Straight seam pipe refers to weld steel tube and steel tube parallel to the longitudinal. Generally, also known as straight seam welded pipe and straight seam steel pipe [1]. Straight seam pipe is made by high frequency welding machine will be plastic strip rolled steel strip and USES the straight seam welded together. In nominal diameter straight seam pipe specifications, according to the wall thickness can be divided into thin-walled straight seam pipe and thick wall tube two straight. According to the shape can be divided into round, square or shaped tube, etc.1. The weldingStraight seam pipe generally adopt high-frequency welding, high frequency welding is a kind of induction (or contact pressure welding) welding, it need to weld filler, no welding spatter, narrow welding heat affected zone, weld moulding beauty, weld the advantages of good mechanical performance, thus is widely used in steel production.

According to the principle of electromagnetic induction and ac charge in the conductor skin effect and proximity effect and eddy current heating effect, make the edge of the weld steel locally heated to a molten state, the squeezing roller, to realize the AC/DC Pulse TIG Welding Machine joint between the crystal butt weld, so as to achieve the purpose of the welding seam, cooled to form a solid straight seam weld.2. The weld gapWill strip into welded pipe unit, the multichannel roll rolling, strip steel rolled up gradually, there is an open space form of round billet, adjust the quantity of the squeezing roller, make the weld gap control in 1 ~ 3 mm, and the joint match on both ends. If clearance is too large, resulting in a decrease of proximity effect, eddy current heat is insufficient, the joint between the weld crystal bad and incomplete fusion or crack generation.

Proximity effect such as the gap is too small a result, the welding heat is too big, cause the burning of the weld; Or weld after extrusion, rolling the deep pit formation, affect the surface quality of the weld.3. The welding temperatureLow carbon steel material, welding temperature control in 1250 ~ 1460 , the wall thickness 3 ~ 5 mm penetration can meet the requirements. Welding temperature is mainly by regulating the high frequency eddy current to control thermal power and welding speed. When the heat input is insufficient, the heated weld edge short of welding temperature, metal organization remains solid, forming not fusion or lack of penetration; When the heat input is too large, weld edge over welding temperature of the heated, burnt or drop, make the weld formation of melt hole.Welded steel pipe refers to the steel belt or steel plate bending deformation shapes such as round, square before welding, jointed on the surface of steel pipe.