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Spiral steel pipe weld gap as too large, then reductions constitute vicinity effect, eddy current lack of heat, poor weld crystal indirect co-occurrence of incomplete fusion or cracking; if the gap is too small, the effect is increased near constitute, excessive heat welding to form welding seam burning; perhaps weld by kneading, constitute pit after rolling, affecting the quality of the weld surface of the tube is heated to the welding of two marginal temperature, at kneading roll kneading, together constitute the metal grain mutual penetration, crystal, ending spiral pipe welds constitute strong kneading force if too small, the number of crystals together constitute small, weld metal strength decreases, cracking may occur after the force;. If kneading excessive force will make the molten metal is extruded weld condition, not only reduces the weld strength, and the list will be a lot of glitches, and even take constitute welding seam defects.