The stress corrosion susceptibility of SCR welded joints under hydrogen pre-charging
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Abstract
This study shows the influence of hydrogen pre-charging on the stress corrosion cracking (SCC) susceptibility of steel catenary riser (SCR) weld joints made of X65 through microstructural analysis, slow strain rate tensile test (SSRT) , and fracture surface analysis. The results reveal that the fine-grained heat-affected zone (FGHAZ) of the welding joints primarily comprises fine and uniform ferrite (F) and pearlite (P), significantly enhancing the mechanical property of this zone compared to other heat-affected zone . In contrast, the coarse-grained heat-affected zone (CGHAZ) is characterized by large block of proeutectoid ferrite (PF) and M-A constituent, resulting in poor SCC resistance in this area. Although the elastic stage of the stress-strain curve of SSRT sample under various hydrogen pre-charging time nearly coincide, hydrogen pre-charging decreases the tensile strength of the samples. Additionally, in a NaCl solution corrosion environment, the stress corrosion susceptibility coefficient EZ of the samples hydrogen uncharged and after four days of hydrogen pre-charging are 0.67% and 11.14%, respectively; in an H₂S corrosion environment, the stress corrosion susceptibility coefficient EZ values for the samples hydrogen uncharged and after four days of hydrogen pre-charging are 11.96% and 46.38%, respectively. This demonstrate that hydrogen pre-charging reduces the SCC resistance of weld joints in both corrosion environment. The samples undergo ductile fracture in the air environment, while quasi-cleavage fracture predominate in both corrosion environment. Hydrogen pre-charging reduces the material toughness and exacerbates microcracks and hole near the fracture surface, thereby reducing the material's resistance to SCC.
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