Stainless Steel Coil Tube — Industrial Riveted Piping System
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.
Product Code: JX-CT-1249
Category: Literature Study / Technical Reference — Chassis Piping Riveting Machine Design and Application
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) is a precision-engineered continuous coil-forming product designed for industrial piping systems, particularly for chassis piping applications in automotive, aerospace, and heavy machinery sectors. This product line represents the culmination of advanced metallurgical research and precision manufacturing methodologies, developed in conjunction with specialized riveting machine design principles for seamless, high-integrity pipe assembly.
The coil tube format offers significant advantages over traditional straight-length pipe stock, including reduced material waste during fabrication, continuous production capability, and enhanced dimensional consistency throughout the coil length. The product is manufactured to meet or exceed international standards for stainless steel tubing, ensuring reliable performance in demanding industrial environments.
2. Material & Properties
2.1 Base Material
The coil tube is fabricated from high-grade Stainless Steel (Austenitic), with primary alloy grades including:
- AISI 304 (UNS S30400): General-purpose grade with excellent corrosion resistance and formability. Contains 18% Chromium (Cr) and 8% Nickel (Ni).
- AISI 316 (UNS S31600): Enhanced corrosion resistance grade with 2% Molybdenum (Mo) addition, suitable for aggressive chemical and marine environments.
- AISI 321 (UNS S32100): Titanium-stabilized grade resistant to intergranular corrosion at elevated temperatures.
2.2 Mechanical Properties
- Tensile Strength (UTS): ≥ 520 MPa (for 304 grade in annealed condition)
- Yield Strength (0.2% Proof Stress): ≥ 205 MPa
- Elongation at Break: ≥ 40% (minimum)
- Hardness: ≤ 210 HB (annealed condition)
- Impact Toughness (Charpy V-Notch): ≥ 47 J at 20°C
- Thermal Conductivity: 16.3 W/(m·K) at 100°C
- Thermal Expansion Coefficient: 17.3 × 10⁻⁶ /°C (20–100°C)
2.3 Corrosion Resistance
The austenitic stainless steel microstructure, stabilized by Chromium and Nickel, provides a self-healing passive oxide film (Cr₂O₃) on the surface. This confers resistance to atmospheric corrosion, mild acids, alkalis, and a wide range of organic and inorganic chemicals. The addition of Molybdenum in 316 grade further enhances pitting and crevice corrosion resistance, with a Pitting Resistance Equivalent Number (PREN) of ≥ 24.
3. Technical Specifications
| Parameter | Specification | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 6.0 mm – 50.8 mm (1/4" – 2") | ASTM A554 / EN 10217 |
| Wall Thickness | 0.5 mm – 3.0 mm | ASTM A554 / GB/T 12771 |
| Bend Radius (Minimum) | ≥ 3 × OD | ISO 4413 |
| Coil Length | Continuous coil, typical 500 m – 3,000 m per coil | Manufacturer Standard |
| Coil Weight | 500 kg – 2,000 kg per coil | — |
| Surface Finish | 2B (Cold Rolled & Annealed) / BA (Bright Annealed) / No. 4 Brushed | ASTM A480 |
| Surface Roughness (Ra) | 0.4 – 1.6 μm (2B finish) | ISO 1302 |
| OD Tolerance | ± 0.1 mm (for OD ≤ 25.4 mm) | EN 10217-7 |
| Wall Thickness Tolerance | ± 10% of nominal | ASTM A554 |
| Roundness Tolerance | ≤ 2% of OD | ISO 1128 |
| Operating Temperature Range | −196°C to +870°C (304 grade) | ASTM A240 |
| Maximum Working Pressure | Up to 15 MPa (depending on OD and wall thickness) | EN 10217 |
| Material Grade | AISI 304 / 304L / 316 / 316L / 321 | ASTM A554 / EN 10217 |
| Joining Method | Riveted / Brazed / Welded (TIG / Orbital) | ASME BPVC Section IX |
4. Manufacturing Process
4.1 Process Flow
- Slit Coil Preparation: Hot-rolled stainless steel strip (2B finish) is slit to the required width using high-precision slitting lines. The strip undergoes incoming quality inspection including chemical composition analysis (Optical Emission Spectroscopy, OES) and mechanical testing.
- Forming (Roll Forming): The slit strip is fed through a series of precision dies in a forming station. Progressive bending converts the flat strip into a semi-circular profile, followed by final round-out to achieve the target outer diameter and wall thickness. This cold-forming process induces beneficial work hardening, increasing yield strength by approximately 30–50% compared to the annealed strip condition.
- Seam Welding: The formed tube seam is closed using a High-Frequency Resistance Seam Welding (HF-RSW) or Transverse Resistance Welding (TRW) process. This produces a full-penetration weld with minimal heat-affected zone (HAZ), preserving the mechanical properties of the base material.
- Heat Treatment (Optional): For applications requiring full annealing, the welded tube passes through a continuous Solution Annealing Furnace operating at 1050°C – 1100°C in a controlled atmosphere (dissociated ammonia or inert gas). This eliminates residual welding stresses, restores full ductility, and homogenizes the microstructure.
