Welding Process Of Steel Pipes

Steel Pipes

Welding is the core step that transforms formed steel pipe blanks into finished pipes, directly determining the strength, tightness, and service life of the product. For electric resistance welded steel pipes (the main product of Hebei Huayang Steel Pipe Co., Ltd.), welding technology is even more critical-different welding methods (such as ordinary ERW and HFW) correspond to distinct performance and application scenarios.

To understand steel pipe welding, we first need to clarify core concepts. What is erw pipe? It is an electric resistance welded steel pipe that uses resistance heat generated by electric current to fuse pipe blank edges-this definition directly points to the core of its welding process. Similarly, hfw meaning (High-Frequency Welding) is an upgraded ERW technology, optimized for high-pressure and high-precision scenarios. Huayang's annual output of 50,000 tons of electric resistance welded steel pipes relies entirely on mature ERW and HFW welding processes, covering civil water supply, industrial fluid transportation, and high-pressure oil and gas transmission.

Below, we focus on the welding processes of electric resistance welded steel pipes (ordinary ERW and hfw steel pipes) and compare them with other mainstream welding methods, highlighting Huayang's technical advantages and practical experience.

Steel Pipes

Ordinary ERW (Electric Resistance Welding) uses low-to-medium frequency current (50Hz-3kHz) to generate resistance heat, suitable for low-pressure electric resistance welded steel pipes (working pressure ≤2MPa). This process is the core of Huayang's civil pipe production line (e.g., scaffolding pipes, indoor gas pipes), with a welding efficiency of 10-20m/min.

Before welding, Huayang strictly controls two key links to avoid welding defects:

Seam Cleaning: The edges of the pipe blank (formed by multi-roll gradient forming) are cleaned with a wire brush and alcohol to remove oil, rust, and oxide-this prevents air bubbles in the weld. For Φ48×3.5mm scaffolding pipe blanks, Huayang's automatic cleaning system ensures a cleaning width of 5mm on each side of the seam.

Electrode Maintenance: The copper electrodes (used to conduct current) are polished daily to maintain a smooth surface (roughness ≤Ra0.8μm). Worn electrodes (with a wear depth exceeding 0.5mm) are replaced immediately to ensure uniform current conduction.

Huayang's ordinary ERW welding process is divided into three stages, with precise control of current, pressure, and temperature:

The pipe blank is clamped by two copper electrodes (upper and lower), and a medium-frequency current (1kHz-3kHz) is applied. The current passes through the pipe blank edges (with high electrical resistance), generating heat that raises the edge temperature to 1200℃-1300℃ (the melting point of low-carbon steel). Huayang uses a current feedback system to adjust the current in real time-for Φ114×4.5mm gas pipe blanks, the current is stabilized at 800A-1000A to avoid overheating or underheating.

When the pipe blank edges reach the plastic melting state, the extrusion rolls (located behind the electrodes) apply pressure (2MPa-5MPa) to squeeze out molten metal and air, fusing the two edges into a single weld. The extrusion pressure is adjusted according to the pipe wall thickness: for 2mm-thin pipes, the pressure is 2MPa (to avoid pipe deformation); for 16mm-thick pipes, the pressure is increased to 5MPa (to ensure full fusion).

After welding, the excess weld bead (height 1-2mm) is removed by a mechanical trimmer-Huayang's trimmer uses a tungsten carbide blade to ensure the weld surface is smooth (deviation ≤0.2mm from the pipe body). This step not only improves the pipe's appearance but also reduces stress concentration at the weld, extending the service life.

For ordinary ERW pipes, Huayang conducts two key inspections to verify welding quality:

Ultrasonic Flaw Detection: A portable ultrasonic detector scans the weld 360° to detect internal defects (such as cracks or inclusions) with a sensitivity of ≥0.5mm. The pass rate of Huayang's ordinary ERW pipe welds is ≥99.5%.

Hydrostatic Pressure Test: The welded pipe is filled with water and pressurized to 1.2 times the rated pressure (e.g., 2.4MPa for 2MPa-rated pipes) for 5 minutes. No leakage or pressure drop indicates a qualified weld. In the 2023 Baoding Affordable Housing Project, 2,500 tons of Φ48×3.5mm ERW scaffolding pipes all passed this test.

Steel Pipes

HFW (High-Frequency Welding) is an upgraded ERW technology, using 300kHz-500kHz high-frequency current to achieve rapid, uniform welding. This process is used for hfw steel pipes (high-performance electric resistance welded steel pipes), suitable for high-pressure scenarios (working pressure ≤10MPa) such as oil and gas transportation. Huayang's hfw steel pipe welding line uses imported German SMS equipment, with a weld strength reaching 95% of the base metal.

