Abstract: Structure Integrity Assessment Procedure (SINTAP)-Failure Assessment Diagram (FAD) method was applied to the SAF2205 pipe mismatch welded joints with surface flaw (The height and length are 1.1 mm and 2.5 mm respectively) at the weld toe.The failure lines of analysis level 1 and 2 of weld metal were derived from the tensile test results including the yield and tensile strength and full engineering stress-stain curve.The crack tip opening displacement values were obtained through fracture mechanics tests at -18℃.Assessment results showed that all assessment points were located within the failure lines of analysis level 1 and 2.So the pipeline structure with surface flaw at the weld toe was safe.Critical flaw size was calculated and fatigue life was estimated according to the above assessment results.