Stainless Steel Coil Tube (Coiltube) — Energy Storage & Industrial Applications
Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. (Product No. 367) is a precision-engineered continuous-length stainless steel tubing, supplied in coil form, designed for demanding thermal energy storage systems, district energy networks, and industrial process applications. This product line draws upon extensive field experience, including documented case studies from commercial district energy station ice-storage systems in major metropolitan areas, where coil tubes serve as the critical heat exchange medium between refrigerant and storage media.
Coil tubes offer distinct advantages over straight-length tubing in terms of material utilization, installation flexibility, and logistical efficiency. The continuous coil configuration eliminates the need for field welding and joining, significantly reducing potential leak points and installation labor costs. Wenzhou Jixing Metal Materials Co., Ltd. supplies coil tubes in a range of diameters, wall thicknesses, and stainless steel grades tailored to specific application requirements.
Material & Properties
The coil tubes are fabricated from high-grade austenitic stainless steels conforming to international standards, selected for superior corrosion resistance, mechanical strength, and thermal stability across a wide operating temperature range.
Available Grades
- 304 (UNS S30408) — General-purpose grade with excellent corrosion resistance in most atmospheric and mildly aggressive environments. Suitable for potable water systems, food processing, and general thermal applications.
- 316 (UNS S31608) — Enhanced chloride resistance due to molybdenum (Mo) addition (2–3%). Recommended for coastal environments, chemical processing, and applications involving chlorinated water or brine solutions — particularly relevant for ice-storage energy systems where salt-based thermal media may be employed.
- 316L (UNS S31603) — Low-carbon variant of 316, optimized for welding applications with reduced risk of intergranular corrosion (IGC) in the heat-affected zone (HAZ).
- 321 (UNS S32100) — Titanium-stabilized grade providing resistance to sensitization at elevated temperatures, suitable for high-temperature thermal storage applications.
- 304L (UNS S30403) — Low-carbon variant of 304, offering improved weldability and resistance to intergranular corrosion.
Key Material Properties (Typical for 304/316 Grades)
| Property | 304 / 304L | 316 / 316L | 321 |
|---|---|---|---|
| Density (g/cm³) | 7.93 | 8.00 | 7.93 |
| Thermal Conductivity (W/m·K, at 20°C) | 16.3 | 14.6 | 16.3 |
| Thermal Expansion Coefficient (×10⁻⁶/K, 20–100°C) | 17.3 | 17.1 | 17.3 |
| Tensile Strength (MPa, annealed) | ≥ 520 | ≥ 520 | ≥ 520 |
| Yield Strength (MPa, 0.2% offset) | ≥ 205 | ≥ 205 | ≥ 205 |
| Maximum Service Temperature (°C) | 870 | 870 | 900 |
| Chromium Content (%) | 18–20 | 16–18 | 18–20 |
| Nickel Content (%) | 8–10.5 | 10–14 | 8–10 |
| Molybdenum Content (%) | — | 2.0–3.0 | — |
Corrosion Resistance Considerations
Based on documented field experience from commercial district energy station ice-storage applications, coil tubes operating in brine-based thermal storage systems are susceptible to several forms of corrosion, including:
- Pitting Corrosion (PC) — Localized attack initiated by chloride ion (Cl⁻) concentration, particularly relevant in saltwater or calcium chloride brine systems used for thermal energy storage.
- Crevice Corrosion (CC) — Occurs beneath gaskets, flange connections, and insulation materials where stagnant fluid accumulates and oxygen depletion promotes localized electrochemical attack.
- Intergranular Corrosion (IGC) — Risk in welded joints where chromium carbide precipitation at grain boundaries depletes the adjacent matrix of chromium, reducing passive film integrity. Mitigated by selecting low-carbon grades (304L, 316L) or stabilized grades (321).
- Stress Corrosion Cracking (SCC) — Austenitic stainless steels are vulnerable to chloride-induced SCC at temperatures above approximately 60°C. Proper grade selection and stress relief procedures are essential.
Engineering Recommendation: For ice-storage energy station applications involving chloride-containing brines, Grade 316L is strongly recommended. The combination of molybdenum alloying and low carbon content provides optimal resistance to both pitting/crevice corrosion and intergranular sensitization at welds. Surface finish quality (Ra ≤ 0.8 μm) and thorough weld post-treatment (pickling and passivation) further enhance long-term durability.
