Stainless Steel Coil Tube (Coiltube) — Product No. 955
1. Product Overview
The Stainless Steel Coil Tube (Coiltube), designated as Product No. 955 by Wenzhou Jixing Metal Materials Co., Ltd, is a precision-engineered coiled tubing product designed for demanding thermal transfer and fluid conveyance applications. This product line is specifically optimized for integration into Fan Coil Tube (FCT) hot air heating systems, particularly within controlled-environment agriculture such as greenhouse thermal management systems.
The coil tube geometry provides a high surface-area-to-volume ratio, enabling efficient heat exchange between the working fluid (typically hot water or steam) and the surrounding air stream. This makes the product an ideal component for radiant heating, convective heating, and indirect air heating applications where corrosion resistance, long service life, and thermal efficiency are critical performance parameters.
The coil tube is manufactured from high-grade austenitic stainless steel, ensuring exceptional resistance to oxidation, scaling, and chemical attack under sustained thermal cycling conditions. The continuous helical winding configuration eliminates the need for field joints or couplings, thereby minimizing leak points and enhancing system reliability over the product lifecycle.
2. Material & Properties
2.1 Base Material Grades
- SAE 304 (UNS S30408 / AISI 304): The standard grade offering excellent general corrosion resistance, formability, and weldability. Suitable for atmospheric and moderately aggressive environments.
- SAE 316 (UNS S31608 / AISI 316): Enhanced grade with molybdenum (Mo) addition (2.0–3.0 wt%) providing superior resistance to pitting and crevice corrosion, particularly in chloride-containing environments.
- SAE 321 (UNS S32108 / AISI 321): Titanium-stabilized grade recommended for high-temperature service above 450 °C, preventing intergranular corrosion during prolonged exposure.
2.2 Key Material Properties
- Corrosion Resistance: The passive chromium oxide (Cr₂O₃) film formed on the stainless steel surface provides self-healing protection against oxidation and general corrosion across a wide pH range (pH 2–12).
- Thermal Conductivity: Approximately 14–16 W/(m·K) at 20 °C, providing adequate heat transfer capability for indirect heating applications.
- Thermal Expansion Coefficient: ~16–18 × 10⁻⁶ /°C, compatible with standard HVAC system design tolerances.
- Maximum Service Temperature: Up to 870 °C for SAE 304; up to 870 °C for SAE 321 (with stabilizing treatment).
- Mechanical Strength: Tensile strength ≥ 515 MPa; Yield strength ≥ 205 MPa (Solution Annealed condition).
- Surface Finish: Available in 2B (cold-rolled and annealed), BA (Bright Annealed), No. 4 (Brushed), and Mirror (8K) finishes.
3. Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Product Name | Stainless Steel Coil Tube (Coiltube) | — |
| Product No. | 955 | Wenzhou Jixing Internal Catalog |
| Material Grade | SAE 304 / SAE 316 / SAE 321 | ASTM A213 / ASME SA-213 |
| Outer Diameter (OD) | 6.35 mm – 50.8 mm (¼" – 2") | ASTM A213 |
| Wall Thickness | 0.5 mm – 3.0 mm (0.020" – 0.118") | ASTM A213 |
| Coil Diameter (Center-to-Center) | 50 mm – 500 mm (2" – 20") | Customer-Specific |
| Coil Length (Uncoiled) | 3 m – 120 m (10 ft – 400 ft) | — |
| Surface Finish | 2B / BA / No. 4 / Mirror (8K) | ASTM A480 |
| Manufacturing Process | Seamless / Welded (TIG) | ASTM A213 / AWS D10.6 |
| Heat Treatment | Solution Annealed + Pickled + Passivated | ASTM A213 |
| Pressure Rating | Up to 1.6 MPa (232 psi) typical | ASME B31.9 |
| Operating Temperature | −196 °C to +870 °C | — |
| Tolerance (OD) | ±0.05 mm to ±0.15 mm (depending on OD) | ASTM A213 |
| Tolerance (Wall Thickness) | ±10% of nominal | ASTM A213 |
| End Preparation | Plain / Beveled / Flanged / Threaded | ASME B16.11 / B1.20.1 |
| Packaging | Coiled on wooden reel or pallet; moisture-proof wrapping | — |
4. Manufacturing Process
4.1 Seamless Coil Tube Production
- Hot Rolling: Stainless steel billets are heated to 1150–1250 °C and hot-rolled into hollow tubes with controlled outer diameter and wall thickness.
- Piercing & Elongation: The hot tube is pierced through a mandrel and elongated through a series of rolling stands to achieve the target dimensions.
- Cold Drawing: The hot-rolled tube is cold-drawn through a precision die to achieve tight dimensional tolerances, improved surface finish, and enhanced mechanical properties.
- Solution Annealing: The tube is heated to 1010–1150 °C and rapidly quenched in water or air to dissolve carbides and restore full austenitic structure.
- Pickling & Passivation: The annealed tube is subjected to acid pickling (HNO₃ + HF mixture) to remove oxide scale, followed by passivation treatment to re-establish the protective chromium oxide layer.
- Coil Winding: The finished tube is wound onto a precision winding machine to form the helical coil configuration with controlled coil diameter, pitch, and number of turns.
- Quality Inspection: Each coil undergoes dimensional verification, surface inspection, and hydrostatic pressure testing prior to packaging.
