What is the reason of stainless steel blind flange cracking?

　　Firstly, the chemical composition of the cracked blind flange was analyzed. The analysis results showed that the chemical composition of the stainless steel blind flange and welding data met the requirements of relevant specifications. The neck surface and sealing surface of the blind 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 blind flange cracks during the pressure test. It is clarified that the defects are related to the internal structure of the blind flange or other unknown elements.

　　The appearance of the leakage blind 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 blind flange, with a length of 3mm and a width of 0.5mm. Rust stains were found on the inner and outer surface of the blind flange bolt hole.

　　A number of non-metallic inclusions were found on the blind flange sealing surface and other positions. Some non-metallic inclusions were scattered on the surface of the blind 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 blind flanges of the same batch.

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