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TECHNICAL BLOG

Welcome to John’s Blog. Answers to frequently asked questions are periodically posted here. The objective is to share information about PVC pipe with readers as well as with utilities, design engineers and pipe installers. The blog provides the latest information on PVC pipe design, installation, and application for water and wastewater infrastructure projects.

If you are interested in having the response to your question considered for posting, e-mail John at techblog@uni-bell.org

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John Houle: Senior Technical Consultant, PVC Pipe Industry

John Houle holds a Master’s Degree in Civil Engineering from the University of Missouri and an MBA from the University of Oregon. He has more than 25 years of experience in the plastic pipe industry in applications engineering, market development, forensic analysis, technical writing, and standards development. 

John Houle,
Senior Technical Consultant, PVC Pipe Industry

 
DI vs PVC: When “Strength” is a Weakness
Posted on February 3, 2016 by John Houle
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The Ductile Iron Pipe Research Association promotes ductile iron as “stronger” than PVC. While it is true that side-by-side laboratory testing would give the nod to DI, laboratory strength does not always transfer to real life.

A case in point is surge pressures. Ductile iron has a higher tensile modulus of elasticity than PVC, which means that any surges generated in DI pipe will be higher than in PVC pipe.

This tech brief uses the design example in the AWWA C900 PVC pipe standard to compare surges in DR18 PVC pipe and PC350 ductile iron pipe. As expected, the DI surges are much higher – so high that:

  • Total pressure in the DI pipe exceeds its allowable pressure capacity
  • System appurtenances might be at risk

Conventional wisdom is turned on its head: “strength” is sometimes a disadvantage.

Click here to read the Tech Brief.

DI vs PVC: When “Strength” is a Weakness

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Reasons Why Water Utilities Choose PVC Pipe
Posted on January 14, 2016 by John Houle
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Water utilities have the choice of several materials for their pipe systems. For more than 50 years, PVC’s share of the municipal water market has increased steadily at the expense of iron and other pressure-pipe materials.

The reasons why so many utilities use PVC include:
• Lower initial cost
• Ease of installation
• Compatibility with existing pipe inventories
• Availability of trenchless options
• Design life of 100+ years

For discussion of these and other reasons for PVC’s growth, click here to read my Tech Brief.

Reasons Why Water Utilities Choose PVC Pipe

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Permeation Explained
Posted on December 16, 2015 by John Houle
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In piping systems, “permeation” is the movement of chemicals through a pipe wall or a gasketed joint. For potable water pipe, permeation is important because there may be adverse effects on the fluid inside the pipe.

Starting in the 1970s, there has been a significant amount of research on permeation. This Tech Brief looks at some of that research, discussing permeation in PVC pipe, in HDPE pipe, and in gasket materials used for PVC pipe joints. Since gasoline is a common contaminant that comes into contact with municipal pressure pipe, there is special emphasis on gasoline permeation.

PVC pipe is well-suited for gasoline-contaminated soils. In contrast, HDPE is not suitable for piping projects where contamination currently exists or may exist in the future.

Click here for my Tech Brief on this subject.

Permeation Explained

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HDPE’s New “High-Strength” Material – What You Need to Know Before You Specify PE4710
Posted on December 11, 2015 by John Houle
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The PE industry has developed a new pressure-pipe material that has been described as “high-strength.” Although the words “high-strength” sound reassuring, the reality is that pipe made from PE4710 is anything but.

The reason is that the new material has the same Hydrostatic Design Basis (HDB) as the earlier-generation PE3608. For both materials, the HDB = 1600 psi per the appropriate standards and test methods. For comparison, PVC’s HDB is 4000 psi.

The obvious question is: how can a PE material be “higher-strength” if its strength is the same?

The answer is that the material can appear to be higher strength if a lower safety factor is used.

One example should suffice: let’s compare Pressure Class 100 psi (PC 100) pipe made from PE3608 and from PE4710. The AWWA C906 standard requires the minimum burst strength to be 365 psi for the lower-strength PE3608. For the new “higher-strength” PE4710 material, the burst strength is only 290 psi. This means the “higher-strength” PE4710 pipe has burst strength 75 psi lower!

The Tech Brief looks at this and three other items that you should be considering as you investigate PE4710. Click here to read.

HDPE’s New “High-Strength” Material – What You Need to Know Before You Specify PE4710

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PVC Pipe: “Loss of Strength” with Time? – No!
Posted on October 22, 2015 by John Houle
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Plastics have a material property that sets them apart from the traditional materials that most engineers studied in school. For traditional materials, there is no distinction between short-term loading and long-term loading – the material responds the same in either case. For plastics, however, there is a significant difference: plastics can handle much higher short-term loads than long-term.

A quick example: AWWA C900 DR18 pipe has a long-term rating of 235 psi, but its short-term rating jumps up to 376 psi. This is equivalent to hoop stresses of 2000 psi and 3200 psi, respectively. For this example, the short-term rating is 60% higher than the long-term rating.

