Types and preventive measures of weld cracks in welded steel pipes

Why do welds crack? What are the types and preventive measures for weld cracks?

Weld cracks can be classified in different ways according to their location, size, causes, and mechanisms. According to the conditions of crack formation, they can be divided into four categories: hot cracks, cold cracks, reheat cracks, and layered tears. According to the cracking of welds at the welding site, most of them are caused by stress, restraint, and rigidity. It can be said that stress, restraint, and rigidity are often the main factors for weld cracking.

The more effective way to solve the cracking of welds caused by stress, restraint, and rigidity is to adopt fixed welding and dispersed welding.

The so-called fixed welding: first fix all the welds of the weldment, or the welds of important parts, with small current, narrow weld bead, and short distance welding. This makes it difficult for the weldment to produce large stress. Even if the weldment is fixed everywhere, it cannot be moved forward in sequence at the same position, and it is even more impossible to use large current and large-size welding rods. Welding should be performed in a different position so that excessive heat is not generated in the local position. The same method can be used to solve the problem of binding and rigid structures.

The so-called dispersed welding, for large structures, must not be welded sequentially at the same position, and the position should be changed for welding.

For large structures, not only must fixed welding be performed first, and then dispersed welding be performed, but the first weld must not use high current and large-size welding rods. For large structures as a whole, all welds must be dispersedly welded from beginning to end, otherwise, although the welds will not crack, the residual stress will be too large.