Pipeline scar is a common defect of welded pipe, and its specific manifestations include crush, indentation and scratch.

Submerged arc welding is mainly suitable for flat position welding. If certain tooling aids are used, corner welding and horizontal welding can be realized. The main factors affecting the shape and performance of submerged arc welding seam are welding process parameters and conditions. The welding process parameters affecting the shape and size of submerged arc welding seam include welding current, arc voltage, welding speed and wire diameter.

Hot crack, in the process of weld cooling, because the sulfur and phosphorus impurities in the steel or welding material form a variety of brittle and hard eutectic with low melting point, in the process of weld cooling, the solidified eutectic with low melting point is in a tensile state, which is easy to crack.

Reinforcement is not only the need of welding process, but also has an impact on the safe operation of the vessel, especially the fatigue life. The welding of pressure vessel is mostly multi pass welding (such as manual welding and automatic welding).

Generally, the welding part needs to go through the process of heating melting metallurgical reaction solidification crystallization solid phase transformation joint formation, which can also be summarized as the following three interrelated processes.

In the welding process, due to some high temperature heating and rapid cooling, thermal strain and compressive plastic strain will occur in the weld and near weld area of base metal, resulting in internal stress and deformation of components. The common welding deformation includes longitudinal deformation, tortuous deformation and distorted deformation. In actual production, these welding deformation usually do not appear alone, They come together and influence each other.

A large number of studies have proved that the hydrogen content of the welded joint, the hardening tendency of the steel and the restraint stress of the joint are the three major factors causing the welding delay crack, and the welding delay crack is caused by the joint action of these three factors.

Welding cracks are relatively dangerous welding defects, which seriously affect the performance and safety of welded structures. Many damage accidents of welded structures are caused by welding cracks.

Sometimes, the defects in the actual production of high frequency welded pipe are not caused by one reason, but usually the result of a variety of factors.

Incomplete penetration during welding refers to the defects caused by the base metal not melting and the weld metal not entering into the root of the joint. According to the welding method of the weldment, it can be divided into incomplete penetration at the root and incomplete penetration in the middle. The liquid weld metal does not enter into the root blunt edge. The one-sided welding of V-shaped or U-shaped groove is incomplete penetration at the root and the liquid metal does not enter into the middle blunt edge, In double V-groove or double U-groove, double side welding is incomplete in the middle.