What is the reason of stainless steel flange cracking?

　　Firstly, the chemical composition of the cracked stainless steel flange was analyzed. The analysis results showed that the chemical composition of the stainless steel flange and welding data met the requirements of relevant specifications. The neck surface and sealing surface of the stainless steel flanges are Brinell hardness respectively, and the Brinell hardness value meets the requirements. On the premise that the chemical composition of the data is qualified, the pipeline device meets the technical requirements, the hardness test is qualified, and the operation standard of the pressure test, the pipeline stainless steel flange cracks during the pressure test. It is clarified that the defects are related to the internal structure of the stainless steel flange or other unknown elements.

　　The appearance of the leakage stainless steel flange was cut off from the pipeline. The macroscopic inspection of the blind flange showed that there were cracks on the inner and outer surface of the stainless steel flange, with a length of 3mm and a width of 0.5mm. Rust stains were found on the inner and outer surface of the stainless steel flange bolt hole.

　　A number of non-metallic inclusions were found on the stainless steel flange sealing surface and other positions. Some non-metallic inclusions were scattered on the surface of the stainless steel flange sealing surface, forming a small pit with the size of 2.0 mm and the small size of 0.8 mm. There were micro cracks visible to the naked eye at the edge of the pit. On site macro inspection shall be carried out for other austenitic stainless steel flange of the same batch.

　　It is found that there are different levels of defects in many stainless steel flange, and obvious cracks are found on the surface of some stainless steel flange. The macro inspection results further indicate that the leakage of stainless steel flange is related to the stainless steel flange itself. In order to further explore the real cause of stainless steel flange leakage, a random sample from the same manufacturer and the same batch was selected for testing.