Effect of raw materials on welding quality in erw steel pipe production process

Keywords:erw steel pipe production process
The influence of raw materials on the welding quality in the production process of erw steel pipe mainly includes three aspects: unstable mechanical properties of steel strip, surface defects of steel strip and large deviation of geometrical dimensions. Therefore, it is necessary to carry out key control from these three aspects.
1) Influence of mechanical properties of steel strip on the quality of steel pipe The steel grade commonly used for welded steel pipe is carbon structural steel. The main grades are Q195, Q215, Q235 SPCC SS400 SPHC and so on. The yield point and tensile strength of the steel strip are too high, which will cause the forming of the steel strip to be difficult. Especially when the wall of the tube is thick, the resilience of the material is large, and the steel tube has a large deformation stress during welding, and the weld seam is prone to cracks. When the tensile strength of the steel strip exceeds 635 MPa and the elongation is less than 10%, the weld is prone to cracking during the welding process. When the tensile strength is lower than 30 0 MPa, the steel strip is easily wrinkled due to the soft material in the forming process. It can be seen that the mechanical properties of the material have a great influence on the quality of the steel pipe, and the quality of the steel pipe should be effectively controlled from the aspect of material strength.

2) Influence of surface defects of steel strip on the quality of steel pipe There are several types of surface defects of steel strip, such as sickle bending, wave shape, longitudinal shearing edge, etc. The file bending and wave shape generally appear in the cold rolling steel strip rolling process. Caused by improper control of the amount of reduction. During the forming process of the steel pipe, the boring and wavy shape will cause the strip to run off or overturn, which will easily cause lap welding of the steel pipe weld and affect the quality of the steel pipe. The edge of the steel strip (that is, the edge of the steel strip exhibits a jagged unevenness), which generally occurs on the slitting belt, and is caused by the blunt or unsharp edge of the slitter disc. Due to the rim of the steel strip, local shortage of meat occurs from time to time, which makes the steel strip susceptible to cracks and cracks during welding and affects the stability of the weld quality.

3) The influence of the geometrical dimension of the steel strip on the quality of the steel pipe When the width of the steel strip is less than the allowable deviation, the pressing force when welding the steel pipe is reduced, so that the welded joint of the steel pipe is not firm, cracks appear or the open pipe is a steel strip. When the width is larger than the allowable deviation, the pressing force when welding the steel pipe increases, and welding defects such as tipping, lap welding or burr appear at the welded joint of the steel pipe. Therefore, the fluctuation of the width of the steel strip not only affects the accuracy of the outer diameter of the steel pipe, but also seriously affects the surface quality of the steel pipe.
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