August 2010 Vol. 237 No. 8


Polyurethane And Pipeline Pigs Make A Perfect Match

Dick Williamson, Jack Rankin and Larry Payne

Pigs have been squealing in pipelines for decades. A lot has changed, however, since the first modern-day pipeline pigs were introduced in the early 1940s. Many would cite the development in recent years of smart pigs, also called inline inspection (ILI) tools, as the biggest change. These pigs, which use sensors and computers to accurately inspect and analyze pipeline conditions and problems, do represent a vital improvement in the technology.

But you might not realize that a lesser-known breakthrough has made all that possible: the introduction of cast polyurethane as a material for manufacturing pipeline pigs. Let us take a look at how cast polyurethane has helped revolutionize the pipeline pig industry through the years.

The Original Pigs
Although various makeshift instruments had been used to clean pipelines for many years, the first iteration of what today would be called a pig wasn’t developed until 1942 when the War Emergency Pipeline System was built in the United States in response to an urgent wartime need for huge quantities of oil and gasoline on the East Coast to supply that area and the armed forces in Europe.

The 20- and 24-inch pipelines were the first of these large sizes. T.D. Williamson, Inc. (TDW), which today is a global leader in pipeline equipment and services, developed a pipeline scraper capable of effectively removing debris and contaminants in the large-diameter piping system. These original pigs had leather cups, but TDW quickly transitioned to neoprene and nitrile rubber materials. The next big material transition would occur more than 20 years later.

The Trouble With Rubber
After World War II, oil and gas companies around the world accelerated construction of pipelines of widely varied sizes, carrying an increasingly diverse array of materials. Meanwhile, pipeline velocities increased dramatically.

Under these more severe conditions and demands, the pigs’ rubber cups, scrapers and blades began to show too much wear and tear on the job. In many cases, the pigs broke apart before going the full distance and completing their tasks between the launcher and the receiver. In addition, different products in the lines—particularly hydrocarbons—proved to be too harsh for the rubber materials. Pipeline companies and their suppliers knew they needed something tougher to handle the job.
Researching A New Material

In the early 1960s, engineers at TDW embarked on several years of internal research and development at their Tulsa, OK headquarters to find a new material with greater durability and chemical resistance.

Their focus? Cast polyurethane, one of the world’s most versatile, durable raw materials. Polyurethane can be formulated for superior load-bearing capability, abrasion resistance and impact absorption. TDW engineers tried many different polyurethane formulations and tested them with various in-house techniques including a rolling drum covered with sand paper, to simulate the pipeline environment. Their work ultimately produced the first polyurethane pig components: scraper cups and blades.

Field Testing Of New Components
In cooperation with several major pipeline companies, TDW’s field testing found that the polyurethane cups were indeed tougher, outperforming neoprene and nitrile rubber by at least five times and in some cases 20 times. Later, testing also showed that the cleaning efficiency of the polyurethane scraper blades was equal to the previously used wire brushes in most applications, and in some instances superior.

The blades eliminated the bristle breakage and brush “caking” that had been occurring during the pigging process. Test runs of more than 10,000 miles indicated that the new blades had a useful life up to 50% longer than wire brushes. Cleaning the polyurethane blades also proved to be much easier than cleaning the wire brushes. Most of the dirt adhering to the polyurethane blades inside the pipeline drops off when the pig is pulled out, and the remaining debris can then be easily washed away with water.
Greater Durability At Lower Costs

These breakthroughs helped improve pipeline efficiency because, at last, the oil and gas industry could adopt pigging as a regular and reliable operation from one launcher to the next receiver. Word soon spread about the successful field tests of cast polyurethane for pipeline pig components, and it quickly became the material of choice.

In addition to superior abrasion resistance, the new pigs had increased dimensional stability and flexibility, which was ideal for use with multiple pipeline configurations. Perhaps just as important, unlike synthetic rubber—which requires high pressure molding—the polyurethane material is cast through a simpler gravity molding process.

The resulting lower tooling costs and faster turnarounds created further savings and provided increased flexibility in manufacturing a variety of parts and sizes of pigs in limited production runs.
An All-Polyurethane Pig

Into the 1970s, cast polyurethane was used for more and more parts in increasingly sophisticated pigging tools.

For smaller pipeline diameters, many oil and gas companies began switching to all-polyurethane pigs that could be produced as a single mold, as opposed to a metal body with polyurethane cups or other components attached.

The advantage of this approach is that it eliminates the considerable labor cost of both assembling the pig and, later, replacing the cups. With an all-polyurethane pig, workers simply replace the whole tool. Such a benefit is particularly attractive to smaller pipeline operators who need to keep their workers focused on core pipeline operations. The cost advantage of the all-polyurethane pigs applies until larger sizes are needed. There, the lower material cost of steel offsets the additional labor of assembly.

Pigs in 2010 … And Beyond
In the years since polyurethane became the go-to material in pipeline pig manufacturing, the applications and the technology have evolved significantly.

Today, there are utility pigs that clean and separate liquids in the line, pigs that perform special operations such as isolating a pipeline and ILI or “smart” pigs that can quickly, accurately and completely assess pipeline conditions.

Polyurethane’s durability and versatility have enabled all these applications—especially in the case of the smart pigs, where computer equipment wouldn’t be workable in the harsh environments of pipelines without the reliability of components made of such a highly corrosion- and abrasion-resistant material.

In addition, the drive to use smart pigs in more situations has increased the demand for utility cleaning pigs to make pipeline interiors more hospitable to smart pig operations. And cast polyurethane has long been proven to be the best material for these cleaning jobs.

Meanwhile, the science of polyurethane formulation is still advancing. Leading polyurethane material companies continue to develop new formulas that are more resistant to sunlight, heat and humidity. These improvements are helping address the pipeline pigging challenges in tropical and desert climates where developing economies are fueling demand for pipeline construction.

Clearly, pipeline pigging has come a long way with cast polyurethane, and as the formulations get better, so, too, will the results. T.D. Williamson is a member of the Polyurethane Manufacturers Association, a trusted resource for the latest technology, practices and expertise having to do with cast polyurethane—one of the world’s most versatile, durable manufacturing materials.

Dick Williamson is the chairman of the board of TDW and grandson of TDW’s founder. He has nearly 50 years of experience in the industry.

Jack Rankin has spent 45 years with TDW and is the manager of Pigging Solutions.

Larry Payne is the manager of Pigging Solutions Market Development and has 40 years of experience in the industry.

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