Effect of water depth on the microstructure and tensile strength of the 5 G position underwater wet welded low carbon steel

Abstract

Underwater wet welding is widely used to maintenance and repair of offshore engineering equipment construction. Up to now, the research underwater wet welding only is carried out in a laboratory scale with a shallow. So the depth factor is ignored, meanwhile the depth of the water will affect cooling rate and hyrostatic pressure. The cooling rate is usually related with the volume fractions of microstructure and mechanical properties. Therefore, the experiment focused on the microstructures, hardness and tensile strength of low carbon steel welded joints that were welded using welding on air and underwater wet welding under several water depths (2.5 m, 5 m and 10m). The spesimens at underwater wet welding under several water depths 2.5 m, 5 m and 10 m produced the tensile strength 277 MPa, 303 MPa and 313 MPa. The increase depth of water makes the cooling rate increase. With increase the cooling rate, the tensile strength of weld metal increased due to increase volume fraction of acicular ferrite. The fracture surface was investigated by SEM (scanning electron microscope) appear porosity of spesimens weld joint at underwater wet welded due to hydrogen absorbed is very high, so the underwater weld metal are easy fragile.