Multi layer welding of butt welding flange

Last article we know the single layer welding of butt welding flange, today let’s see what’s multi layer welding of butt welding flange.

When the butt welding flange is thick, multi-layer welding is required. When there is no backing plate, the first pass is similar to single side welding. When there are backing plates, there should be a certain gap between the butt welding flanges. The current can be slightly larger, but it is still a short-circuit transition.

API 6A Weld Neck Flanges

At this time, the welding current is 130 ~ 140A and the arc voltage is 19 ~ 20V.

During operation, the welding gun should be aligned with the groove center and move at a uniform speed with the right welding method.

At this time, it must be noted that the base plate and groove root should be fully penetrated, and convex weld bead should not appear. For this reason, a small swing should be used and a little stay on both sides of the weld bead to obtain a flat weld bead, so as to create good conditions for the subsequent filling weld bead.

The second and third welding passes shall be welded in the form of uniform swing of welding gun, but a short stay shall be made at the junction of the former and groove surface to ensure full penetration and prevent undercut.

The welding parameters are welding current 120 ~ 130a and arc voltage 18 ~ 19v.

After the fourth layer, due to the weld width is too large, it is easy to produce incomplete penetration and porosity when the swing is too large. Therefore, it is better to use the deposition method as shown in Figure 3, that is, from the fourth layer, two welding passes are welded on each layer.

In these two passes, the first pass should not be too wide, otherwise it will cause the weld bead sagging and the groove left for the second pass is too narrow, which is easy to form incomplete penetration and convex weld bead in the second pass. Therefore, the first pass passes through the center and the second pass overlaps with the first pass.

The cover weld bead of butt welding flange is a modified weld bead, which should be beautiful.