Study on Sulfide Stress Corrosion Cracking Susceptibility of 20# Steel Weld Joints in H2S-Rich Environments

This study aims to clarify the influence of H₂S concentration and temperature on the sulfide stress corrosion cracking (SSCC) susceptibility of 20# steel weld joints. 20# steel is a commonly selected pipe material for ground gas pipelines, and there is a risk of welds cracking after years of service. The selection of a corrosive environment is based on the working conditions of high-sulfur oil fields on site. Slow strain rate tensile (SSRT) tests were conducted under simulated high-sulfur gathering and transportation conditions across varying temperatures and H₂S concentrations. The mechanical properties, SSCC susceptibility, fracture morphology, and elemental composition of fracture surfaces were systematically analyzed. As H₂S concentration increased (5%, 7.5%, 10%) and temperature decreased (30-60 °C), the elongation after fracture and the reduction in area of 20# steel decreased, while the yield strength and SSCC susceptibility increased. The H₂S concentration range of 0-5% represented a critical sensitivity interval for the material, where elongation after fracture decreased by up to 74%. Within the 5-10% H₂S range, elongation decreased by only 2.11%, indicating a slowing trend of fracture toughness deterioration, though SSCC susceptibility still increased by 12%. Increasing the temperature from 30 °C to 60 °C reduced SSCC susceptibility by approximately 30%, confirming higher susceptibility at lower temperatures. Temperature exerts a lesser influence on material performance than H₂S concentration. Also, 20# steel remains within the SSCC brittle fracture sensitivity zone in sulfur-containing environments, necessitating strict quality control to avoid defects and stress concentrations. In high-sulfur environments (H₂S > 5%), further increases in H₂S concentration have a diminished effect on cracking susceptibility.