The main process parameters of high-frequency straight seam welded pipes manufactured by used HFW pipe equipments include welding heat input, welding pressure, welding speed, size of opening angle, position and size of induction coil, position of impedance, etc. These parameters have a great impact on improving the product quality, production efficiency and unit capacity of high-frequency welded pipes. Matching various parameters can make manufacturers obtain considerable economic benefits.

1.Welding heat input

When the used HFW pipe equipments runs high-frequency straight seam welded pipe welding, the welding power determines the amount of heat input to the welding. When the external conditions are certain and the input heat is insufficient, the edge of the heated strip cannot reach the welding temperature, and still maintains the welding temperature. A solid structure that forms a cold weld and cannot even fuse. The lack of fusion caused by too little welding heat input is shown in Figure 1.

Figure 1 Unfused resulting from too small heat input

This lack of fusion during inspection usually manifests as unqualified flattening test, bursting of steel pipe during hydraulic test, or cracking of weld seam during straightening of steel pipe, which is a serious defect. In addition, the welding heat input is also affected by the quality of the edge of the strip. For example, when there is a burr on the edge of the strip, the burr will cause ignition before entering the welding point of the squeeze roller in the process of used HFW pipe equipments, resulting in welding power. The loss of heat reduces the heat input, resulting in an unfused or cold weld. When the input heat is too high, the edge of the heated strip exceeds the welding temperature, resulting in overheating or even overburning, and the weld will crack after being stressed. The blisters and holes formed by excessive heat input are shown in Figure 2.

Fig. 2 Trachoma and holes caused by excessive heat input

These defects are mainly manifested in the failure of the 90° flattening test, the failure of the impact test, and the burst or leakage of the steel pipe during the hydraulic test.

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