ABSTRACT

In this paper, the distribution of residual stresses of X80 pipe girth weld was investigated by both experimental measurements and numerical simulations. The incremental hole-drilling method was used to quantify the residual stresses. The distributions of residual stresses at locations near the fusion line on the outer surface and the weld start position on inner surface of the pipe have been measured. Two-dimensional axi-symmetric models have been utilized to simulate the pipe, and the welding procedure was simulated by WeldsimS code, in which the phase transformation phenomenon in steel was considered. Results show that the predicted distribution of residual stresses deviate to some degree from measured results. However, the trends of the distribution are quite similar. The reasons for these deviations are also discussed.

INTRODUCTION

The recent trend of exploring oil and gas in the Arctic region has attracted much research interests due to environmental and safety concerns. The reliability of structures and materials is one of the most important issues to consider. In an ongoing research project, many candidate materials have been investigated for potential utilization in oil and gas transportation. For the pipe materials, X65 and X80 steels are studied. Welding of pipeline is critical issue for safe transportation of oil and gas. There are many topics to be investigated for welding of the pipe, e.g. the weldability, low-temperature fracture toughness of the weld, microstructure evolution as well as residual stresses. Welding residual stresses are unavoidable in the fabrication of pipeline as well as in service. It has been demonstrated that residual stresses have significant influence on the crack-tip constraint (Ren et al., 2009), ductile crack growth resistance (Ren et al., 2010), cleavage fracture behavior (Ren at al., 2011) and the structural integrity. Therefore, for integrity assessments of engineering component, it is important to accurately depict the residual stress field.

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