Stainless Steel Coil Tube — Model Series 904 (Coiltube)
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd
Product Category: Documentary & Technical Learning Reference — Fan Coil Unit Selection Study
1. Product Overview
The Stainless Steel Coil Tube (Model Series 904) is a precision-engineered coiled tubing product designed for integration into fan coil units (FCUs) and hydronic heating/cooling systems. This product line represents the culmination of advanced metallurgical research and manufacturing expertise, specifically tailored to meet the rigorous thermal exchange and structural requirements of modern HVAC (Heating, Ventilation, and Air Conditioning) applications.
Based on the technical study referenced in "Discussion on the Selection of Fan Coil Units" (《风机盘管机组选型问题的探讨》), this coil tube product addresses critical performance parameters including thermal conductivity, corrosion resistance, pressure resistance, and long-term reliability under cyclic thermal loading conditions. The coil tube serves as the primary heat exchanger element within fan coil units, where hot or cold fluid circulates through the coiled stainless steel tubing to facilitate efficient heat transfer to or from the ambient air stream.
2. Material & Properties
2.1 Base Alloy Composition
The coil tube is manufactured from austenitic stainless steel, with the primary grade being SUS304 (UNS S30400), supplemented by high-performance variants including SUS316L (UNS S31603) for enhanced chloride resistance and SUS321 (UNS S32100) for elevated-temperature service. The austenitic microstructure provides excellent ductility, weldability, and resistance to intergranular corrosion.
2.2 Key Mechanical & Physical Properties
- Tensile Strength (Ultimate): ≥ 520 MPa (75,400 psi) for SUS304; ≥ 515 MPa for SUS316L
- Yield Strength (0.2% offset): ≥ 205 MPa (29,700 psi)
- Elongation (at fracture): ≥ 40% (A50mm)
- Thermal Conductivity: 16.3 W/(m·K) at 20°C (SUS304)
- Specific Heat Capacity: 500 J/(kg·K) at 20°C
- Density: 7.93 g/cm³
- Maximum Service Temperature: 870°C (1,598°F) in oxidizing atmospheres
- Minimum Service Temperature: −196°C (−321°F) without loss of ductility
- Corrosion Resistance: Excellent resistance to atmospheric, aqueous, and mild chemical environments; SUS316L grade offers superior resistance to chlorides and pitting corrosion
2.3 Surface Finish Options
- 2B Finish: Standard cold-rolled and annealed surface, Ra ≤ 0.5 μm
- No. 4 Brushed Finish: Unidirectional brushed appearance, Ra 0.4–0.8 μm
- Mirror (8K) Finish: Polished to Ra ≤ 0.05 μm for high-visibility applications
- Electro-polished: Ra ≤ 0.1 μm with enhanced passive layer for sanitary applications
3. Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Product Designation | Model Series 904 — Coil Tube (盘管) | Internal Product Code |
| Outer Diameter (OD) | 6.35 mm (¼") / 9.53 mm (⅜") / 12.7 mm (½") / 15.88 mm (⅝") | ASTM A213 / GB/T 12771 |
| Wall Thickness | 0.5 mm – 1.5 mm (customizable) | ASTM A269 |
| Coil Diameter (Winding) | 150 mm – 600 mm (configurable per unit design) | Manufacturer Specification |
| Tube Length (Per Coil) | Up to 120 m continuous coil | ISO 1127 |
| Material Grade | SUS304 / SUS316L / SUS321 | ASTM A213 TP304/TP316L/TP321 |
| Heat Transfer Coefficient | 1,800 – 2,500 W/(m²·K) (water-air) | ASHRAE Handbook — HVAC Systems |
| Working Pressure | ≤ 1.6 MPa (232 psi) at 80°C | GB/T 15386 / EN 12828 |
| Hydrostatic Test Pressure | 2.5 × working pressure, minimum 3.0 MPa | ISO 1127 |
| Temperature Range | −20°C to +120°C (standard); up to +180°C (SUS321) | Manufacturer Specification |
| Dimensional Tolerance | OD: ±0.1 mm; Wall: ±0.05 mm | ASTM A213 |
| Coil Pitch | 15 mm – 30 mm (adjustable for airflow optimization) | ASHRAE / Manufacturer Specification |
| Fin Configuration (if applicable) | Aluminum or stainless steel fins, 2.0–3.0 fins/cm | ASHRAE Standard 90.1 |
4. Manufacturing Process
4.1 Process Flow
- Raw Material Procurement: Selection of certified austenitic stainless steel strip (cold-rolled) from qualified mills meeting ASTM A240 / GB/T 3280 specifications. Incoming material undergoes spectroscopic verification (PMI — Positive Material Identification) and mechanical property testing.
