What are the names of common defects in ERW pipes?

What are the names of common defects in ERW pipes?

ERW pipes can have various defects, and the names of the defects are not entirely uniform. Combined with the production characteristics of ERW welded pipes, it is concluded that they have the following defects.

1. Contains content

1) Black overburned inclusions: This type of defect is formed on the surface of the molten metal at the V-shaped opening because the metal oxide is not clamped on the molten surface as the molten metal is extruded. The edge of the strip is smaller than the melting speed, and the melting speed is higher than the discharge speed of the molten metal. After the apex of the V-shaped opening, a narrow sector containing molten metal and metal oxide is formed. These molten metals and metal oxides cannot be completely discharged through normal extrusion, thus forming inclusion regions.
2) White peroxide inclusions: This is actually due to insufficient pre-arc fusion and there is no foreign matter on the fusion surface. Under normal circumstances, burrs or rust form a bridge before they fall on the apex of the V-shaped opening, causing a short circuit and a pre-arc phenomenon caused by a current jump.

2. Insufficient integration

1) Crack: The edges of the two steel strips are not completely fused to form a good weld. The edge of the crack is blue, indicating that the steel strip has been heated. However, the edge of the steel strip is flat and smooth, indicating that the weld is not completely fused. The most direct cause of such defects is insufficient welding heating.

2) Edge wave: The reason is that there is no metal on the fusion surface. Such defects often appear on the outside or inside of the strip edge and are similar to peroxide defects. Preventive measures for insufficient edge fusion: 

① The edge of the steel strip should be flat and parallel to the butt joint; 

② Use a better extrusion amount; 

③ If the defective fracture caused by bulging is silvery gray, a larger welding heat input should be used

3) Internal cold welding: After the incompletely fused weld is damaged, the middle section of the wall thickness will appear as a flat silver-gray strip with fibrous edges. This welding defect is caused by the power required for the welding speed exceeding the rated power amplifier of the welding machine, and the entire end edge of the steel strip does not have enough time to heat to the required optimal temperature and heating depth. through welds. In addition, incomplete discharge of molten metal and incomplete and correct discharge of the joint surface may also cause internal cold welding.

3. Cast welding

Cast welding means that the molten metal on the joint surface is not completely discharged. The cast metal on the fusion surface contains metal oxides such as peroxide, and the fracture morphology changes according to the change in the residual cast metal content. The appearance is flat and brittle, and metallographic examination shows that there is cast metal on the surface of the joint. Preventive measures for casting welding: 

① Increase the welding discharge amount. 

② Increase the strip width.

4. Stomata

The pores on the surface of the welded joint are caused by high welding temperature but insufficient discharge. The fracture surface is fibrous in shape, with spherical bright white spots randomly distributed on the entire fracture surface. When white spots appear on the outer wall, the surface phenomenon of the white spots turns black due to oxidation. Small pores can be seen before the outer burr is removed, and pores can also be seen on the fusion line after the outer burr is removed. Preventive measures for blowholes: 

① Reduce welding investment; 

② Increase extrusion force

5. Jump welding

Jump soldering comes in many forms. Usually, such defects are distributed regularly and continuously, and the defects on the outer side of the wall thickness are similar to corrugated defects, and the spacing is generally equidistant. Preventive measures for skip welding: 

① Increase welding current filtering equipment.

② Check the input voltage. 

③ Check the rollers and shafts