Stainless Steel Coil Tube (Coiltube) for HVAC Fan Coil Unit Systems

Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd. | Catalog No.: 1182

1. Product Overview

The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered continuous tubing product specifically designed for use in Fan Coil Unit (FCU) assemblies within central air conditioning systems. Unlike discrete straight-pipe configurations, the coil tube is supplied in a continuous helical or serpentine coil form, enabling efficient heat exchange performance within compact indoor air-handling units.

Based on extensive technical literature review and industry best practices—particularly as documented in the study "Selection Principles for Fan Coil Units in Central Air Conditioning Systems"—this product is engineered to meet the stringent thermal, mechanical, and corrosion-resistance requirements of modern HVAC (Heating, Ventilation, and Air Conditioning) applications. The coil tube serves as the core heat transfer element, through which chilled water (cooling mode) or hot water (heating mode) circulates to condition indoor air streams.

Wenzhou Jixing Metal Materials Co., Ltd. leverages decades of metallurgical expertise and advanced rolling technology to produce coil tubes with consistent dimensional accuracy, superior surface finish, and reliable long-term service performance in humid, corrosive, and thermally cycling environments.

2. Material & Properties

2.1 Base Alloy Composition

The primary material grade used for this coil tube product is Austenitic Stainless Steel, conforming to the following international standards:

ASTM A213 TP304 / TP316 (American Society for Testing and Materials)
EN 10216-5 / EN 10217-7 (European Norms for welded stainless steel tubes)
GB/T 14976 (Chinese National Standard for cold-rolled seamless stainless steel tubes)

The austenitic microstructure provides an optimal combination of ductility, weldability, and corrosion resistance, making it particularly suitable for coil tube applications where the material must endure repeated thermal expansion and contraction cycles without cracking or deformation.

2.2 Key Mechanical Properties

Tensile Strength (Ultimate Tensile Strength, UTS): ≥ 515 MPa (ASTM A213 TP304)
Yield Strength (0.2% Offset): ≥ 205 MPa
Elongation at Break: ≥ 40% (ensures excellent formability during coiling)
Hardness (Rockwell B): ≤ 95 HRB
Thermal Conductivity: ~16 W/(m·K) at 20°C
Thermal Expansion Coefficient: 17.3 × 10⁻⁶ /°C

2.3 Corrosion Resistance

The austenitic stainless steel matrix, enriched with Chromium (Cr ≥ 18%) and Nickel (Ni ≥ 8%), forms a passive chromium oxide (Cr₂O₃) film that provides outstanding resistance to:

Atmospheric corrosion and condensation-induced degradation
Chilled water and glycol-based heat transfer fluids
Humid indoor air environments (RH up to 95%)
For TP316 grade: Enhanced resistance to pitting and crevice corrosion from chlorides (Mo ≥ 2%)

3. Technical Specifications

Parameter	Specification / Range	Test Standard
Outer Diameter (OD)	φ9.52 mm – φ25.4 mm (φ⅜" – φ1")	ASTM E39 / GB/T 2101
Wall Thickness (WT)	0.5 mm – 1.6 mm	ASTM E10 / GB/T 2101
Coil Pitch (Helix Spacing)	10 mm – 30 mm (adjustable per FCU design)	Internal QC Procedure
Coil Diameter (Bundle OD)	φ150 mm – φ600 mm	ASTM E39
Number of Rows (Passes)	2 – 6 rows (multi-row configurations available)	Design Specification
Tube Length (Uncoiled)	3 m – 15 m per continuous piece	GB/T 2101
Surface Finish	2B Annealed / BA (Bright Annealed) / No.4 Brushed	ASTM A480
End Condition	Plain ends / Beveled ends / Flared ends (customizable)	Per Customer Drawing
Operating Temperature Range	−40°C to +200°C	Material datasheet
Maximum Operating Pressure	1.6 MPa (standard) / up to 2.5 MPa (heavy-wall)	ASME B31.9
Dimensional Tolerance (OD)	±0.05 mm – ±0.10 mm (per OD range)	ASTM A213
Dimensional Tolerance (WT)	±10% of nominal	ASTM A213

4. Manufacturing Process

The production of the Stainless Steel Coil Tube follows a rigorous multi-stage manufacturing workflow designed to ensure dimensional precision, material integrity, and performance consistency:

