Study of Cold Cracking on Offshore Platform Structural Fillet Welds from 440MPa Yield Strength Steel and its Prevention

Abstract

This paper presents a study conducted to evaluate the centerline weld cracking observed on primary structural Node's fillet weld joint connections made of 440MPa Yield Strength Steel using Flux Cored Arc Welding (FCAW) process in the offshore structures during the fabrication and assembly. Non-Destructive Examination (NDE) – Magnetic Particle Inspection (MPI) was selected to inspect the fillet weld joint connections because RT or UT is not practical. Considering the possibility of delayed cracking, fillet welds were inspected using MPI after 3 days of weld completion, and MPI examination has not captured any indication. The significance of cracks observed on these initial MPI examined weld joint connections was noticed by visual inspection after 3 weeks of weld completion, thus, the extent of NDE was conducted and observed the long-delayed cracks, which doubts the possibility of long incubation time of cracking. The laboratory examination of the weld center line crack sample had been performed to acquire the key evidences to verify the damage mechanism as a cold cracking. In this paper, the identification of the major causes of Cold cracking, the discussion of the possible causes of long incubation time, and the optimization of the weld joint design had been studied. It also covers the correction methodology that needs to be adopted to prevent the recurrence.