Fracture Causes of Bolt of Sulfur Recovery Instrument Valve

During routine inspection, a large petrochemical production enterprise found that the bolt of a sulfur recovery instrument valve was fractured. By means of macroscopic observation, chemical composition analysis, metallographic inspection, hardness test and fracture analysis, the reasons for the fracture of bolt were analyzed. The results showed that the solution treatment process of the bolt was not appropriate, so that a chromium-depleted area was formed on both sides of grain boundaries and caused the precipitation of intergranular carbides, resulting in intergranular corrosion. At the same time, the content of nickel and chromium elements in the bolt was relatively low, which made its corrosion resistance low. And service temperature of the bolt was low and did not reach the sensitization temperature. Under the action of corrosive medium, non-sensitized intergranular corrosion of the bolt was aggravated, which eventually led to bolt fracture.