- Pickling & Passivation: The annealed tube is treated with a mixture of Nitric Acid (HNO₃) and Hydrofluoric Acid (HF) to remove oxide scale, followed by passivation to re-establish the protective Chromium oxide film.
- Coiling & Packaging: The finished tube is wound onto a heavy-duty steel coil core with appropriate protective wrapping (polyethylene film, wooden crate, or export-grade packaging) to prevent mechanical damage and corrosion during transit.
4.2 Riveting Machine Integration
For chassis piping applications, the coil tube is processed through a specialized Riveting Machine designed for high-volume, automated assembly of riveted pipe joints. The riveting process involves:
- Automatic cutting of the coil tube to specified lengths using servo-driven shears.
- End-forming to create standardized fittings (threaded ends, flanged ends, or socket ends).
- Rivet insertion and upsetting using pneumatic or hydraulic riveting heads, achieving joint integrity equivalent to welded connections with superior fatigue resistance.
- In-line quality inspection including dimensional verification (CMM or laser scanning) and non-destructive testing (NDT).
5. Applications
5.1 Automotive & Chassis Piping
The primary application domain for this coil tube product is automotive chassis piping systems, including fuel lines, brake hydraulic lines, air conditioning refrigerant lines, and exhaust gas recirculation (EGR) tubing. The coil format enables roll-forming directly into complex chassis routing geometries, minimizing waste and maximizing production throughput.
5.2 Industrial Equipment
- Hydraulic and pneumatic systems — high-pressure fluid conveyance lines
- Food processing equipment — sanitary-grade piping for CIP (Clean-In-Place) systems
- Pharmaceutical equipment — process piping requiring hygienic surface finishes
- Chemical processing — corrosion-resistant transfer lines for aggressive media
- Heat exchangers and radiators — coil tube as a core heat transfer element
5.3 Construction & Architecture
- Decorative handrails and structural bracing
- Building water supply and drainage systems
- Fire suppression piping systems
5.4 Energy & Power Generation
- Boiler and superheater tubes
- Nuclear reactor coolant piping (316L grade)
- Solar thermal collector tubes
6. Quality Certifications & Standards Compliance
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System certification ensuring consistent product quality and continuous improvement |
| ISO 14001:2015 | Environmental Management System certification for sustainable manufacturing practices |
| EN 10204 Type 3.1 | Independent inspection body certificate for material and product conformity |
| ASTM A554 | Standard Specification for Seamless and Wrought Stainless Steel Tube and Pipe |
| EN 10217-7 | Technical Delivery Conditions for Non-Alloy and Stainless Steel Tubes for Pressure Purposes |
| GB/T 12771 | Chinese National Standard for Welded Stainless Steel Tubes for General Application |
| ASME SA-213 / SA-269 | American Society of Mechanical Engineers standards for heat-exchanger and condenser tubes |
| NSF/ANSI 61 | Drinking water system components certification (for potable water applications) |
| CE Marking | European Conformity marking for products intended for the European Economic Area |
| RoHS / REACH | Compliance with EU regulations on hazardous substances and chemical safety |
7. Quality Assurance & Testing Protocol
Each production batch undergoes a comprehensive quality assurance regimen:
- Chemical Analysis: Optical Emission Spectroscopy (OES) verification of alloy composition against ASTM/EN specifications.
- Mechanical Testing: Tensile testing per ASTM A370, hardness testing per ASTM E18 (Rockwell) or E92 (Vickers), and impact testing per ASTM E23.
- Dimensional Inspection: Laser scanning and ultrasonic wall thickness gauging for full-length dimensional verification.
- Non-Destructive Testing (NDT): Eddy current testing (ECT) for surface and subsurface defect detection; dye penetrant testing (PT) for seam weld integrity verification per ASTM E165.
- Hydrostatic Testing: Pressure testing at 1.5 × maximum working pressure per EN 10217-7 to verify leak-tightness and structural integrity.
- Corrosion Testing: Salt spray testing per ASTM B117 (≥ 1,000 hours without red rust for 316 grade) and intergranular corrosion testing per ASTM A262 Practice E.
8. Unique Selling Points
- Continuous Coil Format: Eliminates butt-weld joints inherent in straight-length pipe stock, providing superior fatigue resistance and leak-tightness for critical piping applications.
- Integrated Riveting Capability: The product is specifically designed for compatibility with automated riveting machine systems, enabling high-throughput, labor-efficient assembly of chassis and industrial piping systems with consistent joint quality.
- Multi-Grade Availability: Comprehensive grade range (304, 304L, 316, 316L, 321) accommodates diverse corrosion and temperature requirements without redesigning the piping layout.
- Precision Dimensions: Tight tolerance control (± 0.1 mm OD) ensures interchangeability and compatibility with standard fittings and connectors across global supply chains.
- Waste Reduction: Coil processing achieves material utilization rates exceeding 95%, significantly reducing manufacturing costs and environmental footprint compared to traditional cut-length pipe production.
- Full Traceability: Each coil is heat-number marked and accompanied by a full material test certificate (MTC), enabling complete supply chain traceability from raw material to end-of-life.