Defects in the actual production of high-frequency welded pipes by high frequency welded pipe machine are sometimes not caused by one reason, but are usually caused by a combination of factors. Welding defects can also be caused by other reasons outside the welding area. Therefore, various factors should be comprehensively considered for defects, and the causes should be carefully analyzed to solve the problem.

Inclusions

The formation mechanism of the inclusion defect is a defect formed by the metal oxide not being clamped on the welding fusion surface with the extrusion of the molten metal.

These metal oxides are usually formed on the molten metal surface of the V-angle. When the approach speed of the strip edge is lower than the melting speed, and the melting speed is higher than the discharge speed of the molten metal, it will form a V-shaped apex containing molten metal and The inclusions of metal oxides, the metal oxides cannot be completely discharged by normal extrusion, and the clean metal solution surface is doped with these metal oxides during the forging and welding process to form defects.

Such defects will lead to cracks after flattening of the weld, and inclusions will be seen at the fracture of the weld. Such defects appear in different forms, sometimes appearing singly, and sometimes appearing in chains.

Inclusion Defect Prevention Measures:

(1) The V-shaped angle is strictly controlled at 4~6

(2) The unit is adjusted to ensure a stable opening angle length

(3) The Mn/Si ratio in the chemical composition of the strip is greater than 8:1

(4) Reduce the oxidation of the welding area (a variety of measures, not going into details)

Pre-arc

This kind of defect is actually caused by insufficient fusion caused by the pre-arc. When the high frequency welded pipe machine is used to make pipes, it usually occurs on the edge of the strip steel, or the oxide scale and rust fall before the apex of the V angle to form a bridge, causing a short circuit. The current jump produces a pre-arc phenomenon, and the short-circuit current changes the current direction and reduces the heat at the V corner.

For defects caused by instantaneous shunt, a bright, flat plane fracture can be seen from the weld fracture.

Sometimes there is no burr on the edge of the strip, or oxide skin, rust, etc., but the V angle is too small or the voltage is too high.

caused by discharge.

Pre-arc defect prevention measures:

(1) The V-shaped angle is strictly controlled at 4~6

(2) The edge of the strip is clean and smooth without burrs

(3) Keep the cooling water clean, control the flow direction of the cooling water, and try to avoid the flow to the V angle

Insufficient fusion

This type of defect is due to the fact that the edges of the two strips are heated but not fully fused, and a good weld is not formed.

The most direct cause of insufficient fusion is insufficient heating during welding. There are many related factors that cause insufficient welding heat, such as the output of high frequency power, V angle and heating length, the position of the magnet bar, the working condition and cooling of the magnet bar, the size of the induction coil, the welding speed and so on. These factors interact with each other, and the combined effect leads to such defects.

Insufficient fusion defect prevention measures:

(1) The matching of welding input heat and welding speed, and the characteristics of the raw material of the tube blank

(2) Working condition of magnetic rod

(3) V angle and heating length

(4) Induction coil specifications

The stability and good state of high frequency welded pipe machine are the basic conditions for no defects. Improving the recording and analysis of process parameters can improve the quality of the pipe more comprehensively.