Fracture analysis of the threaded joint of the level gauge in a reabsorption tower

The fracture of the threaded joint of the level gauge in the reabsorption tower has been analyzed. Through the investigation of operational condition, macroscopic examination of the broken threaded joint, chemical composition analysis of the threaded joint material, metallographic examination of the threaded joint and specimens with cracks, mechanical property analysis, microscopic appearance analysis and energy spectrum analysis, the cracking mode can be attributed to Stress Corrosion Cracking (SCC) of austenitic stainless steel caused by the combined action of wet H2S and Cl− in medium. In this case, the material of the broken threaded joint was not 304 stainless steel, but a high Mn substituted Ni steel, beside, the threaded joint produced a lot of induced martensite during large deformation of cold working which greatly increase the sensitivity of SCC, so the material did not meet the requirements was the main factor in this fracture accident.