This invention relates to pipeline repair or hot tapping couplings, and more particularly to a coupling which may be applied to an underwater pipeline and which may be pressure-tested while the pipeline is shut off.
Split couplings have been used for many years to repair above-ground and subsurface pipelines. It was not until the past 10 years that split couplings having gasket seals have been applied to underwater pipelines to repair or hot-tap those pipeines. There are many problems involved in applying couplings to underwater pipelines due to the massiveness of the coupling, the conditions under which the divers must work, and the fact that such pipelines are normally encased in concrete which is cured under almost ideal conditions. Because of the depths, divers can spend only 60 to 80 minutes on the bottom. For 60 minutes at 130 feet, a diver has to decompress for nine minutes at 30 feet and 23 minutes at 20 feet. An additional 75 minutes must be spent in a decompression chamber. After decompressing for almost 2 hours, the diver should wait 12 hours before making another device. For 80 minutes on the bottom, the decompression time is 2 hours and 44 minutes. Furthermore, turbulent weather conditions may stir up the bottom to reduce the visibility to substantially zero. The massiveness of the coupling also contributes to the difficult working conditions.
Because of the foregoing problems, and since good underwater welding is considered only 75 to 85 percent as effective as ordinary welding, bolted-on, self-sealing split couplings have been successfully employed for underwater pipeline repair work. Those couplings include a pair of members each having semicylindrical inner surfaces and a pair of flanges adapted to oppose the flanges of the other member. A gasket continuously extends circumferentially on each semicylindrical surface and along the flanges so that when the coupling is applied to the pipe and the flanges are bolted together, the gasket surrounds the area of the pipe to be repaired or hot-tapped to effectively seal that area. While the seal is adequate and eliminates the necessity for seam welding (although such welding is sometimes done as a precautionary measure), it is generally impossible to test the effectiveness of the seal without pressurizing the line. If the coupling is not properly mated, leaks may occur when the line is pressurized, necessitating inspection and repositioning of the coupling. Furthermore, the coupling cannot be pressure-tested by line pressure which exceeds 80 percent or the like of the average yield strength of the pipe as determined by tensile tests, since such internal pressures would not comply with minimum federal safety standards for liquid pipelines.