In production of rectangular steel pipe , may meet the problem that the tube blank has delamination. To prevent this defect, we should take some measure to prevent this, as follows:

(1) Optimize the cooling time: optimize the cooling process of the rectangular steel pipe slab, specially for the stacking temperature and stacking duration. If the rolled steel plate thickness≤80mm, the residence time in the cooling bed shall not over 5 minutes after the steel plate hot straightened. Steel plates with a thickness >80mm can be appropriately extended to 10 mints to ensure that the temperature of the steel plates is controlled above 500℃ before stacking. The cooling time for steel plate thickness ≤50mm is 12h; the cooling time for steel plate thickness >50mm is 24h, and it is strictly forbidden to unstack and finish in advance.

(2) Optimal control the cooling process: The appearance of bainite in the rectangular steel pipe blanks is caused by the excessive cooling rate. When the cooling rate is reduced to 3-5°C/s, the segregation zone in the core of the steel plate no longer has a bainite structure and forms a conventional pearlite structure. The structural stress of the segregation zone in the center of the slab was significantly reduced after controlled cooling process, and the microcracks caused by the structural stress will reduced.

(3) Centralized furnace loading systemIn actual production

The length and width of the rolled steel plate are quite different. If the stacking of the steel plate is not neat when the steel plate is slowly cooled, it will cause the inspection of the edge of the ultra-wide plate or the inspection of the head of the ultra-long plate to fail. Through the establishment of a centralized furnace system, centralized furnaces with similar length and width of rolled steel plates are arranged to ensure the neat stacking of subsequent steel plates. When necessary, the rectangular tube slab is wrapped with asbestos cloth to enhance the heat preservation effect.