Abstract: In order to evaluate the applicability of the evaluation method of pipeline girth weld defects, the Ramberg-Osgood model parameters were obtained by processing the data of tensile test for different grades of pipeline steel. The failure assessment curves of pipeline steels with different grades based on material properties was established. The stress-strain curves of the girth welds were drawn by the digital image correlation(DIC)technique applying.The failure assessment curves evaluating the girth weld defected pipelines was formed. The research shows that, when the load ratio is less than 0.7, the failure assessment curves of pipeline steels of different grades are basically the same with load ratio increasing.When load ratio is between 0.7 and 1.0, the acceptable zone of failure assessment curve of high grade pipeline steel is larger. In other words, the improvement of pipeline steel grade can promote the safety margin of defected pipelines. The failure assessment curves based on test data can better reflect the performance difference of the material, which should be prior used in the assessment of low matched welded joint of pipeline.

Key words: pipeline, specific material, failure assessment diagram(FAD), girth weld defects, safety assessment