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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

 
PVC Pipe and Diesel Exhaust
Posted on May 2, 2016 by John Houle
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The presence of diesel exhaust residue on PVC pipe does not mean that the pipe should be rejected. In fact, if the pipe is intended for non-potable usage, the exhaust deposits are not a cause for concern.

For potable water applications, however, the interior of the pipe should be protected from the exhaust. If exhaust residue is present in an installed water pipe, the resulting odor is difficult to remove and can be detected in the drinking water.

Of course, it is much easier to prevent a problem than it is to fix one after it has occurred. For this reason, the exhaust should be directed away from the pipe or the pipe should be protected by smoke tarps. Pipe producers typically require that truckers provide smoke protection for pipe that might be exposed to exhaust.

Even if the interior of a water pipe becomes stained by exhaust, it is not necessary to reject the pipe. Instead, the pipe should be cleaned before installation.

For more information on diesel exhaust, click here.

PVC Pipe and Diesel Exhaust

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PVC Water and Sewer Pipe - Lead Free
Posted on April 18, 2016 by John Houle
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City of Flint, Michigan

News about lead-poisoning from old service-line piping has been widespread in the media recently. It seems that the City of Flint switched to a different drinking-water source in an attempt to provide lower-cost water to its residents. The change caused unintended consequences, as the more-aggressive chemistry of the new water caused lead to leach from some of the city’s service pipes.

The thoughts and prayers of Uni-Bell staff and member-company personnel are with those who have suffered from this situation. We all hope that a timely and equitable solution will be found to remedy the problems in Flint.

PVC Pipe – No Lead

Occasionally I hear questions asking if lead can leach from PVC pipes. With lead-poisoning now a universal topic of interest in the water community, I decided that this would be the right time to write a technical document on the subject.

The truth is that lead does not leach from PVC pipe because there is no lead used in its manufacture – no lead in its raw materials and no lead in its processing.

For my Tech Brief on PVC pipe and lead, click here.

PVC Water and Sewer Pipe - Lead Free

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Making Sense of Diameter Types for PVC Pipe
Posted on April 4, 2016 by John Houle
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There are many different outside diameter (OD) types used for PVC pipe for various pressure and non-pressure applications. Not only are there several OD types, there are also associated abbreviations to add to the mix.

The topic can be approached in a logical manner by separating the pipe types for each standards organization and end-use application:

  • AWWA pressure pipe
  • ASTM pressure pipe
  • ASTM solid-wall sewer pipe

For a discussion of different OD regimens and their descriptive acronyms, click here to read my Tech Brief.

Making Sense of Diameter Types for PVC Pipe

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Guide for PVC Sewer Fittings and Laterals
Posted on February 22, 2016 by John Houle
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Uni-Bell has recently published a new document titled, Design and Installation Guide – PVC Fittings and Laterals for Solid-Wall PVC Sewer Pipe. The guide provides information on appropriate system design and proper installation of PVC fittings products where solid-wall PVC pipe is used in non-pressure applications.
 
The guide covers fittings that are available for various dimension ratios and outside diameters of PVC pipe through 60-inch. The information on installation practices is intended to help utilities optimize the performance of PVC fittings. Using PVC fittings with PVC pipe enables utilities to construct their sewer-pipe systems from one material – corrosion-proof PVC.
 
Contents include:
  • List of standards applicable for PVC fittings products and installation
  • Suggested specification language
  • Products available: wide assortment of PVC fitting configurations
  • Design guidance: topics such as burial depth, soil compaction, and accommodating pipe movement
  • Installation considerations and recommendation
For a quick overview of what the guide offers, click here to read my Tech Brief.
Guide for PVC Sewer Fittings and Laterals

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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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