FP-68WA Stainless Steel Coil Tube for Fan Coil Units
1. Product Overview
The FP-68WA Stainless Steel Coil Tube is a precision-engineered coiled piping solution developed by Wenzhou Jixing Metal Materials Co., Ltd, specifically designed for integration into commercial and industrial fan coil units (FCUs). This product represents a high-performance thermal exchange medium that ensures superior heat transfer efficiency, long-term corrosion resistance, and reliable structural integrity under demanding HVAC (Heating, Ventilation, and Air Conditioning) operating conditions.
The coil tube is manufactured to meet the rigorous thermal and mechanical demands of the FP-68WA fan coil unit platform, serving as the primary coolant circuit element that facilitates efficient heat exchange between the refrigerant or hot water medium and the ambient air stream. Its coiled geometry maximizes surface area within a compact envelope, enabling optimal thermal performance in space-constrained installations.
2. Material & Properties
2.1 Base Material Composition
- Primary Alloy: Austenitic Stainless Steel, conforming to AISI 304 / SUS304 or AISI 316L / SUS316L specifications
- Chromium (Cr): 18.0–20.0% (AISI 304) or 16.0–18.0% (AISI 316L)
- Nickel (Ni): 8.0–10.5% (AISI 304) or 10.0–14.0% (AISI 316L)
- Molybdenum (Mo): ≤0.08% (AISI 304) or 2.0–3.0% (AISI 316L)
- Carbon (C): ≤0.08% (AISI 304) or ≤0.03% (AISI 316L, low-carbon variant)
- Maximum Grain Size: ASTM A240 Grade 1 (average grain diameter ≥170 μm)
2.2 Mechanical Properties
- Tensile Strength (Rm): ≥520 MPa (AISI 304) / ≥515 MPa (AISI 316L)
- Yield Strength (Rp0.2): ≥205 MPa (AISI 304) / ≥205 MPa (AISI 316L)
- Elongation (A50mm): ≥40% (AISI 304) / ≥35% (AISI 316L)
- Hardness: ≤217 HB (Brinell) / ≤95 HRB
- Impact Toughness: ≥47 J at −196°C (liquid nitrogen temperature)
2.3 Thermal & Physical Properties
- Thermal Conductivity: 16.3 W/(m·K) at 100°C
- Specific Heat Capacity: 500 J/(kg·K) at 25°C
- Coefficient of Thermal Expansion: 17.3 × 10⁻⁶ /°C (20–100°C)
- Density: 7.93 g/cm³
- Maximum Service Temperature: 870°C (continuous), 1093°C (intermittent)
- Minimum Service Temperature: −196°C (cryogenic service without loss of ductility)
2.4 Corrosion Resistance
The selected austenitic stainless steel grade provides exceptional resistance to:
- General atmospheric corrosion in industrial and coastal environments
- Pitting and crevice corrosion (particularly AISI 316L with Mo addition)
- Intergranular corrosion (low-carbon AISI 316L grade, C ≤ 0.03%)
- Stress corrosion cracking in chloride-containing media
- Scaling and oxidation at elevated operating temperatures
3. Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Product Model | FP-68WA Coil Tube | — |
| Outer Diameter (OD) | Φ9.52 mm (⅜") / Φ12.7 mm (½") / Φ15.88 mm (⅝") | ASTM A213 / EN 10216-5 |
| Wall Thickness (WT) | 0.8 mm / 1.0 mm / 1.2 mm (tolerance ±0.1 mm) | ASTM A213 |
| Coil Inner Diameter (ID) | ≥150 mm (adjustable per unit configuration) | Manufacturer Specification |
| Coil Length / Circumference | Custom, typically 2–8 m per circuit | Project-Specific |
| Number of Rows | 1–4 rows (configurable) | ASHRAE Handbook |
| Tube Pitch (Center-to-Center) | 19.05 mm (¾") standard / 15.88 mm compact | ASHRAE Standards |
| Surface Finish | Bright annealed, Ra ≤ 0.8 μm (inner) / Ra ≤ 1.6 μm (outer) | ASTM A240 |
| Operating Pressure | ≤1.6 MPa (water circuit) / ≤2.5 MPa (refrigerant circuit) | ASME BPV Code |
| Design Temperature Range | −30°C to +120°C (water) / −50°C to +80°C (refrigerant) | ISO 5149 |
| Heat Transfer Coefficient | U-value ≥ 45 W/(m²·K) (air side) | ASHRAE Fundamentals |
| Maximum Flow Velocity | ≤2.5 m/s (liquid) / ≤30 m/s (refrigerant vapor) | Manufacturer Recommendation |
| Seam Type | Continuous welded (TIG/argon arc) or seamless | ASTM A213 / EN 10216-5 |
| End Preparation | Deburred, chamfered, or threaded (per customer requirement) | ASME B1.20.1 |
| Packaging | Wooden crate or export-grade plastic wrapping with moisture barrier | ISO 4180 |
4. Manufacturing Process
4.1 Raw Material Procurement & Inspection
Hot-rolled stainless steel strip or pipe blank is sourced from certified mills with full chemical composition and mechanical property documentation. Incoming material undergoes spectroscopic analysis (OES), hardness testing, and visual inspection to verify conformance with specified grades.
