It is well known that there are many types of welded steel pipes. There are always seamless steel pipes and straight seam steel pipes(LSAW), while straight seam steel pipes have weld seams, and weld seams will produce pores under certain conditions. Generally the factors causing the pores in the weld are: moisture, dirt, scale and iron filings in the flux, welding composition and thickness, steel surface quality and steel edge treatment, welding process and steel tube forming process. The weld hole of the welded pipe not only affects the tightness of the pipe weld, but also causes the pipe to leak, and it will become the induction point of corrosion, which seriously reduces the weld strength and toughness.
Steel surface treatment: in order to avoid the inclusion of iron oxide and other impurities in the unwinding and unwinding, a plate cleaning device should be provided.
Steel sheet edge treatment: rust and burr removal devices should be installed on the side of the steel plate to reduce the possibility of generating air holes. The position of the cleaning device is preferably installed after the edge milling machine and the disc cutter. The structure of the device is a movable wire wheel with two adjustable positions on one side, and the upper and lower sides of the plate are pressed.
Weld appearance: the forming coefficient of the weld is too small, the shape of the weld is narrow and deep, and the gas and inclusions do not easily float out, and the pores and slag are easily formed. Generally, the weld bead forming coefficient is controlled at 1.3-1.5, the thick-walled welded pipe takes the maximum value, and the thin-walled pipe takes the minimum value.
Reduce the secondary magnetic field: in order to reduce the influence of magnetic partial blow, the connection position of the welding cable on the workpiece should be kept away from the welding terminal only, and the partial welding magnetic cable can be prevented from generating a secondary magnetic field on the workpiece.
Process aspect: the welding speed or current should be appropriately reduced to delay the crystallization rate of the weld pool metal to facilitate gas escape. At the same time, if the strip delivery position is unstable, adjustment should be made in time to prevent fine adjustment of the front axle or rear. The bridge remains shaped, causing gas to escape.
Flux composition: when the solder contains an appropriate amount of CaF2 and SiO2, it absorbs a large amount of H2 and generates HF which is highly stable and insoluble in the liquid metal, thereby preventing the formation of hydrogen pores. The deposition thickness of the flux is generally 25-45mm, the flux particle size is large, the density is small, the stacking thickness takes the maximum value, and the minimum value is taken; the large current, the low welding speed stacking thickness takes the maximum value, and the minimum value, in addition, the summer or the air When the humidity is high, the recovered flux should be dried before use.