High frequency welding influence on welding quality of steel pipe

HIGH-FREQUENCY WELDING is a welding process in which the heat source used to melt the joining surfaces is obtained from high-frequency (HF) alternating current (ac) resistance heating.

Steel weld gap control

Adjusting the amount of pressing the squeeze roll is maintained across the weld flush with the opening angle of 7 degrees or less, the gap control between 1-3 mm. Weld control is too large, it may appear poor welding, weld cracking produce incomplete fusion or weld control is too small, due to the excessive heat, weld likely to cause burning, molten metal splash, build-up is too large, affecting the quality of welding. (Splatter reasons: melt extrusion tube side, the internal pressure is greater than the surface of the weld steam pressure)

Regulation of high-frequency induction loop position

Induction coil placement should be in the same center line pipe, induction loop front roll center line distance from the squeeze, squeeze rollers under the premise does not burn , depending on pipe size as close, too far away when the heat affected zone width, weld strength will decrease. Coupled induction coil more tightly as possible, the selection of a single circle, should be equal to the width of the induction coil pipe diameter. Optional lap or two laps great impact on high frequency oscillation frequency and output efficiency.

Impedance (also known as magnet) position control

Impedance is a group or a special magnet whose cross-sectional area of 70% attributable to the inner diameter of the steel pipe section. Its role is to strengthen the electromagnetic induction, eddy currents concentrate the heat weld edges. Sometimes add some magnets outside the weld, can also play a supporting role. Magnet permeability on temperature is large, the lower the temperature the higher the permeability. Magnet should be placed in the heating section V-zone, squeezing front roll center position, the position of the magnet and the magnetic permeability of welded directly affect the efficiency and weld quality.

Heat output control

High-frequency power input to the heat pipe weld area called the input of heat, lack of heat input welding speed is too fast, can not reach the edge of the pipe welding temperature, the formation of incomplete fusion or penetration of the crack but excessive heat input when welding speed is too slow, too prone to burning, so that the weld breakdown, causing metal splash, the formation of pores. By adjusting the speed of the high-frequency voltage or welding method, the size of the control input of heat, the steel pipe weld neither appear nor appear incomplete penetration welding wear phenomenon, reaching the welding quality requirements.

Weled steel pipe specification, Standard and identification

Welded steel pipe (steel pipe manufactured with a weld) is a tubular product made out of flat plates, known as skelp, that are formed, bent and prepared for welding.