Stainless Steel Coil Tube — Product Technical Specification
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered continuous tube product formed through cold drawing and coil winding processes. This product is designed to meet the rigorous performance requirements of heat exchanger systems, particularly in fan coil units (FCU), air conditioning systems, refrigeration equipment, and industrial thermal management applications.
Unlike straight-segment tubing, the coil tube form factor offers superior surface-to-volume ratios, enhanced thermal exchange efficiency, and compact installation profiles. The product is engineered in accordance with the principles outlined in comprehensive performance evaluation frameworks for fan coil systems, ensuring that key indicators — including thermal transfer rate, pressure drop, structural integrity, and long-term corrosion resistance — are optimized simultaneously.
Key Design Philosophy: The coil tube integrates material science excellence with geometric optimization to deliver a holistic performance solution that balances thermal efficiency, mechanical durability, and manufacturing economy.
2. Material & Properties
2.1 Material Grades
- 304 Stainless Steel (AISI 304 / UNS S30400): The standard grade offering excellent corrosion resistance in most atmospheric and aqueous environments. Contains a minimum of 18% Chromium (Cr) and 8% Nickel (Ni).
- 316 Stainless Steel (AISI 316 / UNS S31600): Enhanced grade with Molybdenum (Mo) addition (2–3%), providing superior resistance to pitting and crevice corrosion, particularly in chloride-rich environments.
- 321 Stainless Steel (AISI 321 / UNS S32100): Titanium-stabilized grade suitable for elevated-temperature applications up to 870°C, resisting intergranular corrosion during welding and high-temperature service.
2.2 Mechanical Properties
- Tensile Strength (UTS): 515–730 MPa (depending on grade and condition)
- Yield Strength: 205–310 MPa (0.2% offset)
- Elongation: ≥ 40% (minimum, in annealed condition)
- Hardness: 80–110 HRB (annealed); 130–180 HRB (cold-drawn)
- Density: 7.93–8.00 g/cm³
2.3 Thermal & Physical Properties
- Thermal Conductivity: 14.9–16.3 W/(m·K) at 20°C
- Thermal Expansion Coefficient: 16–18 × 10⁻⁶ /°C (20–100°C)
- Operating Temperature Range: −196°C to +870°C (grade-dependent)
- Specific Heat Capacity: 498–502 J/(kg·K) at 20°C
3. Specifications
| Parameter | Specification / Range | Test Standard |
|---|---|---|
| Outer Diameter (OD) | 3.0 mm – 25.0 mm | ASTM A213 / ASME SA-213 |
| Wall Thickness | 0.3 mm – 2.0 mm | ASTM A213 / ASME SA-213 |
| Coil Winding Diameter | 50 mm – 500 mm | Internal specification |
| Coil Length (Continuous) | 5 m – 300 m (customizable) | Customer requirement |
| Surface Finish | 2B, BA (Bright Annealed), No.4 Brushed, Mirror (Ra ≤ 0.4 μm) | ASTM A480 |
| Surface Roughness (Ra) | 0.2 μm – 1.6 μm (interior); 0.4 μm – 3.2 μm (exterior) | ASTM E19 |
| Dimensional Tolerance (OD) | ±0.02 mm – ±0.10 mm | ISO 1128 |
| Dimensional Tolerance (Wall) | ±0.01 mm – ±0.05 mm | ISO 1128 |
| Roundness Tolerance | ≤ 0.03 mm | ISO 1128 |
| Helix Pitch Accuracy | ±0.1 mm | Internal specification |
| End Condition | Deburred, squared, or beveled (per customer specification) | ASME B1.20.4 |
| Packing | Wooden reel / steel drum / export-grade packaging | ISO 4180 |
4. Manufacturing Process
4.1 Process Flow
- Raw Material Selection: Certified stainless steel seamless tubes conforming to ASTM A213 / ASME SA-213 standards are sourced from approved mills. Incoming material undergoes spectrographic analysis (PMI) and mechanical property verification.
