Stainless Steel Coil Tube (Coiltube) — Technical Specification
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) is a continuous-length tubular product manufactured by Wenzhou Jixing Metal Materials Co., Ltd., designed for high-precision welding applications, heat exchanger fabrication, and process piping systems. Unlike conventional cut-length tubes, coil tubes are produced as continuous coils, enabling automated downstream processing with minimal material waste and superior production efficiency. The coil form factor demands rigorous control over geometric tolerances — particularly ovality (Ovality / Out-of-Roundness) and warpage (Warpage / Distortion) — as these dimensional deviations directly influence weld seam quality, joint integrity, and overall structural reliability in welded assemblies.
This product line represents the company's commitment to delivering high-consistency stainless steel tubing solutions where geometric accuracy is paramount to end-use performance.
2. Material & Properties
2.1 Base Materials
- Austenitic Grades: SUS304 (UNS S30400), SUS304L (UNS S30403), SUS316 (UNS S31600), SUS316L (UNS S31603)
- Super-Austenitic Grades: SUS321 (UNS S32100), SUS347 (UNS S34700)
- Other Available Grades: SUS310S, SUS904L, SUS2205 (Duplex), SUS2507 (Super Duplex)
2.2 Key Mechanical Properties
| Property | SUS304 / 304L | SUS316 / 316L | Test Standard |
|---|---|---|---|
| Tensile Strength (MPa) | ≥ 520 | ≥ 515 | ASTM A270 / GB/T 12771 |
| Yield Strength (MPa) | ≥ 205 | ≥ 205 | ASTM A270 / GB/T 12771 |
| Elongation (%) | ≥ 40 | ≥ 35 | ASTM A270 |
| Corrosion Resistance (Pitting) | Good | Excellent (Mo-bearing) | ASTM G48 |
| Maximum Service Temperature (°C) | 870 | 870 | ASME B31.3 |
2.3 Surface Finish Options
- 2B Finish: Standard cold-rolled, annealed, and pickled surface
- No.4 Brushed: Fine linear grain pattern for decorative applications
- Mirror Polish (Ra ≤ 0.4 μm): For hygienic and pharmaceutical use
- Pickled & Passivated: Enhanced corrosion resistance for industrial environments
3. Specifications
| Parameter | Specification | Tolerance / Standard |
|---|---|---|
| Outer Diameter (OD) | Φ6.0 mm – Φ219.1 mm | ±0.1 mm (per ASTM A270) |
| Wall Thickness (WT) | 0.3 mm – 6.0 mm | ±10% of nominal |
| Ovality (Out-of-Roundness) | ≤ 1% of OD | Critical parameter for weld quality |
| Warpage / Distortion | ≤ 0.15 mm per 100 mm length | Flatness deviation control |
| Coil Inner Diameter (ID) | Φ200 mm – Φ500 mm | As per customer requirement |
| Coil Outer Diameter | Φ600 mm – Φ1500 mm | Customizable |
| Coil Length | Up to 3000 m (continuous) | Depends on OD and WT |
| End Condition | Plain end / Beveled end | Per ASME B16.25 |
| Applicable Standards | ASTM A270, A554, A778; GB/T 12771; EN 10217 | Multi-standard compliance |
4. Manufacturing Process
4.1 Process Flow
- Strip Milling & Slitting: Cold-rolled stainless steel strip is slit to precise widths matching target tube OD and WT. Strip flatness and thickness uniformity are critical pre-requisites.
- Forming (Roll Forming / Cold Forming): The strip is passed through a series of precision rollers that progressively bend the material into a tubular shape. Roller geometry is optimized to minimize residual stress and prevent ovality.
- Welding (TIG / Laser / Plasma): A continuous longitudinal weld seam is formed using inert gas shielding (Ar + He or pure Ar). Weld parameters are dynamically controlled to ensure full penetration and uniform bead profile.
- Online Inspection: In-process sensors monitor ovality, wall thickness, and weld bead geometry in real time. Tubes exceeding tolerance thresholds are flagged or rejected.
- Coiling: The continuous welded tube is wound onto a coil spool with controlled tension to prevent warpage, kinking, or inter-coil contact damage.
- Post-Weld Annealing & Pickling: The coil is heat-treated to relieve residual stresses, followed by acid pickling and passivation to restore corrosion resistance and achieve desired surface finish.
