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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

 
NEW PVC PRESSURE PIPE TAPPING GUIDE
Posted on June 22, 2016 by John Houle
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The PVC Pipe Association has re-issued its “Tapping Guide.” The new guide includes additional diagrams and photos, as well as expanded text — all in a more logical, readable format. For those unfamiliar with the term, “tapping” refers to drilling a hole into a main-line pipe to attach a branch line. The process is often done with the main line under full pressure, so specialized techniques have been developed to streamline the installation process.

The new guide contains four major sections:

1.     Introduction

2.     Direct tapping

3.     Saddle tapping

4.     Sleeve tapping

Introduction
The introductory section provides general information that applies to all types of PVC pipe taps. Included are time-saving tips such as:

  • Use a fluted bit to allow the cut material to move away from the cutting surface.
  • Ensure that the bit has sufficient length to penetrate the full thickness of the pipe.
  • Check the removed cylindrical coupon to verify that proper techniques were used.

Also included is a section titled “Safety Considerations.”


Direct Tapping
Direct tapping is for sizes up to 1-inch, where the corp stop is screwed directly into the pipe wall. This section describes the proper equipment and techniques to cut a hole through the pipe, to cut threads into the pipe wall, and to install the corp stop — all while the main line is under pressure.

Saddle Tapping
This section is for sizes up to 2-inch, where a corp stop is screwed into a metal saddle that wraps around the pipe. The tap is accomplished by attaching a tapping machine to the corp stop and inserting the cutting bit through the corp stop to cut the hole into the pipe.

Sleeve Tapping
A tapping sleeve is required for all branch lines greater than 2-inch and up to size-on-size. The branch line is joined to the main by a connection at a metal sleeve that wraps around the pipe. The sleeve includes a flange to which to tapping machine is attached to cut the hole in the pipe.

Doing It Right
As with most construction projects, using the correct tools and employing the right techniques pays dividends. Following the recommendations of this guide will go a long way towards optimizing the installation process and preventing any problems when tapping PVC pipe.

Click here for the guide.

NEW PVC PRESSURE PIPE TAPPING GUIDE

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Thrust Forces – Restraint Length Calculator
Posted on June 16, 2016 by John Houle
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Thrust forces are developed in a pressure pipe whenever there is a change in flow. This means that thrust restraint may be required when the pipeline changes direction (for example, at an elbow), changes size (at a reducer), or encounters a stoppage in flow (for example, at a closed valve).

Complicated Design Simplified by EBAA’s Calculator

Thrust-restraint design can be complicated, with as many as eight variables to consider.

Fortunately, EBAA Iron has developed an on-line design tool that makes the engineer’s job easier. The designer simply inputs the variables requested and the calculator provides the length of pipe that must be restrained to control pipe movement. The program also provides an output page that lists all of the design inputs, as well as the resulting thrust force and required restraint length.

For my Tech Brief on EBAA Iron’s on-line calculator for restraining PVC pipe joints, click here.

Thrust Forces – Restraint Length Calculator

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External Joint-Restraint Devices for PVC Pipe
Posted on June 10, 2016 by John Houle
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Thrust forces are developed in a pressure pipe whenever there is a change in flow. When joint restraint is required to accommodate these forces, the most commonly used method is external joint-restraint devices. These devices have been used successfully on PVC pipe for more than 25 years.

For my Tech Brief on external joint-restraint devices for PVC pipe joints, click here.

Typically, a restrained length of pipe is required on both sides of an appurtenance. The length of pipe to be restrained is determined by the design engineer. To restrain that pipe length, pipe-to-fitting restraints (usually MJ) and pipe-to-pipe restraints (bell harness) are usually required.

As usual on pipeline projects, there are methods of installation that provide better results. Tightening of nuts on threaded hardware is a good example. The Tech Brief discusses three types of threaded connection and how to best accomplish them.

External Joint-Restraint Devices for PVC Pipe

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Installation of PVC Pipe into a Mechanical Joint (MJ)
Posted on May 25, 2016 by John Houle
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A “mechanical joint” (MJ) is defined in ASTM Standard D3139 as: “a joint in which a positive seal is achieved when a gasket is compressed by means of a mechanical device.” The MJ connection is very commonly used in North American pressure pipelines and usually is installed without any problems.

Occasionally, however, I hear of projects where there are issues with MJs.

Correct Installation Methods Minimize Problems

As with most construction projects, successful installations occur when tried-and-true methods are used. For any pipeline installation where bolts and nuts are used, it is important to tighten the bolts in the correct order (a “star pattern”) and to tighten the bolts to the correct torque value. In the case of an MJ, failure to follow these simple guidelines can result in leaks or other problems.

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

Installation of PVC Pipe into a Mechanical Joint (MJ)

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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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