Stainless Steel Coil Tube (Coiltube) — Large-Scale Coil Tank Storage Systems
Product Reference No.: 1272 | Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd. | Category: Technical Literature & Application Engineering
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) is a precision-engineered helical or spiral tube product designed for integration into large-scale coil tank storage systems. This product category encompasses continuously wound stainless steel tubing formed into compact, space-efficient coil geometries that maximize surface-area-to-volume ratios for thermal exchange, fluid containment, and process engineering applications.
Wenzhou Jixing Metal Materials Co., Ltd. has accumulated extensive expertise in the design, manufacturing, and deployment of large-diameter coil tubes used in industrial storage tanks, heat exchangers, chemical processing vessels, and energy infrastructure. The coil tube serves as a critical structural and functional component in systems requiring high thermal conductivity, corrosion resistance, and mechanical integrity under sustained operational loads.
Definition: A Coil Tube (Coiltube) is a length of stainless steel tubing wound into a helical or spiral configuration, typically used within tank-type heat exchangers, process vessels, and storage systems where compact geometry and efficient heat transfer are required.
2. Material Composition & Properties
2.1 Commonly Used Stainless Steel Grades
- Austenitic Stainless Steel: 304 (UNS S30400), 304L (UNS S30403), 316 (UNS S31600), 316L (UNS S31603) — preferred for general corrosion resistance and cryogenic service
- Super-Austenitic Stainless Steel: 904L (UNS N08904), 254 SMO (UNS S31254) — for aggressive chemical environments
- Duplex Stainless Steel: 2205 (UNS S31803), 2507 (UNS S32750) — for high-strength, chloride-resistant applications
- Super-Duplex Stainless Steel: 2507 (UNS S32750) — for extreme pressure and corrosion conditions
2.2 Key Material Properties
| Property | 304 / 304L | 316 / 316L | 2205 Duplex | 2507 Super-Duplex |
|---|---|---|---|---|
| Tensile Strength (MPa, min) | 515 | 515 | 450–620 | ≥550 |
| Yield Strength (MPa, min) | 205 | 205 | ≥450 | ≥550 |
| Elongation (%) | ≥40 | ≥40 | ≥15 | ≥15 |
| Chromium Content (%, min) | 18.0 | 16.5 | 22.0 | 24.0 |
| Nickel Content (%, min) | 8.0 | 10.0 | 4.5 | 6.0 |
| Operating Temperature Range (°C) | −196 to +870 | −196 to +870 | −50 to +350 | −50 to +350 |
| Corrosion Resistance (Pitting) | Moderate | High | Very High | Exceptional |
| Thermal Conductivity (W/m·K, at 25°C) | 16.3 | 16.3 | 11.4 | 11.4 |
2.3 Alloying Element Functions
- Chromium (Cr): Forms a passive oxide layer (Cr₂O₃) providing primary corrosion resistance
- Nickel (Ni): Stabilizes austenitic crystal structure; enhances ductility and toughness
- Molybdenum (Mo): Increases resistance to pitting and crevice corrosion in chloride environments
- Nitrogen (N): In duplex grades, increases yield strength and pitting resistance (PREN index)
- Titanium (Ti): Stabilizer for intergranular corrosion resistance in sensitization-prone conditions
3. Technical Specifications
| Parameter | Specification / Range | Notes |
|---|---|---|
| Tube Outer Diameter (OD) | 6 mm – 50 mm (standard); up to 150 mm (custom) | Depends on flow rate and pressure requirements |
| Tube Wall Thickness | 0.5 mm – 6.0 mm | Selected per design pressure and corrosion allowance |
| Coil Diameter (Mean) | 200 mm – 5,000 mm | Large-scale coil tanks may exceed 5,000 mm |
| Coil Length (Unwound) | 10 m – 500+ m | Continuous welding for seamless coil construction |
| Number of Coils per Assembly | 1 – 500+ (multi-coil configurations) | Arranged in serpentine or parallel configurations |
| Surface Finish | No. 4 Finish, 2B, Electropolished (Ra ≤ 0.5 µm), Passivated | Electropolishing recommended for hygienic/food-grade |
| Maximum Working Pressure | Up to 4.0 MPa (standard); up to 10.0 MPa (reinforced) | Per ASME BPV Code Section VIII |
| Design Temperature | −196 °C to +450 °C | Material-dependent; cryogenic applications supported |
| Welding Method | Orbital TIG (GTAW), Automatic MIG (GMAW), Laser Welding | Orbital TIG preferred for thin-wall, high-purity applications |
| End Preparation | Flat, Beveled (37.5° ± 2.5°), Flanged, Threaded (NPT/BSP) | Custom end treatments available |
| Tolerance (OD) | ±0.05 mm (precision); ±0.1 mm (standard) | Per ASTM A213 / A269 |
| Applicable Standards | ASTM A213, A269, A778; EN 10216-5, EN 10217-7; ASME B31.3 | Cross-reference to project specifications |
4. Manufacturing Process
4.1 Process Flow Overview
- Raw Material Selection & Inspection: Ingot or strip material is certified per ASTM/EN standards. Chemical composition is verified via Optical Emission Spectroscopy (OES) and wet chemical analysis.
