Defects caused by smelting, ingot casting and other factors not only cannot be completely eliminated during the rolling process and remain on the tube blank, but also new defects will be generated during the rolling process. Therefore, it is impossible to completely avoid tube blank defects. possible. Therefore, the tube blanks must be strictly inspected and surface defects must be thoroughly cleaned, which is an important measure to ensure the quality of steel pipes and improve the yield rate.
Pipe rolling mills with better steel pipe quality at home and abroad attach great importance to this work. Normally, tube blank inspection and surface defect cleaning should be completed at the tube blank production plant, and the tube rolling plant will conduct re-inspection according to the corresponding tube blank technical conditions.
The cleaning method of the tube blank is the same as that of other steel materials. It needs to be comprehensively considered based on cleaning efficiency, cost, quality, metal loss and the properties of the tube blank itself.
In order to expose the surface defects of the tube and facilitate inspection, pickling, peeling and other methods are usually used to remove the oxide scale on the surface of the tube blank.
Modern hot-rolled steel pipe workshops mostly use non-destructive inspection (commonly used ultrasonic automatic flaw detector) to replace manual inspection. This not only significantly improves work efficiency and working conditions, but also improves the quality of inspection.
Surface cleaning methods include grinding wheel grinding, flame cleaning, air shovel cleaning and mechanical peeling.
Modern hot-rolled pipe workshops mainly use the following cleaning methods: (1) Medium and low carbon steel mostly use high-efficiency surface flame cleaning methods. The process is to inspect each piece or non-destructive testing – flame cleaning – shot blasting to remove residues and make the surface smooth;
(2) High carbon steel and alloy steel are ground with grinding wheels
(3) For important purpose steel pipes and high-alloy pipe blanks, the whole pipe is peeled – inspected – and partially ground.
Although peeling and cleaning consumes a lot of metal and costs a lot, it is still economically cost-effective because it can improve the quality of the steel pipe and the yield rate. As the technical requirements for steel pipes continue to increase, some foreign factories peel and clean all pipe blanks (the outer diameter is cut by 2-6mm) to ensure the quality of the steel pipes.
