Stainless Steel Coil Tube (Coiltube) — Technical Product Specification

Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.

Product Reference No.: 1688

Classification: Literature & Technical Reference — Coil Tube Systems for HVAC and Heat Exchange Applications

1. Product Overview

The Stainless Steel Coil Tube (Coiltube) is a precision-engineered, continuous-length stainless steel tubing product wound into a compact spiral or helical configuration. This product form is specifically designed for integration into heat exchanger assemblies, fan coil units (FCU), air handling systems, and thermal transfer applications where high surface-area-to-volume ratios, corrosion resistance, and thermal conductivity are critical performance parameters.

Coil tubes differ fundamentally from straight seamless or welded tubing in their geometry and application philosophy. The coiled configuration maximizes heat transfer surface area within a confined spatial envelope, making them indispensable in compact thermal management systems. Wenzhou Jixing Metal Materials Co., Ltd. supplies coil tubes conforming to international metallurgical and dimensional standards, serving industries including HVAC (Heating, Ventilation, and Air Conditioning), refrigeration, chemical processing, pharmaceutical manufacturing, and food-grade thermal systems.

2. Material Composition and Properties

The coil tube product line is manufactured from austenitic stainless steel grades selected for their superior combination of corrosion resistance, weldability, and thermal performance:

• AISI 304 (UNS S30408 / EN 1.4301): The most widely specified grade for general-purpose coil tube applications. Contains approximately 18–20% Chromium (Cr) and 8–10.5% Nickel (Ni), providing excellent resistance to atmospheric corrosion, dilute acids, and alkaline solutions. Suitable for food-grade and pharmaceutical applications.
• AISI 316 (UNS S31603 / EN 1.4401): Enhanced grade incorporating 2.0–3.0% Molybdenum (Mo), delivering superior resistance to chloride-induced pitting and crevice corrosion. Preferred for marine environments, chemical processing, and applications involving halide-containing media.
• AISI 321 (UNS S32103 / EN 1.4541): Titanium (Ti) stabilized grade suitable for elevated-temperature applications up to 870°C, where resistance to intergranular corrosion is required.
• AISI 316L (UNS S31603 / EN 1.4404): Low-carbon variant of 316 (Carbon ≤ 0.03%), optimized for welding applications where sensitization must be avoided.

Key Mechanical and Physical Properties (AISI 304 Reference)

• Tensile Strength: ≥ 520 MPa (75,000 psi)
• Yield Strength (0.2% offset): ≥ 205 MPa (29,700 psi)
• Elongation at Break: ≥ 40%
• Thermal Conductivity (20°C): 16.3 W/(m·K)
• Linear Expansion Coefficient (20–100°C): 17.3 × 10⁻⁶ /°C
• Density: 8.0 g/cm³
• Maximum Service Temperature: 870°C (oxidation resistance limit)

3. Technical Specifications

Parameter	Specification / Range	Standard Reference
Outer Diameter (OD)	3.0 mm – 25.4 mm (1/8" – 1")	ASTM A213 / GB/T 14976
Wall Thickness	0.25 mm – 1.50 mm	ISO 13679
Coil Inner Diameter (CID)	100 mm – 500 mm	Manufacturer Specification
Coil Outer Diameter (COD)	200 mm – 1200 mm	Manufacturer Specification
Tube Length (per coil)	5 m – 50 m (continuous)	Custom Order Available
Surface Finish	Bright Annealed (BA) / Pickled and Passivated / Brushed	ASTM A473 / EN 10088
Tolerance — OD	±0.05 mm (precision grade) / ±0.10 mm (standard)	ASTM A213
Tolerance — Wall Thickness	±0.02 mm (precision grade) / ±0.05 mm (standard)	ISO 13679
End Condition	Plain / Flared / Threaded / Flanged (per customer specification)	ASME B1.20.1 / DIN 2984
Coil Winding	Single-layer / Multi-layer spiral / Helical	Manufacturer Specification

4. Manufacturing Process

The production of precision stainless steel coil tubes involves a multi-stage metallurgical and forming process:

