Hydrogen Effect on Fracture Toughness of API 5L X70, X65 and X52 Pipeline Steel Welds: An Overview

Steel welds representing three generations of pipeline steel were studied against hydrogen effect, using the fracture toughness parameter J integral which is a measure of the plastic work. The influence of hydrogen on the growth of a partial wall defect is studied and comparisons with the growth of the same defect in air are presented. The tests conducted were three-point bending fracture toughness tests, in air and in a hydrogen environment simulated by electrolysis. Reduction in J0 was observed in all pipeline steel grades as the current density increases, which was more pronounced in the base metal rather than in the heat affected zone. The different microstructures of the welded steels are observed and correlated to the reduction in plasticity. It is concluded that microstructure seems to be the decisive parameter for the selection of a pipeline steel for service in a hydrogen environment.Copyright © 2011 by ASME