Fracture Cause of Stainless Steel Nipple in Benzene Hydrogenation Pipe System

The stainless steel nipple fracture in a benzene hydrogenation pipe system was analyzed by means of metallographic microscopy and scanning electron microscopy. The results show that the main reason of the fracture was the severe nitride inclusion in the steel. With the aggregation or chain distribution of such inclusions, when the nipple were under tensile stress, stress concentration was generated on the position where the inclusion is severely distributed, under the impact of wet hydrogen sulfide stress corrosion cracking occurred. Some safety countermeasures were proposed.