Stainless Steel Coil Tube for Fan Coil Unit Condensate Drainage Systems

1. Product Overview

The Stainless Steel Coil Tube (Coiltube) produced by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular product designed primarily for HVAC (Heating, Ventilation, and Air Conditioning) condensate drainage applications. Manufactured in continuous coil form, this product facilitates seamless installation in fan coil unit (FCU) condensate water pipe networks, where flexibility, corrosion resistance, and long-term durability are critical performance requirements.

Unlike rigid straight-length piping, coil tubes offer superior installation adaptability in complex architectural geometries, reducing the number of fittings and joints required, thereby minimizing potential leak points and enhancing system reliability. The coil configuration also significantly reduces on-site labor time and installation costs, making it an economically advantageous solution for large-scale commercial and residential HVAC projects.

2. Material Composition & Properties

The coil tube is fabricated from austenitic stainless steel, with the following standard grades available:

• 304 (UNS S30400 / 1.4301): The most widely used general-purpose austenitic grade, offering excellent corrosion resistance, formability, and weldability. Suitable for standard indoor condensate drainage applications.
• 316 (UNS S31600 / 1.4401): Enhanced with 2.0–3.0% Molybdenum (Mo) content, providing superior resistance to chlorides and acidic condensate environments. Recommended for coastal or chemically aggressive installations.
• 304L (UNS S30403 / 1.4307): Low-carbon variant (C ≤ 0.03%) designed to resist intergranular corrosion during welding and high-temperature service.
• 316L (UNS S31603 / 1.4404): Low-carbon, high-molybdenum grade combining the corrosion resistance of 316 with improved weldability and reduced sensitization risk.

Key Mechanical Properties (Grade 304, Annealed Condition):

• Tensile Strength (R_m): ≥ 520 MPa
• Yield Strength (R_p0.2): ≥ 205 MPa
• Elongation (A₅₀): ≥ 40%
• Hardness (HV): ≤ 210
• Operating Temperature Range: −196°C to +870°C
• Chromium (Cr) Content: 18.0–20.0%
• Nickel (Ni) Content: 8.0–10.5%
• Carbon (C) Content: ≤ 0.08%

3. Technical Specifications

Parameter	Specification / Value	Standard Reference
Outer Diameter (OD)	6.0 mm, 8.0 mm, 10.0 mm, 12.0 mm, 15.0 mm, 18.0 mm, 20.0 mm, 25.0 mm, 32.0 mm	ASTM A554 / GB/T 14976
Wall Thickness	0.3 mm, 0.4 mm, 0.5 mm, 0.6 mm, 0.8 mm, 1.0 mm	ASTM A554 / EN 10217
Coil Inner Diameter (ID)	300 mm – 600 mm (configurable)	Manufacturer Specification
Coil Length	100 m – 300 m per coil (custom lengths available)	—
Surface Finish	2B (Cold Rolled & Annealed), No. 4 Brushed, Mirror (8K), Electropolished	ASTM A480 / GB/T 4237
OD Tolerance	±0.1 mm (≤ 12 mm OD); ±0.15 mm (> 12 mm OD)	ISO 6508
Wall Thickness Tolerance	±10% of nominal thickness	ASTM A554
Roundness	≤ 0.5% of nominal OD	ISO 6508
Surface Roughness (Ra)	≤ 0.8 μm (2B finish); ≤ 0.4 μm (Mirror finish)	ISO 4287
Coil Weight (Reference)	150 kg – 500 kg per coil (depending on size and length)	—
Delivery Condition	Annealed & Pickled (AP), or Solution Annealed	ASTM A473
End Treatment	Flat cut, notched, or pre-formed with protective caps	—

4. Manufacturing Process

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

1. Raw Material Procurement: High-purity stainless steel strip is sourced from certified mills, with each batch accompanied by a Mill Test Certificate (MTC) verifying chemical composition and mechanical properties in accordance with ASTM E415 (Spectrographic Analysis) and ASTM E10 (Tensile Testing).
2. Coiling & Straightening: The stainless steel strip is precisely uncoiled, straightened, and leveled to eliminate residual stress and ensure uniform width prior to forming.
3. Semi-Automatic Welding (SAW): The strip is formed into a tubular shape and longitudinally welded using Submerged Arc Welding or Automatic Metal Active Gas (MAG) welding with matching filler wire (e.g., ER308L for Grade 304L). The welding process is performed in a controlled argon (Ar) atmosphere to prevent oxidation.
4. Post-Weld Heat Treatment (PWHT): The welded tube undergoes solution annealing at 1050°C–1150°C followed by controlled cooling to restore the austenitic microstructure, relieve welding-induced residual stresses, and homogenize the grain structure.
5. Pickling & Passivation: The annealed tube is subjected to pickling in a mixed acid solution (HNO₃ + H₂SO₄) to remove the heat scale, followed by passivation treatment to form a protective chromium oxide (Cr₂O₃) passive film on the surface.
6. Dimensional Inspection & Testing: Each coil is inspected for outer diameter, wall thickness, roundness, and straightness. Non-Destructive Testing (NDT) methods including Ultrasonic Testing (UT) and Magnetic Particle Inspection (MPI) are employed to detect internal and surface defects.
7. Coil Winding & Packaging: The finished tube is wound into coils on precision mandrels, protected with moisture-absorbing desiccant packs, wrapped in protective film or kraft paper, and secured with steel strapping. Each coil is labeled with product identification, material grade, heat number, and compliance documentation.

