Challenges Involved in Qualifying Butt Weld of Dissimilar Materials and Dissimilar Thicknesses for Subsea Connectors System

Abstract

This paper describes the challenges encountered during qualification of butt welds of dissimilar materials and dissimilar thicknesses for diverless subsea Tie-in-connection systems. These connections are designed for flowlines, umbilical and jumper spools for a temperature range of: -22° to + 135°C, and for a pressure range of 138 bar to 371 bar, and operating at a depth of 240m. To achieve the minimum required strength of the welded joint configuration, tapered weld joint with a taper angle of 14°7' was selected. The specimen could have failed in conventional tensile testing. The problem was overcome by using the as welded geometry for tensile testing. Establishment of technique for performing UT of dissimilar thickness&material weld joint was a challenge. Technique for UT was established by preparing a new reference block of same material and dimensions. For this complex welded joint, special probes were used to perform UT.