- Hot Rolling & Annealing: Stainless steel strips or seamless tubes are hot-rolled to approximate dimensions and subsequently annealed in a protective atmosphere (bell jar or continuous annealing furnace) to achieve solution-treated condition.
- Cold Forming / Coiling: Straight tube is fed into a precision coiling machine (bending roll system) that progressively bends the tube into a helical or serpentine configuration. Bending radii are controlled to prevent ovality, wrinkling, or work-hardening.
- Coil Spacing & Support: Spacers (sleeves, rings, or saddle supports) are inserted between adjacent coil turns to maintain uniform gap spacing, ensuring even fluid distribution and preventing tube-to-tube contact.
- Welding & Joining: Coil-to-coil connections and inlet/outlet headers are fabricated using orbital TIG welding (GTAW) with internal gas shielding (argon/helium) to prevent oxidation. Weld parameters are controlled per WPS (Welding Procedure Specification).
- Non-Destructive Testing (NDT): All welds undergo 100% Visual Testing (VT), followed by Dye Penetrant Testing (PT) or Magnetic Particle Testing (MT). Radiographic Testing (RT) or Ultrasonic Testing (UT) is applied to critical joints per ASME Section V.
- Pneumatic / Hydrostatic Pressure Testing: The completed coil assembly is pressure-tested to 1.5× design pressure (minimum) for a specified hold time (typically 30 minutes), with zero leakage permitted.
- Surface Treatment & Passivation: Pickling and passivation (nitric acid or citric acid treatment) removes scale and re-establishes the passive chromium oxide film. Electropolishing is applied for hygienic-grade applications.
- Final Inspection & Documentation: Dimensional verification, surface finish measurement (profilometer), and compilation of material traceability certificates (MTCs per EN 10204 Type 3.1 or 3.2).
4.2 Critical Process Parameters
| Process Stage | Control Parameter | Tolerance / Target |
|---|---|---|
| Coiling (Bending) | Minimum Bending Radius | ≥ 5× Tube OD (standard); ≥ 3× OD (with mandrel) |
| Coiling (Bending) | Ovality After Bending | ≤ 2% of nominal OD |
| Orbital TIG Welding | Internal Shielding Gas | Argon (99.995% purity); flow 3–6 L/min |
| Orbital TIG Welding | Weld Penetration | Full penetration; no lack of fusion |
| Pressure Testing | Test Pressure | 1.5× Design Pressure (hydrostatic) |
| Passivation | Passivation Efficiency | ≥ 90% per ASTM A967 |
5. Applications
5.1 Primary Application Domains
- Large-Scale Coil Tank Storage Systems: Coil tubes serve as the primary heat transfer and fluid circulation medium in large-diameter storage tanks for cryogenic liquids (LNG, LOX, LIN), chemical intermediates, and process fluids. The coil geometry allows thermal management (heating/cooling) within the tank without requiring external heat exchangers.
- Heat Exchangers (Shell-and-Coil Type): Multi-coil assemblies installed within cylindrical shells for efficient heat exchange in process industries, power generation, and HVAC systems.
- Chemical Processing: Reactor internals, distillation column internals, and storage vessels for aggressive chemicals (acids, alkalis, chlorinated solvents) where corrosion resistance is paramount.
- Food & Pharmaceutical Industry: Hygienic-grade coil heat exchangers for pasteurization, sterilization, and temperature-controlled processing (CIP/SIP compatible).
- Oil & Gas Industry: Subsea coil heat exchangers, wellhead heating coils, and process skid-mounted coil systems for offshore and onshore production.
- Cryogenic Applications: LNG storage tanks, liquid oxygen/nitrogen/argon tanks, and superconducting magnet cooling systems requiring operation at temperatures as low as −196 °C.
- Power Generation: Feedwater heating, condensate recovery, and boiler auxiliary systems in thermal and nuclear power plants.
5.2 Unique Selling Points
- Superior Thermal Efficiency: The helical coil geometry maximizes heat transfer surface area within a compact volume, achieving 30–50% higher thermal performance compared to equivalent straight-tube configurations.
- Space Optimization: Coil tubes reduce the footprint of storage and heat exchange systems by up to 60% compared to conventional parallel-tube arrangements.
- Full Traceability: Every coil tube assembly is accompanied by mill certificates, weld logs, NDT reports, and pressure test documentation, ensuring complete material and process traceability.
- Custom Engineering Capability: Wenzhou Jixing Metal Materials Co., Ltd. offers tailored coil designs — including multi-pass serpentine, spiral, and bundled coil configurations — to meet specific process requirements.
- Corrosion-Resistant Longevity: Premium stainless steel grades (316L,