Causes of crack formation in 95S grade anti-hydrogen sulfide corrosion seamless steel pipes

During the production process of a certain 95S grade anti-hydrogen sulfide corrosion seamless steel pipe, cracks appeared on its outer surface. A series of methods including macroscopic observation, metallographic examination, scanning electron microscopy combined with energy dispersive spectroscopy, transmission electron microscopy analysis, and electron probe microanalysis were adopted to analyze the causes of crack formation. The results show that during the production of continuous casting square billets, due to the segregation of manganese (Mn) and the excessively high cooling rate in the mold, a columnar crystal structure formed at the corners of the square billets. During the rolling of square billets into round billets, cracks generated on the surface, and these cracks further propagated during the seamless steel pipe rolling process, eventually forming crack defects on the outer surface of the steel pipe. Based on the generation mechanism of the outer surface cracks, technicians inspected and adjusted the continuous casting mold, and tracked the production of billets and steel pipes after the adjustment. The surface quality of the products was significantly improved, and the yield and production efficiency of the 95S grade anti-hydrogen sulfide corrosion seamless steel pipe were also increased accordingly.