What are the common causes of elbow cracking

What are the common causes of elbow cracking

The reason for the cracking of the elbow is residual stress. The residual stress of the elbow, in addition to the operational stress caused by the load, is the residual stress that occurs during the manufacturing process. Under the effects of internal pressure, thermal stress, welding residual stress, etc., the bent pipe of the casing heat exchanger will have horizontal tensile stress conditions.

Corrosive environment. The medium inside the casing heat exchanger pipeline is titanium tetrachloride liquid, which also contains chlorides such as iron chloride and sodium chloride. Due to the lack of blowing and discharging equipment in the casing heat exchanger, air and water droplets enter the pipeline during long-term parking, causing the collection of titanium tetrachloride in the pipeline to hydrolyze and block the pipeline. Additionally, the presence of chloride ions in the chloride reduces the ability of the data, leading to accelerated corrosion.

The data of the casing heat exchanger pipeline is 1Cr18Ni9Ti, which easily undergoes stress corrosion in a chloride ion environment and generally exhibits transgranular cracking. The control measure is to use stress corrosion resistant materials. In recent years, various stress corrosion resistant stainless steels have been developed, including high-purity austenitic chromium nickel steel, high silicon austenitic chromium nickel steel, high chromium ferrite steel, and ferrite austenite dual phase steel.

Among them, ferrite austenite dual phase steel is the best choice. After the stabilization treatment after solid solution, some stress can also significantly improve the data's resistance to chloride cracking. However, when considering the use of this partial stress method, various issues that may arise from sensitization should be well balanced.