- Final Dimensional Verification: Each coil undergoes comprehensive measurement of OD, WT, ovality, and warpage against acceptance criteria.
4.2 Critical Control: Ovality and Warpage Management
Ovality (the ratio of the difference between major and minor diameter to the nominal OD) and warpage (longitudinal distortion or deviation from a straight axis) are the two most critical geometric parameters affecting downstream welding performance of coil tubes. Key control strategies include:
- Roller Calibration: Precision calibration of forming rollers ensures uniform cross-sectional geometry throughout the coil length, reducing ovality to ≤ 0.5% of OD for critical applications.
- Tension Control During Coiling: Variable-speed coiling with synchronized tension regulation prevents differential stress accumulation that causes warpage.
- Heat Treatment Optimization: Controlled annealing cycles prevent differential thermal expansion that can introduce post-weld distortion.
- Non-Destructive Testing (NDT): Eddy current and ultrasonic inspection verify weld integrity and detect internal defects that may propagate as geometric deviations.
5. Applications
- Heat Exchangers & Boilers: Coils provide continuous tube supply for automated bending and welding in tube bundle fabrication, minimizing butt welds and improving thermal efficiency.
- Process Piping (Chemical & Petrochemical): SUS316L coil tubes are used for aggressive chemical service where corrosion resistance and weld joint reliability are essential.
- Food & Beverage Industry: Hygienic-grade coil tubes (mirror polish, sanitary welds) for CIP (Clean-in-Place) compatible piping systems.
- Automotive Exhaust Systems: SUS304/SUS321 coil tubes for catalytic converter substrates and exhaust manifold fabrication.
- Medical Equipment: High-purity SUS316L coil tubes for surgical instrument shafts and medical device housings.
- Solar Thermal & HVAC Systems: Flat-plate and evacuated tube solar collectors utilize coil tubes for absorber and heat transfer circuits.
- Structural & Architectural Applications: Decorative railings, handrails, and structural frames requiring high corrosion resistance.
6. Quality Certifications & Compliance
| Certification / Standard | Scope |
|---|---|
| ISO 9001:2015 | Quality Management System |
| ISO 3834 (Part 2) | Quality Requirements for Fusion Welding of Metallic Materials |
| EN 10204 3.1 | Inspection Certificate — Mill Test Report |
| ASTM A270 / A554 | Standard Specification for Welded Austenitic Stainless Steel Tubing |
| GB/T 12771 | Chinese National Standard for Stainless Steel Seamless and Welded Tubes |
| ASME B31.3 | Process Piping — Material and Welding Compliance |
| CE Marking (PED 2014/68/EU) | Pressure Equipment Directive — Module H1 |
| RoHS / REACH | Restriction of Hazardous Substances / Chemical Regulation Compliance |
7. Unique Selling Points
- Precision Ovality Control (≤ 1% OD): Proprietary roller forming technology and online geometric monitoring ensure superior dimensional consistency, directly translating to improved downstream weld quality and reduced rework rates.
- Warpage-Free Coiling: Advanced tension-synchronized coiling systems eliminate longitudinal distortion, ensuring flat, true coils that unroll without kinking or residual bending.
- Multi-Grade Flexibility: Full range from standard austenitic to super-austenitic and duplex grades available in continuous coil form, enabling single-source procurement.
- Weld Quality Assurance: In-process NDT (eddy current, ultrasonic, dye penetrant) and post-weld annealing guarantee full-penetration weld seams with consistent mechanical and metallurgical properties.
- Customization Capability: OD, WT, surface finish, coil dimensions, and end conditions are all customizable to meet specific project requirements.
- Traceability: Each coil is heat-number tracked with complete mill test documentation for full supply chain traceability.
Technical Note: The geometric integrity of coil tubes — specifically the control of ovality and warpage — is not merely a dimensional specification but a fundamental determinant of welded joint quality. Excessive ovality leads to uneven gap fit-up, inconsistent weld penetration, and stress concentration at the seam. Warpage causes misalignment during automated welding, resulting in angular distortion and potential fatigue failure. Wenzhou Jixing Metal Materials Co., Ltd. addresses these challenges through integrated process control from strip preparation through final coiling, ensuring that every coil tube delivered meets the stringent geometric and metallurgical requirements of modern fabrication industries.