Compared with ordinary ERW, HFW welding has three core upgrades at Huayang:

Instead of copper electrodes directly clamping the pipe blank, HFW uses an induction coil to generate a high-frequency magnetic field around the pipe blank. The magnetic field induces eddy currents on the pipe blank surface, which only heat the edge (heating width ≤2mm) instead of the entire pipe body. This "local heating" avoids grain coarsening of the base metal-for Φ325×10mm hfw steel pipe blanks, the edge temperature is precisely controlled at 1250℃-1300℃, while the pipe body temperature remains below 200℃.

HFW welding speed reaches 30-60m/min (3 times that of ordinary ERW), requiring synchronous cooling to prevent weld deformation. Huayang's HFW line is equipped with a water mist cooling system that sprays atomized water on the weld immediately after extrusion-this reduces the weld cooling time from 5 minutes (ordinary ERW) to 30 seconds, improving production efficiency while refining weld grains.

To further improve the toughness of hfw steel pipes, Huayang adds a full annealing step after welding:

The welded pipe is fed into a continuous annealing furnace and heated to 700℃-750℃ (the recrystallization temperature of low-carbon steel);

It is held at this temperature for 5 minutes to eliminate welding internal stress;

It is cooled to room temperature at a rate of 50℃/hour to avoid thermal stress.

After annealing, the impact toughness of Huayang's hfw steel pipes at -40℃ reaches ≥60J/cm², meeting the low-temperature resistance requirements of northern oil and gas pipelines.

For hfw steel pipes (critical for high-pressure safety), Huayang implements a "three-inspection system" to ensure weld quality:

Pre-Welding Inspection: Check the pipe blank's seam gap (controlled at 0.05mm-0.1mm) and induction coil position (coaxiality deviation ≤0.1mm);

In-Welding Monitoring: Use a thermal imager to real-time monitor the weld temperature and a pressure sensor to track extrusion force-any deviation triggers an automatic alarm;

Post-Welding Inspection: Conduct X-ray flaw detection (to detect internal defects) and tensile testing (to verify weld strength). In the 2023 Shanxi-Beijing Natural Gas Pipeline Project, 3,000 tons of Φ325×10mm hfw steel pipes had a weld qualification rate of 100% after X-ray inspection.

Submerged Arc Welding is the main method for EFW (Electric Fusion Welded) pipes, using arc heat and granular flux for welding. Its characteristics are:

Advantages: Suitable for thick-walled pipes (wall thickness ≥20mm) and large diameters (≥800mm);

Disadvantages: Low efficiency (1-5m/min), high cost (needs welding wire and flux), and high risk of slag inclusion.

Huayang does not use SAW but provides customers with comparisons: for pipes with diameter ≤630mm and pressure ≤10MPa, hfw steel pipes are more cost-effective and reliable than SAW-welded EFW pipes.

TIG welding uses an inert gas (argon) to protect the weld, suitable for small-diameter precision pipes (≤50mm). However, its efficiency is extremely low (0.5-1m/min), and it is not suitable for mass production-Huayang only recommends it for custom ultra-small diameter pipes (e.g., Φ15×2mm precision instrument pipes), while ordinary small-diameter pipes (e.g., Φ25×2mm) still use ERW welding.

Huayang has equipped all ERW and HFW welding lines with an intelligent control system that:

Stores welding parameters for 500+ common specifications (e.g., Φ48×3.5mm ERW: current 800A, pressure 3MPa);

Automatically adjusts parameters according to pipe blank thickness and material (e.g., increasing current by 10% for Q345 steel);

Records welding data (current, pressure, temperature) for each pipe, enabling traceability.

Huayang's welding team includes 20+ senior welders (with national level-2 or above certificates), who undergo quarterly training on new technologies (e.g., HFW annealing parameter optimization). In 2024, the team won the first prize in the Hebei Provincial Steel Pipe Welding Skill Competition, verifying their technical proficiency.

In summary, steel pipe welding is a technology-intensive process that requires precise control of heat, pressure, and post-treatment. As a professional manufacturer of electric resistance welded steel pipes, Huayang has accumulated rich experience in ERW and HFW welding-its strict quality control, intelligent equipment, and professional team ensure that every electric resistance welded steel pipe (whether ordinary ERW or high-performance hfw steel pipe) meets national standards and customer requirements, becoming a reliable choice in the market.