main body:

Figure 1: A screenshot is from the topic in the inscription.

Provided by the topic sponsor and authorized for use.

theoretical description:

More consistent with the lack of "clip beads", is a special form of stoma. The phenomenon is described as multilayer welding, the first welding layer has appeared pores, and the liquid metal of the welding layer flows into the cavity is filled but not necessarily is well fused with the inner wall of the cavity. The typical negative film is a black ring or "chord moon", with a white full moon or half moon (round or irregular circle).

Large welding droplets attached to the previously cooled welding path (the same layer or the previous layer) may also be caught in the weld metal during subsequent welding.

According to the existing information in this topic, the welding method in the topic is submerged arc welding, which has another typical mechanism is due to the presence of molten flux in the pores, which is mostly black ball. Unmelted gray-white solder particles are occasionally seen. It is described below as special cases where bead ping may occur in submerged arc welding.

For the beads clip in submerged arc welding, there are some commonalities in this welding method, although not absolute, but has certain reference significance.

For example, it is easier to appear in:

Thick wall material;

Serious corrosion of raw materials;

The groove form of the large depth to width ratio.

And some rules:

More likely to appear in the middle of the weld position;

Compared with the profile, when the double-sided welding of the pipe occurs, the depth direction is more inclined to the internal welding layer position or the root of the double-sided groove, that is, similar to the middle position of the wall thickness slightly to the inner wall;

For the whole weld, it is possible to appear with the pores in the conventional sense.

For the above commonalities, assume a scenario to describe the cause of the bead clip. Don't take a seat.

A badly rusted steel plate on the pipe winding machine after the ramp. With the bending deformation of the steel plate made of steel pipe, a large number of corrosion products peel off and there is a considerable volume in its interior, including rust and external pollutants. Before the welding began, only a complete broom-like object was used for a symbolic cleaning. Historic flux purchased at the beginning of the workshop filled the hopper.

Equipment debugging is completely without debugging, many years ago, the old masters set the parameters have warned the future, the equipment is prohibited. The welding process in the workshop has been hanging on the wall since the factory was built. With the aging of the paper and the accumulation of dust, maybe only the printer that did not know what is still there can remember what was written on it.

Between-layer cleaning? Does not exist, the master shook the smoke in the hand, leisurely said: buried arc welding strength is big, billions of a little bit of slag welding medicine small defect is not a problem at all.

Avoid methods include:

Cleaning before welding, can be seen "slope cleaning before welding" (click the blue link to jump). Especially the pipe, especially the spiral welded pipe, the internal weld is more likely to be affected by the rust in the inner wall in the rotation process, so the cleaning before welding should pay attention to the position outside the groove area;

Use welding materials within the shelf life, according to strictly dry the solder requirements, and control, such as flux recovery magnetic selection, prevent long exposure storage, etc.make use of