ABSTRACT

In the United States, offshore production of oil and gas began in the early 1950’s. Today, in the Gulf of Mexico, there are over 17,000 miles of subsea pipelines gathering and carrying oil and gas from offshore wells to platforms and to facilities onshore. Most of these pipelines are regulated by the Office of Pipeline Safety of the U.S. Department of Transportation (under Code of Federal Regulations 49 CFR), and some subsea pipelines are regulated by the Minerals Management Services of the U.S. Department of the Interior (under Code of Federal Regulations 30 CFR). State regulations also apply in certain locations. Because of the potential significance of leaks in offshore pipelines, there are continuous efforts to report, trend and analyze failures. From the investigation of nearly 1000 incidents in the period 1960 to 1990, the following conclusions were reached [NRC]: 49% of offshore pipeline failures are due to corrosion, but these corrosion induced failures have only caused 2% of the pollution and resulted in no fatalities. In contrast, failures from maritime traffic account for only 14% of the failures but have caused 90% of the pollution damage and have resulted in several fatalities. Fatal accidents include the 1987 Sea Chief vessel accident in which the vessel struck an 8” pipeline operating at 480 psi, causing an explosion that killed two. The struck pipeline had been installed in 1968 under a 3 ft cover of sediments, but erosion had removed much of the initial cover and the line was only under 6” of mud at the time of the accident. In another case, in 1989, the Northumberland vessel struck a 16” gas pipeline. The resulting fire killed eleven. The line, installed in 1972 under 8 ft of cover, was uncovered at the time of the accident. Today, depth of burial is closely regulated in zones of Heavy maritime activity. For example, in the U.S., a minimum cover of 3 ft below bottom or 18” below consolidated rock are required in depths shallower than 12 ft. In deep water ports these depths become 6 ft and 3 ft respectively.