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