Submerged arc welding technology of welded steel pipe

Submerged arc welding of welded steel pipe is a welding method that buries the strong welding arc light. Today, let's talk about the welding process of submerged arc welding.

1. Welding current

With the increase of welding current, the penetration and residual height of the weld also increase, and the weld width changes little, because when the welding current increases, the heat transmitted to the weldment also increases, and the force of the arc on the weld pool also increases, so the penetration increases. With the increase of welding current, the melting amount of welding wire increases, which increases the weld reinforcement, on the contrary, the penetration and reinforcement decrease.

When the welding current is too large, the penetration is deep, the weld width remains unchanged, and the heat affected zone is too large, which will produce defects such as burn through and weld bead, which will also make it difficult for the gas and inclusions in the molten pool to float up and escape, and defects such as pores, slag inclusion and cracks are easy to appear in the weld. If the current is too small and the penetration is insufficient, defects such as poor fusion, incomplete penetration and slag inclusion are easy to appear. Therefore, When increasing the welding current, the arc voltage should be increased to ensure the corresponding weld width and improve the welding quality.

2. Arc voltage

When other parameters remain unchanged, with the increase of arc voltage, the weld width increases, the reinforcement and penetration decrease, the arc voltage is directly proportional to the arc length, the arc length increases with the increase of arc voltage, the area of arc heated weldment increases, and the weld width increases. At the same time, with the increase of arc length, heat will be used to melt flux, but the melting amount of welding wire does not increase, The molten welding wire is distributed in a larger area, so the reinforcement of the weld will be reduced. In addition, due to the increase of arc length, the arc swing will be intensified, the force of molten pool will be weakened, and the penetration will be reduced. In submerged arc welding, the arc voltage is adjusted according to the welding current to ensure the stable combustion of the arc, so the variation range of arc voltage is limited.

However, when the arc voltage is too high, it will not only reduce the penetration and lead to incomplete welding, but also lead to poor weld forming, difficult slag removal, and even undercut. Therefore, the welding current should be increased appropriately while increasing the arc voltage.

3. Welding speed

Other welding parameters remain unchanged. When the welding speed is increased, the welding heat input is reduced, the weld penetration is reduced, the melting amount of welding wire is reduced, and the weld width and reinforcement are also reduced. When the welding speed is too high, the amount of molten metal is insufficient, resulting in defects such as incomplete penetration and undercut. In order to ensure the welding quality, a certain welding heat input is required, that is, increasing the welding speed to improve the productivity, The welding current and arc voltage shall be increased accordingly to ensure the welding quality.

4. Diameter and extension length of welding wire

When the welding current, welding speed and arc voltage remain unchanged, the wire diameter is different and the weld shape changes. When other conditions remain unchanged, the wire diameter is inversely proportional to the penetration, and decreases with the increase of current density, because the increase of current density also increases the amount of molten metal. With the increase of molten metal, the weld shape becomes worse. During submerged arc welding, Arc voltage and welding current shall be increased to ensure weld formation.

Other welding parameters remain unchanged. When the length of the welding wire increases, the resistance also increases, which enhances the preheating effect of the extended part of the welding wire, speeds up the melting speed of the welding wire, resulting in shallow penetration and increased reinforcement. If the welding wire extends too long, the welding wire below the conductive nozzle will turn red. Therefore, the extension length of the welding wire should be controlled and should not be too long.