What are the cooling methods for large-diameter steel pipes?

Release date:

2021-08-16

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Steel Pipe Knowledge

Large-diameter steel pipes refer to those with an outer diameter of 1,000 mm or greater. Large-diameter seamless steel pipes are manufactured by piercing a steel ingot or solid billet, followed by hot rolling, cold rolling, or cold drawing.

　　 Large-diameter steel pipe It refers to steel pipes with an outer diameter of 1,000 mm or greater. Large-diameter seamless steel pipes are manufactured by piercing steel ingots or solid billets, followed by hot rolling, cold rolling, or cold drawing.

　　1. Chain-type cooling bed. In the past, simple chain-type cooling beds were commonly used due to their straightforward design and low cost. However, large-diameter steel pipes were prone to bending caused by chain misalignment, and they could not be smoothly transferred from the input roller table onto the cooling bed. Consequently, such systems are now rarely employed.

　　2. Step‑by‑step cooling bed. This cooling bed consists of a stepping beam and a fixed beam. After cooling, the large‑diameter steel pipes are supported by the stepping beam, advanced by a predetermined distance, and then placed into the toothed grooves of the fixed beam. By appropriately adjusting the frame’s stroke, the large‑diameter steel pipes can be rolled twice with each step, achieving the effect of straightening them. At present, nearly all newly built pipe‑rolling mills employ a step‑type frame cooling bed.

　　3. Spiral cooling bed. This type of cooling bed cools large-diameter steel pipes by using the helical flights on a screw to propel them forward. As the screw rotates, the pipes not only experience an axial thrust but also a lateral force; consequently, while advancing, they also undergo lateral movement, yet their net motion remains purely forward.

　　The faster the cooling rate and the higher the carbon content and alloying element levels, the greater the non‑uniform plastic deformation induced by thermal stresses during cooling, and the larger the residual stresses that develop subsequently. On the other hand, due to microstructural changes occurring during heat treatment—specifically, the transformation of austenite to martensite—the increase in specific volume is accompanied by an expansion of the workpiece. The net effect of these microstructural stress variations is tensile stress on the surface and compressive stress in the core, which is precisely the opposite of the thermal stresses.

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