Raw Material Selection & Inspection:
High-purity stainless steel strip (coil) is sourced from certified mills. Incoming material undergoes spectroscopic analysis (OES) to verify chemical composition, and visual/ultrasonic inspection to detect surface defects or internal inclusions.
Strip Preparation & Slitting:
The master coil is slit to precise widths corresponding to the target tube OD and WT. Edge quality is inspected to ensure clean, burr-free cut edges essential for seamless tube formation.
Tube Forming (Cold Roll Forming):
The flat strip is fed through a series of progressive roll stations that gradually bend and shape the strip into a circular cross-section. For welded tubes, the edges are overlapped and formed into a tight seam.
Welding (for Welded Coil Tubes):
High-frequency induction welding (HF Welding) or TIG (Tungsten Inert Gas) welding is applied to close the longitudinal seam. The weld zone is subsequently ground or buffed to achieve a smooth internal surface, minimizing flow resistance and eliminating potential corrosion initiation sites.
Heat Treatment (Solution Annealing):
The formed tube is subjected to solution annealing at 1050°C – 1150°C followed by rapid water quenching. This process dissolves carbides, restores full austenitic structure, relieves cold-work stresses, and maximizes corrosion resistance and ductility.
Precision Sizing & Straightening:
Post-annealing, the tube passes through sizing rolls and a straightening unit to achieve final OD, WT, and geometric accuracy within specified tolerances.
Coiling (Helical Forming):
The straight tube is fed through a precision coiling mechanism that forms the tube into the desired helical or serpentine coil geometry. The coil pitch, diameter, and number of turns are controlled by CNC (Computer Numerical Control) systems to ensure uniformity across the entire production run.
Surface Finishing:
Depending on the specification, the coil tube may receive additional surface treatment including pickling, passivation (to enhance the passive oxide film), or polishing to achieve 2B, BA, or brushed finishes.
Final Quality Inspection & Testing:
Each coil tube batch undergoes comprehensive testing including hydrostatic pressure testing, dimensional verification, surface inspection, and sampling for mechanical property verification.

5. Applications

5.1 Primary Application: Fan Coil Units (FCU) in Central Air Conditioning Systems

The coil tube is the fundamental heat exchange component within fan coil units, which are the terminal air-handling devices in distributed central air conditioning systems. The selection and design of these coil tubes directly influence system performance, as established by the following engineering principles:

Heat Transfer Efficiency: The compact coil geometry maximizes the heat transfer surface area within a limited installation footprint. The stainless steel material, with its inherent thermal conductivity, ensures efficient heat exchange between the working fluid (chilled/hot water) and the passing air stream.
Compact Design: Coil tubes allow for multi-row configurations that increase capacity without proportionally increasing the unit footprint—critical for space-constrained commercial and residential installations.
Corrosion Durability: In humid environments where condensation is common on cooling coils, stainless steel coil tubes resist the corrosion that would degrade carbon steel alternatives, ensuring long service life and maintained performance.
Low Flow Resistance: Smooth internal surfaces of precision-manufactured coil tubes minimize pressure drop, reducing pumping energy consumption and improving overall system efficiency.

5.2 Extended Applications

Commercial HVAC systems (office buildings, hotels, hospitals, retail centers)
Residential central air conditioning systems
Cleanroom air conditioning and laminar flow systems
Food processing and pharmaceutical plant HVAC (hygienic-grade TP316L available)
Marine and offshore HVAC systems (marine-grade stainless steel options)
Refrigeration condensers and evaporators
Industrial heat exchangers and process cooling systems

6. Quality Certifications & Compliance

Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management framework ensuring that every coil tube product meets or exceeds international standards:

ISO 9001:2015 — Quality Management System certification, demonstrating systematic quality control throughout the production lifecycle.
ISO 14001 — Environmental Management System certification, ensuring environmentally responsible manufacturing practices.
CE Marking — Conformity with European health, safety, and environmental protection standards for HVAC components.
EN 10216-5 / EN 10217-7 — Compliance with European standards for stainless steel welded tubes used in heat exchangers and pressure applications.
ASTM A213 — Conformance with American standards for seamless and welded austenitic stainless steel tubing.
GB/T 14976 — Compliance with Chinese national standards for cold-rolled stainless steel tubes.
ASME B31.9 — Compliance with piping code requirements for refrigeration and air-conditioning systems.
Material Test Reports (MTR): Every batch is accompanied by a full material test report including chemical composition (OES), mechanical properties, hydrostatic test results, and dimensional inspection records.

7. Unique Selling Points

Why Choose Wenzhou Jixing Stainless Steel Coil Tubes for HVAC Applications:

Superior Formability & Ductility:
The high elongation capacity (≥40%) of the austenitic stainless steel enables reliable coiling without cracking, kinking, or thinning at the coil bends—ensuring uniform wall thickness throughout the entire coil geometry.
Exceptional Corrosion Resistance:
Designed to withstand decades of service in humid, condensation-prone HVAC environments. Available in TP304 (standard) and TP316/TP316L (chloride-rich environments) grades.
Precision CNC Coiling:
Computer-controlled coiling ensures consistent pitch, diameter, and turn count across every coil tube, providing repeatable heat transfer performance and simplified installation.
Hydrostatic Pressure Tested:
Every coil tube undergoes 100% hydrostatic pressure testing at 1.5× the maximum operating pressure to guarantee leak-tight integrity.
Customizable Configurations:
Flexible manufacturing capabilities allow customization of OD, WT, coil pitch, number of rows, end conditions, and surface finish to match specific FCU design requirements.
Low Flow Resistance Design:
Smooth internal surfaces and precise dimensional tolerances minimize pressure drop, reducing pumping energy consumption and improving the overall Coefficient of Performance (COP) of the HVAC system.
Full Traceability:
Complete batch traceability from raw material mill certification through final product testing, ensuring accountability and quality assurance at every stage.

Document Reference: Catalog No. 1182 — Stainless Steel Coil Tube Technical Specification | Wenzhou Jixing Metal Materials Co., Ltd.