Stainless Steel Coil Tube — HVAC Fan Coil Unit Application Series

Product Overview

The Stainless Steel Coil Tube (Product No. 796) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular product specifically designed for integration into Fan Coil Unit (FCU) Air Conditioning Systems. These coil tubes serve as the core heat exchange elements within chilled water and hot water distribution circuits, enabling efficient thermal transfer between the refrigerant medium and the conditioned air stream. The product conforms to the technical requirements outlined in the "Fan Coil Unit Air Conditioning Energy Consumption Monitoring System Technical Specification", ensuring compatibility with modern building energy management systems (Building Energy Management Systems, BEMS) and compliance with national energy efficiency standards.

Unlike conventional carbon steel coil tubes, the stainless steel variant offers superior corrosion resistance, thermal conductivity, and long-term structural integrity, making it particularly suitable for environments where water quality variability, chemical exposure, or prolonged service life are critical design considerations.

Material & Properties

Base Material Composition

Grade Options: SUS304 (AISI 304), SUS316L (AISI 316L), and SUS321 (AISI 321) austenitic stainless steels
Chemical Composition (SUS304 Reference):
- 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%
Grade Options: SUS304 (AISI 304), SUS316L (AISI 316L), and SUS321 (AISI 321) austenitic stainless steels
Chemical Composition (SUS316L Reference):
- Carbon (C): ≤ 0.030%
- Chromium (Cr): 16.0% – 18.0%
- Nickel (Ni): 10.0% – 14.0%
- Molybdenum (Mo): 2.0% – 3.0%
- Phosphorus (P): ≤ 0.035%
- Sulfur (S): ≤ 0.030%

Mechanical Properties

Tensile Strength (Ultimate Tensile Strength, UTS): ≥ 520 MPa (SUS304); ≥ 485 MPa (SUS316L)
Yield Strength (0.2% Offset): ≥ 205 MPa (SUS304); ≥ 170 MPa (SUS316L)
Elongation at Break: ≥ 40% (SUS304); ≥ 45% (SUS316L)
Hardness (Brinell, HBW): ≤ 217 (SUS304); ≤ 217 (SUS316L)

Thermal & Physical Properties

Thermal Conductivity: 16.3 W/(m·K) at 25°C (SUS304); 14.3 W/(m·K) at 25°C (SUS316L)
Specific Heat Capacity: 487 J/(kg·K) at 25°C
Thermal Expansion Coefficient: 17.3 × 10⁻⁶ /K (25–300°C)
Density: 7.93 g/cm³ (SUS304); 8.03 g/cm³ (SUS316L)
Maximum Operating Temperature: 870°C (SUS304, intermittent); 870°C (SUS316L, continuous)

Corrosion Resistance Characteristics

Pitting Resistance (PREN): 18–20 (SUS304); 24–26 (SUS316L)
Resistance to: Chloride-induced pitting, intergranular corrosion, stress corrosion cracking (SCC) in acidic media, and atmospheric oxidation
Surface Finish Options: 2B (cold-rolled and annealed), BA (Bright Annealed), No.4 (Brushed), and Mirror (8K) finishes

Technical Specifications

Parameter	Specification	Standard / Reference
Product Designation	Stainless Steel Coil Tube — FCU Series	Internal Product No. 796
Tube Outer Diameter (OD)	6.0 mm, 8.0 mm, 9.53 mm (3/8"), 10.0 mm, 12.0 mm, 15.88 mm (5/8")	ISO 1127; ASTM A213
Tube Wall Thickness (WT)	0.5 mm, 0.6 mm, 0.8 mm, 1.0 mm, 1.2 mm, 1.5 mm	GB/T 12771; EN 10217-7
Coil Outer Diameter (COD)	200 mm – 600 mm (customizable)	Manufacturer Specification
Coil Length per Spool	50 m – 300 m (standard); up to 500 m (special order)	ISO 4413
Bend Radius (Minimum)	≥ 3D (D = tube OD)	ASME B31.9
Operating Pressure (Max)	1.6 MPa (16 bar); 2.5 MPa (25 bar) for heavy-wall variants	EN 12828; GB 50242
Operating Temperature Range	−40°C to +120°C (standard); −196°C to +400°C (special grade)	ASTM A269
Surface Roughness (Ra)	≤ 0.8 μm (inner surface); ≤ 0.4 μm (mirror finish)	ISO 1302
Dimensional Tolerance (OD)	±0.05 mm (precision grade); ±0.10 mm (standard grade)	ASTM A213/A213M
Dimensional Tolerance (WT)	±0.03 mm (precision grade); ±0.05 mm (standard grade)	GB/T 14976
Heat Treatment	Solution Annealing at 1050°C – 1150°C followed by rapid water quench	ASTM A240
Packaging	Wooden pallet with moisture-proof wrapping; steel banding; desiccant included	ISO 4180

