Stainless Steel Coil Tube for HVAC Condensate Drainage Systems
Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular product designed specifically for condensation drainage applications within fan coil unit (FCU) systems and broader HVAC (Heating, Ventilation, and Air Conditioning) infrastructure. Coil tubes are delivered in a coiled configuration, offering superior flexibility during installation, reduced joint count, and enhanced system integrity compared to traditional cut-and-weld pipe assemblies.
This product line addresses the critical engineering challenge of condensate pipe diameter selection in fan coil unit systems, ensuring optimal hydraulic performance, minimal pressure drop, and long-term corrosion resistance in demanding indoor environments.
Material & Properties
Stainless steel coil tubes are fabricated from high-grade austenitic stainless steel grades, selected for their exceptional resistance to pitting corrosion, crevice corrosion, and stress corrosion cracking (SCC) in humid indoor environments where condensate water accumulates.
Primary Material Grades
- SAE 304 (UNS S30400): The standard austenitic grade containing 18% Chromium (Cr) and 8% Nickel (Ni). Suitable for general HVAC condensate applications with moderate chloride exposure.
- SAE 316 (UNS S31600): Enhanced grade with 2–3% Molybdenum (Mo) addition, providing superior resistance to chloride-induced pitting corrosion. Recommended for coastal or high-humidity installations.
- SAE 316L (UNS S31603): Low-carbon variant of 316 with Carbon (C) content ≤ 0.03%, ensuring excellent weldability and resistance to intergranular corrosion (IGC) in post-weld applications.
- SAE 321 (UNS S32100): Titanium-stabilized grade offering resistance to sensitization at elevated temperatures, suitable for steam-assisted HVAC systems.
Mechanical Properties (Typical Values for SAE 304)
- Tensile Strength: ≥ 515 MPa (74,700 psi)
- Yield Strength (0.2% offset): ≥ 205 MPa (29,700 psi)
- Elongation: ≥ 40% (in 50 mm gauge length)
- Hardness (Rockwell B): ≤ 95 HRB
- Density: 7.93 g/cm³
- Thermal Conductivity (20°C): 16.3 W/(m·K)
- Thermal Expansion Coefficient (20–100°C): 17.3 × 10⁻⁶ /°C
Specifications
| Parameter | Specification | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | Φ12.7 mm, Φ15.9 mm, Φ19.1 mm, Φ22.2 mm, Φ25.4 mm, Φ31.8 mm, Φ38.1 mm, Φ48.3 mm, Φ60.3 mm | ASTM A213 / GB/T 12771 |
| Wall Thickness (WT) | 0.5 mm – 2.0 mm (typical range) | ASTM A269 / EN 10217 |
| Coil Diameter | 3 m – 12 m (customizable) | Manufacturer Standard |
| Coil Length | 50 m – 500 m per coil (standard); up to 1,000 m (special order) | — |
| Surface Finish | 2B (cold-rolled and annealed), BA (Bright Annealed), No.4 Brushed, Mirror (8K) | ASTM A480 |
| Tolerance (OD) | ±0.05 mm (precision grade); ±0.10 mm (commercial grade) | ISO 4287 |
| Tolerance (WT) | ±10% of nominal wall thickness | ASTM A213 |
| End Condition | Plain end, Beveled end (45°), or Threaded (BSPT/NPT) | ASME B1.20.1 / BS 5563 |
| Operating Temperature | −196°C to +400°C (SAE 304/316) | — |
| Maximum Working Pressure | Up to 1.6 MPa (16 bar) for condensate applications | EN 10217-2 |
| Minimum Bend Radius | 3D (where D = outer diameter) | Manufacturer Standard |
| Applicable Condensate Flow Rate | 0.5 L/h – 200 L/h (dependent on diameter selection) | ASHRAE 90.1 / SMACNA |
Recommended Condensate Pipe Diameter Selection
Based on hydraulic analysis for fan coil unit condensate drainage systems, the following diameter selection guidelines apply:
| FCU Cooling Capacity (kW) | Estimated Condensate Flow (L/h) | Recommended Tube OD (mm) | Recommended Slope (%) |
|---|---|---|---|
| 2.0 – 3.5 | 0.5 – 1.2 | Φ12.7 – Φ15.9 | ≥ 1.0 |
| 3.5 – 7.0 | 1.2 – 2.5 | Φ19.1 – Φ22.2 | ≥ 0.8 |
| 7.0 – 14.0 | 2.5 – 5.0 | Φ25.4 – Φ31.8 | ≥ 0.5 |
| 14.0 – 28.0 | 5.0 – 10.0 | Φ38.1 – Φ48.3 | ≥ 0.3 |
| > 28.0 | > 10.0 | Φ60.3 and above | ≥ 0.2 |
Manufacturing Process
The production of stainless steel coil tubes follows a rigorous, multi-stage manufacturing sequence designed to ensure dimensional accuracy, metallurgical integrity, and surface quality:
- Steel Coil Procurement and Inspection: Hot-rolled stainless steel coils are sourced from certified mills and subjected to spectrographic analysis to verify chemical composition compliance with specified grades.
- Pickling and Descaling: The hot-rolled coil undergoes acid pickling (HNO₃/HF mixture) to remove mill scale and oxide layers, restoring the passive chromium oxide film.
- Cold Rolling (Cold Reduction): The pickled coil is cold-rolled to reduce thickness from hot-rolled gauge (typically 3–5 mm) to the target wall thickness (0.5–2.0 mm). This process induces strain hardening and improves surface finish.
