Stainless Steel Coil Tube (Coiltube) — Precision HVAC & Industrial Heat Exchanger Series
1. Product Overview
The Stainless Steel Coil Tube, designated internally as Product No. 424 by Wenzhou Jixing Metal Materials Co., Ltd., is a precision-engineered continuous-length tubular product manufactured in a coiled configuration. Unlike conventional straight-length stainless steel tubing, coil tubes are formed into continuous helical or spiral shapes during the manufacturing process, enabling seamless integration into heat exchanger assemblies, HVAC (Heating, Ventilation, and Air Conditioning) systems, and industrial fluid transport applications without the need for field welding or mechanical joining.
This product line is particularly distinguished by its application in painting workshop HVAC coil systems, where precise thermal control is critical to maintaining consistent ambient conditions during electrostatic coating, powder coating, and liquid paint application processes. The coil tube geometry provides a high surface-area-to-volume ratio, facilitating efficient heat transfer between the working fluid (typically chilled water, hot water, or refrigerant) and the process air stream.
2. Material & Properties
Coil tubes are fabricated from austenitic stainless steel grades selected for their superior corrosion resistance, thermal conductivity, and mechanical integrity under cyclic thermal loading conditions.
2.1 Commonly Used Grades
- AISI 304 (UNS S30400) — The most widely specified grade for general-purpose HVAC and food-grade applications, offering excellent corrosion resistance in atmospheric and mildly corrosive environments.
- AISI 316 (UNS S31600) — Enhanced molybdenum (2.0–2.5 wt.%) content provides superior resistance to pitting and crevice corrosion, suitable for marine environments and chemical processing.
- AISI 321 (UNS S32100) — Titanium-stabilized grade resistant to intergranular corrosion, ideal for high-temperature applications up to 870°C.
- AISI 316L (UNS S31603) — Low-carbon variant of 316, minimizing carbide precipitation during welding and heat treatment.
2.2 Key Mechanical & Physical Properties (Typical for Grade 304)
| Property | Value | Unit |
|---|---|---|
| Density | 7.93 | g/cm³ |
| Thermal Conductivity (20°C) | 16.3 | W/(m·K) |
| Thermal Expansion Coefficient (20–100°C) | 17.3 × 10⁻⁶ | /°C |
| Specific Heat Capacity (20°C) | 500 | J/(kg·K) |
| Tensile Strength (Annealed) | ≥ 520 | MPa |
| Yield Strength (0.2% Offset) | ≥ 205 | MPa |
| Elongation at Break (50 mm gauge) | ≥ 40 | % |
| Maximum Operating Temperature | 870 | °C |
| Minimum Operating Temperature | −196 | °C |
2.3 Chemical Composition (AISI 304 — Typical Range)
| Element | Minimum (%) | Maximum (%) |
|---|---|---|
| Carbon (C) | — | 0.08 |
| Chromium (Cr) | 18.0 | 20.0 |
| Nickel (Ni) | 8.0 | 10.5 |
| Manganese (Mn) | — | 2.0 |
| Silicon (Si) | — | 1.0 |
| Phosphorus (P) | — | 0.045 |
| Sulfur (S) | — | 0.030 |
3. Specifications
The following table summarizes the dimensional and performance specifications typical for the coil tube product line. Specific dimensions may be customized per customer requirements.
| Parameter | Specification | Tolerance |
|---|---|---|
| Outer Diameter (OD) | 6.0 mm – 50.8 mm (¼" – 2") | ± 0.05 mm |
| Wall Thickness | 0.30 mm – 3.00 mm | ± 10% |
| Coil Diameter (Flat) | 200 mm – 600 mm | ± 2% |
| Coil Length per Spool | 50 m – 500 m | ± 1% |
| Surface Finish | No. 1, 2B, BA, or Custom | — |
| Surface Roughness (Ra) | ≤ 0.8 μm (2B/BA finish) | — |
| Hardness (Annealed) | ≤ 210 HV | — |
| Pressure Test | 3.0 × Working Pressure, 15 min hold | — |
| Helix Pitch (Spiral Form) | 15 mm – 150 mm (configurable) | ± 0.5 mm |
| End Treatment | Clean-cut, deburred, or threaded | — |
4. Manufacturing Process
The production of high-quality stainless steel coil tubes involves a multi-stage manufacturing sequence requiring precise process control to ensure dimensional accuracy, metallurgical integrity, and surface quality.
4.1 Process Flow
- Raw Material Selection: Cold-rolled stainless steel strip (CRSS) conforming to ASTM A270 or EN 10217-7 specifications is procured from certified mill sources. Incoming material undergoes spectrographic analysis (PMI — Positive Material Identification) to verify chemical composition.
- Coil Slitting: The master coil is slit to the required strip width using precision slitting lines with diamond blades, ensuring edge quality and dimensional accuracy. Slit edges are inspected for burrs and defects.
- Tube Forming: The slitted strip passes through a series of progressively die-formed rollers (roll-forming) or through a seamless tube mill (for welded tubes, a TIG — Tungsten Inert Gas — welding process is employed). The forming process maintains continuous metal flow, minimizing residual stresses.
- Continuous Welding (for welded tubes): If the tube is fabricated via the ERW (Electric Resistance Welding) or TIG method, the weld seam is inspected using ultrasonic testing (UT) and visual examination. Weld quality conforms to ASTM A270, Clause 6.
- Pilot Mandrel Insertion: A hardened steel pilot mandrel is inserted into the tube bore to maintain roundness and diameter stability during the coiling operation. The mandrel prevents ovalization and kinking.
