Factors affecting the welding quality of ERW pipes

With the development of ERW pipe technology, its application fields are constantly expanding. ERW steel pipes use the skin effect and proximity effect of electric current to quickly heat the edge of the pipe blank to the welding temperature for extrusion and welding. Compared with seamless pipes, it is obvious that ERW pipes have a weld seam, and their performance depends largely on the quality of the weld seam.

Factors affecting weld quality are complex, mainly including the following:

1. Raw Material Quality

The chemical composition, inclusions, banded structure, camber, and edge burrs of the raw materials all affect weld quality. Inclusions in the base metal, if not effectively removed during welding, will form stress concentration points in the weld metal, reducing impact toughness and flattening performance. Severe camber and edge burrs can lead to misalignment, difficulty in arc initiation, and weld skewing. HSCO steel pipes use raw materials supplied directly by large steel mills, which undergo rigorous inspection before entering the factory, including chemical composition analysis, mechanical property testing, and surface defect detection.

2. High-Frequency Welding Process Parameters

Welding temperature, speed, extrusion amount, and opening angle are the core parameters affecting weld quality:

●Welding Temperature: Too high a temperature will result in excessive burrs and overheating of the weld; too low a temperature will cause incomplete fusion.
●Welding Speed: The speed must be matched with the input power. Too high a speed will easily lead to incomplete fusion, while too slow a speed will result in excessive heat input.
● Extrusion amount: Typically 0.5-1.5 times the wall thickness, with the upper limit for thick-walled pipes.
● Opening angle: Varies with pipe diameter and wall thickness, generally controlled between 4° and 8°.

3. Welding Process Stability 

Impurities and burrs on the plate edges can cause momentary short circuits, unstable arc ignition, and even localized cold welding during high-frequency welding. Online inspections should be strengthened, including: the reliability of the high-frequency coil installation, the effectiveness of coolant filtration, the suitability of the opening angle, and the removal of burrs from the plate edges. Quality control should be supplemented by hydrostatic testing and ultrasonic testing.

4. Heat Treatment Process 

ERW steel pipes typically undergo online medium-frequency heat treatment. The length of the air cooling section from medium-frequency heating to water cooling is easily overlooked, but it directly affects the phase transformation process and final microstructure of the weld. Excessively high cooling water temperature can lead to insufficient cooling and grain coarsening; excessively low water temperature may result in hardened microstructure. The length of the air cooling section should be matched with the production line speed to ensure a uniform and fine microstructure.

HSCO focuses on customer needs, uses ERW high-frequency welding technology to achieve automated production, and has passed national standards, American standards and other certifications. In the production of welded pipes, all factors that may affect the quality of steel pipe welds are comprehensively prevented. Online non-destructive testing equipment such as hydraulic testing, ultrasonic testing, and X-ray testing protect our quality.

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