Stainless Steel Coil Tube (Coiltube) — Technical Specification
Product Overview
The Stainless Steel Coil Tube (hereinafter referred to as "Coiltube") is a precision-formed tubular product manufactured by Wenzhou Jixing Metal Materials Co., Ltd. This product is produced by coiling straight stainless steel tubing into a helical or spiral configuration, delivering a high surface-area-to-volume ratio ideal for thermal exchange, fluid conveyance, and structural applications. The Coiltube is available in a wide range of grades, dimensions, and coil geometries to meet the demanding requirements of industrial, chemical, pharmaceutical, and energy sectors.
A critical design consideration inherent to coil tube engineering is the management of residual stresses, geometric deformation (ovality), and springback during the cold-forming process. Failure to account for these factors can result in dimensional non-conformance, reduced fatigue life, and premature failure under cyclic thermal or mechanical loading. Wenzhou Jixing Metal Materials Co., Ltd. incorporates advanced forming parameters and post-forming stabilization protocols to ensure that every coil tube product meets or exceeds international dimensional and performance standards.
Material & Properties
The Coiltube is manufactured from high-quality austenitic and duplex stainless steel tubing, selected for superior corrosion resistance, mechanical strength, and formability. The primary material grades offered include:
- 304 / 304L (UNS S30400 / S30403): General-purpose austenitic stainless steel with excellent corrosion resistance, weldability, and ductility. Suitable for food processing, chemical, and architectural applications.
- 316 / 316L (UNS S31600 / S31603): Molybdenum-bearing austenitic stainless steel offering enhanced resistance to pitting and crevice corrosion in chloride-containing environments. Ideal for marine, pharmaceutical, and chemical processing applications.
- 321 (UNS S32100): Titanium-stabilized austenitic stainless steel providing superior resistance to intergranular corrosion and high-temperature scaling. Recommended for heat exchangers and exhaust systems operating above 425°C.
- 310S (UNS S31008): High-temperature austenitic stainless steel with exceptional oxidation resistance, suitable for furnace components and extreme thermal cycling environments up to 1150°C.
- 904L (UNS N08904): High-alloy austenitic stainless steel with outstanding resistance to reducing and oxidizing acids, designed for severe chemical processing environments.
- 2205 Duplex (UNS S31803): Austenitic-ferritic duplex stainless steel combining high yield strength (≥450 MPa) with excellent chloride stress corrosion cracking resistance. Ideal for structural and pressure-containing applications.
- 2507 Super Duplex (UNS S32750): Ultra-high-strength duplex stainless steel with yield strength ≥550 MPa and superior resistance to pitting, crevice corrosion, and stress corrosion cracking in aggressive chloride environments.
Key Mechanical & Physical Properties
| Property | 304/304L | 316/316L | 321 | 310S | 904L | 2205 Duplex | 2507 Super Duplex |
|---|---|---|---|---|---|---|---|
| Yield Strength (MPa, 0.2% offset) | ≥205 | ≥205 | ≥205 | ≥205 | ≥230 | ≥450 | ≥550 |
| Tensile Strength (MPa) | 515–720 | 515–720 | 515–720 | 515–720 | 550–750 | 550–800 | 620–850 |
| Elongation (% at break) | ≥40 | ≥40 | ≥40 | ≥40 | ≥35 | ≥25 | ≥15 |
| Maximum Service Temperature (°C) | 870 | 870 | 900 | 1150 | 1050 | 300 (continuous) | 300 (continuous) |
| Density (kg/m³) | 8000 | 8000 | 8000 | 8000 | 8100 | 7800 | 7800 |
| Thermal Conductivity (W/m·K, 20°C) | 16.3 | 16.3 | 16.3 | 14.2 | 12.0 | 15.0 | 13.6 |
| Pitting Resistance (PREN) | 18–20 | 24–26 | 20–22 | 18–20 | 45–48 | 34–36 | 40–42 |
Specifications
| Parameter | Specification / Range |
|---|---|
| Outside Diameter (OD) | 6.35 mm – 108 mm (1/4" – 4") |
| Wall Thickness | 0.5 mm – 6.0 mm (0.020" – 0.236") |
| Coil Diameter (Mean) | 50 mm – 2000 mm (2" – 80") |
| Coil Length per Spool | 5 m – 500 m (configurable per order) |
| Minimum Bending Radius | ≥3× OD (standard); ≥2× OD (special, with springback compensation) |
| Surface Finish | 2B (cold-rolled annealed), BA (Bright Annealed), No. 4 Brushed, Mirror (Ra ≤ 0.4 μm), Sandblasted |
| End Condition | Plain cut, Beveled, Threaded (BSW/BSP/NPT), Flanged, Socket-welded |
| Dimensional Tolerance (OD) | ±0.05 mm to ±0.3 mm (per ASTM A269 / ASME SA-269) |
| Dimensional Tolerance (Wall) | ±10% of nominal wall thickness |
| Ovality (Post-Coiling) | ≤10% of nominal OD (standard); ≤5% (precision-grade) |
| Coil Pitch Tolerance | ±1.0 mm per turn |
| Weld Seam Type | Continuous welded (AWT/ODW), seamless (for select sizes) |
| Heat Treatment | Solution annealed (1010–1150°C, water/air quench); Stress-relieved post-coiling (optional) |
| Packaging | Wooden pallet with VCI (Vapor Corrosion Inhibitor) wrapping; export-grade seaworthy packaging available |
Manufacturing Process
The manufacturing of high-quality stainless steel coil tubes at Wenzhou Jixing Metal Materials Co., Ltd. follows a rigorous multi-stage process designed to ensure dimensional accuracy, mechanical integrity, and surface quality:
- Raw Material Procurement & Inspection: Stainless steel coils or pipe blanks are sourced from certified mills and subjected to incoming inspection including chemical composition analysis (OES — Optical Emission Spectroscopy), mechanical testing, and visual surface examination.
