Abstract: Failure analysis was carried out for crack in the bottom oil extraction line elbow of hydrogen sulfide stripping tower T5001 in hydrorefining unit, which can provide theoretical basis for cracking failure control of similar elbows. By multi-disciplinary analysis methods of material chemical composition analysis, mechanical property test, crack morphology observation, cross section energy spectrum analysis, metallographic test analysis and bending stress finite element analysis, the various factors that cause bending cracking failure were determined. The results show that the mechanical properties and chemical composition of the elbow meet the standards of 304L. The results of fracture morphology, cross section energy spectrum and metallographic test show that there is corrosion in the inner wall of the elbow and S element and Cl element exsit in the cross section, and the crack extends from the inner wall to the outer wall.The finite element analysis of elbow stress shows that the stress level on the inner arc side of the elbow is highest when the elbow is working, which is 24.8 MPa.The double action of circumferential stress, axial stress and Cl^-, Si^- in the working environment of elbow leads to stress corrosion cracking from inner wall. It is suggested to strictly control the chloride ion content of insulation materials, increase the regular cleaning work of elbow and the connected pipeline system and control the working temperature and pressure of the pipeline within the appropriate range to prevent the similar accidents.