Prevention of pitting on the surface of submerged arc welded steel pipe welds

Surface pitting of submerged arc welded steel pipe welds refers to weld defects where the surface of the weld is partially lower than the normal surface of the weld. It is a common weld surface defect in submerged arc welding.

In actual production, the following measures can be taken to prevent the occurrence of weld pressure pits:
Select the appropriate flux: On the premise of ensuring the internal quality of the weld, a flux with low oxidation, low viscosity, low surface tension and low bulk density should be selected. Sintered fluxes such as SJ101 and SJ301 are superior to fused fluxes such as HJ431 and HJ433. In addition, in order to improve the permeability of the flux, especially when welding with high current, flux with smaller particle size should be selected.
The particles of the flux should be as uniform as possible. Do not mix coarse-grained flux with too-fine flux, otherwise the flux's permeability will be reduced. For continuously recycled flux in submerged arc welding of steel pipes, it must be ensured that excessively fine flux can be removed through the flux recovery system to ensure that the particle size of the flux is relatively uniform. This is particularly important for sintering fluxes and ceramic fluxes with lower particle strength. At the same time, when welding incompletely deoxidized steels such as A3F or Q235B, Mn and high Si fluxes should be selected to enhance the deoxidation effect of the welding process and reduce gas generation. The sintering flux should be one with a higher sintering temperature to reduce the moisture content of the flux.

Use flux correctly: Flux must be kept clean and free of rust, dust, iron oxide and other impurities when used. For recycled flux, the iron oxide in the flux must be removed through magnetic separation. The flux must be removed before use and dried at the specified temperature to ensure the moisture content of the flux. Generally, the moisture content in the flux should be ≤0.1%; during submerged arc welding, the accumulation height of the flux should be minimized on the premise of ensuring an unknown arc. The flux from automatic submerged arc welding inside and outside the steel pipe is recycled. Therefore, the welding system should be equipped with a flux recovery and supply system with flux magnetic separation and screening devices to ensure that magnetic impurities (such as iron oxide) in the flux can be removed and screened. Remove welding slag, dust and fine particles of flux to maintain uniform flux particles. The flux supply system should preferably be equipped with a flux heating and insulation device to heat and maintain the recycled and replenished new flux, so that the flux can be kept above a certain 100°C to prevent the recycled flux from being used again. moist.
Reasonable selection of welding wires and steel plates: In terms of material selection, welding wires and steel plates with low element content such as C, O, N and H should be selected as much as possible to reduce gases generated during the welding process. If the C and O content in the steel plate is higher, a welding wire containing more deoxidizers (such as Mn and Si) should be used. During the welding process, oil, rust, scale and moisture on both sides of the welding wire and steel plate should be completely removed.
Reasonable selection of welding parameters: On the premise of ensuring welding quality, using a smaller welding current can reduce the generation of gas and reduce the pressure at the welding point; appropriately increasing the arc voltage will increase the arc cavity and make the welding slag layer thinner. Reducing the welding speed will increase the existence time of the liquid molten pool and low-viscosity slag, which is beneficial to gas escape and reduces cratering.
Maintain a reasonable welding angle: Increasing the angle of downhill welding will thin the slag layer due to the flow of slag, which is beneficial to reducing shrinkage cavities. In steel pipe submerged arc welding, the welding eccentricity and the inclination angle of the welding wire can be appropriately adjusted to ensure welding at the best angle and reduce and prevent weld shrinkage.
On the premise of ensuring the inherent quality of welding, reasonable selection of welding materials, especially appropriate flux, and reasonable selection and adjustment of welding process parameters can effectively reduce or prevent the occurrence of pressure pits on the surface of submerged arc welded steel pipe welds and obtain intrinsic quality Submerged arc automatic welding seams with excellent appearance.