Stainless Steel Coil Tube (Coiltube) — Model No. 430
1. Product Overview
The Stainless Steel Coil Tube (Coiltube), designated as Product No. 430 by Wenzhou Jixing Metal Materials Co., Ltd., is a precision-engineered continuous tubing product formed into helical or serpentine coil configurations. This product is specifically designed for integration into Fan Coil Unit (FCU) systems, heat exchanger assemblies, and fluid distribution networks where corrosion resistance, thermal efficiency, and mechanical durability are paramount. The coil tube is manufactured in continuous coil form to facilitate downstream processing, installation, and system integration with minimal waste and maximum flexibility.
Unlike discrete pipe segments, the coil tube format enables seamless integration into complex geometries, reducing the need for field welding or soldering joints. This design philosophy aligns with modern HVAC (Heating, Ventilation, and Air Conditioning) engineering principles that prioritize leak-free performance, thermal conductivity, and long-term reliability under cyclic thermal loading conditions.
2. Material & Properties
2.1 Base Material
The coil tube is fabricated from austenitic stainless steel, with common grades including:
- AISI 304 (UNS S30400): The most widely specified grade, offering excellent general corrosion resistance, formability, and weldability. Contains approximately 18% Chromium (Cr) and 8% Nickel (Ni).
- AISI 316 (UNS S31600): Enhanced pitting and crevice corrosion resistance due to the addition of 2–3% Molybdenum (Mo). Suitable for aggressive chemical environments.
- AISI 304L (UNS S30403): Low-carbon variant with Carbon (C) content ≤ 0.03%, ideal for welding applications requiring reduced sensitization risk.
2.2 Mechanical Properties
- Tensile Strength (UTS): ≥ 515 MPa (75,000 psi) for AISI 304 in annealed condition
- Yield Strength (0.2% offset): ≥ 205 MPa (29,700 psi)
- Elongation at Break: ≥ 40%
- Hardness (Brinell): ≤ 201 HB (annealed condition)
- Operating Temperature Range: −196°C to +870°C (−321°F to +1,600°F)
2.3 Physical Properties
- Density: 8.0 g/cm³ (AISI 304)
- Thermal Conductivity: 16.3 W/(m·K) at 100°C
- Thermal Expansion Coefficient: 17.3 × 10⁻⁶ /K (20–100°C)
- Specific Heat Capacity: 0.50 J/(g·K) at 100°C
- Electrical Resistivity: 7.4 × 10⁻⁷ Ω·m at 20°C
2.4 Corrosion Resistance
The austenitic stainless steel microstructure provides inherent resistance to atmospheric corrosion, mild acids, alkalis, and chloride-containing solutions. The passive chromium oxide layer (Cr₂O₃) self-heals under oxidizing conditions, ensuring long-term structural integrity in HVAC condensate environments where waterborne contaminants may be present.
3. Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Product No. | 430 | Wenzhou Jixing Internal Catalog |
| Product Name | Stainless Steel Coil Tube (Coiltube) | — |
| Material Grade | AISI 304 / 304L / 316 / 316L | ASTM A270 / ASTM A269 |
| Outer Diameter (OD) | 6.0 mm – 25.0 mm (customizable) | ISO 21974 |
| Wall Thickness | 0.4 mm – 1.5 mm | ASTM A270 |
| Coil Length | 10 m – 100 m per coil (standard); custom lengths available | — |
| Coil Winding Diameter | ≥ 15× OD (to prevent ovality and kinking) | EN 10217 |
| Surface Finish | Bright annealed, polished, or pickled & passivated | ASTM A403 |
| Tolerance — OD | ±0.05 mm (precision grade); ±0.10 mm (standard) | ASTM A270 |
| Tolerance — Wall Thickness | ±0.02 mm (precision grade); ±0.05 mm (standard) | ASTM A270 |
| Pressure Rating | Up to 1.6 MPa (16 bar) working pressure at 25°C | ASME B31.9 |
| Helical Pitch | 12 mm – 40 mm (configurable per application) | — |
| Number of Turns | 2 – 50 turns per coil assembly | — |
| End Preparation | Plain ends, beveled ends, or threaded ends (NPT/BSP) | ASME B1.20.1 |
| Packaging | Wooden reel or steel drum with moisture-proof wrapping | ISO 4180 |
4. Manufacturing Process
4.1 Raw Material Procurement
Hot-rolled stainless steel strip or seamless pipe stock is procured from certified mills meeting ASTM and EN standards. Incoming material undergoes spectrographic verification (Optical Emission Spectrometry, OES) to confirm chemical composition within specified limits.
4.2 Cold Drawing / Seamless Forming
For smaller diameters (≤ 12 mm OD), the coil tube is produced via cold drawing through precision tungsten carbide dies to achieve tight dimensional tolerances and superior surface finish. For larger diameters, seamless pipe is bent and formed into coil configurations using CNC-controlled bending machinery.
4.3 Coil Winding & Formation
- Tube Straightening: The drawn tube is passed through roller straighteners to achieve geometric straightness ≤ 1 mm/m.
- Helical Bending: CNC bending stations form the tube into precise helical or serpentine coil geometries with controlled pitch, radius, and number of turns.
- Spring-Back Compensation: The bending machine incorporates spring-back compensation algorithms to ensure dimensional accuracy after elastic recovery.
