When preheating welding on site, should fully consider many factors and the should adjust preheating temperature accordingly, otherwise, the purpose of preventing cracks will not be achieved.

1.The diffusion hydrogen content of electrode has great influence on cold crack. Corresponding adjustment shall be made according to the diffusion hydrogen content of electrode.

2.Welding line energy,The energy of transverse welding line is the least, while that of vertical welding line is the most. Preheating temperature of transverse welding position should be increased properly.

3.Welded construction.When welding some heavy forgings on the vessel with the shell, it is difficult to expand or shrink freely due to the large weld restraint, and the radial and circumferential stress of the weld is large. Easy to generate welding cracks. At this time, the preheating temperature should not be too high. Especially in the case of large linear energy, preheating and inter layer temperature should be strictly controlled. Otherwise, additional thermal stress will be generated.

The heat treatment process of steel tube

4.Ambient temperature

In winter, when the ambient temperature is lower than 0 ℃, the influence of ambient temperature on cooling rate should be considered. Preheat temperature should be increased before welding.

What’s more, when do preheating, the following factors should be think about too.

1.For the steel plate with poor weld ability and large thickness, the joint is generally restricted, and use ordinary non low hydrogen welding materials to weld, should preheat before welding.

2.For materials with high thermal conductivity (such as copper, aluminum and their alloys), in order to ensure the fusion of weld metal and base metal.should do preheating before welding.

3.For carbon structural steel and low alloy structural steel with good weld ability, if the plate thickness is small and the restraint is not big, and use low hydrogen welding material, usually don’t need to preheat.

It is worth noting that preheating welding before welding increases energy consumption and worsens welding conditions. Therefore, under allowable conditions should be adopt non preheating or low temperature preheating welding.

As professional supplier of prefabrication pipeline, Hebei HaiHao Group accept all kinds welding works.Welcome your inquiry.Email:sales@haihaogroup.com