Physical and chemical analysis: First, the chemical composition analysis of the cracked flange was stopped, and the analysis result indicated that the chemical composition of the stainless steel flange and the welding data conformed to the relevant specification requirements. The Brinell hardness of the flange neck surface and the sealing surface are respectively stopped, and the Brinell hardness value meets the requirements. Under the premise that the chemical composition of the material is qualified, the pipeline device meets the technical requirements, the hardness test is qualified, and the pressure test operation standard, the pipeline flange cracks during the pressure test process, clarifying the defects and the internal organization of the flange or other unknowns The elements are related.
Analysis of the nature of the crack. The appearance of the crack was cut off the leaking flange from the pipe. Macro inspection of the flange was carried out. It was found that there were cracks on the inside and outside of the flange. The length was 3mm and the width was 0.5mm. Rust stains are produced; more cracks are also found on the inside and outside of the flange bolt holes.
There are many non-metallic inclusions found on the flange sealing surface and other locations, and individual non-metallic inclusions are scattered on the flange sealing surface to form small pits. The pit is 2.0mm in size and 0.8mm in size. There are pits on the edge. Tiny cracks visible to the naked eye. On-site macro inspection of other austenitic stainless steel flanges of the same batch was carried out.
Many flanges have different levels of defects, and some flanges have obvious cracks visible to the naked eye. The macro inspection results further indicate that the butt-welded flange and flange leakage are related to the flange itself. In order to further explore the true cause of flange leakage, the profile crack morphology was randomly selected from the same manufacturer and batch.