Stainless Steel Coil Tube (Coiltube) — Product 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 use in a wide range of industrial, HVAC (Heating, Ventilation, and Air Conditioning), and thermal exchange applications. The coil tube is supplied in coiled form to facilitate downstream processing, including cutting, bending, and fabrication into heat exchangers, fan coil units (FCU — Fan Coil Unit), and refrigeration systems.
This product is engineered to meet rigorous performance evaluation criteria, including those referenced in analytical methodologies for determining the performance indicators of fan coil units. The tube's geometric consistency, thermal conductivity, and mechanical integrity are critical parameters that directly influence the efficiency and service life of end-use systems.
2. Material & Properties
2.1 Base Material Grades
- AISI 304 (UNS S30400) — Austenitic stainless steel with excellent general corrosion resistance; the most widely specified grade for HVAC and food-grade applications.
- AISI 316 (UNS S31600) — Austenitic stainless steel with added molybdenum (Mo) for superior resistance to pitting and crevice corrosion, suitable for aggressive chemical environments.
- AISI 316L (UNS S31603) — Low-carbon variant of 316, ideal for welding applications where sensitization resistance is required.
- AISI 321 (UNS S32100) — Titanium-stabilized austenitic grade for high-temperature applications up to 870°C.
2.2 Mechanical Properties (Typical)
| Property | Specification | Test Method |
|---|---|---|
| Tensile Strength (UTS — Ultimate Tensile Strength) | ≥ 515 MPa (304) / ≥ 585 MPa (316) | ASTM A240 / ASTM A213 |
| Yield Strength (0.2% offset) | ≥ 205 MPa | ASTM A240 |
| Elongation (in 50 mm gauge length) | ≥ 40% | ASTM A240 |
| Hardness (Rockwell B) | ≤ 95 HRB | ASTM A240 |
| Thermal Conductivity (at 25°C) | 16.3 W/(m·K) (304) / 16.3 W/(m·K) (316) | ASTM E1461 |
| Thermal Expansion Coefficient (20–100°C) | 17.3 × 10⁻⁶ /°C | ASTM E228 |
2.3 Chemical Composition (Maximum Limits, wt%)
| Element | 304 | 316 | 316L |
|---|---|---|---|
| Carbon (C) | 0.08 | 0.08 | 0.03 |
| Chromium (Cr) | 18.0 – 20.0 | 16.0 – 18.0 | 16.0 – 18.0 |
| Nickel (Ni) | 8.0 – 10.5 | 10.0 – 14.0 | 10.0 – 14.0 |
| Molybdenum (Mo) | — | 2.0 – 3.0 | 2.0 – 3.0 |
| Phosphorus (P) | 0.045 | 0.045 | 0.045 |
| Sulfur (S) | 0.030 | 0.030 | 0.030 |
3. Dimensions & Specifications
3.1 Geometric Parameters
| Parameter | Range | Tolerance | Standard |
|---|---|---|---|
| Outer Diameter (OD) | 6.0 – 50.8 mm (¼" – 2") | ±0.05 mm (≤ 10 mm OD); ±0.10 mm (> 10 mm OD) | ASTM A213 / ASME B76.1 |
| Wall Thickness (WT) | 0.5 – 3.0 mm | ±10% of nominal | ASTM A213 |
| Coil Length (per coil) | 50 – 500 m (adjustable) | ±2% | Manufacturer Standard |
| Coil Inner Diameter (ID) | 200 – 600 mm | ±10 mm | Manufacturer Standard |
| Surface Roughness (Ra) | 0.4 – 1.6 µm (BA finish); 0.8 – 3.2 µm (2B finish) | — | ASTM B473 |
3.2 Surface Finishes Available
- BA (Bright Annealed) Finish — Smooth, reflective surface with low roughness; ideal for sanitary and food-grade applications.
- 2B Finish — Standard cold-rolled and annealed finish; suitable for general industrial use.
- No. 4 Satin Finish — Uniformly brushed appearance with directional grain; used in architectural and decorative applications.
- Electropolished Finish — Chemically polished to achieve ultra-smooth surface (Ra < 0.25 µm); required for pharmaceutical and bioprocess systems.
4. Manufacturing Process
4.1 Production Flow
- Raw Material Selection & Incoming Inspection — Stainless steel strip or wire rod is verified against chemical composition and mechanical property requirements per ASTM A240/A213 specifications.
- Piercing & Drawing — Billets are pierced to produce seamless tube blanks, then cold-drawn through successive dies to achieve precise OD and wall thickness tolerances.
- Intermediate Annealing — Tubes are annealed at 1050–1150°C in a protective atmosphere (argon or endothermic gas) to relieve cold-work stresses and restore ductility.
- Pickling & Passivation — The oxide scale formed during annealing is removed via acid pickling (nitric + hydrofluoric acid mixture), followed by passivation to restore the passive chromium oxide layer.
- Final Drawing & Sizing — Precision sizing ensures dimensional accuracy within specified tolerances.
- Coiling — The continuous tube is wound into coils of specified length and diameter using a controlled tension coiling system to prevent deformation or ovality.
- Final Quality Inspection — Includes dimensional measurement, hydrostatic testing, visual inspection, and sampling for chemical/microstructural analysis.