- Fixturing & Support: Coil supports (jigs) maintain the formed geometry during downstream processing and shipping.
4.4 Heat Treatment & Annealing
Following cold working, the coil tube undergoes solution annealing at 1050–1150°C followed by controlled air cooling to restore full austenitic microstructure, relieve residual stresses, and maximize corrosion resistance. The annealed microstructure exhibits uniform grain structure with no sensitization carbide precipitation at grain boundaries.
4.5 Surface Treatment
- Pickling: Removal of scale and oxide films using a controlled mixture of nitric acid (HNO₃) and hydrofluoric acid (HF).
- Passivation: Application of citric acid or nitric acid passivation to enhance the chromium oxide passive film, improving corrosion resistance by 3–5× compared to unpickled surfaces.
- Polishing (optional): Mechanical or electropolishing for aesthetic or hygienic applications requiring Ra ≤ 0.4 μm surface roughness.
4.6 Quality Inspection
- Visual Inspection: 100% inspection for surface defects, weld seams, and dimensional conformity.
- Dimensional Verification: Coordinate Measuring Machine (CMM) or laser scanning for OD, wall thickness, pitch, and coil diameter.
- Hydrostatic Pressure Testing: All coils tested at 1.5× working pressure for 5 minutes to verify leak-free integrity.
- Chemical Analysis: OES or wet chemistry per ASTM E1011 / ASTM E415.
- Mechanical Testing: Tensile testing per ASTM A370 for representative samples.
- Corrosion Testing: Salt spray testing per ASTM B117 (≥ 1000 hours without red rust for AISI 316 grades).
5. Applications
5.1 Fan Coil Unit (FCU) Systems
The primary application domain for this coil tube product is within Fan Coil Unit systems used in commercial and residential HVAC installations. The coil tube serves as the refrigerant or hot water circuit within the FCU air handler, enabling efficient heat transfer between the fluid medium and ambient air. The helical coil configuration maximizes heat transfer surface area per unit volume, optimizing thermal performance in compact installation spaces.
5.2 Heat Exchanger Assemblies
Used in shell-and-tube heat exchangers, plate-fin heat exchangers, and air-to-liquid heat exchangers for industrial process cooling and heating applications.
5.3 Refrigeration & Air Conditioning
Coil tubes are integral components in evaporator and condenser units, where they facilitate phase-change heat transfer between refrigerant and heat transfer fluid. The stainless steel construction ensures compatibility with ammonia (NH₃) refrigerant systems, unlike copper alternatives which suffer from stress corrosion cracking.
5.4 Medical & Pharmaceutical Equipment
Used in sterilization equipment, pharmaceutical fluid distribution systems, and medical device manufacturing where hygienic surface finish (Ra ≤ 0.4 μm) and biocompatibility are required.
5.5 Food & Beverage Processing
Applied in pasteurization systems, brewing equipment, dairy processing lines, and food-grade fluid transfer systems requiring compliance with FDA 21 CFR and EU 1935/2004 regulations.
5.6 Marine & Offshore Applications
AISI 316 grade coil tubes are specified for marine HVAC systems, offshore platform cooling circuits, and desalination plant heat exchangers where resistance to chloride-induced pitting corrosion is critical.
5.7 Industrial Process Heating & Cooling
Deployed in chemical processing plants, petrochemical facilities, and power generation systems for thermal management of process streams requiring corrosion-resistant heat transfer surfaces.
6. Quality Certifications & Standards Compliance
6.1 International Standards
| Standard | Scope of Compliance |
|---|---|
| ASTM A270 / A270M | Austenitic stainless steel seamless and welded tubing |
| ASTM A269 / A269M | Austenitic stainless steel seamless, welded, and heavily cold-worked tubing |
| EN 10217-7 | Stainless steel cold-drawn seamless tubes for pressure purposes |
| ISO 21974 | Stainless steel tubes and pipes — dimensional tolerances |
| ASME B31.9 | Pressure piping code for refrigeration piping |
| ISO 4180 | Steel tubes and pipes — packaging requirements |
6.2 Manufacturing Certifications
- ISO 9001:2015 — Quality Management System certification for manufacturing and supply chain processes
- ISO 14001:2015 — Environmental Management System for sustainable manufacturing operations
- CE Marking — Conformity with European Machinery Directive 2006/42/EC and Pressure Equipment Directive 2014/68/EU
- EN 10204 3.1 — Third-party inspection certificates for material and dimensional compliance
- Mill Test Reports (MTR) — Full chemical and mechanical analysis documentation per heat number
6.3 Specialized Certifications
- NSF/ANSI 61 — Drinking water system component certification (where applicable)
- 3-A Sanitary Standards — Dairy and food processing equipment compliance
- PED 2014/68/EU Category I/II — Pressure Equipment Directive conformity for pressurized applications
7. Unique Selling Points
7.1 Superior Corrosion Resistance: The austenitic stainless steel composition provides exceptional resistance to atmospheric, chemical, and chloride-induced corrosion, significantly extending service life compared to carbon steel or copper alternatives in aggressive HVAC environments.
7.2 Continuous Coil Format: The coil tube configuration eliminates the need for field welding joints, reducing leak points by up to 80% compared to discrete pipe segment assemblies. This translates to lower installation costs, reduced maintenance requirements, and improved system reliability.