The causes and prevention measures of bore formation in welding pipe
The porosity of welding seam will not only affect the compactness of welding seam, cause pipeline leakage, but also become the inducing point of pipeline corrosion, and will reduce the strength and toughness of welding seam seriously.
The main factors that affect the porosity of the weld are: the moisture, dirt, oxide scale and scrap iron in the flux, the welding composition and covering thickness, the surface quality of the steel plate and the treatment of the steel plate edge plate, the welding process and the steel pipe forming process, etc.
Corresponding prevention and control measures are as follows:
1.Flux composition.When the welding material should contain an appropriate amount of CaF2 and SiO2, the reaction will take place to absorb a large amount of H2 and generate HF with high stability and insoluble in liquid metal, which can prevent the formation of hydrogen pores.
2.The bulk thickness of the flux is generally 25-45mm. When the flux granularity is large and the density is small, the bulk thickness shall be the maximum, otherwise the minimum value shall be taken;Packing thickness of large current and low welding speed shall be maximum, otherwise minimum.In addition, in summer or when the air humidity is high, the recovered flux should be dried before use.
3.Steel plate surface treatment.In order to avoid uncoiling and leveling the detached oxide iron sheet and other sundries entering the forming process, the panel cleaning device should be set up.
4.Steel plate edge processing.Rust and burr removal devices should be installed at the edges of steel plates to reduce the possibility of pores.
5.Weld appearance.When the forming coefficient of the weld is too small, the shape of the weld is narrow and deep, and the gas and inclusions are not easy to surface, and it is easy to form pores and slag inclusion.Therefore, the general weld forming coefficient should be controlled at 1.3-1.5, with the maximum value for thick-wall welded pipe and the minimum value for thin-wall welded pipe.
6.Reduce secondary magnetic field.In order to reduce the influence of magnetic bias blowing, the welding cable on the workpiece should be connected as far away from the welding terminal as possible to avoid the secondary magnetic field generated on the workpiece by part of the welding cable.
7.Production technology.The welding speed should be appropriately reduced or the current should be increased to delay the crystallization rate of the weld pool metal so as to facilitate the gas escape.At the same time, if the strip delivery position is not stable, it should be adjusted in time to prevent the formation of the front or rear axle by frequent fine-tuning, which will cause difficulties in gas escape.
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