping ; This term has a broader meaning than the term "pipe".

For example, "cold water piping" includes the pipe, tube, or tubing used to conduct the cold water; the fittings used

to control or regulate the rate of flow and the direction

of flow. 'Sot water piping" and "drainage piping" have

similarly broad meanings.

39
Plastic Tubing : A particular size of plastic pipe In which the

outside diameter Is essentially the same as that of copper

tubing. See plastic pipe. (ASTM)

Polybutylene Plastics : Plastics based on polymers made with butene

as essentially the sole monomer. (ASTM)

Poly (vinyl chloride) : A resin prepared by the polymerization of

vinyl chloride with or without the addition of small

amounts of other moncnaers. (PPI)

Poly (vinyl chloride) Plastics: Plastics made by combining poly

(vinyl chloride) with colorants, fillers, plastlcizers

,

stabilizers, lubricants, other polymers, and other compounding

ingredients. Not all of these modifiers are used in pipe

compounds. (PPI)

Potable Water : Water free from Impurities in amount sufficient

to cause disease or harmful physiological effects and

conforming in its bacteriological and chemical quality

to the requirements of the United States Public Health

Service Drinking Water Standards or the regulations of the

public health authority having jurisdiction. (NSPC)

Pressure : When expressed with reference to pipe, the force per

unit area exerted by the fluid in the pipe.

Pressure Shock : A general term indicating a fluctuation in pressure

(water hammer on pressure surge) within a piping system

caused by a relatively abrupt increase or decrease in

flow Velocity. Water hammer is usually associated with a very sudden decrease of flow velocity often giving rise to

high frequency "hammering" noises in pipelines of moderate

length in buildings. Pressure surge is usually associated

with the fluctuating pressures resulting from less sudden

or severe shocks, usually with a lower frequency such as may occur in long pipelines.

Stack : The vertical main of a system of soil, waste or vent

piping.

Thertnoplastic (noun) : A plastic which is thermoplastic in

behavior. (PPI)

Thermoplastic (adjective) : Capable of being repeatedly softened

by increase of temperature and hardened by decrease of

temperature. Note: Thermoplastic applies to those materials whose change upon heating is substantially physical. (PPI)

Trap : A fitting or device constructed in a drain so as to provide,

when properly vented, a water seal for protection against

40
the emission of noxious or explosive sewer gases, without

significantly retarding the flow of sewage or waste water

through it.

Trap Arm : Another name for fixture drain.

Vent: A pipe installed to provide a flow of air to or from a drainage system or element thereof so as to provide protection of trap seals from siphonage and back pressure.

Vinyl Chloride Plastics : Plastics based on resins made by the

polymerization of vinyl chloride or copolymerization of vinyl

chloride with other unsaturated compounds, the vinyl chloride

being the greatest amount by weight. (PPI)

Water Distribution (distributing) Pipe : A pipe within the building

or on the premises which conveys water from the water-service

pipe to the point of usage. (NSPC)

Water Hammer : The term used to identify the hammering noises

and severe shocks that may occur in a pressurized water

supply system when flow is halted abruptly by the rapid

closure of a valve or faucet.

Water Outlet : A discharge opening through which water is supplied

to a fixture, into the atmosphere (except into an open

tank which is part of the water supply system), to a boiler or heating system, or to any devices or equipment

requiring water to operate but which are not part of the

plumbing system. (NSPC)

Note: Definitions found in this section are to be identical with

those identified by the abbreviations (ASTM) , (NSPC), and

(PPI). For those definitions listed but not identified

by one of the abbreviations, some modifications have been

made to definitions which may have been found elsewhere in

the technical literature.

(ASTM) - ASTM D 883-73a

(NSPC) - National Standard Plumbing Code 1975

(PPI) - PPI-TRI-November 1968

41
6.2 Units of Measure and S.I. Conversion Factors

A recent NBS document LC 1056 dated November 1974 and revised

August, 1975 reaffirms, clarifies and strengthens the policy of NBS to

lead in the use of the metric system. In keeping with the intent of

LC 1056, the following guidelines have been adopted for this report:

1. Equations or formulas for which metric equivalents do not

yet appear in the engineering literature are expressed in

U.S. customary units.

' 2. When measurements have been reported in the literature in

U.S. customary tinits, the equivalent values in the International System of Units (S.I.) are reported alongside

enclosed in parantheses.