Specifications
| Parameter | Specification / Range | Standard Reference |
|---|---|---|
| Product Name | Stainless Steel Coil Tube (Coiltube) | — |
| Product No. | 367 | — |
| Material Grades | 304, 304L, 316, 316L, 321 | ASTM A213 / A269, EN 10216-5 |
| Outer Diameter (OD) | 6.0 mm – 108.0 mm (custom sizes available) | ASTM B564, EN 10217 |
| Wall Thickness | 0.5 mm – 6.0 mm (customizable) | — |
| Coil Diameter | 500 mm – 1200 mm (as per customer requirement) | — |
| Coil Length | Continuous; typical lengths 50 m – 300 m per coil | — |
| Surface Finish | Pickled & Passivated (P&P); polished finish available upon request | ASTM A403, EN 1088 |
| Surface Roughness (Ra) | ≤ 0.8 μm (standard); ≤ 0.4 μm (polished) | — |
| Manufacturing Method | Precision cold drawing (CD); seamless | ASTM A269, EN 10216-5 |
| Heat Treatment | Annealed (Solution Annealed); stress-relieved | — |
| Operating Pressure (Typical) | Up to 2.5 MPa (design-dependent) | ASME B31.3 / B31.5 |
| Operating Temperature Range | −196°C to +870°C (grade-dependent) | — |
| Tolerance — OD | ± 0.05 mm (precision grade); ± 0.10 mm (standard) | ASTM A269 |
| Tolerance — Wall Thickness | ± 0.05 mm (precision grade); ± 0.10 mm (standard) | — |
| End Preparation | Plain cut (standard); beveled, threaded, or flanged upon request | ASME B16.25 |
| Welding Compatibility | Compatible with TIG (GTAW), MIG (GMAW), and orbital welding | ASME IX, ISO 15614 |
| Packaging | Wooden pallet with moisture-proof wrapping; export-grade packaging available | — |
Manufacturing Process
The production of high-precision stainless steel coil tubes at Wenzhou Jixing Metal Materials Co., Ltd. follows a rigorous multi-stage manufacturing process designed to ensure dimensional accuracy, metallurgical integrity, and surface quality:
- Raw Material Selection & Inspection: High-quality stainless steel seamless pipe blanks are sourced from certified mills. Incoming material undergoes 100% visual inspection, dimensional verification, and chemical composition analysis (spectrometry) to confirm compliance with specified grades (e.g., ASTM A213 TP304/TP316).
- Heat Treatment (Solution Annealing): Raw pipe blanks are solution annealed at temperatures between 1040°C and 1120°C, followed by rapid water quenching. This process dissolves chromium carbide precipitates, restores full austenitic microstructure, and maximizes corrosion resistance and ductility.
- Precision Cold Drawing: The annealed pipe blanks are cold-drawn through a series of precision-die drawing stations to achieve the target outer diameter (OD) and wall thickness (WT) with tight tolerances. The drawing process is performed in multiple passes, with intermediate annealing as required, to achieve final dimensions within ±0.05 mm tolerance.
- Intermediate Annealing (if applicable): For tubes requiring significant reduction in wall thickness or diameter, intermediate annealing cycles are performed at 1050°C–1100°C to relieve accumulated cold-work stresses and prevent cracking.
- Final Annealing & Stress Relief: A final annealing cycle ensures uniform microstructure, eliminates residual drawing stresses, and optimizes mechanical properties. For applications requiring high-temperature service, a dedicated stress-relief anneal may be applied.
- Pickling & Passivation: The tube surface is treated with a nitric-hydrofluoric acid (HNO₃/HF) pickling solution to remove mill scale, oxide films, and any iron contamination from tooling. This is followed by a passivation treatment (typically 20–30% nitric acid solution) to enrich the surface chromium content and establish a stable, protective chromium oxide (Cr₂O₃) passive film.
- Dimensional & Quality Inspection: Each coil undergoes comprehensive quality control including:
- 100% hydrostatic pressure testing (to verify internal integrity and weld soundness)
- Dimensional verification (OD, wall thickness, straightness) using calibrated measurement equipment
- Surface quality inspection (visual and magnetic particle inspection for surface defects)
- Chemical composition verification (spectrometric analysis)
- Hardness testing (Vickers or Rockwell) to confirm annealed condition
- Corrosion resistance testing (ASTM A967 passivation verification; optional salt spray testing per ASTM B117)
- Coiling & Packaging: Tubes are coiled onto precision-wound coils of the specified diameter, wrapped in moisture-proof protective film, and secured on export-grade wooden pallets with corner protection. Each coil is labeled with a unique batch identification, material certificate reference, and shipping documentation.
Applications
The stainless steel coil tubes produced by Wenzhou Jixing Metal Materials Co., Ltd. serve a wide range of industrial, commercial, and municipal applications:
Thermal Energy Storage Systems
- Ice Storage Energy Stations: Coil tubes serve as the primary heat exchange medium in latent-heat thermal energy storage (LHTES) systems, transferring cooling capacity between refrigerant and ice/brine storage media. The continuous coil configuration maximizes heat exchange surface area within confined installation spaces typical of commercial district energy stations.
- District Heating & Cooling Networks: Used in secondary loop piping, heat exchanger bundles, and distribution manifolds for urban district energy systems.
- Solar Thermal Systems: Employed in evacuated tube collectors, storage tank immersion coils, and heat transfer fluid circuits.
Industrial Process Applications
- Chemical processing plant piping and heat exchanger tubes
- Pharmaceutical and bioprocessing equipment (CIP/SIP compatible)
- Food and beverage processing (dairy, brewing, bottling)
- Power generation — condensate systems, feedwater piping, and auxiliary circuits
- Oil and gas — sub