Abstract: The pipe elbow of pre-hydrogenation unit in catalytic reforming unit of a petrochemical company was split. The splitting causes of the elbow were analyzed by means of macroscopic observation, wall thickness measurement, chemical composition analysis, mechanical property test, metallographic examination, fracture morphology analysis, X-ray diffraction analysis and thickness calculation. The results show that the elbow of pre-hydrogenation unit not only had environmental corrosion, but also was scoured by materials and exfoliated corrosion products under the acidic HCl-H₂S-NH₃-H₂O corrosive environment. Corrosion and scour promoted each other, resulted in serious wall thickness thinning of the outer arc side of the elbow, which eventually led to local splitting due to insufficient bearing capacity.