Stainless Steel Coil Tube (Coiltube) — Industrial Heating & Heat Exchange Element
1. Product Overview
The Stainless Steel Coil Tube (also referred to as Coiltube or Coiled Tubing) manufactured by Wenzhou Jixing Metal Materials Co., Ltd is a precision-engineered continuous helical tubing product designed for use in thermal management systems, particularly in fresh air handling units (AHUs), heating and cooling coils, and industrial heat exchangers. The coil tube is formed from seamless or welded stainless steel pipe through a cold-coiling process, producing a uniform helical geometry that maximizes heat transfer surface area within a compact volumetric envelope.
This product represents a critical component in HVAC (Heating, Ventilation, and Air Conditioning) systems where anti-freeze protection, thermal efficiency, and long-term corrosion resistance are paramount. The coiled configuration enables efficient fluid circulation through heating or cooling media while maintaining structural integrity under repeated thermal cycling conditions.
2. Material & Properties
The coil tube is fabricated from high-grade austenitic stainless steel, selected for its exceptional combination of corrosion resistance, thermal conductivity, and mechanical strength across a wide temperature range.
- Primary Material Grades: AISI 304 (UNS S30400), AISI 316 (UNS S31600), and AISI 321 (UNS S32100)
- Corrosion Resistance: Excellent resistance to atmospheric corrosion, acidic environments, and chlorinated water solutions (particularly for 316 grade containing 2–3% Molybdenum)
- Operating Temperature Range: −196°C to +870°C (304 grade); −273°C to +870°C (316 grade)
- Thermal Conductivity: 14–16 W/(m·K) at 20°C
- Tensile Strength: ≥ 520 MPa (304), ≥ 515 MPa (316)
- Yield Strength: ≥ 205 MPa (304), ≥ 170 MPa (316)
- Surface Finish: 2B, BA (Bright Annealed), or No. 4 Brushed finish available
- Weldability: Excellent — compatible with TIG (Tungsten Inert Gas), MIG (Metal Inert Gas), and orbital welding processes
3. Technical Specifications
| Parameter | Specification | Tolerance |
|---|---|---|
| Outer Diameter (OD) | 6.0 mm – 50.8 mm (¼" – 2") | ±0.1 mm |
| Wall Thickness | 0.5 mm – 3.0 mm | ±0.05 mm |
| Coil Pitch (Spacing) | 5.0 mm – 25.0 mm | ±0.2 mm |
| Coil Length (Straightened) | 1.0 m – 500.0 m | ±1.0% |
| Coil Bundle Diameter | 50 mm – 500 mm | ±1.0 mm |
| Maximum Working Pressure | 1.6 MPa – 6.4 MPa (per ASME B31.3) | — |
| Hydrostatic Test Pressure | 1.5 × Working Pressure | — |
| Maximum Flow Velocity | ≤ 3.0 m/s (liquid); ≤ 30 m/s (gas) | — |
| Surface Roughness (Ra) | ≤ 0.8 μm (BA finish); ≤ 1.6 μm (2B finish) | — |
| Material Standard | ASTM A269, ASTM A312, EN 10217-7 | — |
| Dimensional Standard | ASME B36.19M, DIN 11850, GB/T 14976 | — |
| Anti-Freeze Design Rating | Rated for operation down to −40°C with glycol solutions | — |
| Service Life (Design) | ≥ 25 years under normal operating conditions | — |
4. Manufacturing Process
The production of the stainless steel coil tube follows a rigorous multi-stage manufacturing protocol to ensure dimensional accuracy, metallurgical integrity, and surface quality:
- Raw Material Selection & Inspection: Certified stainless steel seamless pipe or ERW (Electric Resistance Welded) pipe is sourced from approved mills with full chemical composition and mechanical property documentation per ASTM A269/A312.
- Pipe Pre-Processing: Incoming pipe undergoes end preparation (cutting, chamfering, deburring), internal cleaning, and visual/ultrasonic inspection to eliminate surface defects and internal inclusions.
- Cold Coiling: The straight pipe is fed through a precision CNC-controlled coiling machine with servo-driven feed mechanisms. A forming die system ensures uniform helical geometry with controlled pitch and diameter without inducing plastic deformation or work hardening beyond acceptable limits.
- Stress Relief Annealing (if required): For applications requiring reduced residual stress, the coiled tube may undergo solution annealing at 1050°C – 1150°C followed by controlled cooling to restore full austenitic microstructure.
- Welding & Assembly: Coil tube bundles are welded to header manifolds (inlet/outlet) using TIG welding with inert gas shielding (Argon or Argon/Helium mixtures). Weld joints undergo visual inspection and, where applicable, dye penetrant testing (DPT) or radiographic testing (RT).
- Surface Treatment: Optional passivation (nitric acid or citric acid based) and pickling to remove welding discoloration and restore chromium oxide protective layer.
- Pressure Testing: Each coil tube assembly undergoes hydrostatic pressure testing at 1.5× the maximum design working pressure, held for a minimum of 10 minutes with zero leakage tolerance.
- Final Inspection & Packaging: Dimensional verification, material traceability confirmation, and protective packaging (desiccant-sealed with anti-corrosion wrapping) prior to shipment.