When a log-log plot is made of PVC pipe stress at failure vs. time of load application, the failure points will lie along a line that slopes downward as time increases. This is logical, given the discussion above.

Proponents of non-plastic materials have chosen to use this downward-sloping line as evidence that PVC pipe “loses strength with time” or “degrades over time.” However, this is not the case – the line’s slope merely proves that PVC pipe can withstand higher short-term stresses than long-term stresses.

To read more, click here for the Tech Brief on this subject.

PVC Pipe: “Loss of Strength” with Time? – No!

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PVC Gasketed Pipe Reality: “Leakage” Not Allowed
Posted on September 21, 2015 by John Houle
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Rumors have been circulating that AWWA standards allow gasketed pipe to leak. In fact, some websites for fused HDPE pipe include calculators that show huge “allowable” water-loss quantities based on this misperception.

Nothing could be further from the truth.

The reality is that AWWA standards do not allow pipes to leak. AWWA documents include pressure and leakage tests to verify that newly installed pipelines have proper materials and installation. These documents include what is known as “make-up water” to accommodate variables in testing such as entrapped air, movement of pipeline components, and slight increase in pipe diameter. However, the standards state that leaks discovered during testing must be repaired.

Click here for the Tech Brief on this subject.

PVC Gasketed Pipe Reality: “Leakage” Not Allowed

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PVC VS. POLYPROPYLENE (PP) NON-PRESSURE PIPE FOR SANITARY SEWERS
Posted on June 25, 2015 by John Houle
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Attached is a two-page material comparison sheet that addresses some important issues in sanitary sewer pipe selection. The document also serves as a quick reference for comparing PVC and PP non-pressure pipe. Click here to read.

The long-standing technique for making a decision is to draw a vertical line down the middle of a piece of paper, listing the positives to the left and the negatives to the right. If you follow this process for PVC pipe, you will find the left side filled with positive attributes. Here are a few:

Longevity
PVC has become the material of choice for sanitary sewers because of long-term reliability coupled with low maintenance requirements.

Joint Integrity
PVC joints are designed to be leak-free when tested at 25 feet of head per ASTM D3212. This is a stringent test method that includes testing joints that are deflected both radially and longitudinally to simulate extreme jobsite conditions.

Stringent Post-Installation Acceptance Tests
Low-pressure air testing and deflection-mandrel testing are routinely performed on installed PVC sanitary sewer lines. Because of PVC pipe’s material properties, these tests have proven to provide a high degree of assurance that the installed lines will perform as designed.

I encourage you to compare and contrast the two materials. The conclusion I reached is that PVC’s positive attributes are reasons to keep any unproven pipe material on the sidelines. In this case, I would kick PP to the curb until it has shown itself to be a viable product for the long term.

PVC VS. POLYPROPYLENE (PP) NON-PRESSURE PIPE FOR SANITARY SEWERS

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EPD FOR PVC PIPE - THE REAL DEAL!
Posted on June 8, 2015 by John Houle
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In the sustainability world, many manufacturers claim that their products are “green.” Often the evidence supporting these claims is flimsy at best.

The recently published Environmental Product Declaration (EPD) for PVC pipe does not fall into this category. The document was:

  • Developed in compliance with International Standards Organization (ISO) standards.
  • Certified by NSF Sustainability, a division of NSF International.
  • Based on a Life Cycle Assessment (LCA) developed by Sustainable Solutions Inc. that was reviewed by an independent third-party panel of sustainability experts.

The PVC pipe industry did it right. Other pipe materials should do the same.

Click here to read the PVC pipe EPD.

EPD FOR PVC PIPE - THE REAL DEAL!

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DEFLECTION MANDRELS FOR AWWA C905 PIPE
Posted on May 14, 2015 by John Houle
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External loads usually govern the design of non-pressure pipes. For PVC sewer pipelines, one of the acceptance tests to ensure proper installation has occurred involves pulling a deflection mandrel through the pipe. Product standards for PVC gravity sewer pipes typically provide calculation methods and tables for sizing of these mandrels.


AWWA standards, on the other hand, are intended for pressure applications – hence there are no mandrel discussions, calculation methods, or tables provided.

The Technical Brief “Sizing of Deflection Mandrels for AWWA C905 Pipe” addresses this issue by explaining the calculation method and providing mandrel sizes for 14- to 48-inch CIOD pipe.

To find out more, click here to read the Tech Brief.

DEFLECTION MANDRELS FOR AWWA C905 PIPE

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Transitioning Between Ductile Iron and PVC Pipes
Posted on December 10, 2014 by John Houle
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When it is necessary to transition between PVC and DI pipe, there are several considerations to keep in mind.

First, although both products are made to the same Cast-Iron outside diameter (CIOD) regimen, ductile iron pipe tolerances are much looser than those for PVC pipe. This has an effect on some joining situations.

Second, the geometry of the two products’ spigot ends is very different. This means that inserting PVC bells into DI spigots is easily accomplished, while inserting DI spigots into PVC bells is more problematic.

To find out more, click here to read the Tech Brief.

Transitioning Between Ductile Iron and PVC Pipes

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