Spiral steel pipe is low carbon steel or low alloy steel strip at a certain angle helix (called molding angle) rolled into a tube, then welded together to form the tube, it can be used a narrow strip production of large diameter pipe. Spiral is mainly used for oil and gas pipeline, outer wall with its specifications expressed. Spiral single-sided and double-sided welding welding, pipe should ensure that hydrostatic test, weld tensile strength and cold performance to meet the requirements.
The service life of spiral steel pipe and spiral steel surface decarburization is a definite link, if the surface decarburization, the spiral strength and wear resistance will be reduced, directly affect the spiral of life. If the decarburization of a spiral is not clean, then spiral hardness and wear resistance of the surface layer will be a corresponding decrease and the quenching process, because of changes in the volume of the outer surface caused by the workpiece the formation of cracks.
Solving the main problem of surface decarburization is to carry out the heat treatment step, since decarburization and oxidation spiral are performed simultaneously, so the heat treatment process, the spiral should try to prevent contact with the air, this can improve the decarburization phenomenon. The medium resulting spiral surface decarburization is mainly oxygen, water vapor and carbon dioxide an oxidizing gas, when these gases and heated contact spiral, spiral may cause oxidation and decarburization, therefore, controlling the furnace carbon dioxide and carbon monoxide ratio is very important. In fact, the spiral forging furnace, a protective nitrogen gas added is very effective, nitrogen can dissipate some of the oxidizing gas, reducing spiral decarburization.
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