How to control the weld reinforcement of submerged arc welded steel pipe

First of all, for steel pipes with large wall thickness (>14.3mm), grooves should be made and pre-welded. If the pre-welding conditions are not mature, then after the internal welding, the outer weld can be processed into a U-shaped groove for welding by gouging or automatic grinding with a grinding wheel.

Second, check whether the welding line energy is appropriate. The first is to check the degree of overlap of the inner and outer welds; then the width of the waist of the weld bead is checked. The regulation on the coincidence amount is generally greater than 1.5 mm, but if it exceeds 3.0 mm, it means that the line energy is relatively large. The greater the energy of the welding line, the greater the melting wire per unit time, the greater the penetration, and the greater the weld reinforcement. Therefore, when welding high-strength steel plates, multi-pass welding is generally used to reduce the line energy of each layer, and to keep the shape factor of the weld within 1.3-2.0 mm.

In addition, a thinner front wire should be used for multi-wire welding. Generally, under the same current condition, the penetration depth of welding wire with Ф3.2 mm is larger than that of Ф4 mm. Because the current density of thin wire>thick wire. Therefore, when other conditions remain unchanged, the penetration depth of the front wire with Ф3.2mm is about 20% larger than that of the front wire with Ф4 mm. This effect of reducing the reinforcement of the outer weld is more obvious when the bevel is not opened or the groove is not planed for the outer weld. However, when welding a steel pipe with a wall thickness greater than 14.3 mm and the current of the front wire is about 1000 A, the front wire of Ф4 mm should be used, otherwise the stable combustion of the arc may be affected.

Finally, it is worth noting that the position of the inner and outer welding heads must be adjusted for spiral welding. During internal welding, adjust the position of the internal welding head to reduce or eliminate the "saddle-shaped" internal weld; during external welding, adjust the spatial position of the welding head to reduce or eliminate the "fishback" external weld, which needs to be adjusted The eccentric value of the outer welding spot, and the diameter of the spiral welded pipe is different, the eccentric value of the outer welding spot is also different.