PVC Pressure Pipe Endures Over Ten Million Cycles

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detection programs are not necessary in the sectors where the water distribution lines are constructed with PVC pipes. “This fact allows us to concentrate our limited resources where they are most needed, in the sectors built with iron pipe,” states Mr. Perreault, who points out that flushing is also a thing of the past for the PVC sectors.

To this day, the Technical Services officials for the West Infrastructures Division of Quebec City, which includes the Burroughs of SainteFoy-Sillery and Laurentien, are specifying PVC pipes for constructing and rehabilitating its water distribution system. While Mr. Proulx is

the water distribution system as well as the sanitary and storm sewer systems.

A majority of North American cities are recognizing the efficiency and high reliability of PVC pipes by authorizing their use for infrastructure construction. The Burroughs of Sainte-Foy Sillery decision makers have gone one step further in recognizing the superior performance of the PVC material by specifying its sole use in order to promote sustainable development.

In addition to the citizens living in the burroughs, all Quebec City citizens are benefiting from the superior performance of PVC water pipes; their use allows the city engineers to devote their efforts to the sectors

“THIS FACT ALLOWS US TO CONCENTRATE OUR LIMITED RESOURCES WHERE THEY ARE MOST NEEDED, IN THE SECTORS BUILT WITH IRON PIPE” now enjoying a well-deserved retirement, Mr. Perreault is supported by a new technical team, which includes Mr. Donald Desrosiers, P. Eng. Mr. Desrosiers also recognizes the several qualities of PVC pipes that make it a reliable investment for underground infrastructure for

where conventional materials are currently failing due to corrosion, knowing that the PVC sectors will continue to offer their superior level of performance.

At this juncture where all North American

Mr. Perreault (right) was one of the decision makers who laid the groundwork for lasting infrastructure by using PVC for the Burrough of Sainte-Foy. Mr. Desrosiers (left) is a part of the current team that continues the legacy of lasting infrastructure by using PVC for Quebec City’s

cities are struggling to breach the infrastructure gap, which is caused mainly by corrosion, there are solutions available that will allow the building of reliable infrastructure within a sustainable development concept.

The professionals of the Sainte-Foy-Sillery Laurentien Burroughs of Quebec City have shown it is possible. Follow their lead and you will soon be writing one of the most durable chapters of your own city’s history.

PVC Pressure Pipe

Endures Over

Ten Million Cycles

Figure 1: Test Apparatus for cyclic testing. The blue pipe is AWWA C900, DR18, from Phase I. The white pipe is ASTM D2241, SDR41, introduced in Phase II

By Craig Fisher, P.E. Technical Director

N

o, it is not a typographical error. Ten specimens of six-inch, DR 18, AWWA C900 pipe endured

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over 10 million cycles without any failures. Ten Million! That is a one with seven zeros after it: 10,000,000!

The researchers at Utah State University (USU) cycled the DR 18,

which has a Pressure Class of 150 psi, between 185 psi and 235 psi for exactly 10,209,535 cycles. At 18 cycles per minute, it took a total of 394 days and two research phases to finish the testing. The test was stopped without any of

the AWWA C900 specimens failing. The pump and the pressure relief valve did not fare as well.

During the testing, USU failed six pumps and five relief valves in order to log ten million cycles on CONTINUED ON PAGE 10

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9

TABLE 1. TEST PRESSURES Test

Specimen Description

AND

STRESSES

Minimum Pressure

Maximum Pressure

Mean Stress

Stress Amplitude

(psi)

(psi)

(psi)

(psi)

One

DR 18, AWWA C900, PC 150 psi

185

235

1787

213

Two

SDR 41, ASTM D2241, PR 100 psi

82

123

2000

400

Three

SDR 41, ASTM D2241, PR 100 psi

0

154

1500

1500

Four

SDR 41, ASTM D2241, PR 100 psi

56.5

149

2000

900

CONTINUED FROM PAGE 9

the PVC pipe. The test set-up is shown in Figure 1 on page 9. The blue pipe is the AWWA C900 pipe, and the white pipe is sixinch, SDR 41, ASTM D2241 pipe.

This testing was a part of Phase II of USU’s research project on the cyclic capabilities of PVC pressure pipe. In the Spring 2001 edition of the PVC News, we reported on the research results from Phase I and said that more data points would be collected.

Well the data is in, and the results are impressive.

