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原文传递 Safety Effects of Less Prescriptive Requirements for Low-Stress Natural Gas Transmission Pipelines Are Uncertain.

题名：	Safety Effects of Less Prescriptive Requirements for Low-Stress Natural Gas Transmission Pipelines Are Uncertain.
关键词：	pipeline；natural；stress；script；rtai；lines；distribution；ects；ncert；nsmi
摘要：	A network of transmission and distribution pipelines covering more than 2.6 million miles transport the majority of natural gas consumed in the United States. Gas transmission pipelines typically move natural gas across state lines and over long distances, from sources to communities. These pipelines are typically 12 to 42 inches in diameter and can generally operate at pressures up to 72 percent of specified minimum yield strength (SMYS). By contrast, local distribution pipelines generally operate within state boundaries to receive gas from transmission pipelines and distribute it to commercial and residential end users. Local distribution pipelines typically range from less than 0.5 to more than 24 inches in diameter and operate well below 20 percent of SMYS. Connecting the long-distance transmission pipelines to the local distribution pipelines are lower stress transmission pipelines that may transport natural gas for several miles at pressures between 20 and 30 percent of SMYS. The major causes and consequences of accidental releases of gas from pipelines differ for transmission and distribution pipelines. Corrosioneither internal or externalis one of the leading causes of releases from gas transmission pipelines. Given the high pressure of the gas as it is transported through these pipelines, failures can lead to catastrophic ruptures, releasing high volumes of gas that can ignite and explode. For distribution pipelines, in contrast, damage from excavation and other outside forces is the major cause of accidental releases. Distribution pipeline failures are more likely to involve slow leaks with limited volume because the internal gas pressure is much lower than for transmission pipelines. Whatever the cause, however, leaks can lead to gas migrating to and accumulating in buildings, potentially igniting and causing a firewhich could result in injury or death to residents. Natural gas has traveled underground along migration pathways, such as sewer lines, finding an ignition source some distance from the location of the release. Therefore, monitoring pipeline integrity is important to prevent both leaks and ruptures. PHMSA administers a national regulatory program intended to ensure the safe transportation of natural gas and hazardous liquid by pipeline. In general, PHMSA has full responsibility for inspecting interstate pipelines and enforcing regulations pertaining to them, although some states are designated as interstate agents to assist PHMSA.PHMSA also has arrangements with the 48 contiguous states, the District of Columbia, and Puerto Rico to assist with overseeing intrastate pipelines. PHMSA and participating state pipeline safety offices oversee operators compliance with two types of safety requirements: minimum safety standards and a supplemental, risk-based integrity management program. The minimum safety standards generally cover the design, construction, testing, inspection, operation, and maintenance of all pipelines, but generally do not account for differences in the kinds of threats and the degrees of risk that individual pipelines face. By contrast, PHMSAs integrity management program requires operators to periodically9 assess their pipelines to identify threats and mitigate risks to pipeline segments in areas where the consequences of a pipeline failure would be most severe, such as populated areas.
报告类型：	科技报告