5. Applications

The stainless steel coil tube is engineered for a diverse range of industrial and commercial applications, with particular emphasis on HVAC condensate drainage systems:

• Fan Coil Unit (FCU) Condensate Drainage: Primary application — the coil tube serves as the condensate water collection and drainage piping in fan coil units used in commercial buildings, hotels, hospitals, and residential complexes. The corrosion-resistant properties ensure long-term service life even in the presence of acidic condensate (pH 4.0–6.5).
• Air Handling Unit (AHU) Condensate Lines: Used in central air handling units for condensate collection and routing to building drainage systems.
• VRF (Variable Refrigerant Flow) Systems: Condensate drainage piping in multi-zone VRF HVAC systems where flexibility of routing is essential.
• Domestic & Commercial Plumbing: Cold and hot water supply lines, gas piping (after appropriate certification), and sanitary drainage systems.
• Food & Beverage Processing: Hygienic fluid transport in breweries, dairies, and food processing plants where sanitary-grade stainless steel is required.
• Chemical & Pharmaceutical Industries: Process piping for mildly corrosive fluids, reagent transfer, and clean-in-place (CIP) systems.
• Automotive & Aerospace: Fuel lines, brake lines, and exhaust system components requiring high-temperature resistance and fatigue durability.
• Medical Equipment: Instrumentation tubing and fluid delivery lines in medical devices requiring biocompatibility and sterilization resistance.

6. Quality Certifications & Standards Compliance

Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management system ensuring that all stainless steel coil tube products meet or exceed international standards:

• ISO 9001:2015: Quality Management System certification ensuring consistent product quality and continuous improvement processes.
• ISO 14001:2015: Environmental Management System certification demonstrating commitment to sustainable manufacturing practices.
• ISO 45001:2018: Occupational Health and Safety Management System certification.
• EN 10204 3.1: Third-party inspection and material certification available upon request.
• CE Marking: Compliance with European Construction Products Directive (CPD) and relevant harmonized European standards.
• GB/T 14976: Chinese National Standard for seamless and welded stainless steel tubes for general engineering.
• GB/T 12771: Chinese National Standard for welded stainless steel tubes for fluid transport.
• ASTM A554: Standard specification for seamless and welded austenitic stainless steel hydraulic fluid tubing.
• JIS G3446: Japanese Industrial Standard for austenitic stainless steel welded tubes for fluid transport.

Each production batch is accompanied by a Mill Test Certificate (MTC) documenting chemical composition analysis, mechanical test results, and heat treatment records. Third-party testing by accredited laboratories (e.g., SGS, BV, TUV) is available for project-specific verification requirements.

7. Unique Selling Points

• Superior Corrosion Resistance: The austenitic stainless steel construction provides exceptional resistance to condensate-induced corrosion, eliminating the need for periodic pipe replacement and reducing total cost of ownership (TCO) over the system lifecycle.
• Installation Efficiency: The coil form factor enables rapid deployment with minimal cutting and fitting, reducing installation time by up to 60% compared to straight-length piping solutions.
• Hygienic Surface Quality: Smooth inner surface finish (Ra ≤ 0.8 μm) prevents condensate biofilm accumulation, reducing maintenance frequency and ensuring hygienic operation in food-grade and medical environments.
• Customizable Specifications: Flexible manufacturing capability allows for custom outer diameters, wall thicknesses, coil lengths, and surface finishes tailored to specific project requirements.
• Full Traceability: Each coil is heat-number tracked with complete production documentation, ensuring full supply chain traceability and facilitating quality audits.
• Environmental Sustainability: Stainless steel is 100% recyclable with no loss of material properties, supporting circular economy principles and green building certification programs (LEED, BREEAM, Green Star).

Technical Note: When installing stainless steel coil tubes for condensate drainage applications, it is recommended to maintain a minimum slope of 1:100 (1%) along the pipe run to ensure gravity-driven condensate flow. All joints should be sealed using appropriate stainless steel-compatible fittings (e.g., compression fittings, orbital-welded connections) to maintain the integrity of the corrosion-resistant system. Avoid contact with carbon steel during installation to prevent galvanic contamination and crevice corrosion.