Forming Process Of Steel Pipes

Steel pipe forming is the core link that determines the structure, precision, and performance of steel pipes. Different forming processes are developed to meet diverse application needs-for example, electric resistance welded steel pipes (including ERW and hfw steel pipes) rely on welding after plate forming, while seamless steel pipes are formed by piercing solid billets. At Hebei Huayang Steel Pipe Co., Ltd., the focus is on ERW-based forming processes, which account for over 90% of its production capacity (annual output of 50,000 tons of electric resistance welded steel pipes).

Understanding forming processes is closely linked to clarifying core concepts. For example, what is erw pipe? It is an electric resistance welded steel pipe formed by rolling a steel plate into a pipe blank and welding via resistance heat-this definition directly reflects its "plate forming + welding" process characteristics. Similarly, hfw meaning (High-Frequency Welding) emphasizes the upgraded forming-welding integration technology for high-performance pipes. Below, we focus on the forming processes of ERW pipes (ordinary and hfw steel pipes) and compare them with other mainstream processes.

Steel Pipes

Before forming, strict raw material preparation is required to ensure subsequent process stability-this is a key step Huayang never compromises on.

Huayang uses hot-rolled low-carbon/medium-carbon steel coils (Q195-Q345) for ERW pipe forming, with the following inspection standards:

Chemical composition: Carbon content ≤0.25% (ensures good weldability for resistance welding), sulfur/phosphorus content ≤0.035% (avoids brittle cracks during forming);

Surface quality: No rust, pits, or cracks (detected by a laser surface scanner, rejecting coils with defects deeper than 0.5mm);

Dimensional precision: Thickness deviation of steel coils ≤±0.05mm (controlled by ultrasonic thickness gauges), ensuring uniform wall thickness of the formed pipe.

In 2024, Huayang rejected 12 batches of unqualified steel coils (accounting for 1.5% of total procurement), laying the foundation for high-quality forming.

The steel coils are first uncoiled and leveled (using a 12-roller leveler to ensure flatness deviation ≤0.1mm/m), then cut into fixed-length plates (6m-12m, customizable per customer needs). Next, the plate edges are trimmed into a V-shape (angle 30°-45°, width 5mm-8mm) using a precision edge trimmer-this "V-edge" design increases the contact area during welding, ensuring full fusion of the pipe blank edges.

Steel Pipes

Huayang adopts the "multi-roll gradient forming process" for ERW pipe forming, which is divided into three stages to gradually bend the flat plate into a cylindrical pipe blank-this avoids excessive stress concentration and ensures dimensional precision.

The trimmed steel plate is fed into the pre-forming unit, which is equipped with 4-6 sets of horizontal rolls. The rolls apply gradually increasing pressure (5kN-15kN) to bend the plate into a U-shape. Key control points:

Curvature consistency: The radius of the U-shaped bottom is equal to half the pipe's inner diameter (e.g., Φ219mm pipes require a bottom radius of 109.5mm);

Edge alignment: The two edges of the U-shaped plate are kept parallel, with a gap ≤0.3mm (monitored by a visual alignment system).

The U-shaped plate enters the intermediate forming unit (3-4 sets of vertical rolls), which further bends the two sides of the U-shape upward to form a semi-circular pipe blank. Huayang's unique "elastic forming" technology is used here:

The rolls apply flexible pressure (8kN-20kN) to avoid plastic deformation of the steel plate;

The semi-circular opening is controlled to 30°-40°, ensuring smooth entry into the final forming stage.

The semi-circular blank enters the final forming unit (2-3 sets of combined horizontal-vertical rolls), which closes the opening to form a cylindrical pipe blank. This stage is critical for dimensional precision:

Outer diameter control: A laser diameter measuring instrument real-time monitors the pipe blank outer diameter, with deviation adjusted to ≤±0.1mm (e.g., Φ325mm pipes are controlled at 325±0.1mm);

Ovality control: The combined rolls adjust the pressure on different sides to ensure ovality ≤0.5% (e.g., Φ114mm pipes have an ovality ≤0.57mm);

Seam gap control: The gap between the two edges of the pipe blank is kept at 0.1mm-0.2mm, creating optimal conditions for subsequent welding.

After forming, the pipe blank undergoes two key treatments before welding:

Seam preheating: The pipe blank edge is preheated to 300℃-400℃ using an induction heater (reducing welding stress for ERW pipes);

Sizing and straightening: A 6-roll sizing machine adjusts the pipe blank to the standard outer diameter, and a straightening machine corrects bending (straightness deviation ≤1mm/m).

