Effect of Water Depth on the Microstructure and Mechanical Properties of SS400 Steel in Underwater Welding

Abstract

The application of underwater welding is for repairing the damage underwater structures and oil pipelines to extend the lifetime of the facilities. Generally, underwater welding studies were performed in shallow depth water. It is important to investigate the properties of the underwater welding joint based on the depth of water in meter scale. In this work, the shielded metal arc welding (SMAW) was used to conduct the welding process of SS400 low carbon steel. The water depth of 2.5 m, 5.0 m, and 10.0 m were evaluated, while the welding electric current were varied in the range from 80 A to 110 A. Underwater welding processes were carried out using the E7016 electrode. Non-destructive and destructive tests were conducted including the X-ray analysis, microstructure investigation, tensile, and hardness tests. The X-ray analysis showed that there were many defects for all underwater welding specimens. The water depth of 2.5 m joint specimens provided the highest tensile strength. It decreased as increasing of water depth level. Stability of welding arc due to the water pressure was the main reason. Tensile strength increased slightly as the welding current increasing due to deeper penetration. For all specimens, the highest hardness was found in the HAZ which was adjacent to the fusion zone.