Stainless Steel Coil Tube (Coiltube) — HVAC & Evaporative Cooling Systems

Product Overview

The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular product designed for demanding thermal-fluid transfer applications, particularly within semi-centralized air conditioning systems that combine evaporative cooling with dry fan coil units. This product category, indexed as Item No. 1053, represents a specialized class of coiled stainless steel tubing engineered to meet the rigorous requirements of modern HVAC (Heating, Ventilation, and Air Conditioning) infrastructure.

Coil tubes in this application serve as critical heat exchange elements within evaporative cooling circuits and dry fan coil assemblies. Their helical geometry maximizes surface area-to-volume ratios, enabling efficient thermal transfer between the working fluid and the ambient medium. Wenzhou Jixing Metal Materials Co., Ltd. leverages decades of metallurgical expertise and advanced manufacturing capabilities to deliver coil tubes with exceptional dimensional accuracy, corrosion resistance, and mechanical integrity.

Material & Properties

The coil tubes are fabricated from high-grade austenitic stainless steel, with the following material specifications:

• Base Material: Grade 304 (UNS S30400) or Grade 316L (UNS S31603) austenitic stainless steel, selected based on the specific corrosion environment and fluid compatibility requirements.
• Chromium Content: 18%–20% Cr (Chromium), providing inherent passivation and corrosion resistance through the formation of a stable chromium oxide layer.
• Nickel Content: 8%–12% Ni (Nickel), ensuring austenitic microstructure stability and ductility at both ambient and elevated operating temperatures.
• Molybdenum Content (316L only): 2%–3% Mo (Molybdenum), enhancing resistance to pitting and crevice corrosion in chloride-containing environments.
• Carbon Content: ≤ 0.03% C (for 316L), minimizing carbide precipitation and intergranular corrosion susceptibility.
• Surface Finish: Electropolished or mechanically polished to Ra ≤ 0.4 μm (Surface Roughness Average), reducing fluid friction losses and inhibiting biofilm formation.
• Operating Temperature Range: −196°C to +450°C, accommodating cryogenic to high-temperature thermal cycling.
• Maximum Working Pressure: Up to 2.5 MPa (362.6 psi) at ambient temperature, with reduced pressure ratings at elevated temperatures per ASME BPV Code guidelines.
• Thermal Conductivity: Approximately 16.3 W/(m·K) for Grade 304 at 20°C, providing reliable heat transfer performance.

Specifications

Parameter	Specification	Standard / Tolerance
Outer Diameter (OD)	6.0 mm – 50.8 mm (¼" – 2")	±0.1 mm
Wall Thickness (WT)	0.5 mm – 3.0 mm	±10% of nominal
Coil Pitch	12 mm – 50 mm	±0.5 mm
Coil Diameter	100 mm – 600 mm	±2.0 mm
Tube Length (Developed)	1.0 m – 20.0 m (custom lengths available)	±25 mm
End Form	Plain cut, threaded (G/BSP/NPT), flanged, or soldered	Per ISO 7 / ASME B1.20.1
Material Grade	SUS 304 / SUS 304L / SUS 316 / SUS 316L	JIS G4305 / ASTM A213 / ASTM A269
Surface Treatment	Passivated, electropolished, or pickled	ASTM A967
Hydrostatic Test Pressure	1.5× working pressure	ASTM A213 Section 6
Packaging	Wooden crate with moisture barrier, coiled and strapped	ISO 4180
Product Index	No. 1053	Wenzhou Jixing Internal Catalog

Manufacturing Process

The production of stainless steel coil tubes at Wenzhou Jixing Metal Materials Co., Ltd. follows a rigorous, multi-stage manufacturing protocol designed to ensure consistent quality and performance:

1. Raw Material Selection & Certification:

   Virgin stainless steel strip or seamless tube blanks are procured from certified mills with full mill test certificates (MTC) in accordance with EN 10204 Type 3.1. Each batch undergoes spectroscopic analysis (PMI — Positive Material Identification) to verify chemical composition against the specified grade requirements.

2. Coil Forming / Cold Bending:

   Flat stainless steel strip is cold-formed into helical coils using precision CNC-controlled coil forming machines. Alternatively, seamless stainless steel tubes are cold-bent into coil configurations using mandrel-supported bending equipment to prevent cross-sectional deformation and wall thinning. The forming process is performed at controlled temperatures (≤ 60°C) to avoid strain-induced sensitization.

3. Solution Annealing (if required):

   For applications requiring maximum corrosion resistance, coils may undergo solution annealing at 1050°C ± 20°C followed by rapid water quenching. This process dissolves carbide precipitates and restores full austenitic grain structure.

4. Pickling & Passivation:

   Post-forming, coils are treated with a nitric-hydrofluoric acid pickling solution to remove mill scale and oxidation. Subsequently, passivation is performed using a 20%–30% nitric acid solution per ASTM A967 to establish a uniform, protective chromium oxide film.

5. End Processing:

   Tube ends are machined, threaded, or fitted with flanges according to the customer's specification. All end connections are verified for thread gauge compliance and flange flatness (≤ 0.1 mm TIR — Total Indicator Reading).

6. Non-Destructive Testing (NDT):

   Each coil undergoes hydrostatic pressure testing at 1.5× the maximum working pressure with a hold time of minimum 10 seconds. Additional eddy current testing (ECT) or ultrasonic testing (UT) may be applied to detect internal or surface defects.

