Differences between Hot-rolled Seamless Steel Pipe and Cold-rolled Seamless Steel Pipe

Hot-rolled Seamless Steel Pipe vs. Cold-rolled Seamless Steel Pipe:

1. In terms of processing technology

Hot rolling is hot working, and cold drawing is cold working. Hot rolling is rolling above the recrystallization temperature, and cold rolling is rolling below the recrystallization temperature.

2. Distinguish from appearance

Cold-rolled seamless steel pipe has a bright surface, and the diameter is smaller than that of hot-rolled seamless steel pipe. The diameter of hot-rolled seamless steel pipe is larger than that of cold-rolled seamless steel pipe, and the surface has obvious oxide scale or red rust.

3. In terms of accuracy

The precision of cold-rolled seamless steel pipe is higher than that of hot-rolled seamless steel pipe, and the price is also higher than that of hot-rolled seamless steel pipe.

4. Distinguish from the use

Hot-rolled steel pipe is used in places where the size requirements are not high, such as fluid transportation and mechanical structure, and cold-rolled steel pipe is used in places with high requirements such as precision instruments, hydraulic systems, and pneumatics. In terms of wall thickness, cold-drawn seamless pipes are more uniform than hot-rolled seamless pipes.

Advantages and disadvantages of hot-rolled seamless pipe:

Advantage: 
Hot rolling can destroy the casting structure of the ingot, refine the grain of the steel, and eliminate the defects of the microstructure, so that the steel structure is dense and the mechanical properties are improved.

Disadvantages:
1. The tensile properties of the steel in the thickness direction are greatly deteriorated, and there is a possibility of interlaminar tearing when the weld shrinks. The local strain induced by weld shrinkage often reaches several times the yield point strain, which is much larger than the strain induced by the load.
2. Residual stress caused by uneven cooling. It may have adverse effects on deformation, stability, fatigue resistance, etc.

Seamless steel pipe process flow:

Hot-rolled seamless steel pipe(extruded seamless steel pipe): round tube billet → heating → perforation → three-roller skew rolling, continuous rolling or extrusion → tube removal → sizing (or diameter reduction) → cooling → billet tube → straightening → water pressure Test (or flaw detection) → mark → storage.

Cold-drawn (rolled) seamless steel pipe: round tube billet → heating → perforation → heading → annealing → pickling → oiling (copper plating) → multi-pass cold drawing (cold rolling) → billet → heat treatment → straightening → water Pressure test (flaw detection) → marking → storage.

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