Pipeline Operation & Maintenance: A Practical Approach, Second Edition
1 Elements of Pipeline Operation and Maintenance
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Buried pipelines transport large quantities of a product from the source of supply to the marketplace. Almost 70% of petroleum liquid products are transported by pipelines (Fig. 1.1; AOPL, 2000). Statistically they provide the safest form of transportation. In 1998, total fatality in the United States amounted to 0.027 × 10−3 % in comparison to all other form of transportation and they are equally as good worldwide.
The first oil pipeline in North America, which measured 175 km (109 mi) in length and 152 mm (6 in.) in diameter, was laid from Bradford to Allentown, Pennsylvania, in 1879. Since the late 1920s, virtually all oil and gas pipelines have been made of welded steel. Although the first cross-country pipeline that connected some major cities was laid in 1930, it was not until World War II that large-scale pipelines were installed. In the 1960s, larger-diameter pipelines ranging from 813 to 1,016 mm (32 to 40 in.) were built. In 1967 the first long-distance, large-diameter, cross-border, high-pressure pipeline made of high-grade steel was built. The Iranian Gas Trunk Line I was constructed to Azerbaijan—it consisted of NPS 48/ NPS 42 pipe, grade 448 MPa (X-65). Discovery of oil on Alaska's North Slope resulted in the construction of the largest northern pipeline, the Trans-Alaska Pipeline System (TAPS), with a 1,219-mm- (48-in.-) diameter and 1,287-km (800-mile) length. The line was commissioned in 1979.
The purpose of natural gas and crude gathering and transmission pipelines is similar (Thompson 2004), however, the operating conditions and equipment are different. High-pressure gas transmission pipelines use compressors and are connected to low-pressure gas distribution systems through the “city gate” valving and the metering station. This allows the delivery of natural gas to the consumers via small-diameter, low-pressure lines. Natural gas is often treated in scrubbers or filters to ensure that it is dry prior to distribution. Compressibility of natural gas allows for line-packing and this allows volume delivery swings through the use of the pipeline as a storage facility. Gases from different sources of supply meeting acceptable gas quality specifications are mixed and deliveries are based on contractual requirement—firm or interruptible. Gas pipeline operation is generally managed by balancing supplies and deliveries within the contractual arrangements while optimizing the line-pack and compression fuel within a gas network.