1. Raw Material Selection: Cold-rolled stainless steel strip (cold-rolled coil) is sourced from certified mills, conforming to ASTM A240 or EN 10088 chemical composition requirements. Incoming material undergoes spectroscopic verification (PMI — Positive Material Identification) to confirm alloy grade.
2. Slitting and Leveling: The coil strip is slit to the required width and passed through a precision leveling line to eliminate residual stresses and ensure flatness within 0.05 mm/m.
3. Tube Forming: The flat strip is fed through a progressive die roll-forming system or a continuous welding and rolling mill. For seamless tube production, the strip is formed into a tube shape and welded using high-frequency resistance welding (HFRW) or orbital TIG (Tungsten Inert Gas) welding, followed by cold expansion to achieve near-seamless dimensional uniformity.
4. Heat Treatment (Solution Annealing): The formed tube is subjected to solution annealing at 1040–1120°C followed by rapid quenching (water or air cool) to dissolve carbides and restore full austenitic microstructure, ensuring maximum corrosion resistance and ductility.
5. Pickling and Passivation: Post-heat-treatment, the tube surface is pickled in a mixed acid bath (HNO₃ + H₂SO₄) to remove oxide scale, followed by passivation with nitric acid or citric acid to establish a protective chromium oxide (Cr₂O₃) film.
6. Coil Winding: The finished tube is wound into the specified coil configuration using a precision CNC coil winding machine, ensuring uniform pitch, consistent coil diameter, and controlled spring-back. The winding process is monitored to prevent tube distortion or surface damage.
7. Quality Inspection: Each coil undergoes dimensional verification (OD, wall thickness, coil diameter), surface inspection, hydrostatic pressure testing (minimum 1.5× working pressure for 10 seconds), and optional eddy current testing for wall thickness uniformity.

5. Applications

Stainless steel coil tubes are integral components in the following application domains:

• Fan Coil Units (FCU): Coil tubes serve as the primary heat transfer element in fan coil units used in commercial and residential HVAC systems. The coiled geometry maximizes contact area between refrigerant/cooling water and the air stream, enabling efficient sensible and latent heat exchange.
• Air Conditioning Heat Exchangers: Used in evaporator and condenser assemblies for split systems, VRF (Variable Refrigerant Flow) units, and packaged air conditioners.
• Refrigeration Systems: Applied in evaporators, condensers, and liquid sub-coolers for industrial refrigeration, cold storage, and process cooling.
• Process Cooling and Heating: Utilized in heat exchangers for chemical, pharmaceutical, and food processing industries where product purity and corrosion resistance are paramount.
• Water Heating Systems: Integrated into tankless water heaters, solar thermal collectors, and domestic hot water recirculation systems.
• Heat Recovery Systems: Employed in air-to-air and water-to-water heat recovery units for energy-efficient building HVAC.

6. Unique Selling Points

• Superior Corrosion Resistance: Austenitic stainless steel composition provides long-term durability in aggressive environments, eliminating the need for protective coatings and reducing lifecycle maintenance costs.
• Hygienic Surface Quality: Bright annealed and passivated surfaces meet FDA and EHEDG (European Hygienic Engineering and Design Group) standards, suitable for food-grade and pharmaceutical applications.
• High Thermal Efficiency: Optimized coil geometry and precise dimensional tolerances ensure maximum heat transfer coefficient (U-value) performance.
• Custom Configurability: Full customization of OD, wall thickness, coil diameter, coil pitch, and end conditions to meet specific OEM requirements.
• Weldability and Fabrication Flexibility: Excellent welding characteristics allow downstream integrators to fabricate custom heat exchanger assemblies with minimal post-weld treatment.
• Environmental Sustainability: Stainless steel is 100% recyclable without degradation of material properties, supporting circular economy principles.

7. Quality Certifications and Compliance

Wenzhou Jixing Metal Materials Co., Ltd. maintains adherence to the following quality and regulatory frameworks:

• ISO 9001:2015 — Quality Management System Certification
• ISO 14001:2015 — Environmental Management System
• ASME BPE (Bioprocessing Equipment) — Applicable for pharmaceutical-grade coil tube configurations
• CE Marking — Conformity with European Directive 2014/68/EU (Pressure Equipment Directive) where applicable
• ASTM / ASME Compliance — Material and product testing per ASTM A213, ASTM A269, and ASME B31.3
• GB/T Standards — Compliance with Chinese National Standards for stainless steel tube products
• Mill Test Reports (MTR) — Full chemical and mechanical property certification provided with each shipment
• NACE MR0175 / ISO 15156 — Compliance for sour service applications (316 and 316L grades)

8. Technical Notes and Literature Reference

This product specification is informed by technical literature on the domestic fan coil unit industry, specifically referencing the study "国产风机盘管的现状与发展" (Current Status and Development of Domestic Fan Coil Units). This reference addresses the evolution of coil tube design, material selection trends, and performance optimization strategies in China's HVAC manufacturing sector. The document highlights the transition from copper coil tubes to stainless steel alternatives driven by corrosion resistance requirements, food safety regulations, and lifecycle cost analysis.

9. Ordering and Customization

Customers may specify coil tube configurations by providing the following parameters:

• Stainless steel grade (304, 316, 321, 316L, or custom alloy)
• Outer diameter and wall thickness
• Coil inner diameter and coil outer diameter
• Tube length per coil
• Surface finish requirement
• End condition (plain, flared, threaded, or custom)
• Quantity and packaging requirements

Wenzhou Jixing Metal Materials Co., Ltd. provides engineering support for coil tube integration into heat exchanger designs, including finite element analysis (FEA) of thermal performance and flow resistance calculations.