Stainless Steel Coil Tube for Air Handling Unit Cooling Systems
Product Overview
The stainless steel coil tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered continuous tube product specifically designed for cooling coil assemblies in air handling units (AHUs). These coil tubes are supplied in pre-coiled, continuous-length formats that facilitate efficient manufacturing of heat exchanger cores, minimizing waste and reducing assembly time in HVAC (Heating, Ventilation, and Air Conditioning) production lines.
Unlike discrete tube segments, coil tubes offer uninterrupted material continuity, which ensures uniform wall thickness, consistent mechanical properties, and superior thermal performance throughout the entire length of the tube. This product is engineered to meet the rigorous demands of industrial air handling systems, where reliability, corrosion resistance, and thermal efficiency are paramount.
Material & Properties
Coil tubes for cooling coil applications are predominantly fabricated from austenitic stainless steel grades, selected for their exceptional combination of corrosion resistance, formability, and thermal conductivity.
- Common Grades: AISI 304 (UNS S30400), AISI 304L (UNS S30403), AISI 316 (UNS S31600), AISI 316L (UNS S31603)
- Surface Finish: 2B (cold-rolled and annealed), No. 4 (brushed), or BA (Bright Annealed)
- Internal Surface: Electro-polished or pickled and passivated to ensure hygienic fluid flow and prevent biofilm accumulation
- Corrosion Resistance: Excellent resistance to condensate water, chemical coolants, and ambient atmospheric conditions
- Temperature Range: Operational service from −196°C to +450°C (depending on grade)
- Mechanical Properties: Tensile strength ≥ 520 MPa; elongation ≥ 40% (annealed condition)
- Thermal Conductivity: 16.3 W/(m·K) at 25°C (AISI 304)
Specifications
| Parameter | Specification |
|---|---|
| Outer Diameter (OD) | 3.0 mm – 25.4 mm (1/8" – 1") |
| Wall Thickness (WT) | 0.3 mm – 1.2 mm |
| Coil Diameter (CD) | 100 mm – 600 mm (adjustable per customer requirement) |
| Coil Length (Continuous) | 50 m – 2000 m per coil |
| Tolerance on OD | ±0.05 mm – ±0.10 mm |
| Tolerance on Wall Thickness | ±0.02 mm – ±0.05 mm |
| Roundness | ≤ 0.05 mm |
| Coiling Tension | Controlled to prevent springback and deformation |
| Standard References | ASTM A213, ASTM A269, ASME B36.19M, EN 10216-5, GB/T 14976 |
| End Treatment | Plain cut, beveled, or threaded (customizable) |
Manufacturing Process
The production of high-quality stainless steel coil tubes involves a multi-stage process designed to ensure dimensional precision, metallurgical integrity, and surface quality:
- Steel Strip Preparation: Cold-rolled stainless steel strip is sourced from certified mills and inspected for surface defects, grain orientation, and chemical composition compliance.
- Edge Milling and Slitting: Strip edges are milled and slit to precise widths, ensuring clean weld seams during the forming process.
- Forming (Roll Forming / Swaging): The flat strip is progressively formed into a tubular cross-section using a series of precision rollers. For seamless coil tubes, a swaging process is employed where the strip is wrapped and reduced through calibrated dies to achieve full-wall fusion.
- Welding (for welded coil tubes): A high-frequency induction welding (HF welding) process creates a tight, continuous weld seam. Post-weld heat treatment eliminates residual stresses and ensures metallurgical homogeneity at the weld zone.
- Precision Sizing and Calibration: The formed tube passes through a series of sizing rollers and calibration dies to achieve exact outer diameter and wall thickness tolerances.
- Coiling: The finished tube is wound onto a core at controlled tension to form a continuous coil. Coiling parameters (tension, speed, core diameter) are optimized to prevent kinking, ovality, or stress-induced deformation.
