Causes and preventive measures of defects such as pores and slag inclusions in submerged arc welding seams

Causes and preventive measures of defects such as pores and slag inclusions in submerged arc welding seams pipe

The main defects that may appear in the process of submerged arc welding are not only insufficient penetration, burn through and poor forming, but also porosity, crack and slag inclusion. This paper mainly introduces the causes and preventive measures of porosity and slag inclusion.

Stomata

The main causes and preventive measures are as follows:

1.Moisture absorption of flux or moisture, dirt and iron oxide chips in flux will cause pores, which is more prominent in the recovery of flux. Moisture can be eliminated by drying. The drying temperature and elbow shall be specified by the flux manufacturer. Correct storage and preservation can prevent the flux from absorbing water. Vacuum flux recycler is used to effectively separate flux and dust and reduce the possibility of pores.

2.Insufficient flux coverage will cause air holes due to arc exposure and air entrainment. Appropriate measures shall be taken to prevent flux from scattering when welding small-diameter circumferential welds.

3.The viscosity of molten slag is too high, and the gas dissolved in high-temperature liquid metal overflows in the form of bubbles. The viscosity of molten slag is high. Bubbles cannot pass through the molten slag and block the weld surface to form pores. It can be solved by adjusting the chemical composition of flux and changing the viscosity of molten slag.

4.Arc magnetic bias blowing will occur during welding. In DC welding, arc magnetic bias blowing will cause pores in the weld. Magnetic bias blowing is affected by many factors, such as the connection position of welding cable on the workpiece, poor contact at the connection, and the welding cable at the joint will produce secondary magnetic field. In different parts of the same weld, the direction of magnetic bias blowing is different.

Magnetic bias blow often occurs on a section of weld near the end, so there are more pores on this section of weld, AC power supply shall be used, and the connection position of welding cable on the workpiece shall be far away from the weld terminal to avoid secondary magnetic field.

5.Rust, oil stain or other dirt in the welding groove of contaminated workpiece and nearby will produce a large amount of gas during welding and promote the formation of pores, which shall be removed before welding.

Slag inclusion

Slag inclusion is related to the deslagging performance of the flux, as well as the assembly and welding process of the workpiece. When the butt weld is poorly assembled, slag inclusion is easy to occur at the bottom of the weld, and the flat and slightly convex weld is easier to deslag than the deep concave or undercut weld.

The first weld of double pass welding is easy to deslag when fused with the upper edge of the groove, and slag inclusion is easy to occur when welding the second weld. When welding deep groove, slag inclusion is not easy to occur in the weld composed of small weld bead, and slag inclusion is likely to occur in the weld composed of large weld bead.