Stainless Steel Coil Tube — Technical Product Specification
Product Overview
The Stainless Steel Coil Tube is a continuous-length tubular product formed into a helical coil configuration, supplied in bulk for downstream processing such as bending, forming, welding, and fabrication. Manufactured by Wenzhou Jixing Metal Materials Co., Ltd., this product is engineered to meet stringent dimensional tolerances, surface finish requirements, and mechanical performance standards demanded by industrial applications including heat exchangers, automotive exhaust systems, fluid conveyance lines, and structural assemblies.
A critical quality parameter in coil tube production is roundness (circularity deviation) and warpage (out-of-plane distortion). These geometric characteristics directly influence the integrity of downstream welding operations, joint strength, and overall product reliability. This specification addresses the manufacturing controls and quality assurance measures implemented to minimize roundness deviation and warpage, ensuring optimal weldability and structural performance.
Material & Properties
Material Grades
- Austenitic Stainless Steels: SUS304 (UNS S30400), SUS304L (UNS S30403), SUS316 (UNS S31600), SUS316L (UNS S31603)
- Duplex Stainless Steels: SUS321 (UNS S32100), SUS321H (UNS S32109)
- Custom Grades: Available upon request per customer specification
Mechanical Properties (Typical, Annealed Condition)
| Property | SUS304 / 304L | SUS316 / 316L | Test Standard |
|---|---|---|---|
| Tensile Strength (Rm) | ≥ 520 MPa | ≥ 520 MPa | ASTM A269 / ASTM E8 |
| Yield Strength (Rp0.2) | ≥ 205 MPa | ≥ 205 MPa | ASTM A269 / ASTM E8 |
| Elongation (A50mm) | ≥ 40% | ≥ 40% | ASTM A269 / ASTM E8 |
| Hardness (HV) | ≤ 210 | ≤ 210 | ASTM E92 |
| Thermal Conductivity (20°C) | 16.3 W/(m·K) | 14.6 W/(m·K) | — |
| Corrosion Resistance (pH) | Good (pH 4–10) | Excellent (pH 2–12) | ASTM G48 / G150 |
Chemical Composition (Typical, wt%)
| Grade | C | Mn | P | S | Si | Cr | Ni | Mo |
|---|---|---|---|---|---|---|---|---|
| SUS304 | ≤ 0.08 | ≤ 2.0 | ≤ 0.045 | ≤ 0.03 | ≤ 0.75 | 18.0–20.0 | 8.0–10.5 | — |
| SUS304L | ≤ 0.03 | ≤ 2.0 | ≤ 0.045 | ≤ 0.03 | ≤ 0.75 | 18.0–20.0 | 8.0–10.5 | — |
| SUS316 | ≤ 0.08 | ≤ 2.0 | ≤ 0.045 | ≤ 0.03 | ≤ 0.75 | 16.0–18.0 | 10.0–14.0 | 2.0–3.0 |
| SUS316L | ≤ 0.03 | ≤ 2.0 | ≤ 0.045 | ≤ 0.03 | ≤ 0.75 | 16.0–18.0 | 10.0–14.0 | 2.0–3.0 |
Specifications
| Parameter | Specification / Tolerance | Test Method |
|---|---|---|
| Outer Diameter (OD) | Φ 3.0 mm – Φ 100.0 mm | ASTM A269 |
| OD Tolerance | ± 0.05 mm (precision grade); ± 0.10 mm (standard grade) | ASTM A269 |
| Wall Thickness (WT) | 0.15 mm – 6.0 mm | ASTM A269 |
| WT Tolerance | ± 10% (standard); ± 5% (precision) | ASTM A269 |
| Roundness (Circularity Deviation) | ≤ 0.5% of nominal OD (precision grade); ≤ 1.0% of nominal OD (standard grade) | ASTM E29 / ISO 1101 |
| Warpage (Flatness Deviation) | ≤ 0.3 mm/m (precision grade); ≤ 0.5 mm/m (standard grade) | ASTM E29 / ISO 1101 |
| Coil Diameter | Φ 300 mm – Φ 1200 mm (configurable) | — |
| Coil Length | 5 m – 300 m per coil (continuous) | — |
| Surface Finish | 2B (standard), BA (Bright Annealed), No. 4 (Brushed), HL (Hairline), Custom | ASTM A480 |
| Surface Roughness (Ra) | ≤ 0.4 μm (2B); ≤ 0.2 μm (BA); ≤ 0.8 μm (No. 4) | ASTM E1927 |
| Heat Treatment | Solution Annealing (1040–1150°C) + Water Quench | ASTM A269 |
| Delivery Condition | Annealed (soft), Half-Hard, or Cold-Worked per request | ASTM A269 |
| End Condition | Plain cut, Beveled (per specification) | — |
| Coating / Passivation | Passivation per ASTM A967; Optional protective film | ASTM A967 |
Manufacturing Process
The production of high-quality stainless steel coil tubes involves a multi-stage process chain with rigorous dimensional and geometric control at each step:
- Strip Preparation: Cold-rolled stainless steel strip is supplied from certified mills, verified for chemical composition, surface quality, and mechanical properties prior to tube formation.
