Fracture Analysis on Bolts Used for Valve of Gas-hold Spheric Tank

The bolts used for valve of gas-hold spheric tank were fractured abnormally in service. The fracture reason was analyzed by means of macroscopic observation, analysis by scanning electronic microscope and energy spectrum, metallographic examination and so on. The results showed that stress corrosion cracking was happened because of low stress and environmental corrosion. The cracking reason was that many high chrome carbonide precipitated at grain boundary which induced the reduction of chrome content and corrosion resistance of grain boundary. It could be solved by improving environmental condition and stabilizing treatment to the material.