7. Dimensional Inspection & Final QC:

   Comprehensive dimensional verification is performed using laser scanning or coordinate measuring machines (CMM). Surface roughness is confirmed via contact profilometry. All inspection data is recorded in the product's traceability documentation.

8. Packaging & Shipment:

   Finished coils are wrapped in anti-corrosion VCI (Vapor Corrosion Inhibitor) paper, secured within wooden export-grade crates, and labeled with product identification, material certificates, and handling instructions per ISO 4180.

Applications

The Stainless Steel Coil Tube (Item No. 1053) is specifically engineered for integration into semi-centralized air conditioning systems that employ the following configurations:

Primary Application Domains:

• Evaporative Cooling Systems: The coil tube serves as the condenser or evaporator element within direct and indirect evaporative cooling circuits, where the helical geometry enhances heat and mass transfer between the refrigerant and ambient air.
• Dry Fan Coil Units (FCU): In dry fan coil configurations, the stainless steel coil tube functions as the primary heat exchanger, facilitating sensible heat exchange without moisture condensation on the coil surface.
• Semi-Centralized HVAC Architecture: The coil tubes are deployed in distributed terminal units that interface with a central plant, enabling zone-level temperature control with improved energy efficiency compared to fully centralized or fully decentralized systems.

Industry Applications:

• Commercial and industrial building HVAC systems
• Data center cooling infrastructure
• Pharmaceutical and cleanroom environmental control
• Food and beverage processing facilities (hygienic-grade applications)
• Marine and offshore HVAC systems (316L grade for chloride resistance)
• Chemical processing plants requiring corrosion-resistant heat exchange
• Hospital and laboratory ventilation systems

System Integration Benefits:

Within the evaporative cooling + dry fan coil semi-centralized air conditioning architecture, the stainless steel coil tube provides the following system-level advantages:

• Enhanced latent and sensible heat transfer coefficients due to optimized helical geometry
• Reduced fouling tendency compared to carbon steel alternatives, extending maintenance intervals
• Elimination of galvanic corrosion risks when paired with aluminum fins or copper refrigerant circuits
• Compatibility with food-grade and pharmaceutical-grade refrigerants and secondary loop fluids

Quality Certifications

Wenzhou Jixing Metal Materials Co., Ltd. maintains the following quality management and product certifications, ensuring full compliance with international standards:

• ISO 9001:2015 — Quality Management Systems certification, covering design, manufacturing, and quality assurance processes.
• ISO 14001:2015 — Environmental Management Systems certification, demonstrating commitment to sustainable manufacturing practices.
• CE Marking — Conformity with European directives for pressure equipment and HVAC components.
• EN 10204 — Material Testing Certificates (Type 3.1) issued for each production batch, documenting chemical composition and mechanical properties.
• ASTM Standards Compliance: Products manufactured to ASTM A213 (seamless austenitic stainless steel tube), ASTM A269 (welded austenitic stainless steel tube), and ASTM A967 (chemical cleaning and passivation).
• JIS G4305 — Japanese Industrial Standard for stainless steel tube, applicable for export to Japan and Southeast Asian markets.
• GB/T 14976 — Chinese National Standard for cold-rolled stainless steel seamless tubes, applicable for domestic market compliance.
• ASME BPV Code (Section VIII) — For pressure vessel and heat exchanger applications requiring code-stamped components.
• NSF/ANSI 61 — For potable water and food-grade applications requiring drinking water safety certification.

Unique Selling Points

Wenzhou Jixing Metal Materials Co., Ltd. distinguishes itself in the stainless steel coil tube market through the following competitive advantages:

• Precision Coil Geometry: Proprietary CNC coil forming technology ensures pitch accuracy of ±0.5 mm and uniform cross-sectional integrity throughout the entire coil length, directly translating to optimized heat transfer performance in HVAC applications.
• Full Material Traceability: Each coil tube is accompanied by a complete material passport including mill certificates, PMI results, NDT reports, and dimensional inspection data, enabling seamless integration into regulated industries.
• Custom Engineering Capability: The company offers fully customizable coil dimensions, end configurations, surface treatments, and material grades to meet specific project requirements for semi-centralized HVAC systems.
• Hygienic-Grade Surface Finish: Electropolished surfaces with Ra ≤ 0.4 μm meet pharmaceutical and food industry requirements, eliminating dead-leg contamination risks in fluid distribution loops.
• Integrated System Knowledge: With deep expertise in evaporative cooling and dry fan coil system design, the company provides engineering support beyond mere component supply, offering system-level optimization recommendations.
• Cost-Effective Longevity: The superior corrosion resistance of austenitic stainless steel eliminates the need for cathodic protection or frequent replacement, delivering a total cost of ownership (TCO) advantage over carbon steel alternatives over the system lifecycle.

Technical Notes & Standards Reference

The design and application of these coil tubes within semi-centralized air conditioning systems should reference the following technical literature and standards:

• ASHRAE Handbook — HVAC Systems and Equipment (latest edition)
• ASHRAE Standard 15 — Methods for Calculating Total Solar Heat Gain of a Window or Door Assembly
• EN 12831 — Heating systems in buildings: Calculation of design heat loads
• ISO 12100 — Safety of machinery: General principles for design
• 《蒸发冷却+干式风机盘管半集中式空调系统探讨》 — Technical discussion on evaporative cooling and dry fan coil semi-centralized air conditioning systems (internal technical literature, Item No. 1053)

For detailed engineering consultation, custom specifications, or bulk procurement inquiries, contact Wenzhou Jixing Metal Materials Co., Ltd. directly. All products are supplied with full technical documentation and are available for on-site engineering review.