3. No S.I. equivalent for descriptive data not affecting

calculations or results is required. For example, when

nominal values of units appear as adjectives such as 3-inch

pipe, 2 X 6-inch stud, and 2-oz. bottle, etc. designations

expressed in customary units are acceptable.

4. Exceptions to the exclusive use of S.I. units are allowed

when communication or readership would be limited by the

exclusive use of S.I. units.

5. The following conversion factors from ASTM E380-74 are

, appropriate for units of measure that appear in this report:

Acceleration

1 foot per second per second = .3048 meter per second

per second

Length

1 inch (in.) = 0.0254 meter (m)

1 foot (ft.) = 0.3048 meter (m)

Mass

1 slug = the unit of mass to which 1 pound force can impart

an acceleration of 1 foot per second per second

1 pound-mass (Ibm) - .4535924 kilogram

Temperature

1 Degree Fahrenheit (°F) = (LS)""*" kelvin (K) or (°K)

Temperature Fahrenheit (°F) = (459.67 + temp. ''F)/1.8

kelvins (K)

42
Time

1 hour (h) = 60 minutes (min.) = 3600 seconds (s)

Velocity

1 foot per second (fps) = 0.3048 meter per second (m/s)

Force

1 pound-force (Ibf) = 4.448222 newtons (N)

Pressure

1 pound-force per square inch (psi) = 6894.757 pascals (Pa)

6.894757 kilopascals (kPa)

.006894757 megapascal

(MPa)

1 inch of water column at 60* F = 248.84 pascals (Pa)

Volume

1 U.S. liquid gallon (gal.) = 0.003785412 meter^ (m^)

3.785412 liters (l)

Flow Rate

1 U.S. gallon per minute (gpm) = 0.0000630902

meter ^/second (m^/s)

= 63.0902 centimeters^/

second (cm^/s) = 0.0630902 liters/second

(l's)

1 cubic foot per second (cfs) = 0.028316585 meters/second

(mVs)

= 28.31685 liters/second (L/s)

6.3 Acknowl edgemen t s

The authors wish to acknowledge significant support from the

following individuals at the Center for Building Technology during

this investigation:

1. Hot water cycling test assembly fabrication, erection,

repair, and test-data gathering: J. T. Cohen and M. Martin.

2. Hot water cycling test data gathering: M. J. Orloski.

43
G^c/sherUn'

suggestions, and review: J. h. Snell and

Data reduction and analysis: Y.M. Chang.

44
NBS-114A (REV. 7-73)

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. WBSIR 77- 1261

2. Gov't Accession

No.

3. Recipient's Accession No.

4. TITl,n: AND SUBTITLE

Laboratory Tests of Thermoplastic Piping Assemblies

Subjected to Water Hammer and Intermittent Hot Water Flow

5. Publication Date

6. Performing Organization Code

7 AU'rHOR(S) Daniel E. Rorrer, James R. Shaver, and Robert S.Wyl

8. Performing Organ. Report No. Y

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Taslc/Work Unit No. I+62UI9O

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

Final

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less (actual summary ol most si^iticant information. If document includes a significant

bibliography or literature survey, mention it here.) Evaluation procedures are described that were used at the National Bureau of

Standards (NBS) for simulating the long-term effects of water hammer (shock pressure)

and cyclic hot water flow (thermal cycling) on chlorinated polyvinyl (CPVC)

thermoplastic pressure piping assemblies. Also included are the procedures used to

study the effects of thermal cycling of two (2) polyvinyl chloride (PVC) thermoplastic

drainage stack assemblies. The results obtained using these test procedures are presented and, in addition, related work of other investigators is briefly reviewed.

The shock pressure results show that a fatigue life curve can be established for

CPVC as a function of temperature and pressure. As the temperature is decreased the

number of shock pressure applications necessary to produce failure increases. An

estimated use -life of at least 50 years was indicated at the maximum test temperature

of 180 F (82° C) with pressures of 150 psi (1034 kPa)

With intermittent hot water flow all test assemblies were performing satisfactorilAr when the test was terminated after more than 1500 cycles had been completed.

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)

Intermittent hot water exposure tests of thermoplastic pipe; pressure shock in thermoplastic pipe; water hammer in thermoplastic pipe.

18. AVAILABILITY ^Unlimited

I I For Official Distribution. Do Not Release to NTIS

[ ' Order From Sup. of Doc, U.S. Government Printing Office

' Washington, D.C. 20402, SD Cat. No. CH

|yJ Order From National Technical Information Service (NTIS) ^

Springfield, Virginia 22151

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