Clear Advantage: Mechanical Contractor uses Transparent PVC Pipe to Cut Dual-containment Costs

An innovative New England mechanical contractor cut installation costs for dual-containment systems that safeguard chemical-processing pipelines in computer and semiconductor manufacturing operations.

In the process, the firm created a piping system that is more secure and functional for the computer manufacturer.

Holden Mechanical Contractors installs process piping and dual-containment systems within a 50-mile radius of its Worcester headquarters. Dual-containment systems consist of an exterior pipe surrounding a supply pipe that carries hazardous chemicals used in the manufacturing process. Dual-containment systems, which are mandated by state safety regulations, must contain a hazardous chemical leak for at least 15 minutes.

Holden recently worked with a computer manufacturer that uses sulfuric acid, hydrochloric acid, hydrogen peroxide and other hazardous chemicals to engrave or etch wafers for its chip-making process. For this application, Holden abandoned traditional white, opaque PVC pipe in favor of transparent Excelon R-4000 rigid PVC pipe from Thermoplastics Inc.


Holden used the pipe in schedule 40 weight because its heat-formability on the job site and compliance with dual-containment regulations made this grade most suitable for the contractor’s needs. Traditional white PVC pipe, by contrast, contains pigments and additives, and doesn’t tolerate reheating and heat-forming.

Heat-formability enabled Holden to heat and configure this clear PVC pipe to the plant layout, thus eliminating more than 90% of couplings and elbows. That reduced the number of potential leak points by up to 50%.

“We discovered how to bend the Excelon pipe largely through trial and error,” says Paul Polewarczyk, Holden’s executive vice president and lead supervisor on dual-containment jobs. “We tried heating it with air, but when we bent it, it would kink. We also tried forcing air into the pipe and bending it, but this caused mushrooming.

“Then one of our employees read up on the early days of pipe fitting and discovered that steel pipe could be bent if it was packed with sand and then heated.”

After packing the PVC pipe with sand, Holden workers heat it to between 150°F and 160°F in a four-foot oven on the job site. They heat it until the PVC begins to appear cloudy, then they place it in a jig to create the proper configuration.

When the pipe cools, it returns to its original clarity. Workers then dump out the sand, blow out the remaining sand with compressed air and swab out the interior. They wrap the pipe, take it to the pre-clean room, wipe it down thoroughly, wrap it up again and install it.

“The fabricating areas we work in are very congested,” Polewarczyk says. “And it’s nearly impossible to go in and lay out a pipe routing and then take it offsite to be formed. With the Excelon pipe the guys are able to go in, measure it and fabricate it just a couple of feet away. That saves us time and money.”

This heat-forming process allows Holden to bend 10-ft. lengths of transparent PVC pipe into configurations that eliminate fittings and couplings. Since each fitting or coupling is a potential leak point, Holden not only improved workplace safety, but also lowered the computer manufacturer’s liability risk and improved overall system integrity.

“We heat the end of the pipe and just swage the ends using a flaring tool,” Polewarczyk says. “In fact, our swaging method is known nationwide. We’ve spoken with people in Texas who saw some photographs of an installation method that was not identified. But, by the way the piping was installed with the swaging, they were able to identify the method as ours.”

Containment Piping

A Holden Mechanical employee installs a transparent PVC pipe for this dual-containment
application where hazardous chemicals are used.

In installing the dual-containment system, Holden matches the size of the outer pipe to the size of the inner pipe. For a 1/4″ inner pipe, for example, the Holden workers use a 1″ outer pipe. For a 1/2″ inner pipe, they use a 2″ outer pipe, and for a l” inner pipe, they will use a 3″ outer pipe.

As an extra safety precaution, Holden installs triple-containment systems over walkways or in areas where employees may be working.

By design, all dual-containment piping is pitched to a low point where a box containing a leak-detection sensor is located. When the sensor detects a liquid, it sets off an alarm. Pipe also is installed around all overflow lines, and half sections are installed as troughs to further prevent leakage.

Seeing is believing

Using a transparent pvc pipe enables Holden Mechanical to preserve the “continuity of sight” in its dual-containment configurations.

“Aesthetically, when you look at the dual-containment system’s configuration, it looks fluid,” Polewarczyk says. “When you have a PVC coupling in there, you have a shoulder where the two pieces butt together. That shoulder represents a catch spot for liquid. But when we swage it, we eliminate a potential leak point and provide for continuous flow.”

Although heat-formability was the primary reason Holden selected Excelon pipe, the computer manufacturer found transparency to be very important once the system started up. Because the piping is transparent, leak sources can be located sooner once the leak alarm sounds. This allows the manufacturer’s safety technicians to fix the primary piping system quicker. That, in turn, leads to a reduced risk of making bad parts when the leak interrupts the controlled flow of each precisely measured chemical. It also means less wasted reagent and fewer production delays overall.

Other industrial end users who work with hazardous chemicals are choosing the transparent PVC pipe for their dual-containment systems, Polewarczyk says. “It’s safer for the employees and the environment, and it can be installed more quickly and economically than conventional PVC piping.”