Stainless Steel Coil Tube (Coiltube) — HVAC Fan Coil Unit Series

Product Overview

The Stainless Steel Coil Tube (Coiltube) is a precision-engineered heat exchange component manufactured by Wenzhou Jixing Metal Materials Co., Ltd. Specifically designed for integration into double-pipe fan coil unit (FCU) systems with fresh air supply configurations, this coil tube delivers exceptional thermal transfer efficiency, corrosion resistance, and long-term structural integrity. The product represents a critical component in modern HVAC (Heating, Ventilation, and Air Conditioning) infrastructure, where reliable and efficient heat exchange is paramount to maintaining optimal indoor environmental conditions.

Unlike conventional copper or carbon steel coil tubes, the stainless steel variant offers superior resistance to oxidation, scale formation, and chemical degradation, making it particularly suitable for applications involving high-humidity environments, aggressive media, or extended service lifecycles. The coil tube geometry—characterized by a continuous helical winding—maximizes the surface-area-to-volume ratio, thereby enhancing convective and conductive heat transfer rates within the fan coil unit heat exchanger.

Material & Properties

Base Material Composition

The coil tube is fabricated from austenitic stainless steel, primarily utilizing grades conforming to international standards such as AISI 304, AISI 316, and AISI 316L. The selection of material grade is determined by the specific operational environment and chemical exposure requirements of the end application.

Key Material Properties

• Corrosion Resistance: Exceptional resistance to atmospheric corrosion, acidic environments, and chlorinated solutions (particularly in 316/316L grades), ensuring longevity in humid or chemically aggressive conditions.
• Thermal Conductivity: While lower than copper (approximately 15–16 W/(m·K) for 304 grade vs. 385 W/(m·K) for copper), the stainless steel coil tube compensates through optimized geometry design and enhanced surface treatment, achieving competitive overall heat transfer coefficients.
• Mechanical Strength: High yield strength and tensile strength provide resistance to vibration-induced fatigue and pressure cycling common in HVAC systems.
• Hygienic Surface: The smooth, non-porous surface of stainless steel prevents bacterial growth and biofilm formation, meeting sanitary and cleanroom requirements.
• Temperature Range: Operable across a wide temperature spectrum, from cryogenic conditions up to approximately 800°C (1472°F), accommodating extreme thermal cycling.
• Weldability: Excellent weldability enables seamless integration with headers, manifolds, and terminal connections without compromising structural integrity.

Specifications

Parameter	Specification / Range	Standard / Note
Material Grade	AISI 304 / 316 / 316L	ASTM A213 / A269
Outer Diameter (OD)	3.0 mm – 12.7 mm (1/8" – 1/2")	Customizable
Wall Thickness	0.3 mm – 1.5 mm	ASME B36.19M
Coil Diameter	150 mm – 600 mm	Application-dependent
Coil Length	1.0 m – 10.0 m (per spool)	Custom order available
Surface Finish	2B / No.4 / Electropolished / Passivated	ASTM A480
Maximum Operating Pressure	Up to 1.6 MPa (232 psi)	System-dependent
Operating Temperature	-196°C to +450°C (-321°F to +842°F)	Continuous service
Tolerance on OD	±0.05 mm – ±0.10 mm	ISO 286
Coil Pitch	8 mm – 25 mm (configurable)	Heat transfer optimization
End Connection	Butt-weld / Solder / Flanged / Threaded	Per customer requirement
Coating / Treatment	Passivation / PTFE coating (optional)	Enhanced anti-fouling
Compliance	ASTM, ASME, EN 10217, GB/T 14976	Multi-standard certified

Manufacturing Process

The production of stainless steel coil tubes at Wenzhou Jixing Metal Materials Co., Ltd. follows a rigorous, multi-stage manufacturing protocol designed to ensure dimensional accuracy, metallurgical integrity, and surface quality.

1. Raw Material Selection & Inspection:

   High-purity stainless steel wire rod is sourced from certified mills and subjected to spectroscopic analysis to verify chemical composition compliance with the specified grade. Incoming material undergoes visual inspection for surface defects and dimensional verification.

2. Wire Drawing & Annealing:

   The steel wire rod is cold-drawn through progressively smaller die sets to achieve the target tube diameter and wall thickness. Periodic annealing at controlled temperatures (typically 1050°C–1150°C) relieves residual stresses and restores ductility, preventing cracking during subsequent forming operations.

3. Tube Forming (Spiral/Coil Winding):

   The formed tube is precisely wound into a helical coil geometry using CNC-controlled coiling machinery. The winding process maintains consistent coil pitch, diameter tolerance, and tube roundness throughout the entire spool length. Real-time monitoring systems ensure geometric accuracy within ±0.10 mm tolerance.

4. Welding & Header Assembly:

   Tube ends are welded to inlet and outlet headers (manifolds) using TIG (Tungsten Inert Gas) welding or orbital welding techniques. Weld seams are inspected via dye penetrant testing (DPT) or ultrasonic testing (UT) to ensure leak-tight integrity.

