In the United States alone, the major components of the natural gas system include nearly 450,000 km (280,000 mi) of transmission pipelines, 145,000 km (90,000 mi) of gathering lines, 1,345,000 km (835,000 mi) of distribution mains, and 450,000 km (280,000 mi) of service lines. This pipeline system provides gas to over fifty million customers. The gas transmission industry has an enviable safety record as a result of proper design and construction practices and operating and maintenance procedures. Nearly $2.7 billion per year is spent in the United States on operating and maintenance activities (Eiber et al., 1990). Continuing advances in inspection and monitoring will assist the gas industry in continuing to optimize and improve its operating and maintenance programs.
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