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Pigging: benefits boost growth in sewer/water market.

Pipe pigging--propelling a projectile called a "pig" through pipe--has been in use for years by owners and operators of petroleum and natural gas pipelines, and is routinely used in the piping systems of chemical and coatings plants, pulp and paper manufacturers, and other industries.

Pigs have many uses which vary widely by industry. Pigs clean pipes of buildup, foreign materials and loose sediment. Pigging can confirm a pipeline's flow integrity, increase carrying capacity, and lower energy costs by reducing the pump pressure required to sustain flow through piping--all benefits that can apply to water and sanitary sewer systems.

Although pigging is not unknown to the public works sector, it is not used with the frequency found in other industries operating piping systems. The reason appears to be a lack of information and concern about problems that could be encountered when using a new, unfamiliar process, believes Spencer Cubage, president of Pipeline Pigging Products, Houston, manufacturer of poly pigs and pigging accessories.

"Despite efforts at utility meetings and conferences such as the American Water Works Association, many water system managers remain unfamiliar with pigging," Cubage says. "Of those who are aware of the pigging process, many municipal managers and operators are concerned about downtime and customer complains while a section of pipe is pigged. Therefore, many may decide to take no action."

Another deterrent is that unlike pipelines in other industries, pipes in most water and sewer systems do not have entry and retrieval fittings to accommodate pigs, and constructing them is at added expense.

Pigging pluses

With the emphasis today on trenchless rehabilitation, using pigging in appropriate situations deserves consideration.

Cubage says that pigging is most appropriate for water lines and force sewer mains. Because pigs are propelled through pipe by pressure and flow volume, pigging is not suited for use in gravity-flow sewer systems. Smaller pipes require high psi and larger diameters need less pressure, but more flow.

Pigging cleans by propelling pigs through sections of pipe. Usually pigs in progressively larger sizes are passed through the system. Pigs are available in a variety of sizes and designs, and it is important to match pig and application.

For utility pigging, Cubage says "poly pigs" constructed of open cell polyurethane foam with several types of external wrappings are used. They are propelled through pipe by pressure and volume of the system's water or sewage flow. High-pressure air should not be used in water and sewer pipes.

Says Cubage: "In raw water transmission mains, the primary reason for pigging is to increase flow rates and lower pump pressures. In water distribution pipes, it is usually a combination of water quality or lack of it. Pigging removes iron, manganese and other minerals that can cause aesthetic and taste problems in potable water mains. In sewer force mains, pigging is almost always to remove flow restrictions."

Cubage describes the basic steps for pigging a section of utility pipe:

* Confirm that there are proper launch and retrieval fittings on each end of the pipeline to be pigged;

* Isolate the line being pigged from the rest of the system;

* Run a flow test to determine flow direction, rate, etc.;

* Run a soft, low density swab type pig first to "prove" the pipeline;

* Pass a series of pigs through the pipe, increasing in diameter, density and abrasives;

* Run a soft, low-density swab-type pig to check pipeline condition; and

* Thoroughly flush the pipeline.

Different requirements

"There are differences in pigging requirements for water and sewer projects because of the many different types of pipe used, including carbon steel, cast iron, ductile iron, PVC, HDPE, concrete-asbestos and concrete reinforced cylinder In nominal pipeline sizes, these various pipe materials can have large differences for the inside diameter. So, sizing pigs properly is very important. Of course, almost always, these water/sewer lines are rated to relatively low pressures such as 150 psi maximum, so proper pig selection and the series of pigs to be used is critical," Cubage said.

Water and sewer system owners and managers that do employ pigging either do the work with their own crews or hire specialist contractors.

One such contractor is Flowmore Services, Houston, sister company of Pipeline Pigging. Flowmore has cleaned more than 3 million linear feet of pipe ranging from 2 to 70 inches and is one of the most experienced contractors in utility pigging.

"Pigging is the fastest, most efficient way to clean miles of piping," says Tim Geohagan, Flowmore manager of field services. "Pigging can remove iron and manganese deposits that have collected over many years in older water systems. Sometimes old cast iron lines will be pigged so that they will carry higher volumes of water and to improve water quality. Sewer force mains are pigged to remove solids, and air pockets which will cause a blockage in a hydraulic line."

Geohagan agrees that lack of knowledge about pigging's benefits and concern that a pig may become stuck in a line or break the pipe are the primary reasons that utilities do not use the procedure more often. He believes as more public works professionals become aware of what pigging will do, more utility projects will come.

"Seeing is believing," says Geohagan. "When officials see what comes out of a potable water or force main after a pigging job and see the difference in flow rates, they are truly amazed."

Cubage agrees. "We expect there to be more and more pigging used in the water/sewer business in the future. Today, many engineering companies are designing pig launchers and traps for water and sewer applications. These are for upcoming, newly installed projects. And, many older systems are being retrofitted for pig launching stations. In the water industry, the word is being spread, so we feel that this industry segment is growing."

He concludes: "I think when water and sewer people look at the benefits that others in their industry are achieving, they may decide to incorporate pigging into future operations. When they experience increasing water quality complaints, low flow volumes, high pumping pressures and other issues, they may decide that pigging can help them, too."


Pigging companies:

Pipeline Pigging Products, (281) 351-6688, or circle reader service number 187

Flowmore, (281) 351-6688, or circle reader service number 188

Inline, (713) 973-0079, or circle reader service number 189
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Title Annotation:Rehabilitation Technology
Author:Griffin, Jeff
Publication:Underground Construction
Date:Jul 1, 2004
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