We know the quality of the raw materials have a deep influence on the quality of the ERW steel pipe, but how? Below we will discuss how the quality of steel trips influence the quality of ERW steel pipe during the production.
1.Why the mechanical properties of the steel trips can affect the quality of ERW steel pipe?
For ERW steel pipe, the commonly used steel type is carbon steel. The steel standard and grade includes API 5L GR.B -X70, ASTM A53 GR.A/B/C, ASTM A500 GR.A/B/C etc.
If the strip yield point and tensile strength is too high, it will cause difficulties during the steel strip forming. Specially for producing thick wall ERW steel pipe, cracking is easy to happen during pipe welding due to the large resilient materials, large deformation stress. When the tensile strength of steel strips exceeds 635 MPa and elongation less than 10%, cracking can be happen during the welding process. When the tensile strength is less than 300MPa, the strip material in the molding process can easily have a wrinkled surface, because the low tensile strength means soft physical properties. Therefore, the mechanical properties have great influence on the quality of ERW steel pipe. Particularly, the tensile strength of the material effectively controlled the quality of the ERW steel pipe.
2.How the impact on the steel strips surface defects influence the quality of ERW steel pipe?
The steel strips surface defects includes common camber, wavy edge slitting etc. Camber and wavy are generally appeared in the cold rolled strip rolling process, it is controlled by the improper reduction. During the ERW steel pipe forming process, camber will cause steel strips deviation or flip.
Uneven strip edge is generally appeared in the slitting, the slitting machine causes the disc blade blunt or sharp result. Because of the uneven strip edge, the steel strips might have unexpected crack which affect the stability of the welding quality.
3.Why the steel strip geometry will influence the quality of ERW steel pipe?
When the width of steel strips is less than the tolerance, the pressing force will be reduced. It will cause unstable welding seam or welding seam cracking. When the width of steel strips is greater than the tolerance, the squeeze pressure increased, it will cause burrs or lap welding and other welding defects. Therefore, the fluctuations of the steel strips width, can affects the accuracy of the outer diameter of the steel pipe. Also, it can seriously affect the quality of the surface of the steel pipe.
The fluctuation of the steel strip thickness can affect the accuracy of the finished steel pipe thickness. If the steel strips have vary thickness, it will cause unstable pressure force and welding temperature during the steel pipe welding process, in the end it resulting in unstable quality ERW steel pipe welding. Therefore, before steel pipe welding, we need to check each roll of steel strips surface quality as well as the geometry of each roll. For those does not meet the quality standard steel strips, we will not used for the production of ERW steel pipe to avoid unnecessary losses.
