How effective is preheating in preventing cracks in the insulation layer of welded sealed straight stainless steel electric heating coils?

Preheating plays an important role in avoiding cracks in the insulation layer of welded sealed straight-tube stainless steel electric heating rings, which is mainly reflected in the following aspects:
Reducing the cooling rate: During welding, the weld and heat-affected zone will undergo a process of rapid heating and cooling. If the cooling rate is too fast, it is easy to produce hardened tissue, which is hard and brittle and has high crack sensitivity. Preheating can increase the initial temperature of the weldment, slow down the cooling rate after welding, avoid the formation of hardened tissue, and thus reduce the possibility of cracks.
Reducing welding stress: During welding, due to uneven heating of various parts of the weldment, a large welding stress will be generated. Preheating can make the overall temperature distribution of the weldment more uniform, reduce the temperature gradient during welding, and thus reduce the welding stress caused by thermal expansion and contraction. Lower welding stress helps prevent cracks in the weld and heat-affected zone.
Improve the toughness of the welded joint: Proper preheating can make the structure of the welded joint more uniform and the grains refined, thereby improving the toughness and crack resistance of the joint. Welded joints with good toughness can better withstand stress and deformation during welding and reduce the generation of cracks.
Generally speaking, for the welding of stainless steel electric heating rings, the preheating temperature needs to be determined according to the specific material, thickness, welding process and other factors. Usually, for stainless steel with a larger thickness or a higher content of alloy elements, the preheating temperature may need to be controlled between 100-200℃. Through reasonable preheating treatment, the welding quality can be significantly improved, cracks can be effectively avoided when welding the insulation layer of the sealed straight-tube stainless steel electric heating ring, and the reliability and service life of the electric heating ring can be improved.