Fatigue properties of ferrite/bainite dual-phase X80 pipeline steel welded joints

Abstract

Fatigue properties are important parameters for the safety design and security evaluation of pipelines. In this work, fatigue life and fatigue crack propagation of full-thickness X80 pipeline steel joints compared with the base metal (BM) was investigated. Full-thickness BM specimens showed superior fatigue life compared with that of welded joints. The fatigue crack initiation of full-thickness X80 welded joint specimens occurred at the outside weld toe and then grew inward until a fracture was formed. During fatigue crack growth in the heat-affected zone (HAZ), crack growth rate linearly increased with increased ΔK in each HAZ subregion. However, the change rate of fatigue crack growth rate (da/dN) differed among HAZ subregions. This difference was related to the variation in crack path and fracture mode because of the possible microstructural sensitivity of fatigue crack propagation behaviour.

Keywords

X80 steel HAZ Fatigue property Failure mode Microstructure Crack propagation

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