Effect on the Microstructure and Mechanical Properties of the Structural Steel Welded in Marine Environment

Abstract

Recently, oil deposits were found in ever deeper waters. In this context, it is important to study the water depth effect on parameters in repair and maintenance operations of pipelines for extraction and/or transportation of crude oil, of which there is limited information in literature. This paper shows a study of the effect of the water depth on the microstructure and mechanical properties in joining structural steel welded in a marine environment in steels with a maximum CE (carbon equivalent) of 0.37 %. Wet welding coupons of steel ASTM A36 were joined by the manual metal arc welding (MMAW) process at depths of 10, 20, 30, and 40 m, using AWS Broco SoftTouch as filler metal (3.17 mm diameter) inside a simulation hyperbaric chamber. Image analysis was applied to welded coupons, with the aim to obtain the phase quantification and porosity as well as mechanical properties. The results show that there is an inverse relationship between the increase in depth at which the welding is performed and the mechanical properties, while the filler metal properties were kept constant. Microstructural changes vary as a function of the depth at which repair-maintenance is performed, with an increase in growing phase shift which is highly undesirable because of their brittleness and hardness.