Study on stress corrosion behavior of 30CrMo steel in different concentrations of chlorine containing thiosulfate solutions
Guo Cheng, Longyu Ren, Yuchen Zhao, Xiong Xiao, Lei Zhang, Zhu Wang, Hongyu Zhou, Wenyue Zheng
Abstract
30CrMo steel is a core material for oil and gas field equipment (e.g., sucker rods, drill pipe joints), but its long-term service in sulfur-containing downhole often causes stress corrosion cracking (SCC) failure. This study systematically elucidates the SCC behavior of 30CrMo steel under H 2 S simulation systems constructed with chloride-containing acidic thiosulfate of different concentrations. Tests showed the corrosion rate exhibited a non-monotonic relationship with thiosulfate concentration, peaking at 0.340 mm/y in 1 × 10 −2 mol/L solution, with a dense FeOOH layer and loose mackinawite layer formed on the surface. Severe pitting (maximum depth 99.73 μm) occurred at 1 × 10 −3 mol/L, accompanied by the highest subsurface hydrogen concentration. Moreover, the SCC mechanism evolved with concentration: low (1 × 10 −4 mol/L) and high (1 × 10 −1 mol/L) dominated by anodic dissolution (AD) and Hydrogen Enhanced Local Plasticity (HELP); intermediate (1 × 10 −3 -1 × 10 −2 mol/L) exhibited significant synergy between AD and Hydrogen Enhanced Decohesion (HEDE). This study revealed thiosulfate concentration’s regulatory effect on 30CrMo steel’s HE-SCC behavior, providing a simple, safe new strategy for service safety assessment of sulfur-containing oil and gas field equipment materials.