4.2 Forming & Coiling
- Blanking & Cutting: Precision laser or shear cutting of strip material to required width and length.
- Roll Forming: Progressive multi-station roll forming to achieve target outer diameter and wall thickness with tight dimensional tolerances (±0.1 mm).
- Coil Winding: CNC-controlled spiral winding machine forms the coil geometry with consistent pitch, diameter, and number of turns. The winding process maintains controlled tension to prevent work hardening and geometric distortion.
4.3 Welding & Joining
- Longitudinal Welding: TIG (Tungsten Inert Gas) welding using ER308L or ER316L filler wire under argon shielding, producing a full-penetration weld with minimal heat-affected zone (HAZ).
- Header Connections: U-bend returns or fixed headers are fabricated using orbital TIG welding for leak-tight, corrosion-resistant joints.
- Weld Quality: 100% visual inspection; 10% dye penetrant testing (DPT) or radiographic testing (RT) per ASME Section IX.
4.4 Heat Treatment & Annealing
Post-forming solution annealing is performed at 1050–1150°C followed by rapid water quenching to:
- Relieve residual stresses introduced during forming
- Dissolve carbides and restore full austenitic microstructure
- Improve corrosion resistance and ductility
- Achieve bright, clean surface finish without pickling (bright annealing in controlled atmosphere furnace)
4.5 Surface Treatment & Finishing
- Acid Pickling & Passivation: (if required) Nitric-hydrofluoric acid pickling followed by passivation to remove scale and enrich chromium oxide surface layer.
- Internal Cleaning: Ball blasting or chemical cleaning of internal bore to remove scale, weld spatter, and oxide inclusions.
- External Polishing: Mechanical polishing to achieve specified surface roughness for enhanced heat transfer performance.
4.6 Quality Control & Testing
- Dimensional Inspection: Coordinate measuring machine (CMM) verification of OD, wall thickness, coil ID, and pitch.
- Pressure Testing: Hydrostatic test at 1.5× maximum operating pressure for 30 minutes minimum, with zero leakage permitted.
- Leak Testing: Helium mass spectrometer leak detection (sensitivity ≤1×10⁻⁹ Pa·m³/s) for high-integrity applications.
- Corrosion Testing: Salt spray testing (ASTM B117) for ≥500 hours without pitting initiation; intergranular corrosion testing per ASTM A262 Practice E.
- Chemical Verification: Spectroscopic re-verification of final product composition.
5. Applications
5.1 Primary Application — FP-68WA Fan Coil Unit
The FP-68WA Fan Coil Unit is a modular HVAC system designed for commercial buildings, hospitals, hotels, and institutional facilities. The stainless steel coil tube serves as the core heat exchange element, enabling:
- Cooling Mode: Chilled water or refrigerant circulation through the coil absorbs heat from the air stream, providing sensible and latent cooling.
- Heating Mode: Hot water circulation through the coil provides radiant and convective heating.
- Dehumidification: Low-temperature coil surfaces condense moisture from the air stream for humidity control.
5.2 Secondary Applications
- Commercial HVAC Systems: Air handling units (AHUs), rooftop units, and packaged terminal air conditioners (PTACs)
- Medical & Pharmaceutical Facilities: Clean room air systems requiring corrosion-resistant, cleanable heat exchangers
- Food & Beverage Industry: Cooling coils for cold storage, refrigerated display cases, and process cooling
- Marine & Offshore: HVAC systems in vessels and platforms where chloride resistance is critical
- Industrial Process Cooling: Heat exchangers in chemical processing, power generation, and manufacturing
- Residential Premium HVAC: High-end residential climate control systems requiring long service life
6. Quality Certifications & Compliance
6.1 Product Certifications
- ISO 9001:2015 — Quality Management System (Wenzhou Jixing Metal Materials Co., Ltd)
- ISO 14001:2015 — Environmental Management System
- ISO 45001:2018 — Occupational Health and Safety Management System
- CE Marking — Conformity with European Directive 2014/68/EU (Pressure Equipment Directive, PED)
- EN 10204 3.1 Certificate — Material Test Certificate per European standard
6.2 Applicable Standards
| Standard | Scope |
|---|---|
| ASTM A213 | Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubes for High-Temperature Service |
| ASTM A269 | Standard Specification for Seamless and Welded Austenitic Stainless Steel Sanitary Tubing |
| EN 10216-5 | Non-ferrous metal tubes and pipes — Technical delivery conditions — Part 5: Specific technical delivery conditions for austenitic stainless steel tubes |
| ASME BPV Section VIII | Boiler and Pressure Vessel Code — Rules for Construction of Pressure Vessels |
| ASME B31.5 | Pressure Piping — Hydraulic Power |
| ASHRAE Standard 34 | Standard Methods for Calculating Cooling and Heating Capacities of Unitary Air-Conditioning and Air-Source Heat Pump Equipment |
| ISO 5149 | Industrial piping — Designation and marking of piping systems |
| JIS G3448 | Seamless and welded stainless steel tubes for heat exchangers |
6.3 Third-Party Verification
- TÜV Rheinland — Product conformity assessment for European market
- SGS — Material verification and performance testing
- BV (Bureau Veritas) — Factory inspection and quality audit
- Intertek