Manufacturing Process

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

Raw Material Procurement and Inspection:
Virgin stainless steel coils (hot-rolled coil, HRC) or cold-rolled coils (CRC) are sourced from certified mills. Incoming material undergoes spectroscopic analysis (Optical Emission Spectrometry, OES) and mechanical property verification to confirm compliance with the specified grade chemistry and physical characteristics.
Coil Decoiling and Leveling:
The raw coil is decoiled and passed through a precision leveling line to eliminate residual stresses, flatness defects, and edge waviness. Tension control systems maintain uniform strip tension throughout the process.
Slitting:
The leveled strip is slit to the required width using a high-precision slitting line with blade clearance optimization to minimize edge defects, burrs, and dimensional variation.
Forming (Tube Milling):
The slit strip is fed through a multi-stand tube mill (typically 6–10 stands) that progressively forms the flat strip into a closed circular tube. Roll gap settings are calibrated to achieve the target OD and WT within specified tolerances.
Welding (if applicable — ERW/ERWT process):
For electric resistance welded (Electrode Resistance Welding, ERW) tubes, the formed tube passes through a high-frequency induction welding station where the seam edges are fused. Post-weld heat treatment (Post-Weld Heat Treatment, PWHT) may be applied to relieve weld residual stresses and restore full annealed mechanical properties.
Heat Treatment (Solution Annealing):
The formed tubes are solution annealed in a continuous annealing furnace at 1050°C – 1150°C in a protective atmosphere (reduced hydrogen or vacuum) to dissolve carbides, eliminate cold-work hardening, and achieve a uniform austenitic microstructure. Rapid quenching prevents sensitization and ensures optimal corrosion resistance.
Pickling and Passivation:
Post-annealing tubes are subjected to acid pickling (nitric acid / hydrofluoric acid blend) to remove oxide scale, followed by passivation treatment to establish a stable chromium oxide protective layer on the surface. This step is critical for achieving the specified corrosion resistance performance.
Coiling:
The finished tubes are coiled into the required coil diameter using a precision coiling machine with controlled winding tension to prevent deformation, kinking, or surface marking. Coil cores and end caps are fitted to protect the tube ends.
Quality Inspection and Testing:
Comprehensive in-process and final inspection protocols are applied, including dimensional verification (laser micrometry), hydrostatic pressure testing, visual surface inspection, and material certification documentation.
Packaging and Dispatch:
Inspected coils are wrapped with moisture-proof polyethylene film, secured with steel strapping, and palletized on treated wooden bases for safe transport. Each shipment is accompanied by a Mill Test Certificate (MTC) and Quality Assurance (QA) documentation.

Applications

Primary Application — HVAC Fan Coil Units

The primary design intent of this coil tube product is integration into Fan Coil Units used in commercial and residential building air conditioning systems. In this application, the stainless steel coil tube serves as the refrigerant (chilled water or hot water) circulation conduit within the heat exchange core, where it transfers thermal energy to or from the air stream generated by the unit's fan assembly.

Key application advantages in FCU systems include:

Energy Efficiency: The high thermal conductivity of austenitic stainless steel ensures efficient heat transfer rates, directly contributing to lower energy consumption as monitored by the Fan Coil Unit Air Conditioning Energy Consumption Monitoring System. Reduced energy consumption translates to lower operational costs and compliance with building energy performance standards.
Corrosion Resistance in Variable Water Quality: Unlike carbon steel tubes prone to internal corrosion from treated water, inhibitors, or residual chlorine in some HVAC water treatment schemes, stainless steel coil tubes maintain structural integrity over extended service periods (20+ years).
Hygienic Performance: The smooth, non-porous surface finish inhibits biofilm formation and bacterial growth, which is critical for indoor air quality (Indoor Air Quality, IAQ) in occupied spaces.
Compatibility with Monitoring Systems: The consistent thermal properties and predictable heat transfer coefficients of stainless steel tubes facilitate accurate energy consumption monitoring and building automation system integration.

Secondary Applications

Industrial Process Cooling: Heat exchanger tubes in chemical processing, pharmaceutical manufacturing, and food processing plants where corrosion resistance and sanitary requirements are paramount.
Marine and Offshore Systems: HVAC and cooling systems on vessels and offshore platforms where chloride-laden environments demand high-grade corrosion resistance (SUS316L recommended).
Medical and Laboratory Facilities: Air conditioning systems in hospitals, cleanrooms, and laboratory environments where hygienic standards and chemical resistance are critical.
Data Centers: Precision cooling systems for server rooms where reliability, corrosion resistance, and thermal performance are essential.
Residential High-End HVAC: Premium residential air conditioning systems where long-term durability and low maintenance are valued.

Quality Certifications and Standards Compliance

Applicable International and National Standards

ASTM A213/A213M: Standard Specification for Seamless and Welded Austenistic Stainless Steel Tubes for High-temperature Service
ASTM A269: Standard Specification for Seamless and Weld