Fracture Failure Assessment Analysis and Process Improvement of Vessel Bending Test

Abstract

The high-purity ethylene dichloride (EDC) head tower is an important pressure vessel in the vinyl chloride production process. During the manufacturing process, the bending test of 2 product specimens broke. In this paper, the failure analysis of the bending test fracture of the welding test plate was carried out, and a systematic analysis, including chemical composition, mechanical properties, and microstructure, was carried out. The causes of fracture of welded test plates during the manufacturing process of the head tower were studied. The results show that the incorrect heat treatment process leads to the extension strength, hardness, and impact performance, being lower than the standard requirements. The combined fracture analysis shows that the material is brittle, which makes the welding test board brittle fracture. At the same time, metallographic analysis shows that the steel is tempered. The comprehensive performance of duplex stainless steel in the tempered state is significantly lower than the original solid solution heat treatment performance. Thus, the bending test fracture of the welding test board of the equipment is caused by the improper heat treatment process, resulting in the microstructure and performance of the material not meeting the relevant requirements. According to the cause of the fracture, the heat treatment and welding process are improved. The heat treatment was carried out first, and then the duplex steel was welded to prevent the heat treatment state of the duplex steel supply from changing. Finally, a qualified specimen was obtained.