Pipe coupling can be a labor intensive process, requiring specialized workers in the skilled trades.

By Chuck Raymond, Macomb Group

DTE Energy, the Detroit-based generator, transmitter and distributor of energy to 2.1 million customers in Southeastern Michigan, is the state’s largest electric utility. With a system capacity of 11,084 MW, DTE uses coal, natural gas, nuclear fuel, hydroelectric pumped storage and renewable resources to generate its electrical output. DTE’s Monroe Power Plant, located near Lake Erie in Monroe, Mich., is the largest plant of its type in the state and fifth largest in the U.S. according to DTE. The facility, situated on a 1,200 acre site, is comprised of four units and has a capacity of 3,200 MW.

The Monroe plant is in the second of three phases of a $600 million upgrade: the DTE Monroe Energy Scrubber Project, which represents a clean coal commitment for the nearly 40-year old facility. “We are reducing sulfur dioxide (SO2) emissions by installing scrubbers in the power plants,” said Jason Beaubien, DTE major enterprise project start-up manager.

Flue Gas Desulfurization (FGD), commonly referred to as the scrubber, is designed to control 95 percent of SO2 emissions, according to Beaubien. “One Monroe FGD will control 12 percent of the forecasted fleet SO2 emissions,” he said. Two scrubbers are to be brought online in Phase II. In Phase I, which was completed in 2009, two FGD scrubbers went online.

The U.S. Environmental Protection Agency has placed a high priority on greatly reducing SO2 emissions. When gaseous emissions combine with water, they form a dilute aqueous solution of sulfurous acid, which can easily oxidize in the atmosphere to become sulfuric acid (H2SO4). The EPA has long warned that dilute H2SO4 is a major component of acid rain. Given the agency’s intense scrutiny on reducing such emissions from coal-fired plants, DTE also places a high priority on completing its initiative on time.

The challenge for piping contractors

Installation represents a major problem for contractors who are responsible for $1.5 million worth of fiberglass piping. Project managers and contractors generally prefer fiberglass or FRP piping instead of steel for the FGDs. The reason is resistance to corrosion. “FRP piping is the preferred material based on the high chlorides, abrasive qualities of the slurry, and cost,” Beaubien said, adding that alloy piping was not considered because the cost would be considerably higher than with FRP piping.

Chemicals that run through the pipes are high in corrosive properties. This is a problem for steel, which is far more susceptible to corrosion than is fiberglass. Sealing the latter, however, is another matter. Just how challenging that project could be became painfully clear during the first phase, which was implemented during the height of the winter season. Fiberglass piping has unique coupling and connection issues. It is difficult to seal in the cold and the task becomes more onerous when there is moisture in the air.

Beaubien said the previous project was challenged by suspect field joints that failed due to environmental conditions during the joint fusion process in the construction phase. “The fusion process of the FRP joints requires a controlled environment which was difficult to obtain at times with the elements found near Lake Erie in the winter months,” the manager said. Beaubien said that later during commissioning, DTE Energy experienced some joint failures, particularly with field joints.

“We didn’t have couplings on the previous build, so the field joints were wrapped with layers of fiberglass,” Beaubien said. It was here that the piping contractor ran into trouble

The trouble with curing

The use of the curing process for coupling and sealing pipes has been left fundamentally unchanged through the years. Most pipe joints require resin applied to the joint that then must be cured. The surface resin is cured with heat applied either through a catalyst or externally, and the coupling cannot be disturbed for as much as two days, perhaps even longer depending on weather conditions. Delays can obviously jeopardize the project timeline. According to Marc Robertson, power generation specialist for Victaulic, a developer and manufacturer of mechanical pipe joining systems, the process is too time consuming.

“It’s all very labor intensive and you might need to hire specific people in the trades who are familiar with these specialties to complete the process,” Robertson said. He noted that fiberglass piping contractors face other issues such as the possible need for additional curing with a heat blanket and greater protection from the elements. “Worse yet, you may have to completely tear it out and start over if any leaks are detected during testing,” Robertson said. “It means that everything has to be dried out and reworked.”

One of the piping contractors found that to be the case during Phase I. External methods were insufficient, and heat blankets and even industrial blow dryers did not completely solve or resolve the problems with adhesion. Making matters worse for the contractor, the adhesive, which apparently had not been properly cured, most likely due to the impact of Michigan’s bitter winter on the curing process, tended to peel away. The result: the failure of joints reported by Beaubien resulting in expensive repairs that are bound to impact the contractor’s expenditures.

Finding an alternative

The piping contractor, with assistance from the Macomb Group, a distributor of pipe valves and fittings, sought an alternative coupling method that could stand up to the elements and perhaps eliminate the need for the curing process. What their research discovered was that an aluminum coupling (296A) manufactured by Victaulic could resolve the dual time and connection issues. “We groove pipe and create rigid joints instead of flexible ones that would have bowed or caused other problems to the fiberglass,” said Victaulic’s Robertson. “Fiberglass piping can be easily fractured so we are careful not to add additional stress to the particular groove that we use.” The grooves for the 296A are placed at the end of the pipe.

Time and cost savings occur with the coupling attachment process. A gasket is installed on the outside diameter of the pipe, the housing is placed and fitted over the gasket and the coupling is attached. The company says installation can be conducted in severe weather or even when the piping is submerged. “There is no waiting period and no curing,” Robertson said, adding that the installation process is completed in minutes through the use of a “simple mechanical joint.” The company states there is no special training required to complete the coupling installation.

DTE’s Beaubien agreed that the coupling saved the contractor and the utility a significant amount of time. “During the construction phase, significant man-hours were reduced as the field joints could be assembled in a few minutes versus hours with the wrapped joint method,” Beaubien said. “With hundreds of connections on the spool pieces, the savings in construction were substantial.” The project manager also determined that the joints did not require the special enclosures and scaffold configurations to maintain temperature that wrapped joints would require. “These also reduced costs,” he said.

Results from testing

DTE conducted pressure testing of the piping with the couplings. Beaubien said that DTE’s comprehensive and intensive testing confirmed that the couplings and the piping performance were meeting the utility’s exacting standards. DTE continues to monitor the couplings and their performance. “We fully expect them to be successful,” Beaubien said.

DTE plans to continue use of fiberglass piping with the coupling at another of its locations.

Original article can be found at http://www.power-eng.com/articles/print/volume-117/issue-9/features/coupling-for-fiberglass-an-alternative-to-curing.html