The mechanical properties and low-temperature fracture toughness of API 5L X65 offshore pipeline welded joints were studied. Structure Integrity Assessment Procedure (SINTAP) which is internationally the latest and the most influential safety assessment standard was applied to the API 5L X65 pipeline joints with surface flaw (the height and length are respectively 2.2mm and 5mm) at the weld toe. According to the ISO standard BS7448, the fracture toughness of the welded joints were determined with the crack tip opening displacement (CTOD) as parameter at the temperature of 0℃. For the heat affected zone (HAZ) specimens, microstructure analysis was performed to insure that the tip of the crack was located in the coarse grain zone in order to obtain valid and reliable results. The failure lines of analysis level 1 and 3 of the weld were derived from the tensile test results. The results of the assessment show that all assessment points (Lr , Kr) are located within the failure lines of analysis level 1 and 3. So the pipeline structure is safe. This study laid the foundation of application of SINTAP to pipeline structure assessment.