- Surface Preparation: Tubes undergo degreasing, pickling, and passivation to remove scale, oxides, and contaminants, ensuring a clean surface for subsequent processing.
- Cold Drawing: Tubes are cold-drawn through precision tungsten carbide (WC) or diamond dies to achieve exact dimensional tolerances, improved surface finish, and enhanced mechanical properties (work hardening effect).
- Intermediate Annealing: Where required, stress-relief annealing is performed at 1050–1150°C followed by controlled cooling to restore ductility and prevent cracking during subsequent forming operations.
- Coil Forming (Bending): The straight tube is fed through a CNC-controlled bending station equipped with hydraulic servo systems. The bending process employs a combination of mandrel support, guide rollers, and tension control to form a precise helical coil without ovalization, wrinkling, or wall thinning.
- Heat Treatment (Post-Forming): A solution anneal at 1050–1150°C followed by air cooling or controlled furnace cooling is performed to relieve residual stresses introduced during coil forming and to restore full corrosion resistance.
- Final Surface Treatment: Depending on application requirements, tubes may receive additional pickling, passivation, electropolishing, or PTFE (Polytetrafluoroethylene) internal coating.
- Quality Inspection: Comprehensive non-destructive testing (NDT) including eddy current testing, ultrasonic testing (UT), hydrostatic pressure testing, and dimensional metrology is conducted per batch.
4.2 Critical Process Controls
- Bending Mandrel Technology: Internal mandrel support prevents tube collapse and maintains circular cross-section during helical forming, critical for maintaining flow characteristics and thermal performance.
- Coil Pitch Uniformity: CNC servo-controlled feed systems ensure pitch accuracy of ±0.1 mm throughout the coil length, directly impacting heat transfer surface area and pressure drop characteristics.
- Residual Stress Management: Post-forming annealing eliminates residual stresses that could lead to stress corrosion cracking (SCC) in aggressive environments.
5. Applications
5.1 HVAC & Fan Coil Units (FCU)
Stainless steel coil tubes serve as the primary heat exchange element in fan coil units, where they transfer thermal energy between the refrigerant/coolant and the air stream. The coil geometry maximizes heat transfer surface area within a compact envelope, directly contributing to the Comprehensive Performance Evaluation Indicators (CPEI) of the FCU system, including:
- Seasonal Energy Efficiency Ratio (SEER)
- Static pressure performance
- Airflow uniformity
- Sound pressure level
5.2 Refrigeration & Cryogenic Systems
Used in evaporators, condensers, and chiller units where corrosion resistance and low-temperature ductility are paramount. 316-grade coil tubes are preferred for applications involving chlorinated refrigerants or brine solutions.
5.3 Food & Pharmaceutical Processing
Employed in pasteurizers, sterilizers, and hygienic heat exchangers where sanitary requirements mandate materials compliant with FDA 21 CFR 184.1950 and EU Regulation 1935/2004. Mirror-polished (Ra ≤ 0.4 μm) interior surfaces prevent product contamination and facilitate CIP (Clean-in-Place) procedures.
5.4 Chemical & Petrochemical Industry
Utilized in heat recovery systems, condensers, and evaporators processing aggressive chemicals. The inherent corrosion resistance of austenitic stainless steel eliminates the need for costly protective coatings.
5.5 Marine & Offshore Applications
316L and 904L grade coil tubes are deployed in marine cooling systems, desalination plants, and offshore platform utilities where chloride-induced pitting corrosion is a primary degradation mechanism.
5.6 Power Generation
Applied in condenser tubes, feedwater heaters, and auxiliary cooling systems in thermal power plants, nuclear facilities, and combined heat and power (CHP) installations.
