This amendment modifies the restriction on movement of pipelines containing liquefied gases under § 195.424. On June 21, 1971, the Federal Railroad Administrator issued Notice 71-19 (36 FR 12175, June 26, 1971), proposing to delete the requirement in § 195.424(b) for isolation of the line section being moved and substitute a new requirement that continuous flow of the commodity be maintained but at a substantially reduced line pressure. As stated in the notice, isolation of a line section during movement is costly to the industry and may create an unnecessary hazard. When a line section is Isolated, valves upstream and downstream of the section are closed, stopping the flow. of commodity in the section. If a line section so isolated is exposed to the sun, the heat generated can cause the internal line pressure to
rise above the normal operating pressure of the pipeline, resulting in stresses which could be harmfuL On the other hand, continuous flow of commodity in the section
beihg moved will- dissipate added heat from the sun, and the internal line pressure will not rise above the normal operating pressure. In addition to proposing that pipelines containing liquefied gases be moved under flow conditions, the notice also proposed a concomitant reduction in line pressure below that required by § 195.424(a) to provide a further safeguard against accidental escape of the unusually hazardous liquefied gases.