Stainless Steel Coil Tube (Coiltube) — Product Technical Specification
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) is a precision-engineered tubular product supplied in continuous coil form, designed for seamless integration into HVAC (Heating, Ventilation, and Air Conditioning) systems, fluid transport networks, and industrial heat exchange applications. Manufactured by Wenzhou Jixing Metal Materials Co., Ltd, this product represents a high-performance solution for applications requiring superior corrosion resistance, thermal conductivity, and mechanical durability under demanding operating conditions.
Coiltube products are distinguished from standard straight-length tubing by their continuous helical winding configuration, which enables automated feed-through manufacturing processes, minimizes material waste during downstream forming operations, and facilitates efficient inventory management in large-scale production environments. The coil form factor is particularly advantageous for Fan Coil Units (FCUs) and Fresh Air Handling Systems (FAS), where extensive lengths of tubing are required for serpentine coil assemblies and piping manifolds.
2. Material Composition and Properties
2.1 Base Alloy Designations
The stainless steel coil tubes are fabricated from austenitic stainless steel grades conforming to international standards, with the primary grades being:
- SAE 304 / AISI 304 (UNS S30400) — The industry-standard austenitic grade offering excellent general-purpose corrosion resistance, weldability, and formability. Contains approximately 18% Chromium (Cr) and 8% Nickel (Ni).
- SAE 316 / AISI 316 (UNS S31600) — Enhanced grade incorporating 2–3% Molybdenum (Mo) for superior resistance to pitting and crevice corrosion in chloride-containing environments.
- SAE 316L / AISI 316L (UNS S31603) — Low-carbon variant of 316 (carbon content ≤ 0.03%) designed for improved weldability and resistance to intergranular corrosion in sensitization-prone applications.
- SAE 321 / AISI 321 (UNS S32100) — Titanium-stabilized grade providing enhanced resistance to sensitization at elevated temperatures, suitable for high-temperature HVAC condensate and refrigerant circuits.
2.2 Mechanical Properties (Typical for Annealed Condition)
| Property | SAE 304 | SAE 316 | SAE 316L | SAE 321 |
|---|---|---|---|---|
| Tensile Strength (Rm) | ≥ 515 MPa | ≥ 515 MPa | ≥ 485 MPa | ≥ 515 MPa |
| Yield Strength (Rp0.2) | ≥ 205 MPa | ≥ 205 MPa | ≥ 170 MPa | ≥ 205 MPa |
| Elongation (A50) | ≥ 40% | ≥ 40% | ≥ 40% | ≥ 40% |
| Density | 8.00 g/cm³ | 8.03 g/cm³ | 8.03 g/cm³ | 8.00 g/cm³ |
| Thermal Conductivity (20°C) | 16.3 W/(m·K) | 16.3 W/(m·K) | 16.3 W/(m·K) | 14.2 W/(m·K) |
| Thermal Expansion Coefficient (20–100°C) | 17.3 × 10⁻⁶ /K | 17.3 × 10⁻⁶ /K | 17.3 × 10⁻⁶ /K | 17.3 × 10⁻⁶ /K |
| Maximum Service Temperature | 870°C | 870°C | 870°C | 900°C |
2.3 Corrosion Resistance Characteristics
The passive chromium oxide film (Cr₂O₃) formed on the surface of these austenitic alloys provides a self-healing protective barrier against atmospheric corrosion. The addition of Molybdenum in 316/316L grades enhances resistance to localized attack in chlorinated environments, including coastal HVAC installations, food processing plants, and pharmaceutical clean rooms. The Equivalent Pitting Resistance Number (PREN) for 316L exceeds 24, indicating excellent resistance to pitting and crevice corrosion under aggressive aqueous conditions.
3. Technical Specifications
3.1 Dimensional Parameters
| Parameter | Specification | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 6.00 mm – 38.10 mm (1/4" – 1-1/2") | ASTM A213 / GB/T 12771 |
| Wall Thickness | 0.50 mm – 3.00 mm | ASTM A269 / EN 10217 |
| Coil Inner Diameter (ID) | 300 mm – 600 mm (adjustable per order) | Manufacturer Specification |
| Coil Length | 50 m – 300 m (continuous) | Manufacturer Specification |
| Coil Weight | 500 kg – 2,500 kg per coil | Manufacturer Specification |
| OD Tolerance | ± 0.10 mm (for OD ≤ 12.70 mm); ± 0.15 mm (for OD > 12.70 mm) | ASTM A213 |
| Wall Thickness Tolerance | ± 10% of nominal | ASTM A213 |
| Roundness (Out-of-Roundness) | ≤ 2% of OD | ASTM A213 |
| Surface Finish | Pickled & Bright Annealed (PBA); or Precision Cold-Finished (PCF) | ASTM A269 |
| End Condition | Plain end, or cut-to-length with protective caps | Manufacturer Specification |
| Coating | Bare (uncoated); optional passivation treatment | ASTM A380 |
3.2 Applicable Standards and Compliance
| Standard | Description | Scope of Application |
|---|---|---|
| ASTM A213 / A213M | Standard Specification for Seamless Austenitic Stainless Steel Tubing for High-temperature Service | Material designation and mechanical properties |
| ASTM A269 / A269M | Standard Specification for Seamless and Wrought Stainless Steel Tubing, Instrumentation, and Similar Applications | Dimensional tolerances and surface quality |
| GB/T 12771 | Seamless Stainless Steel Tubes for Fluid Transport (Chinese National Standard) | Domestic Chinese market compliance |
| EN 10217-7 | Technical Delivery Conditions for Seamless Stainless Steel Tubes for General Purposes | European market compliance |
| ISO 13906 | Stainless Steel Tubes for Fluid Transport — Part 3: Seamless Tubes | International dimensional and quality requirements |
| JIS G 3459 | Seamless Austenitic Stainless Steel Tubes | Japanese market compliance |
4. Manufacturing Process
4.1 Process Flow Overview
The production of high-quality stainless steel coil tubes follows a rigorous multi-stage manufacturing sequence designed to ensure dimensional accuracy, metallurgical integrity, and surface quality:
- Steel Billet Preparation — High-purity stainless steel ingots or continuous-cast billets are produced via Vacuum Arc Remelting (VAR) or Argon Oxygen Decarburization (AOD) processes to achieve tight chemical composition control and minimize inclusions.
