Influence of H₂S Corrosion on Tensile Properties and Fracture Toughness of X80 Pipeline Steel

Tensile and fracture properties of X80 pipeline steel were studied in a mimic petrochemical environment. X80 pipeline steel specimens were firstly exposed to air or H₂S corrosive medium. Then their tensile properties and δ-∆a resistance curves were obtained in experiments. The influence of H₂S corrosion on the X80 pipeline steel’s crack growth resistance curve, fracture toughness, and plastic work loss was analyzed. The comparison between the test results after two pretreatments indicates that there was no significant difference in the X80 pipeline steel’s ultimate tensile strength before and after H₂S corrosion. But fracture elongation, area reduction and fracture toughness varied greatly (a substantial decrease in elongation and reduction of area). The crack growth resistance curve of the specimen in air was obviously higher than the crack growth resistance curve of the corroded one. Under stable crack growth stage, the crack initiation toughness δ _0.2BL of the specimen in air was 0.732 mm, 2.02 times that of the corroded one (0.364 mm). In the case of similar crack growth ∆a, the plastic work required in the crack growing process (U_P) of the specimen in air was 2.29 times that of the H₂S-corroded specimen (\( {U}_P^{\hbox{'}} \) ). H₂S corrosion resulted in a significant reduction of the fracture toughness of X80 pipeline steel. Hence, H₂S corrosion should be avoided in the process of natural gas transportation by pipelines, so as to protect the pipeline steel from toughness degradation.