According to 49 CFR 192.1009, a gas distribution operator must report, every year, information related to failure of compression couplings; an ongoing problem. In February 2010, at a meeting with
EGW Utilities of Dallas, PLCS was alerted to the fact that there had been a number of serious incidents in Texas where steel gas pipes had pulled out of compression and bolted couplings causing major gas escapes. As a response to those events, the Railroad Commission of Texas, Pipeline Safety Section issued directives that all standard bolted couplings must either be replaced by a "restraint" coupling or a pumpkin welded to the pipe over each coupling. The proposed repair cost would be massive, given the many thousands of these types of couplings that exist in the ground today.
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Work site of PLCS Coupling Restraint System Field Trial in Texas |
Replacing the original coupling is highly impractical and very
expensive, especially if gas flow is to be maintained during the operation. This may require a bypass, large excavations, a number of expensive fittings and disruption to traffic. Usually a coupling can only be removed by taking out a section of pipe and replacing it with two couplings and a spool piece. Welding a pumpkin over the coupling is also very expensive when considering the cost of the certified pipeline welder, the pumpkin, welding equipment and on-site power generation. Not to mention the risk of burning through the pipe, which would be catastrophic, or the rapid cooling of a pipe in service potentially causing heat affected zones and subsequent hydrogen cracking of the area that was welded.
In just under two years, PLCS developed the Coupling Restraint System as a better solution to this problem. The System is a modified version of PLCS's already proven and very successful Dresser Style 90/NORMAC Compression Coupling Encapsulation product.
The installation involves cleaning the pipe by grit blasting down to bare metal, fastening a plastic mold over the coupling and filling it with the super strong Tensile-Max resin, which permanently bonds the coupling and pipe ends together so the pipe will never pullout. Tests at GTI and Laboratory Testing Inc. show the Coupling Restraint System has three times the pullout rating of a standard restraint coupling.
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Completed Repair |
The whole process is easy, takes less than an hour to complete and is an extremely cost-effective method of keeping pipelines together and safe. The Coupling Restraint System brochure, test results and installation video can be viewed on our website at: http://www.plcsusa.com/coupling-restraint-system.html.
Unique Products for the Gas Distribution Engineer
Although cast iron gas mains have been in use for over 100 years, they are still very viable. When iron ages it forms a protective skin that prevents any further deterioration. Cut out a piece of cast iron pipe and look at the pipe wall cross section. You will see that it is usually as good as new under this top surface. Studies have shown that the cast iron pipes presently in use will last at least a further two hundred years. Engineers wish they could confidently say the same about any other type of pipe. The cost of replacing the many thousands of miles of all sizes of cast iron pipes throughout the country would be absolutely prohibitive and in most cases completely unnecessary. 
The problem with cast iron pipes is that there is a potential leakage point at every joint. The changeover to dry natural gas greatly increased the leakage of gas through these joints as it dried out all the joint packings. Some companies fogged with swellants such as monoethylene glycol (MEG) to try to resurrect the elasticity of the joint packings but most companies have done nothing to improve the quality of the joints.