Failure Analysis on Cracking of 304 Stainless Steel Elbow

The 304 stainless steel elbow of a company failed due to circumferential cracks after 5 years of service. The failure causes of the elbow cracks were analyzed by means of macroscopic observation, metallographic examination, scanning electron microscopic analysis, chemical composition analysis, mechanical properties test and intergranular corrosion test. The results show that the cracks of 304 stainless steel elbow were intergranular cracks formed by stress corrosion. The elbow was exposed to air and adhered to the weak corrosion medium produced by rain water and salt for a long time. In addition, the tensile stress on the outer surface of pipe wall caused by oxygen conveyed by pipe and poor intergranular corrosion resistance of the elbow material itself. Finally, the elbow cracked and failed.