Tube Mill Line: Process Flow, Working Principle, Applications

With the continuous increase in requirements for steel pipe quality and production efficiency across industries such as construction, energy, and machinery manufacturing, the tube mill line—as the core equipment for welded steel pipe production—is steadily evolving toward higher precision, higher automation, and greater operational stability.

This article provides a systematic overview of the tube mill line from the perspectives of process flow, working principle, application fields, and technical advantages.

I. Process Flow of the Tube Mill Line

A complete tube mill line typically consists of the following main processes:

Uncoiling and Leveling

The steel coil is unwound by the uncoiler and then leveled to eliminate internal stress, ensuring adequate strip flatness for subsequent forming.

Shearing and End Welding

The strip head and tail are sheared and automatically welded together to ensure continuous and stable production.

Forming Section

The steel strip passes through multiple forming stands, where it is gradually bent from a flat strip into a round pipe or square/rectangular tube shape.

High-Frequency Welding

High-frequency induction welding technology is used to heat the open edges of the tube blank, which are then pressed together to form a strong and uniform weld seam.

Internal and External Burr Removal

Weld beads on both the inner and outer surfaces are removed to improve surface quality and overall pipe performance.

Sizing and Straightening

Sizing mills and straightening units ensure accurate outer diameter tolerance and straightness of the finished pipe.

Online Inspection and Fixed-Length Cutting

Non-destructive testing systems are used to monitor weld quality in real time, followed by automatic cutting to preset lengths.

Finished Product Collection and Packaging

Qualified pipes are transferred to the run-out table for bundling, storage, or shipment.

II. Working Principle Analysis

The core operating principle of a tube mill line is continuous forming combined with high-frequency welding.
During production, the steel strip is gradually shaped into a tubular form by multiple forming rolls. High-frequency current generates skin effect and proximity effect along the strip edges, rapidly heating the welding zone to a plastic state. Under the pressure of squeeze rolls, a reliable metallurgical bond is formed.

This welding method offers several advantages, including:

Small heat-affected zone

High welding speed

High weld strength

Excellent suitability for continuous, high-speed production

III. Application Fields

Thanks to its stability and adaptability, the tube mill line is widely used across various industries:

Construction and structural engineering: scaffolding pipes, structural pipes, square and rectangular tubes

Oil and gas industry: transmission pipelines, low-pressure fluid pipes

Machinery manufacturing: equipment pipes, precision structural tubes

Automotive and home appliance industries: welded pipes for components

Agriculture and municipal engineering: irrigation pipes, water supply and drainage pipes

In the international market, the tube mill line—also commonly referred to as “Molino de Tubos”—has become essential equipment for steel pipe manufacturers seeking large-scale and standardized production.

IV. Core Advantages of the Tube Mill Line

High Production Efficiency

The continuous production mode enables high-speed operation, making it suitable for large-volume orders.

Excellent Dimensional Accuracy and Consistency

Multi-pass forming and precise sizing control ensure stable outer diameter and wall thickness.

High Degree of Automation

Integration with PLC control systems and online inspection equipment significantly reduces labor dependency.

High Material Utilization

Low welding loss and high yield rate help reduce overall production costs.

Strong Production Flexibility

By changing roll sets and adjusting process parameters, the line can produce pipes of different sizes and cross-sectional shapes.

Against the backdrop of the steel pipe industry’s shift toward high quality and intelligent manufacturing, the tube mill line has become more than just production equipment—it is a critical tool for enhancing competitiveness and product value. With the ongoing integration of automation, online inspection, and energy-saving technologies, tube mill lines will continue to demonstrate strong technical advantages across a wider range of applications.

V. Frequently Asked Questions (FAQ)

Q1: What is the investment required for a complete tube mill line, and what is the payback period?

A: The investment depends on configuration level, capacity requirements, and automation degree. The payback period is closely related to capacity utilization, product value, and local market conditions. A detailed ROI analysis is recommended, with priority given to equipment featuring modular upgrade capabilities.