5. Applications
The stainless steel coil tube is widely deployed across multiple industrial and commercial sectors:
- HVAC Systems: Heating and cooling coils in fresh air handling units (FAHU), air source heat pumps, and chiller units — with specific anti-freeze design considerations for cold-climate installations
- Anti-Freeze Heating Coils: In fresh air units operating in sub-zero environments, coil tubes are designed with sufficient flow velocity and glycol-based heat transfer fluid to prevent ice formation and subsequent mechanical damage (refer to anti-freeze methods for heating coils in fresh air units)
- Industrial Heat Exchangers: Shell-and-coil heat exchangers, condensers, and evaporators in chemical processing, pharmaceutical manufacturing, and food & beverage industries
- Refrigeration Systems: Evaporator and condenser coils in commercial refrigeration units, cold storage facilities, and industrial process cooling
- Water Treatment: Ultrafiltration (UF) and reverse osmosis (RO) systems requiring corrosion-resistant tubing for high-purity water production
- Power Generation: Condensate recovery systems, turbine cooling loops, and waste heat recovery units
- Marine & Offshore: Seawater cooling coils and desalination plant heat exchange elements leveraging 316/316L grade resistance to chloride-induced pitting corrosion
6. Anti-Freeze Design Considerations
In fresh air handling units operating in cold climates, heating coil tubes are susceptible to freezing when ambient temperatures drop below 0°C and the heat transfer fluid circulation is interrupted or insufficient. Wenzhou Jixing Metal Materials Co., Ltd incorporates the following anti-freeze design principles into their coil tube products:
- Minimum Flow Velocity Design: Coil geometry is optimized to maintain fluid velocity above the minimum threshold (typically ≥ 0.5 m/s) even at reduced flow rates, preventing localized heat loss and ice nucleation.
- Glycol Compatibility: Material selection (304/316) ensures full compatibility with ethylene glycol (EG) and propylene glycol (PG) heat transfer fluids at concentrations up to 60% by volume.
- Drainage Capability: Coil tube configurations permit complete fluid drainage to eliminate trapped liquid that could freeze and expand, causing tube rupture.
- Thermal Mass Optimization: Wall thickness is balanced between thermal conductivity (thin wall for rapid heat transfer) and thermal mass (sufficient mass to delay temperature drop during transient shutdown conditions).
- Temperature Sensor Integration Points: Coil tube assemblies are designed with provisions for RTD (Resistance Temperature Detector) or thermocouple mounting to enable automated anti-freeze control logic in the HVAC management system.
7. Quality Certifications & Compliance
All coil tube products manufactured by Wenzhou Jixing Metal Materials Co., Ltd conform to the following international standards and certifications:
| Certification / Standard | Scope of Compliance |
|---|---|
| ISO 9001:2015 | Quality Management System certification covering design, manufacturing, and inspection processes |
| ISO 14001:2015 | Environmental Management System certification for sustainable manufacturing practices |
| CE Marking | Conformity with EU Machinery Directive (2006/42/EC) and Pressure Equipment Directive (PED 2014/68/EU) |
| EN 10204 3.1 | Material test certificates for each batch of raw stainless steel pipe |
| ASME B31.3 | Pressure Piping Code compliance for process piping applications |
| GB/T 14976 | Chinese national standard for seamless stainless steel tubes for fluid transport |
| ASTM A269 / A312 | American material standards for austenitic stainless steel seamless and welded tubes |
| NORSOK M-650 (optional) | Norwegian offshore standard for corrosion-resistant materials in marine environments |
8. Unique Selling Points
- Precision CNC Coiling: Automated coiling machinery ensures repeatable pitch accuracy of ±0.2 mm, eliminating the variability associated with manual coiling methods and guaranteeing uniform heat transfer performance across the entire coil length.
- Anti-Freeze Engineering Heritage: Product design incorporates lessons learned from field experience with fresh air unit heating coil freeze events, resulting in geometries and material specifications optimized for cold-climate reliability.
- Full Traceability: Each coil tube assembly carries a unique batch identifier linked to raw material mill certificates, dimensional inspection records, and pressure test documentation — enabling complete supply chain traceability.
- Custom Geometry Capability: Wenzhou Jixing Metal Materials Co., Ltd offers fully customized coil tube configurations (pitch, diameter, length, header layout) to meet specific OEM requirements for HVAC equipment manufacturers.
- Cost-Effective Longevity: The use of austenitic stainless steel eliminates the need for internal coatings or cathodic protection, reducing lifetime maintenance costs by an estimated 40–60% compared to carbon steel alternatives with protective linings.
- Food & Pharmaceutical Grade Available: BA-finish coil tubes meeting 3-A Sanitary Standards for applications in food processing, dairy, and pharmaceutical heat exchange systems.
9. Ordering Information
Customers should specify the following parameters when requesting quotations:
- Material grade (304, 316, 321, 316L, or custom)
- Outer diameter and wall thickness
- Coil pitch and total tube length
- Surface finish requirement (2B, BA, No. 4, or custom)
- Header/manifold configuration (if applicable)
- Required certifications and test documentation
- Operating conditions (fluid type, temperature range, working pressure)
- Order quantity and delivery timeline
Wenzhou Jixing Metal Materials Co., Ltd — Precision stainless steel coil tube solutions engineered for thermal performance, corrosion resistance, and long-term reliability in demanding industrial environments.