5. Surface Treatment & Passivation:

   The assembled coil tube undergoes pickling and passivation to remove mill scale, welding discoloration, and surface contaminants. This process forms a stable chromium oxide layer that enhances corrosion resistance. Optional electropolishing or PTFE (Polytetrafluoroethylene) coating may be applied for specialized applications.

6. Hydrostatic Pressure Testing:

   Each coil tube unit is subjected to hydrostatic pressure testing at 1.5 times the maximum design operating pressure to verify structural integrity and weld soundness. Test duration is maintained for a minimum of 5 minutes with zero pressure drop acceptance criteria.

7. Final Quality Inspection & Packaging:

   Completed units undergo dimensional verification, visual inspection, and documentation review. Products are protected with anti-corrosion packaging materials and labeled with traceability information including heat number, batch code, and test certificates.

Applications

The stainless steel coil tube is engineered for deployment in a wide range of HVAC and industrial heat exchange applications. The reference study on "Operation and Regulation Analysis of Double-Pipe Fan Coil Unit Plus Fresh Air Systems" highlights the critical role of coil tube performance in system efficiency and controllability.

Primary Applications:

• Double-Pipe Fan Coil Units (FCU):

  Used as the core heat exchanger element in dual-circuit fan coil units, where separate hot and cold water loops provide simultaneous heating and cooling capacity. The stainless steel coil tube enables independent thermal regulation, reducing energy consumption and improving temperature control precision in commercial and institutional buildings.

• Fresh Air Handling Systems:

  Integrated into outdoor air handling units and energy recovery ventilators (ERV), where resistance to condensation corrosion and outdoor atmospheric exposure is essential.

• Commercial & Industrial HVAC:

  Deployed in office buildings, hospitals, laboratories, cleanrooms, and manufacturing facilities requiring high air quality and reliable thermal management.

• Food & Beverage Processing:

  Utilized in refrigeration coils, pasteurization heat exchangers, and dairy processing equipment where hygienic standards (FDA, 3-A) mandate corrosion-resistant, easily cleanable surfaces.

• Pharmaceutical & Biotechnology:

  Applied in controlled-environment chambers, cleanroom HVAC systems, and bioreactor cooling loops where GMP (Good Manufacturing Practice) compliance is required.

• Marine & Offshore:

  316L-grade coil tubes serve in marine HVAC systems where saltwater exposure demands maximum chloride resistance.

• Chemical Processing:

  Employed in acid-resistant heat exchangers and process cooling systems handling aggressive chemical media.

Quality Certifications & Compliance

Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management system and holds the following certifications and compliance credentials:

• ISO 9001:2015 — Quality Management System certification ensuring consistent product quality and process control.
• ISO 14001 — Environmental Management System certification demonstrating commitment to sustainable manufacturing practices.
• ISO 45001 — Occupational Health and Safety Management System certification.
• CE Marking — Conformity with European Union directives for product safety and environmental protection.
• Material Test Certificates (MTC): — EN 10204 3.1 certified material test reports provided with each shipment, documenting chemical composition, mechanical properties, and test results.
• Third-Party Inspection: — Products available for SGS, BV (Bureau Veritas), or TUV inspection upon customer request.
• NACE MR0175 (Optional): — Compliance for sour service applications where hydrogen-induced cracking resistance is required.

Unique Selling Points

• Superior Corrosion Longevity: Compared to traditional carbon steel or copper coil tubes, stainless steel variants offer 3–5 times longer service life in corrosive environments, significantly reducing maintenance frequency and total cost of ownership (TCO).
• Enhanced System Efficiency: The smooth surface finish and optimized coil geometry minimize fouling resistance, maintaining stable heat transfer performance over extended operating cycles—a critical factor identified in the double-pipe FCU system regulation analysis.
• Hygienic & Food-Grade Compliance: The non-porous, passivated surface meets stringent sanitary requirements, eliminating dead zones where microbial growth could compromise product safety.
• Customizable Engineering: Full design flexibility in coil diameter, pitch, tube OD, wall thickness, and end connections enables precise thermal performance matching to specific system load calculations.
• Traceability & Documentation: Complete batch traceability from raw material mill certificates through final product testing ensures full supply chain transparency and regulatory compliance.
• Energy Efficiency Contribution: Reduced fouling and stable thermal performance directly translate to lower fan and pump energy consumption, supporting green building certifications such as LEED and Green Star.

Technical Note: The integration of stainless steel coil tubes in double-pipe fan coil unit systems, as analyzed in referenced operational studies, demonstrates measurable improvements in temperature control accuracy (±0.5°C), energy efficiency (COP improvement of 8–12%), and system response time compared to conventional single-pipe configurations. The corrosion-resistant properties of the stainless steel material further ensure that these performance advantages are maintained throughout the design service life of 20–25 years.

Technical Support & Customization

Wenzhou Jixing Metal Materials Co., Ltd. provides comprehensive technical support including thermal performance calculations, coil tube sizing based on system load profiles, material selection guidance for specific chemical environments, and custom engineering solutions tailored to project-specific requirements. Engineering consultation is available for system designers, HVAC contractors, and end-users seeking optimized heat exchange solutions.