- Coiling: The formed tube is wound onto a pay-off reel to produce the final coil configuration. Coiling tension is carefully controlled to avoid permanent deformation. The coil diameter is maintained within specified tolerances.
- Heat Treatment (Annealing): Cold-worked coil tubes are solution-annealed at 1040–1120°C followed by rapid quenching to restore full annealed mechanical properties and relieve residual stresses. This step is critical for maintaining corrosion resistance and formability.
- Pickling & Passivation: Following annealing, the coil tube is pickled in a mixed acid solution (HNO₃/HF or H₂SO₄/HNO₃) to remove the oxide scale formed during heat treatment. Passivation is then performed using a 20–30% nitric acid solution to enrich the surface chromium oxide layer, enhancing passive film stability.
- Surface Finishing: Depending on the application, the tube may undergo mechanical polishing, electropolishing, or chemical brightening to achieve the required surface roughness and aesthetic finish.
- Final Inspection & Testing: Each coil spool undergoes comprehensive final inspection including dimensional verification (OD, wall thickness, coil diameter), hydrostatic pressure testing, surface defect inspection (eddy current or magnetic particle testing), and chemical analysis. Certificates of Conformance (CoC) and Mill Test Reports (MTR) are issued.
5. Applications
The stainless steel coil tube finds extensive application across multiple industries, driven by its combination of corrosion resistance, thermal efficiency, and the inherent advantages of the coiled form factor:
5.1 HVAC & Air Handling Systems
- Painting Workshop HVAC Coils: As highlighted in the referenced study on "Investigation into Precise Control Methods for HVAC Coil Tubes in Painting Workshops," coil tubes are integral to maintaining tightly controlled temperature and humidity conditions in industrial painting environments. Precise thermal regulation ensures consistent paint film formation, minimizes defects such as runs, sags, and orange peel, and maintains solvent evaporation rates within optimal ranges.
- Chilled Water & Hot Water Coil Assemblies: Used in air handling units (AHUs), fan coil units (FCUs), and rooftop units for commercial and industrial buildings.
- Refrigerant Coil Systems: Evaporator and condenser tubes for refrigeration and air conditioning systems.
5.2 Industrial Heat Exchangers
- Plate & Fin Heat Exchangers: Coil tubes are brazed or soldered to aluminum fins to create high-efficiency compact heat exchangers.
- Shell & Tube Heat Exchangers: U-tube configurations utilizing continuous coil lengths to maximize heat transfer area within a compact footprint.
- Air-to-Air Heat Recovery Units: Cross-flow and counter-flow heat exchangers for energy recovery in ventilation systems.
5.3 Food & Beverage Processing
- Sanitary Heat Exchangers: Double-wall jacketed coils for pasteurization, sterilization, and tempering processes in dairy, brewing, and beverage industries.
- CIP (Clean-in-Place) Systems: Coil tubing for chemical circulation in cleaning and sanitizing loops.
5.4 Chemical & Pharmaceutical Processing
- Reactor Cooling & Heating Coils: Internal coil inserts for jacketed reactors providing precise temperature control during chemical reactions.
- Distillation Column Reboilers & Condensers: Coil configurations for efficient vapor-liquid heat exchange.
5.5 Automotive & Aerospace
- Brake Cooling Systems: Coil tubes for high-performance braking system heat management.
- Cabin Air Conditioning: Compact coil assemblies for vehicle HVAC systems.
- Aviation Fuel Heating & Cooling: Coil heat exchangers for fuel temperature regulation in aircraft systems.
5.6 Oil & Gas
- Subsea Heat Exchangers: Spiral coil configurations for oil and gas processing platforms.
- Gas Turbine Cooling: Internal cooling coils for turbine blade cooling circuits.
6. Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains rigorous quality management systems and ensures compliance with international standards governing stainless steel tubing:
6.1 Quality Management Systems
- ISO 9001:2015 — Quality Management System certification ensuring consistent product quality and customer satisfaction.
- ISO 14001:2015 — Environmental Management System certification demonstrating commitment to sustainable manufacturing practices.
- ISO 45001:2018 — Occupational Health and Safety Management System certification.
6.2 Product Standards
- ASTM A270 / A270M — Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing for General Application.
- ASTM A554 — Standard Specification for Seamless Austenitic Stainless Steel Tube for Heat-Transfer Applications.
- EN 10217-7 — Technical Delivery Conditions for Cold-Drawn Stainless Steel Tubes for Particular Purposes.
- GB/T 12771 — Chinese National Standard for Fluid Transport Stainless Steel Tubes (equivalent to ASTM A270).
- JIS G3446 — Japanese Industrial Standard for Cold-Rolled Stainless Steel Tubes.
- AMS 5510 / AMS 5525 — Aerospace Material Specifications for stainless steel tubing (where applicable).
6.3 Testing & Inspection Certifications
- Mill Test Reports (MTR) — Provided with each shipment, documenting chemical composition, mechanical properties, and heat treatment records.
- Certificates of Conformance (CoC) — Verifying compliance with specified standards and customer requirements.
- Hydrostatic Pressure Test Reports — Documenting pressure test results for each coil spool.
- NACE MR0175 / ISO 15156 — Compliance for sour service applications (where applicable).
- 3.1 Certification (EN 10204) — Third-party inspection and testing reports available upon request.
7. Unique Selling Points
The coil tube product line from Wenzhou Jixing Metal Materials Co., Ltd. offers several distinguishing advantages that set it apart in the competitive stainless steel tubing market:
- Continuous-Length Efficiency: The coil form eliminates the need for field welding, reducing labor costs, minimizing leak points, and ensuring continuous fluid flow with uniform hydraulic characteristics throughout the entire length.
- Precision Coiling