Stainless Steel Coil Tube (Coiltube) — Technical Product Specification
1. Product Overview
The Stainless Steel Coil Tube (hereinafter referred to as "Coiltube") is a continuously wound, seamless or welded tubular product manufactured from austenitic, ferritic, or duplex stainless steel grades. Unlike straight-length tubing, the Coiltube is produced in continuous coil form, enabling high-volume downstream processing including cold drawing, bending, forming, and cut-to-length operations. This product category is particularly significant in the HVAC (Heating, Ventilation, and Air Conditioning) industry, where it serves as the core heat-exchange medium in fan coil unit (FCU) systems, as well as in process piping, food-grade applications, and structural uses.
Wenzhou Jixing Metal Materials Co., Ltd. (Product No. 1150) supplies stainless steel Coiltube engineered to meet stringent international standards for dimensional accuracy, mechanical integrity, and corrosion resistance. The product is designed to facilitate energy-efficient thermal transfer in air conditioning systems while maintaining long-term service life under aggressive environmental conditions.
2. Material & Properties
2.1 Common Material Grades
- Austenitic Grades: SUS304 (UNS S30400), SUS304L (UNS S30403), SUS316 (UNS S31600), SUS316L (UNS S31603) — offering excellent corrosion resistance, weldability, and formability.
- Ferritic Grades: SUS430 (UNS S43000), SUS409 (UNS S40900) — providing good atmospheric corrosion resistance at a lower cost basis.
- Duplex Grades: SUS31803 (UNS S31803), SUS2205 (UNS S32205) — combining high tensile strength with superior pitting and crevice corrosion resistance.
2.2 Key Mechanical Properties
- Tensile Strength (UTS): 515–730 MPa (depending on grade and temper condition)
- Yield Strength (0.2% offset): 205–450 MPa
- Elongation at Break: ≥35% (annealed condition)
- Hardness: 80–120 HRB (annealed); up to 38 HRC (cold-worked/hardened condition)
- Density: 7.93–8.00 g/cm³
- Thermal Conductivity: 14.6–16.3 W/(m·K) at 20°C
- Thermal Expansion Coefficient: 16–18 × 10⁻⁶ /°C
- Maximum Service Temperature: 870°C (SUS304); 1093°C (SUS316L)
2.3 Corrosion Resistance
The austenitic stainless steel grades used in Coiltube production exhibit a passive chromium oxide film (Cr₂O₃) that self-heals in oxidizing environments. SUS316L, with its 2–3% molybdenum (Mo) content, demonstrates superior resistance to pitting and chloride-induced stress corrosion cracking (SCC), making it the preferred grade for marine and chemical processing environments. The equivalent pitting resistance (PREN) for SUS316L is approximately 24–26, calculated as:
PREN = %Cr + 3.3 × %Mo + 16 × %N
3. Specifications
| Parameter | Specification / Range | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 6.0 mm – 108.0 mm (¼" – 4") | ASTM A511 / EN 10216-5 |
| Wall Thickness (WT) | 0.50 mm – 6.00 mm | ASTM A511 / JIS G3459 |
| Coil Inner Diameter (ID) | 300 mm – 600 mm (adjustable) | Manufacturer specification |
| Coil Length | Continuous (up to 2000 m per coil) | — |
| Tolerance — OD | ±0.05 mm (precision drawn); ±0.10 mm (standard) | ASTM A511 |
| Tolerance — WT | ±0.025 mm (precision); ±0.05 mm (standard) | ASTM A511 |
| Surface Finish | No. 1 (annealed bright), 2B, BA (Bright Annealed), #4, #8 (mirror) | ASTM A480 / EN 10088-2 |
| End Condition | Plain end, beveled end, or custom-formed | Per customer drawing |
| Heat Treatment | Solution annealed at 1050–1150°C, followed by water or air quench | ASTM A511 |
| Packaging | Wooden pallet, steel banding, VCI (Vapor Corrosion Inhibitor) wrapped | ISO 11607 |
4. Manufacturing Process
4.1 Production Flow
- Raw Material Preparation: Stainless steel strip (cold-rolled coil) is supplied by certified mills (e.g., POSCO, Outokumpu, Baosteel) and inspected for chemical composition and mechanical properties via spectroscopic analysis (OES) and tensile testing.
