Fatigue and failure of steel of offshore gas pipeline after the laying operation

The presented paper is mainly aimed at estimating the residual lifetime of metal used for the offshore gas pipeline under a low amplitude cyclic load applying S- and J-methods for pipelaying. Taking into account the preliminary effect of deformation on the welded joint and the base material of the pipe, the tests on fatigue have been carried out and physical and mechanical regularities in fatigue failure in offshore gas pipeline materials have been established. The obtained results show that the plasticity and embrittlement of the pipe wall employing S- and J-methods for pipelaying do not practically affect the residual lifetime of metal under low amplitude cyclic loading, but rather exert a significant influence within a high amplitude range under the preliminary deformation process that activates the accumulation of fatigue defects and strain aging. (C) 2016 Politechnika Wroclawska. Published by Elsevier Sp. z o.o. All rights reserved.