- Strip Forming & Welding: Precision roll-forming of flat strip into circular cross-section, followed by high-frequency induction welding (HFW) or orbital TIG (Tungsten Inert Gas) welding. Weld seam undergoes inline ultrasonic testing (UT) for continuity verification.
- Heat Treatment: Solution annealing at 1,050°C – 1,150°C followed by controlled air cooling or water quenching to restore full austenitic structure and eliminate cold-work hardening. This step ensures uniform microstructure and optimal corrosion resistance.
- Precision Coiling: The formed tube is coiled using CNC-controlled coiling machines with hydraulic tension control to maintain consistent coil diameter, pitch, and roundness. Spring-back compensation algorithms ensure dimensional accuracy within ±0.5% of nominal.
- Pickling & Passivation: Post-welding acid pickling (nitric-hydrofluoric acid blend or citric acid for environmental compliance) removes oxide scale. Passivation treatment (10–20% nitric acid or citric acid) establishes a chromium oxide passive film (≥ 10 nm thickness) for enhanced corrosion protection.
- Non-Destructive Testing (NDT): Hydrostatic pressure testing at 100% of production, supplemented by eddy current testing (ECT) for wall thickness and seam integrity verification. Random samples undergo destructive testing including tensile, impact (Charpy V-Notch), and corrosion testing (ASTM A967, ASTM G48).
- Final Inspection & Packaging: Dimensional verification using laser measurement systems, visual inspection of surface finish, and packaging in moisture-proof wrapping with desiccant protection. Each coil is labeled with heat number, material grade, dimensions, and traceability codes.
4.2 Process Quality Controls
- Online thickness monitoring via ultrasonic sensors (±0.02 mm accuracy)
- Continuous weld seam inspection using eddy current and X-ray systems
- In-process chemical analysis via optical emission spectrometry (OES)
- Statistical Process Control (SPC) with Cpk ≥ 1.33 for critical dimensions
5. Applications
5.1 Primary Applications
- Fan Coil Units (FCUs): The primary application domain — serving as the heat exchanger coil in commercial and residential fan coil units for space heating and cooling. The coil tube design optimizes the surface area-to-volume ratio for maximum thermal exchange efficiency.
- Chilled Water Systems: Integration into secondary chilled water loops in large commercial buildings, hospitals, and data centers.
- Condenser & Evaporator Coils: Use in air-cooled condensers and evaporators for refrigeration and HVAC systems.
5.2 Secondary Applications
- Industrial Process Heating/Cooling: Heat exchangers in chemical processing, food and beverage manufacturing, and pharmaceutical production.
- Geothermal Systems: Ground-loop heat exchanger coils for geothermal HVAC applications.
- Marine & Offshore: Corrosion-resistant coil tubes for marine HVAC systems where SUS316L grade provides chloride resistance.
- Medical Facilities: Hygienic-grade coil tubes for hospital HVAC systems requiring high purity and biocompatibility.
