Defects in Fusion Zone of J55 Oil Casing

‌The causes of defects in the fusion zone of J55 petroleum casing mainly include crack defects caused by subcutaneous bubbles at the corners and sides of the continuous casting slab, as well as the expansion of crack defects caused by the user's small pipe diameter and insufficient trimming during pipe making.

After J55 oil casing was produced as ERW casing, the welded pipe failed to pass flaw detection in the heat-affected zone of the fusion line. Through metallographic, scanning electron microscopy and process investigation and analysis, it was found that the crack defects at the edge of the J55 hot-rolled raw plate originated from subcutaneous bubbles at the corners and sides of the continuous casting slab. When users are making pipes, due to the small pipe diameter and insufficient edge trimming, the crack defects on the edges of the hot-rolled original plates have significantly expanded. Therefore, the formation of defects in the fusion zone of J55 oil casing is the result of multiple factors, including quality problems of raw materials and insufficient control during the processing process‌.