4.2 Key Process Controls
- Hydrostatic Pressure Testing — Each coil is tested at 1.5× the maximum working pressure for a minimum dwell time of 15 seconds to verify weld integrity and absence of internal defects.
- Eddy Current Testing (ECT) — Non-destructive testing (NDT) to detect surface and near-surface discontinuities in continuous production.
- Intergranular Corrosion Testing (IGCT) — Per ASTM A262 Practice No. 1A/1E to verify resistance to sensitization, particularly for welded assemblies.
5. Applications
5.1 HVAC & Thermal Exchange Systems
Stainless steel coil tubes are integral components in fan coil units (FCU), air handling units (AHU), and chiller systems. The performance of these units is evaluated using analytical methods that assess heat transfer coefficients, pressure drop, and airflow characteristics — all of which are directly influenced by the tube's geometry, surface condition, and material thermal properties.
5.2 Additional Applications
- Refrigeration & Cryogenic Systems — Condenser and evaporator tubes in industrial refrigeration plants.
- Food & Beverage Processing — Heat exchangers for pasteurization, sterilization, and brewing systems (FDA-compliant grades).
- Pharmaceutical & Bioprocess — Electropolished coil tubes for sanitary heat exchange in cleanroom environments.
- Chemical Processing — Corrosion-resistant tubing for aggressive media handling (316/316L grades).
- Power Generation — Boiler tubes and superheater elements in utility-scale plants.
- Automotive Industry — Exhaust system components and turbocharger intermediate pipes.
6. Quality Certifications & Compliance
6.1 Standards Compliance
- ASTM A213 — Standard Specification for Seamless Austenitic Stainless Steel Tubes for High-temperature Service.
- ASTM A269 — Standard Specification for Seamless and Wrought Austenitic Stainless Steel Tubing for Chemical and Other Severely Corrosive Environments.
- ASME B76.1 — Boilers and Pressure Vessels — Pressure Vessel Impact Test Standards (tube sizing).
- EN 10216-5 — European standard for welded and seamless stainless steel tubes for pressure purposes.
- GB/T 12771 — Chinese national standard for seamless stainless steel tubes for general application.
6.2 Certifications Held
| Certification | Scope |
|---|---|
| ISO 9001:2015 | Quality Management System |
| ISO 14001:2015 | Environmental Management System |
| ISO 45001:2018 | Occupational Health & Safety Management System |
| TÜV CE Marking | Compliance with EU Machinery & Pressure Equipment Directives |
| NORSOK M-650 | Material specification for oil & gas industry applications |
| 3-A Sanitary Standards | International Dairy & Food Grade compliance |
6.3 Documentation Provided
- Mill Test Certificate (MTC) — EN 10204 Type 3.1, covering chemical composition, mechanical properties, and heat treatment records.
- Heat Traceability — Full batch/heat number traceability from raw material through final product.
- Hydrostatic Test Report — Documented pressure test results for each coil lot.
- NDT Report — Eddy current and ultrasonic testing results (upon request).
7. Unique Selling Points
Wenzhou Jixing Metal Materials Co., Ltd differentiates its stainless steel coil tube product through the following value propositions:
- Precision Dimensional Control — Advanced cold-drawing equipment and inline measurement systems ensure OD and wall thickness tolerances that exceed standard specifications, reducing downstream machining costs.
- Enhanced Surface Quality — Multi-stage pickling and passivation processes yield superior surface integrity, critical for maximizing heat transfer efficiency in fan coil unit applications.
- Comprehensive Performance Validation — Product specifications are aligned with analytical evaluation methodologies for thermal system performance, ensuring that coil tube geometry and material properties contribute optimally to overall system efficiency.
- Flexible Customization — Available in a broad range of grades, dimensions, and surface finishes to meet specific project requirements, with the ability to produce custom coil lengths and packaging configurations.
- Global Compliance & Traceability — Full adherence to international standards with complete documentation and heat traceability, facilitating regulatory approvals in diverse markets.
- Cost-Efficient Supply Chain — Coiled form reduces transportation costs, minimizes material waste during fabrication, and enables continuous processing in automated manufacturing lines.
8. Packaging & Shipping
- Coils are wrapped with moisture-proof plastic film and secured with steel strapping bands.
- Wooden pallets or export-grade wooden crates are used for additional protection during ocean freight.
- Custom labeling includes heat number, grade, dimensions, coil weight, and quantity for easy identification.
- Maximum coil weight per unit: 3,000 kg (adjustable based on customer requirement).
9. Technical Support & After-Sales Service
Wenzhou Jixing Metal Materials Co., Ltd provides comprehensive technical support including:
- Application engineering consultation for thermal system design and material selection.
- Welding procedure qualification support (WPS — Welding Procedure Specification) for downstream fabricators.
- Non-conformance resolution and root cause analysis with corrective action reporting.
- Ongoing product development collaboration for emerging applications and performance optimization.
10. References
"Determination of Performance Evaluation Indicators for Fan Coil Units by Analytical Method" — This study provides the analytical framework for evaluating thermal performance of fan coil unit assemblies, including the influence of coil tube geometry, material properties, and surface condition on overall system efficiency metrics such as sensible heat ratio (SHR), total cooling capacity, and coefficient of performance (COP).