Welding Process: Core Technology of Electric Resistance Welded Steel Pipes
For electric resistance welded steel pipes, the welding process is the soul that determines product quality and performance. To grasp this core technology, we first clarify erw pipe meaning and what is erw pipe: ERW (Electric Resistance Welding) refers to a welding method that uses resistance heat generated by current to fuse metal. Correspondingly, electric resistance welded steel pipe is a pipe product formed by rolling steel strips into tubes and welding joints through this technology. Hebei Huayang Steel Pipe Co., Ltd. (hereinafter referred to as "Hebei Huayang") has polished its welding technology for decades, especially in hfw steel pipe production, forming unique technical advantages. This article will decode the welding process of electric resistance welded steel pipes with Huayang's practice as the main line.
Pre-Welding Preparation: The Foundation of High-Quality Welding
The quality of electric resistance welded steel pipe starts before welding. Hebei Huayang has established a strict pre-welding preparation system, covering raw material pretreatment and precision blanking, to eliminate potential defects from the source. The company uses high-quality low-alloy steel strips from Baosteel and Shougang as raw materials. Before entering the production line, each steel strip must go through derusting, degreasing and edge trimming processes.
Huayang's pre-welding workshop is equipped with 6 sets of automatic edge planers, which can process the steel strip edges into a 30° bevel with a roughness of Ra1.6μm, ensuring sufficient contact area during welding. For hfw steel pipe production, the company has higher requirements: the edge thickness deviation of the steel strip is controlled within ±0.05mm, because the high-frequency welding process is more sensitive to the uniformity of the joint. This rigorous pre-treatment ensures that the subsequent welding process is stable and reliable, laying a solid foundation for the high quality of electric resistance welded steel pipe.
Forming Before Welding: Precision Guarantee for Joint Alignment
Forming is a key link connecting raw materials and welding. It requires rolling the flat steel strip into a tubular shape with aligned edges, which directly affects the welding quality of electric resistance welded steel pipe. Hebei Huayang adopts the "multi-pass progressive forming" technology independently developed on the basis of imported equipment, which avoids the problem of uneven edge alignment caused by one-time forming.
The company's forming production line is equipped with 18 sets of precision rollers. Each pass of rolling has a dedicated parameter standard. The online laser alignment system can monitor the edge gap of the steel pipe in real time, ensuring that the gap is controlled within 0.1mm. For hfw steel pipe with small diameter and thin wall, Huayang has added a secondary correction link to prevent edge misalignment caused by elastic deformation. This precise forming technology makes the joint of the steel pipe fit perfectly before welding, creating favorable conditions for the fusion of electric resistance welded steel pipe.
Core Welding Stage: Dual Technical Paths of ERW and HFW
The welding stage is the core of electric resistance welded steel pipe production. Hebei Huayang has formed two technical systems: conventional ERW and HFW, to meet the needs of different products. First, clarify hfw meaning: HFW (High-Frequency Welding) is a branch of ERW, which uses high-frequency current (50kHz-400kHz) to realize rapid welding, and the produced hfw steel pipe has better weld performance.
For conventional ERW welding, Huayang uses low-frequency current (50Hz-60Hz) and adopts double-sided welding technology. The welding current is controlled between 800A-1200A according to the wall thickness of the electric resistance welded steel pipe. This technology is suitable for thick-walled electric resistance welded steel pipe (wall thickness ≥8mm) used in construction machinery. In the production of hfw steel pipe, the company uses induction heating welding, where high-frequency current generates eddy current on the pipe edge through the induction coil, and the edge is quickly heated to 1300-1400℃ (melting point) in 0.5 seconds. Under the extrusion of the pressure roller, the molten metal is extruded to form a weld without adding any welding materials.
Huayang's intelligent welding control system is the key to ensuring stable quality. The system can automatically adjust current, voltage and extrusion force according to the material and thickness of the steel strip. For example, when producing API 5L grade B hfw steel pipe, the system will increase the welding current by 10% and extend the heat preservation time by 0.2 seconds to ensure weld fusion. This precise control makes the weld strength of Huayang's electric resistance welded steel pipe reach 95% of the base metal.
Post-Welding Treatment: The Last Barrier to Quality
Post-welding treatment directly affects the service life and safety of electric resistance welded steel pipes. Hebei Huayang has established a "three-step post-welding process" including heat treatment, deburring and non-destructive testing. After welding, the electric resistance welded steel pipe is sent to the continuous annealing furnace for stress relief treatment. The temperature is controlled at 650-700℃, and the holding time is adjusted according to the pipe diameter, which can eliminate 80% of the welding stress.
In terms of deburring, Huayang uses mechanical internal and external deburring tools to remove weld burrs, ensuring that the inner wall of the pipe is smooth and the flow resistance of the medium is reduced. The most critical link is non-destructive testing: the company uses ultrasonic testing equipment imported from Germany and X-ray flaw detectors to conduct 100% inspection on the welds of electric resistance welded steel pipes. Even tiny cracks with a width of 0.1mm can be accurately identified.
All hfw steel pipe and conventional electric resistance welded steel pipe products of Huayang must pass these tests before leaving the factory. The product qualification rate has remained above 99.8% for many years, and has obtained ISO9001 and API 5L certifications, which are widely used in key projects such as the West-East Gas Pipeline and the Myanmar-China Oil Pipeline.
In conclusion, the welding process of electric resistance welded steel pipes is a systematic project integrating precision, intelligence and strictness. Hebei Huayang's practice shows that only by controlling every link from pre-welding preparation to post-welding inspection can we produce high-quality electric resistance welded steel pipe and hfw steel pipe. With continuous technological innovation, Huayang is constantly raising the technical threshold of the industry and contributing to the development of the global electric resistance welded steel pipe industry.