6. Quality Certifications & Compliance
6.1 Manufacturing Certifications
- ISO 9001:2015 — Quality Management System
- ISO 14001:2015 — Environmental Management System
- ISO 45001:2018 — Occupational Health and Safety Management System
- EN 1090 — Structural Steel Fabrication (where applicable)
6.2 Product Standards Compliance
- ASTM A213 / ASME SA-213 — Stainless Steel Seamless Tubes for Boilers, Heat Exchangers, and Similar Applications
- ASTM A269 — Stainless Steel Tubing, Seamless and Welded (Austenitic and Austenitic-Ferritic Cr-Ni Stainless Steel)
- EN 10216-5 — Metallic Heat Exchanger Tubes and Jackets — Seamless Tubes — Technical Delivery Conditions — Part 5: Austenitic Stainless Steel Tubes
- JIS G3446 — Seamless Stainless Steel Tubes for Heat Exchangers
- GB/T 14976 — Seamless Stainless Steel Tubes for Fluid Transport (Chinese National Standard)
- GB/T 13296 — Seamless Stainless Steel Tubes for Heat Exchangers (Chinese National Standard)
6.3 Industry-Specific Approvals
- NSF/ANSI 61 — Drinking Water System Components (for potable water applications)
- 3-A Sanitary Standards — Dairy and Food Industry Equipment
- ASME U Stamp — Pressure Vessel Components (where applicable)
- PED 2014/68/EU — Pressure Equipment Directive Compliance
- CRN (Canadian Registration Number) — For Canadian market pressure equipment
6.4 Testing & Inspection Protocols
- Hydrostatic Testing: 100% batch testing at 1.5× working pressure (per ASTM A213)
- Eddy Current Testing (ECT): Continuous inline inspection for wall thickness uniformity and defect detection
- Positive Material Identification (PMI): XRF (X-Ray Fluorescence) verification of chemical composition
- Mechanical Testing: Tensile, hardness, and impact testing per ASTM E8 / E10 / E192
- Corrosion Testing: Salt spray testing (ASTM B117), intergranular corrosion testing (ASTM A262 Practice E), and pitting resistance index (PREN) verification
- Dimensional Metrology: Coordinate Measuring Machine (CMM) verification of OD, wall thickness, roundness, and coil pitch
7. Unique Selling Points
- Integrated Performance Optimization: Designed with reference to comprehensive fan coil unit performance evaluation methodologies, ensuring that thermal efficiency, pressure drop, and structural integrity are simultaneously optimized — not traded off against each other.
- Precision Helical Geometry: CNC servo-controlled coil forming achieves pitch accuracy of ±0.1 mm, ensuring uniform heat transfer coefficients and predictable pressure drop characteristics across the entire coil length.
- Superior Corrosion Resistance: Full austenitic stainless steel construction with post-forming annealing ensures maximum PREN (Pitting Resistance Equivalent Number ≥ 24 for 316 grade), eliminating degradation in aggressive service environments.
- Customizable Specifications: Full flexibility in OD, wall thickness, coil diameter, coil length, surface finish, and end treatment to match specific application requirements.
- Traceable Quality: Full material traceability from mill certification through final inspection, with comprehensive test reports (MTR — Material Test Report) provided with every shipment.
- Long Service Life: Expected operational lifespan exceeding 20–30 years under normal conditions, significantly reducing lifecycle costs compared to carbon steel alternatives requiring protective coatings or linings.
8. Ordering Information
| Item | Description |
|---|---|
| Manufacturer | Wenzhou Jixing Metal Materials Co., Ltd. |
| Product Catalog No. | 1568 — Coiltube Series |
| Minimum Order Quantity | 100 meters (standard grades); negotiable for custom specifications |
| Lead Time | 15–30 working days (standard); 30–60 working days (custom) |
| Packing | Wooden reel, steel drum, or export-grade crate with moisture barrier |
| Documentation | MTR, Certificate of Conformity, Test Reports, Packing List, Commercial Invoice |
Note: All specifications are subject to continuous improvement. Wenzhou J