Residual stress analysis in multi-pass underwater wet welded X80 pipeline steel

Underwater wet welding of X80 pipeline steel was performed using different welding currents. Onshore dry welding with welding current of 175 A was also implemented for comparison of underwater wet welded specimens. Influence of welding current on distribution of microstructure, hardness, temperature and residual stress was obtained. The results show that microstructure in underwater welded joints is different from that in onshore welded joints with the same welding current, with weld metal exhibiting a structure of proeutectoid ferrite, granular bainite, lath bainite and acicular ferrite, and coarse grained heat affected zone exhibiting a structure of predominant lath bainite and small amount of granular bainite. Underwater wet welded joint exhibits higher hardness, cooling speed and residual stress level compared to terrestrial welded joint with the same welding current. The residual stress levels in underwater wet welded joints are high. In the current range from 175 to 205 A, the amount of ferrite side plate and acicular ferrite in weld metal increases with increasing welding current. However, the maximum hardness, peak equivalent residual stress and peak longitudinal stress decrease moderately.