4.2 Welded Coil Tube Production (Alternative)
- Strip Slitting: Cold-rolled stainless steel strip is slit to the required width to achieve the desired tube outer diameter and wall thickness.
- Forming: The strip is formed into a C-shape or U-shape and then rolled into a circular tube cross-section.
- TIG Welding (Gas Tungsten Arc Welding): The tube seam is welded using TIG welding (AWS D10.6) with inert gas shielding (argon or argon-helium mixture) to ensure a clean, corrosion-resistant weld.
- Weld Annealing: The welded tube is annealed to relieve residual stresses in the weld zone and restore metallurgical homogeneity.
- Winding & Inspection: The tube is wound into the coil configuration and subjected to full quality control procedures.
5. Applications
5.1 Greenhouse Heating Systems (Primary Application)
The coil tube is a core component in Fan Coil Tube (FCT) hot air heating systems for greenhouse thermal environment management. In this application, the coil tube serves as the heat exchange element through which hot water or steam circulates, transferring thermal energy to the air stream generated by fans. The system maintains optimal growing temperatures for crops by precisely controlling the heat output and distribution throughout the greenhouse volume.
Key performance characteristics in greenhouse applications include:
- Uniform Heat Distribution: The helical coil geometry ensures even heat emission across the entire coil surface, minimizing temperature gradients within the greenhouse.
- Corrosion Resistance: High humidity environments (RH 70–95%) combined with potential exposure to fertilizers, pesticides, and root-zone irrigation chemicals make stainless steel coil tubes far superior to carbon steel alternatives in terms of service life.
- Low Maintenance: The absence of joints and the inherent corrosion resistance of stainless steel eliminate the need for periodic anti-corrosion coating applications.
5.2 Additional Applications
- HVAC Systems: Heating, ventilation, and air conditioning units requiring durable, corrosion-resistant heat exchangers.
- Food & Beverage Industry: Sanitary heat transfer in brewing, dairy processing, and food sterilization equipment (SAE 316 preferred).
- Chemical Processing: Heat exchange in corrosive chemical environments where stainless steel is required for process compatibility.
- Marine & Offshore: Heating systems in marine environments where chloride-induced corrosion is a primary concern.
- Pharmaceutical Industry: Clean-in-place (CIP) compatible heat transfer in GMP-regulated manufacturing facilities.
- Agricultural Drying Systems: Indirect heating for grain drying, seed germination, and controlled-environment agriculture.
- Underfloor Heating: Embedded coil tubes for radiant floor heating in commercial and residential buildings.
6. Quality Certifications & Standards
6.1 Applicable International Standards
| Standard | Description |
|---|---|
| ASTM A213 / ASME SA-213 | Standard Specification for Seamless and Welded Austenitic Stainless Steel Tube for High-Temperature Service |
| ASTM A480 | Standard Specification for Chromium and Chromium-Nickel Stainless Steel Plate, Sheet, and Strip for General Application |
| EN 10216-5 | Non-alloy and Alloy Steel Tubes — Technical Delivery Conditions — Part 5: Non-alloy and Alloy Steel Tubes for Heat Exchangers |
| GB/T 14976 | Chinese National Standard for Seamless Stainless Steel Tubes for Cold-Rolled and Cold-Drawn Applications |
| GB/T 17898 | Chinese National Standard for Welded Stainless Steel Tubes |
| AWS D10.6 | Specification for Welding Stainless Steel |
| ASME B31.9 | Pressure Piping — Process Piping |
6.2 Quality Assurance System
- ISO 9001:2015: Quality Management System certification ensuring consistent product quality and process control throughout the manufacturing lifecycle.
- ISO 14001:2015: Environmental Management System certification demonstrating commitment to sustainable manufacturing practices and environmental compliance.
- Mill Test Certificates (MTC): Each batch of coil tube is accompanied by a full material test certificate (EN 10204 Type 3.1) documenting chemical composition, mechanical properties, and heat treatment records.
- Hydrostatic Testing: All coils undergo hydrostatic pressure testing at 1.5× the design pressure to verify structural integrity and weld quality.
- Spectroscopic Analysis: Chemical composition verification via optical emission spectroscopy (OES) or X-ray fluorescence (XRF) to ensure conformance to the specified grade requirements.
- Dimensional Inspection: Full-length dimensional verification including outer diameter, wall thickness, straightness, and coil geometry using calibrated measurement instruments.
- Surface Inspection: Visual and magnetic particle inspection (MPI) to detect surface defects, cracks, and inclusions that could compromise product performance.
7. Unique Selling Points
- Integrated Design for Greenhouse Applications: The coil tube is specifically engineered for fan coil tube hot air heating systems, offering optimized heat transfer performance for controlled-environment agriculture.
- Joint-Free Continuous Coil: The seamless helical winding eliminates field joints, reducing leak risk and maintenance requirements to near zero.
- Multi-Grade Availability: Customers can select from SAE 304, SAE 316, and SAE 321 grades to match their specific environmental and temperature requirements.
- Customizable Dimensions: Coil diameter, tube OD, wall thickness, and coil length can be tailored to meet project-specific design requirements.
- Full Traceability: Complete material traceability from raw material mill certificate through final product inspection ensures full compliance with regulatory and quality requirements.
- Extended Service Life: The combination of stainless steel corrosion resistance and the elimination of joints provides a service life exceeding 25 years under normal operating conditions, significantly outperforming carbon steel alternatives.