Background

Uni-Bell first contracted with USU in 1999 to re-evaluate the cyclic capabilities of PVC pressure pipe. At the time, there were two competing theories.

UTAH

edition of The Handbook of PVC Pipe: Design and Construction shows Vinson’s theory.) The Europeans had a competing theory that stated the cyclic life was

DURING THE TESTING, STATE UNIVERSITY FAILED SIX

PUMPS

AND FIVE RELIEF VALVES IN ORDER TO LOG TEN MILLION CYCLES ON THE

The first theory was developed

by Vinson and stated that the cyclic life of PVC was a function of peak stress only. (The third

PVC

PIPE .

a function of only the stress amplitude. Dr. Moser completed the first phase of the testing in the summer of 2000 and pub-

Stress Amplitude (psi)

lished his finding in February of 2001. That testing showed that the cyclic life of PVC was a function of two variables - not one.

PVC pipe fatigue is a function of both the mean stress and the stress amplitude. (The fourth edition of the Handbook, published in August of 2001, shows Moser’s 2001 theory.)

Phase I The first phase involved only AWWA C900 pipe. As mentioned earlier, this pipe was cycled from 185 psi to 235 psi, which resulted in an average stress of 1,787 psi and a stress amplitude of 213 psi.

Vinson’s formula predicted failure at 322,000 cycles. After successfully logging 3.5 million cycles, the first phase of testing was concluded and a new cyclic theory for PVC was published. However, Dr. Moser stated that more data points were needed in order to fine-tune the design chart that he developed.

Phase II So in April of 2001, Uni-Bell entered its second contract on this project with USU in order to continue the work begun in Phase I. This time, ASTM D2241 PVC pipe would be subjected to pressures and amplitudes well beyond that recommended in the design standards. Also, the testing on the AWWA C900 pipe would be re-started.

SDR 41, ASTM D2241 pipe, with a Pressure Rating of 100 psi, was selected for the abusive cyclic

Number of Cycles Figure 3: New cyclic design chart updated after collecting extra data points from the second phase of testing.

CONTINUED ON PAGE 19

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The How-To Handbook of PVC Pipe 522 PAGES The only complete reference for those who plan, design, install and operate PVC systems for municipal water mains, sanitary sewer and storm water drainage systems.

If you are planning, or now operate a PVC pressure or non-pressure system, this handbook is a must!

O N L Y Figure 2: The cyclic pressures applied during testing followed a sawtooth pattern.

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(Includes postage and handling for US and Canadian orders.)

Payable in US Funds, Texas Residents add 8.25 percent sales tax.

Plus air mail charges: ❑ Mexico $16/bk ❑ All Other Countries $28/bk

CONTINUED FROM PAGE 10

pressure combinations. Using pipe with a higher dimension ratio allowed higher stresses to be generated in the pipe wall at lower pressures. Generating the same stresses in DR 18 would require a prohibitively expensive pumping system.

Also, the researchers learned in Phase I to expect equipment failures. The extreme pressures take their toll on the equipment, and so, replacement pumps were a large part of the equipment cost in the research budget.

Table 1 on page 10 shows the average pressure and amplitude for the four pressure combinations. The corresponding wall stresses are also listed.

The pattern of cyclic pressure applied was a sawtooth.

The computer screen in Figure 2 (above) displays the pressure wave applied. The minimum and maximum pressures on Test One were regulated to within +/- 5 psi. A more accurate control system was used on Test Two, Three, and Four. Pressures were regulated to within +/- 3 psi. Temperature was 22°C +/- 2 (71.6°F +/- 3.6).

Cyclic Design Graph With the help of the new data points, a fine-tuned design graph is now available. It appears in Figure 3 on page 10.

The chart is a wonderful design tool for engineers involved in turf irrigation or sewer force main design.

Those types of systems sometimes see surges of greater magnitude with greater frequency. We plan a follow-up article that provides a cyclic design example for a force main system.

Mail coupon with your check to: Uni-Bell PVC Pipe Association 2655 Villa Creek Drive, Suite 155 Dallas, Texas 75234 Indicate preferred format: ❑ Hard-Bound ❑ CD-ROM PC Requirements for Electronic Version: • I386, I486, Pentium or Pentium Pro processor-based personal computer • Microsoft Windows 95 or Windows NT 3.51 or later • 8 MB of RAM (16 MB for Windows NT) available to Acrobat Reader • 10 MB of available hard disk space • CD-ROM drive

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