- Coil Winding / Pipe Forming: The strip is fed through a series of progressive roll-forming stations (typically 12–18 passes) that gradually bend the flat strip into a circular cross-section. For welded Coiltube, a high-frequency induction welding (HF-IW) or laser welding process fuses the longitudinal seam. For seamless Coiltube, the tube is produced via cold drawing or rotary piercing from solid bar stock.
- Weld Seam Inspection: 100% electromagnetic (EM) eddy current testing and ultrasonic testing (UT) are performed on the weld seam to detect voids, cracks, or incomplete fusion.
- Heat Treatment (Annealing): Welded Coiltube undergoes solution annealing at 1050–1150°C in a protective atmosphere (argon or vacuum) to relieve residual stresses, restore full austenitic microstructure, and enhance corrosion resistance.
- Pickling & Passivation: Post-annealing, the tube is pickled in a mixed acid bath (HNO₃/HF) to remove oxide scale, followed by passivation in a citric acid or dilute nitric acid solution to establish a uniform chromium oxide passive film.
- Precision Sizing & Straightening: Cold-calibrated rolls adjust the outer diameter and wall thickness to final tolerance. The coil is then straightened and wound onto the shipping coil form.
- Final Inspection & Packaging: Each coil undergoes dimensional verification, surface inspection, and material certification (MTC — Material Test Certificate per EN 10204 3.1). The coil is wrapped in VCI paper, strapped with steel bands, and secured on a wooden pallet.
4.2 Microstructural Control
Critical to the performance of austenitic stainless steel Coiltube is the suppression of intergranular corrosion (IGC) through careful control of carbon content. Grades designated with the "L" suffix (e.g., 304L, 316L) maintain carbon ≤0.030 wt%, minimizing chromium carbide (Cr₂₃C₆) precipitation in the sensitization temperature range of 450–850°C. Additionally, the cold-work strain during the forming process is monitored to prevent excessive martensitic transformation (α' phase) in SUS304, which can compromise ductility and corrosion resistance. The volume fraction of retained austenite (γ-phase) is verified via X-ray diffraction (XRD) analysis.
5. Applications
5.1 HVAC — Fan Coil Unit (FCU) Systems
The primary application domain of this Coiltube product is in fan coil unit air conditioning systems. The Coiltube is formed into serpentine or zig-zag heat exchanger coils where refrigerant or chilled water flows through the tubes while ambient air is drawn across finned surfaces. Key performance considerations include:
- Thermal Efficiency: The high thermal conductivity of austenitic stainless steel ensures efficient heat transfer between the fluid medium and the surrounding air, contributing to the overall Coefficient of Performance (COP) of the HVAC system.
- Energy-Saving Technology: As documented in research on fan coil unit energy conservation, the use of precision-drawn stainless steel Coiltube with optimized fin-and-tube geometry reduces fan power consumption and improves part-load efficiency. The uniform wall thickness and smooth internal surface of the Coiltube minimize flow resistance and pressure drop.
- Hygienic Performance: The passivated stainless steel surface inhibits microbial growth, making it suitable for hospital, laboratory, and pharmaceutical clean-room HVAC systems.
5.2 Additional Application Domains
- Food & Beverage Processing: SUS316L Coiltube for sanitary-grade piping, pasteurization equipment, and CIP (Clean-in-Place) systems (FDA-compliant, 3-A Sanitary Standards).
- Petrochemical & Marine: SUS316L and duplex-grade Coiltube for heat exchangers, condensers, and seawater cooling systems resistant to chloride pitting.
- Automotive & Aerospace: Precision-drawn Coiltube for fuel lines, exhaust components, and structural tubing in lightweight vehicle architectures.
