Relationship between Welding Speed and Weld Quality of High Frequency Longitudinal Welded Pipe

The relationship between welding speed and weld quality of high-frequency straight seam welded pipes should be understood dialectically and should not be neglected, mainly reflected in the heating stage and crystallization stage.

Heating stage
Under the working condition of high-frequency straight seam welded pipe, the edge of the tube blank is heated to the welding temperature. During this period, the edge of the tube blank is exposed to the air without protection, and it inevitably reacts violently with oxygen and nitrogen in the air, which significantly increases the nitrogen and oxides in the weld. According to measurements, the nitrogen content in the weld increases by 20 to 45 times, and the oxygen content increases by 7 to 35 times. Slower, poorer welding quality.
Not only that, the longer the edge of the heated tube billet is exposed to the air, that is, the slower the welding speed, the deeper the non-metallic oxides will be produced. These non-metallic oxides are difficult to squeeze out of the weld during the subsequent extrusion crystallization process. After crystallization, they remain in the weld in the form of non-metallic inclusions, forming a fragile interface, thereby damaging the continuity of the weld structure and reducing the strength of the weld. However, the welding speed is fast and the oxidation time is short. There will not be too much non-metallic oxide residue, so the weld strength is high.
crystallization stage
According to the principle of metallurgy, in order to obtain high-strength welds, it is necessary to refine the grain size of the weld structure as much as possible. The basic way of refinement is to form enough crystal nuclei in a short time, so that they contact each other before the crystallization process ends. This requires increasing the welding speed to make the weld leave the heating zone quickly, so that the weld crystallizes rapidly under a large degree of undercooling. Look, from the perspective of cooling after welding, under the premise of meeting the basic welding conditions, the faster the welding speed, the better the welding quality.