Weld treatment of ERW steel pipe

Posted by BAOWI STEEL MANUFACTURING CO.,LTD on June 24th, 2024

ERW steel pipe (a53b erw) uses the principle of electromagnetic induction and the skin effect, proximity effect and eddy current heating effect of the charge to locally heat the steel at the edge of the weld to a molten state, and achieves butt welding through the extrusion of intercrystalline bonding, thereby achieving the purpose of welding.

1. Control of weld gap

The strip steel is fed into the welded pipe unit and rolled by multiple rollers. The strip steel is gradually rolled into a round tube billet with an open gap. The compression degree of the extrusion roller is adjusted to control the welding gap between 1 and 3 mm. And make the weld flush. If the gap is too large, the proximity effect is weakened, the eddy current is insufficient, and the intercrystalline bonding of the weld is poor, resulting in non-fusion or cracking. If the gap is too small, the proximity effect increases, and the welding heat is too large, it will cause the weld to burn, otherwise the weld after extrusion rolling will form a deep pit, affecting the surface quality of the weld.

2. Welding temperature control

The welding temperature is mainly affected by the high-frequency eddy current thermal power. According to the formula, the high-frequency eddy current heating power is mainly affected by the current frequency. The eddy current heating power is proportional to the square of the current excitation frequency, and the current excitation frequency is affected by the excitation voltage and current. As well as the influence of capacitance and inductance.
When the input heat is insufficient, the edge of the heated weld cannot reach the welding temperature, and the metal structure remains firm, resulting in incomplete fusion or incomplete penetration.
3. Control of extrusion force
After the two edges of the tube billet are heated to the welding temperature, under the extrusion of the extrusion roller, common metal grains are formed, which make them permeate and crystallize each other, and finally form a firm weld. If the extrusion force is too small, the number of eutectics formed will decrease, the strength of the weld metal will decrease, and cracks will occur after the force; if the extrusion force is too large, the molten metal will be squeezed out of the weld, which will not only reduce the strength of the weld, but also produce a large number of internal and external burrs.
4. Adjustment of the position of the high-frequency induction coil
The high-frequency induction coil should be as close to the position of the extrusion roller as possible. If the induction coil is far away from the pressure roller, the effective heating time is long, the heat-affected zone is wide, and the welding strength is reduced; on the contrary, the edge of the weld is not fully heated, resulting in poor forming after extrusion.
5. After welding and extrusion, the weld will produce weld marks, which need to be removed. The cleaning method is to fix the tool on the frame and scrape off the weld mark by the rapid movement of the welded pipe. The burrs inside the welded pipe are generally not removed.
High-frequency welding is an induction welding (or crimping welding) that does not require weld fillers and welding slag. The welding heat-affected zone is narrow, the welding shape is beautiful, and the welding mechanical properties are good. Therefore, it is widely used in the production of steel pipes.

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