- Architectural & Decorative: Mirror-finish (#8) Coiltube for handrails, balustrades, and architectural cladding.
- Medical Devices: Biocompatible SUS316L Coiltube for implantable components, surgical instrument tubing, and dialysis equipment.
6. Quality Certifications & Standards Compliance
6.1 Applicable International Standards
- ASTM A511 — Standard Specification for Seamless and Welded Austenitic Stainless Steel Pipes
- ASTM A213 — Standard Specification for Seamless Austenitic Chromium-Nickel Stainless Steel Tubing for Heat-Transfer Equipment
- ASTM A480 — Standard Specification for Chromium and Chromium-Nickel Stainless Steel Plate, Sheet, and Strip
- EN 10216-5 — Non-ferrous metallic tubes — Welded tubes — Part 5: Stainless steel tubes for general purposes
- JIS G3459 — Cold- or Hot-Worked Stainless Steel Tubes for General Purposes
- ISO 6508-1 — Metallic materials — Vickers hardness test
6.2 Quality Assurance System
- ISO 9001:2015 — Quality Management System certification for manufacturing and supply chain processes.
- ISO 14001:2015 — Environmental Management System certification covering energy consumption, waste management, and emission control.
- EN 10204 Type 3.1 — Material Test Certificate (MTC) issued by authorized inspection personnel, certifying chemical composition and mechanical properties for each production batch.
- Mill Test Reports (MTR) — Traceable documentation linking each coil to its raw material heat number, processing parameters, and final inspection results.
6.3 Inspection & Testing Protocol
| Test Category | Method | Frequency |
|---|---|---|
| Chemical Composition | Optical Emission Spectroscopy (OES) | Every heat/batch |
| Tensile Strength & Elongation | ASTM E8 / E8M — Universal Testing Machine | Every heat/batch |
| Weld Seam Integrity | Electromagnetic Eddy Current Testing (100%) + Ultrasonic Testing (UT) | Continuous (100% inline) |
| Dimensional Accuracy | Laser micrometer / Calibrated dial gauge | Every coil |
| Surface Quality | Visual inspection + Profilometry (Ra ≤ 0.4 μm for BA finish) | Every coil |
| Corrosion Resistance | ASTM A967 — Passivation verification; ASTM G48 — Pitting resistance (PREN) | Per grade qualification |
| Intergranular Corrosion | ASTM A262 Practice E — 6% HCl / Copper-copper sulfate acid test | Per grade qualification |
7. Unique Selling Points
- Precision Dimensional Control: Cold-drawn Coiltube achieves OD tolerance of ±0.05 mm and wall thickness tolerance of ±0.025 mm, ensuring optimal fit for fin insertion and heat exchanger assembly without gaps that cause air bypass.
- Energy-Efficiency Contribution: The smooth internal bore surface (Ra ≤ 0.2 μm) reduces hydraulic resistance by up to 15% compared to standard-drawn tubing, directly lowering the pumping power requirement in closed-loop HVAC systems.
- Full Traceability: Each coil is individually serialized with a unique batch code linked to the raw material mill certificate, processing parameters, and final inspection data, enabling complete supply-chain traceability.
- Custom Grade & Finish Availability: Products are available in over 20 stainless steel grades with surface finishes ranging from No. 1 through mirror (#8), accommodating both functional and aesthetic requirements.
- Extended Service Life: The solution-annealed, passivated microstructure provides a service life exceeding 25 years in typical HVAC applications, with no degradation of mechanical properties or corrosion resistance over time.
- Environmental Sustainability: Stainless steel Coiltube is 100% recyclable without loss of material properties. The production process adheres to ISO 14001 environmental management protocols, minimizing carbon footprint and waste generation.
8. Conclusion
The Stainless Steel Coil Tube (Product No. 1150) from Wenzhou Jixing Metal Materials Co., Ltd. represents a technologically advanced, quality-assured product designed for demanding thermal management and fluid conveyance applications. Its precision engineering, material integrity, and