Experimental Residual Stress Investigation of Weld Joints Fabricated at a Close Proximity in S420 Structural Steel

Abstract

There is a lack of quantitative data regarding the determination of minimum distances between weld joints in offshore structures. Existing welding standards, codes and specifications provide recommendations for minimum distances between two adjacent weld joints. The issue arises when violations of the minimum recommendations are discovered in the field or need to be exceeded during construction. This paper is a continuation on a previous paper by the same authors, where the focus was to study the mechanical and material properties of welds in close proximity. The interest in this paper is to study the residual stresses that appear during the welding process, where metal undergoes heating and cooling cycles. This process induces significant levels of residual stresses, leading to increased fatigue failure potential during the operational phase of the structural elements. The measurements were obtained by using ultrasound measurement technique. The results were later verified using X-ray Diffraction and Incremental Centre-Hole Drilling. The ultrasound measurement technique detected a distinct change in residual stresses in the weld joints, with max peaks in the weld centre line. One interesting observation from the Incremental Centre-Hole Drilling measurement in one of the as-welded specimens weld joints was that the longitudinal residual stress was in tension while the transverse direction was in compression, which was also shown in the ultrasonic measurement. In the future, a contour plot measurement would be useful to confirm the results. Another interesting observation was the high compression stresses induced locally on the specimen’s surface likely due to manual grinding with abrasive paper. The outcome of this specific experimental setup can provide a baseline for performing further investigations.