Underwater Wet Welding for HSLA Steels: Chemical Composition, Defects, Microstructures, and Mechanical Properties

The effect of water depth on underwater wet welds was investigated by underwater wet shielded metal-arc welding technique. The microstructures, chemical composition, welding defects, and mechanical properties were studied. The contents of alloying elements decrease, while the oxygen content increases with water depth. Within 55 m depth, the carbon monoxide reaction is controlling the oxygen content which will further control the contents of alloying elements. The columnar microstructures in weld metal obtained at shallow water consist of grain boundary ferrite, side-plate ferrite, and acicular ferrite, while those at depth greater than 11 m exhibit more proeutectoid ferrite due to the loss of alloying elements. Mechanical properties are a strong function of depth owing to the increase in oxidation of alloying elements and porosity. Welds obtained within 11 m show preferable strength, ductility, and toughness. The mechanical properties significantly drop from 11 to 25 m because of the increased porosity and oxidation of alloying elements.