Cost-Effective Methods of Reducing Leakage Occurring in Overturns of Liquid-Carrying Cargo Tanks: Overturn Integrity of MC 306-Type Cargo Tanks

摘要

Product retention items on MC 306-type cargo tanks which represent potential leakage points in overturn accidents were identified in pressure tests of 61 cargo tanks at carrier sites and laboratory tests of 119 pressure/vacuum vents. The manhole assembly, loading/unloading venting, and pressure-actuated venting device were identified as primary leakage sources in overturn accidents. Maintenance practices of 10 carriers were surveyed. Most large carriers perform systematic maintenance on their tanks, but small carriers do not. In general, maintenance done on cargo tanks is devoted primarily to vehicular components, and most carriers do not perform adequate maintenance on product retention items. A cargo tank compartment overturn simulator was designed and constructed, then used in 90 degree and 180 degree tests of new and used manhole assemblies and venting devices. These tests identified pressure-actuated venting in filler covers and loading/unloading venting as the primary sources of overturn leakage. Regulation changes were formulated and presented to an industry representation. On the basis of program test results and industry evaluation, changes are recommended to Parts 173, 177, and 178 (49 CFR) to: (1) require leakage checks before tanks are operated, (2) increase frequency and scope of inspections and maintenance, and (3) instill overturn integrity as a construction and maintenance requirement throughout the operating life of MC 306-type tanks.