Q2: How long does it take to change pipe sizes on the production line?

A: Modern lines typically use quick roll-change systems, with size changeovers taking 30–90 minutes. Lines equipped with multi-function stands or “no-roll-change” technology can reduce this time to less than 15 minutes.

Q3: Does size changeover significantly affect production output?

A: The impact on single-batch output is limited and mainly depends on batch size. Proper production scheduling and reduced changeover frequency can effectively minimize capacity loss.

Q4: How is weld quality consistency ensured?

A: Quality is ensured through multiple measures:

Process control: closed-loop welding temperature control systemsOnline inspection:

Ultrasonic testing (for lack of fusion, porosity, etc.)

Eddy current testing (surface defects)

Laser diameter measurement (dimensional monitoring)

Q5: What is the automation level, and how many operators are required?

A: A standard configuration typically requires 3–5 operators. Fully automated lines can achieve automatic coil loading, welding parameter adjustment, and finished pipe bundling. “Lights-out production” is technically feasible, though investment and maintenance costs must be considered.

Q6: What technical support do equipment manufacturers usually provide?

A: Support typically includes:

Pre-sales: plant layout planning and process design

Installation phase: on-site guidance, commissioning, and training

Operation phase: remote technical support, preventive maintenance, spare parts supply

Upgrade services: automation and process optimization

Q7: What materials can the production line process, and what are the raw material requirements?

A: Common materials include low-carbon steel, low-alloy steel, stainless steel (with special configuration), galvanized and coated steel.
Key raw material requirements:

Thickness tolerance: ≤ ±5%

Width tolerance: ≤ ±1 mm

Larger coil weight is preferred to reduce downtime

Q8: How can long-term adaptability of the production line be ensured?

A: Modular design, reserved drive power, wider processing ranges, and open control systems are recommended to accommodate future product upgrades.

Q9: Is daily maintenance complicated? What are the main costs?

A: Daily maintenance is relatively standardized and includes lubrication, roll inspection, weld system cleaning, and checks of transmission and electrical systems.

Q10: What are the main differences between tube mill lines from different manufacturers?

A: Differences mainly lie in core component brands, design philosophy, control system intelligence, service network coverage, and industry experience. Customers are advised to visit operating reference lines of the same type.

Why Choose Aogang as Your Partner

As a professional manufacturer in the steel pipe production equipment industry, Aogang Machinery Co., Ltd. has accumulated extensive experience and technical expertise in tube mill lines and welded pipe production systems. Choosing Aogang means not only selecting high-performance equipment, but also a complete, efficient, reliable, and intelligent manufacturing solution.

High-Speed Stability and Precision Forming

Aogang tube mill lines feature robust mechanical structures, with maximum line speeds up to 130 m/min. Even under high-speed operation, they ensure consistent dimensional accuracy and forming quality, meeting stringent industrial standards.

Advanced Technology Integration for Efficient Production

The production line integrates PLC automatic control systems, servo motor drives, and high-frequency induction welding, combined with burr-free cutting systems, enabling fully automated and continuously efficient operation with uniform weld seams and clean cutting edges.

Wide Size Range and Flexible Customization

Aogang equipment supports the production of round pipes, square and rectangular tubes, oval tubes, and various customized profiles. It is compatible with multiple materials such as low-carbon steel, galvanized steel, and high-strength steel, meeting diverse industry needs in construction, automotive, furniture, and energy sectors.

Intelligent Size Changeover and Energy Efficiency

Self-developed intelligent sizing and quick size-change systems allow fast specification changes without dismantling tooling, significantly improving production flexibility. At the same time, advanced variable-frequency control and centralized fume extraction systems help reduce energy consumption and environmental impact.

Comprehensive Service System and Technical Support

Aogang provides complete pre-sales, in-sales, and after-sales services, including plant layout planning, installation and commissioning, operator training, remote technical support, and timely spare parts supply. With over 20 years of industry experience and successful project deliveries worldwide, Aogang has earned strong international customer trust and long-term partnerships.