Abstract: Evaluation principle and grading method on spiral seam defects of pipeline are described. On the basis of Grade 1A of Code BS 7910, preliminary failure evaluation method of spiral seam defects of pipeline is proposed, and applied calculation is conducted on UT data acquired from Lingyuan-Xinmiao pipeline section in Taqing-Tieling Oil Pipeline. Evaluation results about fracture failure and plastic collapse failure of spiral seam defects of pipeline display that some flaws in pipes detected are not safe when an internal pressure is greater than 4.5 MPa. It is concluded that the preliminary failure evaluation provides a useful outcome for reference in making decision of inspection, integrity assessment and repair of spiral seam pipeline, and hence is a step of fundamental importance and practical significance before more accurate data become available for higher grade assessment.