Polyamide Pipe Selected to Carry High-Volume Gas to Chemical Plant

August 2015, Vol. 242, No. 8

Special to Pipeline & Gas Journal

PA12, a high-performance polyamide pipe, has found a niche in the oil and gas market, allowing it to enter a realm that has long been dominated by metallic pipe.

VESTAMID® NRG PA12, developed by Germany-based Evonik Corp., can handle extreme stresses, but unlike other thermoplastic pipes, it can also handle high-pressure systems. This expanded capability changes the game when choosing a pipe material for oil and gas transport.

DTE Energy selected it for a compressed natural gas pipeline to connect its new cogeneration power plant on State Route 7 – about five minutes from Marietta, OH – to an industrial chemical manufacturing customer a mile away.

“The job was originally drawn with carbon steel before the engineers specified PA12 on the underground portion because it doesn’t corrode or need cathotic steel protection,” said Timmy Yeater, project manager with Pioneer Pipe.

The cleaner-burning, gas-fired plant now produces steam and electricity for Solvay Specialty Polymers, which was looking for a permanent solution after American Municipal Power closed its coal-powered plant as part of a federal settlement agreement in 2010.

Bridging the Gap

PA12 pipe fills the performance gap between traditional metallic pipe systems and other types of thermoplastic pipe. It is a hydrocarbon-based polymer that is lightweight, flexible and can be coiled in long lengths. This makes transport and jobsite setup easier and reduces the number of connections required.

Unlike metallic pipe, corrosion maintenance and repair costs are eliminated with PA12 pipe. Using PA12 instead of metallic pipe may result in a throughput gain of up to 20% for the same diameter because the surface roughness is less than half that of steel.

PA12 shares many of the same benefits of thermoplastic pipe in terms of durability, corrosion-resistance, resistance to slow crack growth (SCG) and rapid crack growth (RCG), installation efficiency and performance. But its pressure-handling capability of 250 psig allows it to be specified on jobs previously considered unsuitable for a thermoplastic pipe.

PA12 is also resistant to petrochemicals. This was especially important at this location, once the site of a coal plant that deposited fly ash and other wastes in surrounding landfills. A tough material that would not be compromised by underground contamination was needed to traverse the area. PA12 has a 10-year track record in gas pipelines and offshore projects and has been used in motor vehicles for fuel lines and air-brake tubing for decades.

Butt Fusion, Leak-Free Joints

The joining method of PA12 pipe is through the process of butt fusion, which ensured the safety and security of the gas pipeline was given the utmost attention. McElroy of Tulsa, OK has been designing and manufacturing the most extensive line of machines for thermoplastic pipe fusion for the past 60 years.

McElroy’s fusion machines have been designed with mainly polyethylene, fusible PVC and polypropylene in mind. But the emergence of PA12 provided an opportunity to bring their same machines and the reliability of pipe fusion to a new pipe material.

Fusion occurs by heating two pipe ends to a designated temperature, then pressing them together with sufficient force, causing the pipe and fitting to become one solid piece with no leak path. The resulting fusion produces a joint as strong or stronger than the pipe itself.

The fusion process for PA12 is similar to polyethylene fusion. The necessary equipment and processes are the same, but the fusion parameters, including the machine pressures, are slightly different. PA12 fuses at a higher temperature and forms a single-bead joint, instead of a double-bead joint.

Pioneer spent several days making joints on pipe samples and bend testing with technical support from McElroy and Evonik in a successful effort to adapt to the parameters of the fusion process for PA12 pipe.

“After a couple days of practice, we had consistent joints every time we made a weld. It paid off in the end with several craftsmen trained and a quality product installed with zero leaks during testing,” Yeater said.

The Pioneer team operated a TracStar® 28 to fuse the 4-inch PA12 pipe, consistently producing excellent joints. The carriage on the track-mounted vehicle was easily removed, allowing Pioneer’s crew to make fusion joints in the ditch and continue installation from both directions.

PA12 and its joining methods have been tested and comply with ASTM F2785, ISO 22621 and ISO 16486 specifications. For natural gas distribution, it has earned a hydrostatic design basis of 3,150 psi at room temperature and 1,600 psi at 800 degrees C.

Ease of Installation

For the Pioneer crew, the ease of installation was a standout despite the juxtaposition of the jobsite, which presented some challenges that required both open trench and boring methods.

Between the new cogeneration plant and Solvay, the pipeline would traverse steep slopes and bends, extending under a four-lane highway and an earthen dam. While PA12 pipe lent itself efficiently to long straight runs, PA12 fittings were used to make offsets and easy route changes.

“We were able to fabricate the entire length of bore before installation because of the flexibility of PA12 pipe,” Yeater said. “Had we been using carbon steel, we would have had to stop every 20 feet to make a weld and continue pulling, adding days to the installation.”

This allowed for a seamless installation from digging the ditch to testing and backfilling, saving time and money. After final tie-ins were made, the systems were blown down before commissioning. Targets were clean after a day of system cleaning.

“There is no long-term maintenance worries due to corrosion and rust getting into the system. This is a huge plus for the customer,” Yeater said.

The total length of PA12 was 2,000 feet for the underground portion. The length of the carbon steel line that ran aboveground was 2,000 feet. The PA12 pipeline is supplying gas at 200 psig with the ability to handle up to 250 psig.

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