What the manufacturing process of straight seam steel tube ?
The manufacturing process of ERW (Electric Resistance Welded) welded tubes (straight seam welded tube ) involves a series of precise steps to transform steel coils into straight seam tubes. Here's a detailed breakdown of the entire process:.
1.Material Preparation
Uncoiling and Leveling: Steel coils are loaded onto an uncoiler and passed through a leveling machine to flatten any curvature and ensure uniform thickness ..
Shearing and end Welding: The head and the end of the steel strip are sheared and welded together to form a continuous loop, allowing uninterrupted feeding into the production line. This is facilitated by accumulator to maintain constant tension.
Accumulating: some 700 meters length steel strip is stored the accumulator,which can ensure the tube mill continuously production during changing steel coil and shearing and welding .
2.Forming
Roll Forming: The flattened steel strip is gradually shaped into a cylindrical form (open-seam pipe) through a series of contour rolls. This multi-stage process involves:
Initial Bending: The strip edges are curled upwards.
Fin Passes: Subsequent rolls close the edges into a perfect circle 56.
Edge Alignment: Critical to ensure parallel edges for a high-quality weld. Techniques like "over-bending" the edges are used to minimize residual stress.
3.Welding
High-Frequency Resistance Welding: The open-seam pipe passes through a welding station where:
HF Current Application: A high-frequency (200–400 kHz) electrical current is applied via contacts or an induction coil. This exploits the skin effect and proximity effect, concentrating heat on the strip edges 16.
Forging Pressure: Squeeze rolls apply pressure to fuse the molten edges without filler metal 69.
Key Parameters: Welding speed, heat input, pressure, V-angle, and impedance position are tightly controlled. For example, thick-walled pipes may use ~400 kHz and speeds of 20 m/min.
Weld Flash Removal
Internal/External Bead Trimming: Immediately after welding, excess material (flash) is removed from inside and outside the tube using carbide cutters or scrapers. This ensures a smooth surface and prevents defects in subsequent processes
4.Sizing and Straightening
Sizing Rolls: The tube passes through calibrated rolls to achieve precise outer diameter and roundness tolerances
Straightening: Multi-roll straighteners correct any curvature or deformations introduced during previous steps .
5.Cutting and End Finishing
Flying Cut off Saws: Moving saws cut the continuous tube into predetermined lengths without stopping the production flow 56.
Chamfering/End Facing: Pipe ends are beveled (for welding) or squared off using rotating tools to meet dimensional specs.
6.Quality Control and Testing
Non-Destructive Testing (NDT):
Ultrasonic Testing (UT): Detects internal weld defects like lack of fusion or inclusions 5.
Eddy Current Testing: Identifies surface cracks and inconsistencies 1.
Hydrostatic Testing: Pipes are pressurized to verify structural integrity and leak resistance under specified standards 57.
Visual and Dimensional Inspection: Includes checks for surface defects, accurate dimensions, and straightness
Applications: Straight seam welded tubes are used in water and gas pipelines, structural applications (e.g., buildings, bridges), automotive, machinery, oil and gas (e.g., pipelines, drilling), and energy (e.g., boilers, heat exchangers)
Advantages:
Economic Efficiency: Lower cost compared to seamless tubes, especially for large diameters 1.
High Quality: Controlled processes ensure good weld strength and dimensional accuracy 13.
Versatility: Can be customized in size, material, and coating
This process ensures tubes meet stringent standards for various industries, with continuous advancements improving efficiency and quality