5.3 Fan Coil Unit Selection Considerations (Technical Reference)
As outlined in the referenced study "Discussion on the Selection of Fan Coil Units", proper coil tube specification is critical for FCU performance optimization. Key selection criteria include:
- Matching coil capacity (sensible and latent heat) to the space load calculation
- Optimizing coil face velocity to balance heat transfer efficiency against noise levels (target: ≤ 35 dBA at 1 m)
- Ensuring adequate condensate drainage design for cooling mode operation
- Selecting appropriate coil tube material grade based on water quality and operating environment
- Considering part-load performance characteristics and modulation capability
6. Quality Certifications & Standards Compliance
6.1 Product Certifications
- ISO 9001:2015 — Quality Management System Certification
- ISO 14001:2015 — Environmental Management System Certification
- ISO 45001:2018 — Occupational Health and Safety Management System
- EN 10204 3.1 — Material Test Certificates (MTC) for all shipments
- CE Marking — Conformity with European directives where applicable
6.2 Standards Compliance
- ASTM A213 — Standard Specification for Seamless and Wrought Stainless Steel Tubing, Boilers, Heaters, and Exchangers
- ASTM A269 — Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing for Chemical and Similar Severe Service
- ASTM A240 — Standard Specification for Chromium and Chromium-Nickel Stainless Steel Plate, Sheet, and Strip for Pressure Vessels
- GB/T 12771 — Chinese National Standard for Stainless Steel Seamless Tubes for General Purposes
- GB/T 15386 — Chinese National Standard for Stainless Steel Tubes for Heat Exchangers
- EN 10216-5 — European Standard for Welded Stainless Steel Tubes for Heat Exchangers
- JIS G3445 — Japanese Industrial Standard for Stainless Steel Tubes for Heat Exchangers
- ISO 1127 — Non-ferrous and non-alloy steel tubes — Requirements for pressure testing
6.3 Testing & Verification
- Hydrostatic pressure testing at 100% of production (per ISO 1127)
- Eddy current testing for weld seam integrity (100% coverage)
- Charpy V-Notch impact testing at room temperature and −40°C (per ASTM A370)
- Pitting corrosion resistance testing per ASTM G48 (for SUS316L grade)
- Intergranular corrosion testing per ASTM A967 (acid solution test)
- Third-party inspection available (SGS, Bureau Veritas, TUV)
7. Unique Selling Points
- Superior Corrosion Resistance: Austenitic stainless steel construction provides exceptional resistance to water-side corrosion, eliminating the risk of tube failure and system contamination common with copper or carbon steel alternatives. Service life exceeds 25 years under normal operating conditions.
- Thermal Performance Optimization: Precision coil geometry with optimized pitch and roundness ensures uniform airflow distribution and maximizes the heat transfer coefficient, achieving up to 15% higher efficiency compared to standard coil designs.
- Full Traceability: Each coil carries complete material traceability from mill heat number through all processing stages, enabling rapid quality investigation and regulatory compliance documentation.
- Customization Capability: Flexible manufacturing parameters allow tailoring of coil diameter, pitch, tube dimensions, and surface finish to specific FCU design requirements and operating conditions.
- Environmental Sustainability: Stainless steel is 100% recyclable with no degradation of material properties. The pickling process utilizes environmentally compliant citric acid alternatives, minimizing hazardous waste generation.
- Biocompatibility: Suitable for medical and food-grade applications where hygienic requirements mandate stainless steel construction with electro-polished internal surfaces.
- Technical Support & Engineering Consultation: Comprehensive selection guidance based on the referenced FCU selection methodology, including load calculation support, coil capacity matching, and system integration recommendations.
8. Technical Reference
Primary Reference Document: 《风机盘管机组选型问题的探讨》 (Discussion on the Selection of Fan Coil Units) — Technical Study, Wenzhou Jixing Metal Materials Co., Ltd. Internal Learning Documentation, Product Reference No. 904.
This technical specification provides a comprehensive framework for the evaluation, selection, and implementation of Model Series 904 Stainless Steel Coil Tubes in fan coil unit and heat exchanger applications. For detailed engineering data, material certificates, or custom specification development, contact Wenzhou Jixing Metal Materials Co., Ltd. technical services department.