Huayang's ERW pipe forming process takes only 2-3 minutes per 6m pipe, with a forming precision pass rate of 99.7%-this efficiency and precision lay the foundation for the company's status as a leading electric resistance welded steel pipe manufacturer.

Steel Pipes

HFW steel pipes are high-performance variants of electric resistance welded steel pipes, and their forming process is an upgraded version of ordinary ERW forming-optimized for high-pressure scenarios. The core differences at Huayang are:

Huayang uses imported German SMS high-frequency forming-welding integrated lines for hfw steel pipes, with the following upgrades:

Servo-controlled rolls: The forming rolls are driven by servo motors (positioning accuracy ±0.01mm), ensuring consistent pressure application;

Real-time stress monitoring: A strain gauge system monitors the pipe blank stress during forming, avoiding over-stretching (stress control ≤250MPa);

Cooling control: A water-cooling system cools the pipe blank during forming, preventing grain coarsening (temperature controlled at 200℃-250℃).

Unlike ordinary ERW pipes (seam gap 0.1mm-0.2mm), hfw steel pipes use "narrow seam forming" (gap 0.05mm-0.1mm) to match high-frequency welding:

The final forming rolls apply higher pressure (25kN-35kN) to reduce the seam gap;

A plasma cleaning device removes oxide from the seam edge, ensuring welding quality.

The biggest advantage of hfw steel pipes is the integration of forming and welding-Huayang's process achieves "forming-welding synchronization":

The pipe blank is formed and immediately enters the high-frequency welding station (no intermediate storage, avoiding seam misalignment);

The forming rolls and welding electrodes are coaxial, ensuring the weld is centered (weld offset ≤0.1mm).

This integration ensures Huayang's hfw steel pipes have excellent pressure resistance: Φ325×10mm pipes can withstand 12MPa hydrostatic pressure, meeting the national standard for natural gas transportation (GB 9711). In the 2023 Shanxi-Beijing Natural Gas Pipeline Project, 3,000 tons of these pipes passed strict forming-welding quality inspections, with a weld qualification rate of 100%.

Seamless steel pipes are formed by piercing solid steel billets, with the following characteristics:

Process complexity: Requires heating (1200℃-1250℃), piercing, rolling, and sizing-production efficiency is 1/5 of ERW pipes;

Cost: Raw material and energy costs are 50% higher than electric resistance welded steel pipes;

Application: Suitable for ultra-high pressure scenarios (≥20MPa) where welding is not allowed.

Huayang does not produce seamless pipes but provides customers with objective comparisons: for most low-to-high pressure scenarios (≤10MPa), hfw steel pipes or ordinary ERW pipes are more cost-effective.

EFW pipes (Electric Fusion Welded) use spiral forming for large-diameter pipes:

Process: Steel coils are rolled into spiral pipe blanks at 30°-60°, with low precision (ovality ≥1%);

Efficiency: Forming speed is 1-5m/min, only 1/10 of HFW pipes;

Application: Limited to large-diameter (≥800mm) medium-pressure scenarios.

Huayang's technical team often explains to customers: if the pipe diameter is ≤630mm, ERW forming (especially HFW) is superior in precision and efficiency; only when diameter exceeds 630mm is spiral EFW forming considered.

Huayang has equipped all forming lines with MES (Manufacturing Execution System), which:

Real-time collects forming parameters (pressure, temperature, speed) and stores them in a database;

Automatically adjusts parameters when deviations occur (e.g., increasing roll pressure if outer diameter is too small);

Generates forming quality reports for each batch, ensuring traceability.

For special specifications (e.g., non-standard outer diameter, thick-walled pipes), Huayang provides customized forming:

Adjusts roll profiles and forming pressure for non-standard diameters (e.g., Φ180×9mm pipes);

Optimizes preheating temperature for thick-walled pipes (≥16mm) to avoid cracking.

In 2024, Huayang completed 80 customized forming orders, with a customer satisfaction rate of 98%.

In summary, steel pipe forming is a technology-intensive link that directly affects product quality and cost. As a professional manufacturer of electric resistance welded steel pipes, Huayang has accumulated rich experience in ERW and HFW forming processes-its multi-roll gradient forming, high-precision control, and customized solutions make it a reliable partner for customers in civil, industrial, and high-pressure scenarios.