At present, the general longitudinal welded pipe for common fluids in the market is generally used in high frequency resistance welding production. Its characteristics are high production efficiency, small welding heat affected zone and low quality requirement for the bonding surface. However, any change in the shape of V-shaped opening in the forming process may lead to welding quality problems.


Groove processing is to use groove joints as pipe fittings in the pipeline pretreatment process. Its working principle is to drive the rotating pipe with a groove rolling machine. The radial pressure of the follow-up pressure roll in the radial direction of the pipe is applied to the structure of the pressure roll welded pipe to cool out the designated groove in a fixed position.


"Groove cracking" is the basic reason for the insufficient strength of the weld, coupled with the serious deformation of groove processing, resulting in stress concentration and tearing of the weld. Raw material is the source of product quality, and its characteristics must be mastered in production. From the point of view of welding, the influence of raw materials on weld quality is mainly reflected in the two aspects of material welding and structure. The shape of alloying elements and welding quality will also be affected. The high content of sulfur and phosphorus in the material can easily lead to crystallization segregation; the high content of carbon can promote the formation of martensite, brittle the weld metal; the grain size of the metal structure is too large, the direction of the weld crystal will be enhanced; and it is easy to promote the separation of impurities. Inclusions contain non-metallic materials, layering, width and thickness fluctuations. Various factors may lead to weld cracking and reduce weld strength.


The main welding parameters of ERW steel pipe include input power, original production speed, opening angle, welding pressure, induction coil (induction contact) and impedance position. The unreasonable setting of welding parameters is an important reason for the cracking of rolling groove. If the input power is not enough, the speed is too fast, the input heat is insufficient, the edge of the strip is not fully melted, and the solid oxide at the end can not be extruded to form low-temperature welding defects; on the contrary, the input heat is too large, metal splash and return inclusions and other defects. Secondly, welding pressure is also important. If the welding pressure is insufficient, the fusion line on both sides of the metal structure streamline is not obvious and the welding strength does not meet the requirements; on the other hand, the welding pressure is too high, the weld line is irregular and the rising angle of the metal streamline is too large, which should be reduced only when the welding pressure is appropriate, the fusion line is not deformed, and the metal streamline angle is 45 ~60 ideal state to ensure the welding strength.