- Coil Loading & Leveling: The strip is fed through a precision leveling unit to eliminate pre-existing coil set, residual stresses, and edge waviness. This step is critical for controlling downstream roundness and warpage.
- Forming (Tube Milling): Multi-stand roll forming progressively bends the flat strip into a tubular geometry. Roll profiles are precision-machined and regularly calibrated to ensure consistent OD, wall thickness, and circularity throughout the production run.
- Welding: The formed tube is welded along the longitudinal seam using one of the following methods:
- Automatic Argon Welding (TIG/ATIG): Inert gas shielding on both inside and outside of the weld seam for superior weld quality and corrosion resistance.
- High-Frequency Induction Welding (HF): High production rates with precise heat input control.
- Electro-Pulse Welding (EPW): For precision applications requiring minimal heat-affected zone (HAZ).
- Weld Seam Finishing:
- Internal: Mechanical grinding (rotary knife) or electrolytic polishing (EP) to achieve Ra ≤ 0.4 μm.
- External: Mechanical grinding or chemical polishing to match the specified surface finish.
- Heat Treatment (Solution Annealing): The welded tube is passed through a continuous annealing furnace at 1040–1150°C followed by rapid water quenching. This dissolves chromium carbides formed during welding, restoring full corrosion resistance and ductility. Crucially, the furnace atmosphere (protective gas or vacuum) prevents oxidation and scaling.
- Pickling & Passivation: Post-annealing pickling removes any residual scale or discoloration using a controlled acid bath (HNO3/H2SO4 mixture). Subsequent passivation per ASTM A967 forms a stable chromium oxide layer for enhanced corrosion protection.
- Dimensional Inspection & Roundness Control:
- Inline laser measurement of OD and roundness at high frequency (≥ 100 Hz sampling rate).
- Roundness deviation is calculated as (Dmax − Dmin) / Dnominal × 100%.
- Warpage is measured by traversing the tube along its length on a precision straightedge or coordinate measuring system.
- Statistical Process Control (SPC) is applied to monitor dimensional trends and detect drift.
- Coiling & Packaging: The finished tube is wound onto a precision-machined coil former with controlled tension to prevent deformation. Each coil is wrapped with protective film or paper, secured with steel strapping, and labeled with mill test certificate (MTC) information.
Roundness & Warpage Control — Critical Quality Measures
Roundness deviation and warpage are the two most significant geometric defects that compromise weld quality in downstream fabrication. Excessive ovality causes uneven weld bead deposition, incomplete fusion, and reduced joint strength. Warpage introduces angular misalignment at butt joints, leading to residual stresses and potential crack initiation under cyclic loading. The following controls are implemented:
- Roll Profile Optimization: Finite element analysis (FEA) of the forming process to minimize residual stress gradients that cause post-annealing distortion.
- Controlled Annealing Cooling: Uniform furnace temperature profiles (± 10°C) prevent differential thermal contraction that exacerbates warpage.
- Post-Annealing Straightening: Light cold-rolling or draw-through passes to correct minor dimensional drift introduced during thermal processing.
- Coil Tension Management: Programmable tension controllers maintain uniform winding force, preventing inter-coil contact deformation.
Applications
- Heat Exchangers & Condensers: Coil tubes are mandrel-bent into hairpin or serpentine configurations for compact heat transfer surfaces in HVAC, refrigeration, and power generation systems.
- Automotive Exhaust Systems: Catalyst carrier tubes and exhaust manifold components requiring high-temperature resistance and low-emission compliance (Euro 6 / Tier 3).
- Fluid & Gas Conveyance: Pharmaceutical, food-grade (FDA compliant), and chemical processing piping systems where corrosion resistance and sanitary requirements are paramount.
- Structural & Mechanical Assemblies: Frameworks, guardrails, furniture components, and architectural elements requiring corrosion resistance in aggressive environments.
- Medical Devices: Surgical instrument tubing, implant housings, and diagnostic equipment components requiring biocompatibility and sterilization compatibility.
- Energy & Petrochemical: Fuel cell components, solar thermal collector tubes, and refinery process piping exposed to chloride-containing environments.
Quality Certifications
- ISO 9001:2015 — Quality Management System certification ensuring consistent product quality and continuous improvement processes.
- ISO 14001:2015 — Environmental Management System certification demonstrating responsible manufacturing practices.
- ISO 45001:2018 — Occupational Health and Safety Management System certification.
- EN 10204 / EN 10204-3.1 — Third-party inspection and certification for material conformity.
- ASTM / ASME — Product conformity to applicable American standards for stainless steel tubing.
- JIS G 3459 — Japanese Industrial Standard for austenitic stainless steel tube.
- GB/T 12771 — Chinese National Standard for austenitic stainless steel seamless and welded tube.
- Mill Test Certificates (MTC) — Full chemical analysis and mechanical test reports issued per EN 10204 3.1 for every production lot.
- Third-Party Inspection (TPI) — Available upon request: SGS, Bureau Veritas, TÜV, or Lloyd's Register.
Unique Selling Points
- Precision Roundness Control: Proprietary forming and inspection technology achieves roundness deviation ≤ 0.5% of nominal OD, significantly reducing downstream welding defects and improving joint integrity.
- Warpage Minimization: Advanced FEA-optimized roll