Abstract: This paper analyzes the hidden peril (potential danger) existed in Northeast Oil Pipeline Network resulted from construction, especially the influence of welded seam defects of spiral seam pipes and the defect in circumferential welded seam on the pipeline safety. The author considers that it is difficult to eliminate the "innate" defects of welded seam for the running oil pipeline networks. The views on the technical reform of Northeast Oil Pipeline Networks and effective countermeasures against the hidden peril in the pipeline networks are put forward.