- Post-Treatment: Tubes undergo pickling, passivation, and/or electro-polishing to remove scale, restore chromium oxide passive layer, and enhance corrosion resistance.
- Quality Inspection: Every coil undergoes ultrasonic testing (UT), hydrostatic pressure testing, dimensional verification, and surface inspection prior to packaging.
Applications
Stainless steel coil tubes are integral components in a wide range of thermal management and fluid transfer systems:
- Air Handling Units (AHUs): Primary application — forming the tube side of cooling and heating coils where chilled water or hot water circulates to condition air streams.
- HVAC Heat Exchangers: Used in finned-tube heat exchangers for commercial and industrial HVAC systems.
- Condensers and Evaporators: Refrigeration and air conditioning systems requiring corrosion-resistant tube assemblies.
- Industrial Process Cooling: Heat recovery systems, plate-fin exchangers, and process water cooling circuits.
- Food and Pharmaceutical Equipment: Hygienic-grade coil tubes for pasteurization, CIP (Clean-in-Place) systems, and cleanroom air handling.
- Marine and Offshore HVAC: Systems exposed to saltwater-laden air requiring AISI 316L-grade corrosion resistance.
- Data Center Cooling: Precision air conditioning coils for server room thermal management.
Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains rigorous quality management systems and adheres to international standards:
- ISO 9001:2015 — Quality Management System certification ensuring consistent product quality and continuous improvement.
- ISO 14001:2015 — Environmental Management System for sustainable manufacturing practices.
- ASTM A213 / A269 — Compliance with American standards for stainless steel tubing.
- ASME B36.19M — Adherence to wall thickness and dimensional specifications for stainless steel tubing.
- GB/T 14976 — Compliance with Chinese national standards for seamless stainless steel tubing.
- EN 10216-5 — European standard for welded stainless steel tubes for heat exchangers.
- Mill Test Certificates (MTC / EN 10204 3.1): Full chemical and mechanical test documentation provided with each shipment.
- Third-Party Inspection: Available upon request (SGS, Bureau Veritas, TÜV).
Unique Selling Points
- Continuous Coil Supply: Delivered as a continuous coil eliminates the need for field joining, reducing leak points and improving manufacturing throughput for AHU coil assembly.
- Ultra-Tight Tolerances: Precision manufacturing ensures consistent hydraulic performance and optimal heat transfer across the entire coil length.
- Superior Corrosion Performance: AISI 316L grade options provide exceptional resistance to chloride-induced pitting, extending service life in aggressive environments.
- Customizable Geometry: Coil diameter, tube OD, wall thickness, and length are tailored to specific coil winding machine configurations and design requirements.
- Hygienic Surface Finish: Electro-polished internal surfaces with Ra ≤ 0.4 μm meet FDA and EHEDG requirements for food-grade and pharmaceutical applications.
- Cost-Efficient Production: Coil format reduces material waste by up to 95% compared to cut-length supply, offering significant economic advantages for high-volume coil manufacturers.
Research Context: Cooling Coil Characteristics in Air Handling Units
Technical studies on cooling coil performance in air handling units demonstrate that the geometric and material properties of coil tubes directly influence the overall thermal efficiency (COP) of the AHU system. Key research findings indicate that:
- Tube outer diameter and wall thickness affect the fin-to-tube contact resistance and overall heat transfer coefficient (U-value).
- Coil tube uniformity (consistent OD and roundness) ensures balanced airflow distribution across the coil face, preventing localized bypass and maldistribution losses.
- Stainless steel's low fouling tendency compared to carbon steel extends maintenance intervals and sustains design heat transfer performance over the equipment lifecycle.
- Optimal coil pitch, tube rows, and fin density must be matched with appropriate tube sizing to achieve target temperature approach and humidity control.
Wenzhou Jixing Metal Materials Co., Ltd. provides engineering consultation to assist AHU manufacturers in selecting the optimal coil tube specifications that balance thermal performance, pressure drop, and lifecycle cost for specific air handling applications.