In the production of ERW steel pipe, high frequency technology used by pipe manufacturer, other welding of important components, welding of alloy steel and welding of thick parts all require preheating before welding. The main roles of preheating before welding are as follows:
(1) Weld peheating can slow down the cooling rate after welding, which is conducive to the spread of diffusible hydrogen in the weld metal, and avoids producing hydrogen to result in cracking. At the same time, it also reduces the degree of hardening of the weld and heat affected zone and improves the crack resistance of the welded joints.
(2) Weld preheating can reduce the welding stress. Uniformly preheating or entirety preheating can reduce the temperature difference (also known as temperature gradient) between welds in the weld area. In this way, on the one hand it reduces the welding stress, on the other hand, it reduces the welding strain rate, which is help to avoid welding cracks.
(3) Weld preheating can reduce the restraint degree of the welded structure, especially to reduce the degree of restraint of the corner joint. With the increase of the preheating temperature, the crack rate decreases.
The choice of preheating temperature and interlayer temperature is not only related to the chemical composition of steel and electrode, but also to the rigidity of welded structure, welding method, ambient temperature and so on. It should be determined after considering these factors. In addition, the preheating temperature in the direction of the steel plate thickness uniformity and uniformity in the weld area, has an important impact on reducing the welding stress. The width of the local preheating should be determined according to the degree of restraint of the workpiece to be welded, generally it should be around the weld area three times the wall thickness, and is not less than 150-200mm. If the preheating is not uniform, not only does not reduce the welding stress, but also will appear to increase the welding stress situation.
So when Prime Steel Pipe manufactures ERW steel pipe or other welded pipe, we will take control of preheating temperature strictly, so that we can produce perfectly good carbon steel pipe.