Defects of J55 Casing Fusion Zone:
After ERW casing, it was found that the welded pipe in heat affected zone of fusion line was not qualified. Metallographic analysis, scanning electron microscopy and technological research were carried out. The results show that J55 pipe is in fusion line. There is a deep crack defect at the edge of the plate in the heat affected zone. Because of the small diameter of the pipeline and the insufficiency of repairing quantity in the pipeline manufacturing process, the crack defects of the users are obviously enlarged. Cracks on the edge of hot-rolled slab originate from subcutaneous bubbles at the corner and side of casting slab.

J55 oil jacket fusion zone defect:
After the ERW oil jacket, the welded pipe in the heat affected zone of the fusion line was found to be unqualified. Metallographic analysis, scanning electron microscopy and process research were carried out. The results show that the J55 welded pipe is on the fusion line. There is a certain depth of crack defect at the edge of the original plate in the heat affected zone. During the pipe making process, the user has a small pipe diameter and insufficient trimming amount, resulting in a significant increase in crack defects. The crack at the edge of the hot rolled original sheet originates from the corners of the cast slab and the subcutaneous bubbles.

Defects of J55 Casing Fusion Zone:
After ERW casing, it was found that the welded pipe in heat affected zone of fusion line was not qualified. Metallographic analysis, scanning electron microscopy and technological research were carried out. The results show that J55 pipe is in fusion line. There is a deep crack defect at the edge of the plate in the heat affected zone. Because of the small diameter of the pipeline and the insufficiency of repairing quantity in the pipeline manufacturing process, the crack defects of the users are obviously enlarged. Cracks on the edge of hot-rolled slab originate from subcutaneous bubbles at the corner and side of casting slab.