GAS Pipeline Leakage in Urban Subsurface Soil

Studies carried out for a natural gas distribution company are presented, in which the causes that led to a leakage in a 4“elbow are determined. The damage was detected in a tract under a highway; a major erosive process by solid particles from the outside was found during excavation. This erosive process, however, was not the cause of the failure, but a consequence of a gas leak from a through crack in the circumferential weld. The crack at the root toe of the weld propagated through the heat affected zone (HAZ) of the elbow. It was found that the chemical composition of the elbow did not match specification, high carbon equivalent contributed to brittleness in the HAZ. The failure is attributed to bending loads due to ground settlements and traffic of heavy vehicles on top of the right of way, during highway construction and repair.