- Hot Rolling / Pipe Making — Billets are heated to 1,100–1,200°C and pierced through a rotary piercing mill to form hollow round bars. Alternatively, the Mannesmann (plug) method or autogenous welding (seamless weld) techniques may be employed depending on the target diameter range.
- Hot Finishing — The hot-rolled tubes undergo hot rolling through a series of reducing stands to achieve approximate final dimensions. This stage establishes the initial geometry and reduces the wall thickness to near-final specification.
- Pickling and Annealing — Tubes are subjected to acid pickling (typically in a mixture of hydrochloric acid and nitric acid) to remove mill scale and oxidation. Subsequent annealing at 1,050–1,150°C in a controlled atmosphere (bell jar or rotary hearth furnace) restores the fully austenitic microstructure, eliminates residual stresses, and achieves the required mechanical properties.
- Cold Drawing / Cold Rolling — For precision applications requiring tighter tolerances and superior surface finish, tubes undergo cold drawing through tungsten carbide (WC) or tool steel dies. This process reduces the outer diameter and wall thickness to final dimensions while improving mechanical properties through work hardening. A final cold work anneal may be applied to balance strength and ductility.
- Coil Winding — The finished tube is continuously wound onto precision-mandrel coil pay-off reels using tension-controlled winding systems. The winding process ensures uniform layering, minimal deformation, and controlled residual stress in the coil configuration.
- Final Inspection and Packaging — Each coil undergoes 100% dimensional verification, surface quality assessment, and chemical composition confirmation prior to protective packaging (waterproof wrapping, wooden crate or steel frame containment).
4.2 Key Process Control Points
- Chemical Composition Control: Spectroscopic analysis (OES) and wet chemical testing ensure compliance with ASTM/EN chemical specifications for each heat lot.
- Microstructural Verification: Metallographic examination confirms the absence of detrimental phases (delta ferrite, carbide precipitation) and validates the austenitic grain structure.
- Hydrostatic/Pneumatic Testing: Tubes are pressure-tested to verify wall integrity and absence of defects, with test pressures typically set at 1.5× the maximum design pressure.
- Eddy Current Testing (ECT): Non-destructive testing (NDT) via eddy current probes detects surface and near-surface defects, ensuring defect-free product delivery.
5. Applications
5.1 HVAC — Fan Coil Units and Fresh Air Systems
The primary application domain for this stainless steel coil tube product is in the construction of Fan Coil Units (FCUs) and Fresh Air Handling Systems (FAS). In these systems, stainless steel tubing is formed into serpentine coil configurations that serve as the primary heat exchange surface. Key advantages in this application include:
- Resistance to condensate corrosion in cooling coils, where sub-atmospheric temperature surfaces produce acidic condensation (pH 4–6).
- Long service life exceeding 20 years without degradation, compared to 8–12 years for carbon steel alternatives.
- Compatibility with all common refrigerants (R-410A, R-32, R-134a, R-22) and hot water/glycol heating media.
- Hygienic surface characteristics suitable for clean room and medical facility ventilation systems.
5.2 Additional Industrial Applications
- Food and Beverage Processing: Transfer lines for dairy, brewing, and pharmaceutical applications requiring sanitary-grade tubing (FDA-compliant surfaces).
- Chemical Processing: Corrosive fluid transfer in acid handling, chlorinated water treatment, and petrochemical installations.
- Marine and Offshore Systems: Seawater cooling circuits and ballast water systems where chloride-induced corrosion is a critical design constraint.
- Automotive Industry: Exhaust system components, fuel delivery lines, and sensor housings requiring thermal and corrosion resistance.
- Construction and Architecture: Structural tubing for handrails, guardrails, and decorative architectural elements.
- Medical Devices: Instrumentation tubing and fluid transfer components in surgical equipment and diagnostic devices.
6. Quality Certifications and Traceability
6.1 Product Certifications
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