RIASSUNTO
ABSTRACT
Pipeline failure data for the Gulf of Mexico are analyzed. Over 125 failures are considered with information primarily from government sources. Data show that failures have increased significantly from 7 in 1969 to over 40 in 1975. Fortunately, contamination levels are actually decreasing on a per failure basis because of pollution safety equipment and regional air reconnaissance. Pipeline failures are divided into four categories for analyses purposes including: (11 corrosion and normal wear, (21 abrasion and fatigue, (3) construction-related mishaps, and (41 sediment movement. Sediment instabilities may be directly or indirectly related to three of the four failure categories. The data show a need for detailed site surveys and stability analyses to improve pipeline performance. Additional improvements will come from the use of pipeline corridors in heavily developed areas but detailed feasibility studies will be needed prior to implementation.
INTRODUCTION
Offshore pipeline mileage has increased substantially the last two decades as development flourishes and at greater distances from land. This is most obvious in the Gulf of Mexico off Louisiana and Texas where heavy development has occurred. Over the last 20 years, pipeline mileage has increased to over 8,000 miles and continues to increase at a rate of several hundred miles per year. Thus, it may be inferred that pipelining is the most cost effective, safest, and preferred method of transporting oil and gas from the continental shelf to land. Worldwide, over 12,000 miles of offshore pipeline are in-place. The present trend is for larger diameter lines with costs often exceeding $1 million/mile. Understandably, as pipeline mileage increases, the problems associated with marine pipelines will increase.
Pipeline design requires consideration of two general performance categories: (1) short-term and (2) long-term stability. Short-term stability is involved with emplacement from a lay barge or some other construction technique where control of pipeline curvature and tension is critical for prevention of buckling.
Because the life of an oil or gas field may often exceed 10 to 20 years, pipelines are also analyzed for potential long-term problems such as corrosion, wave loadings, and anchor or fish trawl damage. Many long term instabilities, however, are not well defined and analyses do not currently exist.
Elaborate pipe handling and diver inspection methods have all but eliminated short-term problems for shallow water facilities and improved deepwater construction methods are undergoing development. By comparison, long-term instabilities are more difficult to define and important because of possible environmental contamination, public criticism, costly repairs and lost production. Improved performance is often anticipated by burial, anchorage, and weighting; but these solutions are not always the final answer.
The objective of this study is to review the available pipeline failure data and examine the causes, distribution, and trends in failures. Although all failure data will be reviewed, primary emphasis is upon site hazards including geotechnical instabilities such as slumping or liquefaction. Analysis of failure data and consequent technological developments will ultimately lead to improved pipeline design and performance.