- Intermediate Annealing: Where required, the cold-rolled coil is annealed at 1,050–1,100°C in a protective atmosphere (CO/CO₂ or N₂) to relieve residual stresses and restore ductility.
- Forming and Seaming: The flat strip is formed into a tube using a seam welding process. Resistance seam welding (RSW) or gas tungsten arc welding (GTAW/TIG) is employed to create the longitudinal seam, achieving full penetration and fusion.
- Post-Weld Annealing and Pickling: The welded tube undergoes solution annealing to homogenize the weld heat-affected zone (HAZ) and restore corrosion resistance. Subsequent pickling removes any discoloration.
- Hydrostatic Pressure Testing: Each tube length is subjected to hydrostatic testing at 1.5 times the maximum design pressure to verify seam integrity and absence of leaks.
- Dimensional Inspection and Surface Finishing: Tubes are measured for OD, WT, and straightness. Surface finish is achieved through mechanical polishing, electropolishing, or passivation treatment.
- Coiling and Packaging: The finished tube is coiled at controlled tension to maintain dimensional stability, wrapped in protective film, and packaged on wooden reels or steel drums for shipment.
Applications
Stainless steel coil tubes from Wenzhou Jixing Metal Materials Co., Ltd. serve a diverse range of applications across multiple industries:
HVAC and Building Services
- Condensate drainage piping for fan coil units (FCUs), air handling units (AHUs), and Variable Refrigerant Flow (VRF) systems
- Chilled water and hot water distribution in commercial HVAC systems
- Refrigerant lines in split-system air conditioning
- Condensate collection and discharge in dehumidification systems
Industrial and Process Applications
- Condensate recovery systems in steam distribution networks
- Food and beverage processing equipment (sanitary-grade 316L)
- Pharmaceutical cleanroom piping systems
- Chemical process condensate handling (corrosion-resistant grades)
Architectural and Decorative Applications
- Exterior rainwater drainage systems
- Architectural features and facade cladding support structures
- Marine and coastal building services (316/316L grades)
Quality Certifications and Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management system and adheres to the following international and national standards:
Management System Certifications
- ISO 9001:2015 — Quality Management Systems
- ISO 14001:2015 — Environmental Management Systems
- ISO 45001:2018 — Occupational Health and Safety Management Systems
Product Standards Compliance
- ASTM A213/A213M — Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing for High-Temperature Service
- ASTM A269/A269M — Standard Specification for Seamless and Welded Austenitic Stainless Steel Sanitary Tubing
- EN 10217-2 — Heat-resistant, stainless and duplex steel tubes for technical use
- GB/T 12771 — Welded stainless steel tubes for general use (Chinese National Standard)
- GB/T 14976 — Cold-rolled or cold-drawn seamless steel tubes for fluid transport
- JIS G3446 — Welded austenitic stainless steel tubes for general use (Japanese Industrial Standard)
Testing and Inspection Protocols
- Chemical composition verification via Optical Emission Spectroscopy (OES)
- Mechanical testing: tensile testing per ASTM E8/E8M, hardness testing per ASTM E18
- Hydrostatic pressure testing per ASTM A269 (100% inspection)
- Non-destructive testing (NDT): eddy current testing, dye penetrant inspection (DPI), and radiographic testing (RT) as required
- Corrosion testing: salt spray testing per ASTM B117 (≥ 500 hours for 316L), pitting resistance index (PREN) evaluation
- Surface roughness measurement per ISO 4287 (Ra ≤ 0.4 μm for mirror finish)
Unique Selling Points
1. Engineered for Condensate Applications: Unlike generic stainless steel tubing, these coil tubes are specifically dimensioned and graded for HVAC condensate drainage, incorporating hydraulic optimization based on FCU capacity analysis.
2. Factory-Coiled Delivery: Pre-coiled configuration eliminates on-site cutting and field welding, reducing installation time by up to 60% and minimizing the number of potential leak points in the system.
3. Full-Grade Traceability: Each coil carries a unique heat number with complete mill test certificates (MTC), enabling full material traceability from raw steel through to final installation.
4. Corrosion Resistance Guarantee: With PREN values exceeding 24 (for 316L grade), these tubes provide a design life exceeding 50 years even in aggressive condensate environments containing chlorides, sulfates, and organic acids.
5. Custom Diameter Selection Guidance: The manufacturer provides technical consultation for optimal condensate pipe diameter selection based on system capacity, building layout, and slope constraints, ensuring reliable drainage performance.
Installation and Handling Recommendations
- Maintain a minimum slope of 0.2% (1:500) for continuous condensate drainage; increase to 0.5% for horizontal runs exceeding 5 meters
- Use stainless steel-compatible fasteners and clamps to prevent galvanic corrosion
- Install air break fittings and traps at system low points to prevent siphoning
- Apply passivation treatment (10–20% citric acid or nitric acid solution) after installation to ensure full passive film development
- Periodic inspection recommended every 12 months for condensate flow verification and corrosion monitoring
Summary
The Stainless Steel Coil Tube product line from Wenzhou Jixing Metal Materials Co., Ltd. represents a purpose-engineered solution for HVAC condensate drainage systems, combining superior material properties, precision manufacturing, and application-specific design guidance. By addressing the critical engineering challenge of condensate pipe diameter selection and delivering factory-coiled, fully certified tubing, this product ensures reliable, long-lasting, and maintenance-minimized performance across commercial, industrial, and institutional building environments.