- Tube Drawing & Forming: Raw stock is cold-drawn through precision-die tooling to achieve the target outside diameter and wall thickness. This process work-hardens the material, improving mechanical strength while maintaining formability.
- Solution Annealing: Tubes are heated to the appropriate solution-annealing temperature (typically 1010–1150°C depending on grade) and rapidly quenched to dissolve carbide precipitates, restore full ductility, and achieve a uniform austenitic microstructure. This step is critical for ensuring corrosion resistance and preventing intergranular corrosion susceptibility.
- Pickling & Passivation: Post-annealing tubes undergo acid pickling (typically using a mixture of nitric and hydrofluoric acids, or a citric acid-based eco-friendly alternative) to remove oxide scale, followed by passivation to form a stable chromium oxide protective film on the surface.
- Cold Coiling (Helical/Spiral Forming): Straight tubes are fed through a precision coiling head equipped with adjustable forming rollers. Critical process parameters include:
- Minimum bending radius control — ensuring the bending radius does not fall below 3× OD to prevent wall thinning, kinking, or cracking
- Springback compensation — the forming tooling is programmed to over-bend slightly to account for elastic recovery, ensuring the final coil diameter matches the specification
- Ovality control — multi-roller forming systems with post-forming sizing stations maintain ovality within acceptable limits
- Residual stress management — controlled forming speeds and roller pressure distributions minimize localized stress concentrations
- Post-Coiling Stress Relief (Optional): For applications requiring minimal residual stresses (e.g., pressure vessels, fatigue-critical service), coils are subjected to a stress-relief annealing cycle at 425–550°C for 1–2 hours followed by controlled cooling.
- Final Inspection & Testing:
- Dimensional verification (OD, wall thickness, coil diameter, pitch) using laser micrometers and coordinate measuring systems
- Visual inspection for surface defects, kinks, or deformation
- Hydrostatic pressure testing (typically 1.5× maximum working pressure) to verify weld seam integrity
- Non-destructive testing (NDT) — magnetic particle inspection (MPI) or dye penetrant testing (PT) for surface defect detection
- Chemical composition verification via portable XRF (X-Ray Fluorescence) analyzer
- Spectral analysis for microstructure confirmation (metallographic examination)
- Packaging & Dispatch: Coils are wound onto wooden spools or pallets, wrapped with VCI film and moisture-absorbing desiccant packs, and secured for transport. Each shipment is accompanied by a Mill Test Certificate (MTC) conforming to EN 10204 Type 3.1 or equivalent.
Design Considerations — Critical Engineering Notes
Key Insight from Coil Tube Design Engineering: One of the most frequently overlooked issues in coil tube design is the interaction between the minimum bending radius and the resulting residual stress state. When a tube is cold-coiled, the outer fibers experience tensile plastic strain while the inner fibers undergo compressive plastic strain. Upon unloading, elastic springback occurs, but a permanent residual stress distribution remains. If not properly accounted for, these residual stresses can:
- Accelerate fatigue crack initiation under cyclic loading
- Promote stress corrosion cracking (SCC) in chloride environments
- Cause dimensional drift during subsequent heat treatment or service exposure
- Lead to unexpected buckling under external pressure
Wenzhou Jixing Metal Materials Co., Ltd. addresses these concerns through optimized forming parameters, post-forming stress relief, and comprehensive quality assurance protocols that ensure every coil tube product performs reliably throughout its design service life.
Applications
Stainless Steel Coil Tubes manufactured by Wenzhou Jixing Metal Materials Co., Ltd. find extensive application across multiple industries:
- Heat Exchangers & Radiators: Coil tubes serve as the primary heat transfer elements in shell-and-coil heat exchangers, air-cooled condensers, and automotive/industrial radiators. The helical geometry maximizes surface area within a compact footprint.
- Refrigeration & Air Conditioning: Used in evaporators, condensers, and chiller coils where efficient heat exchange with refrigerants is required.
- Chemical Processing: Reactor internals, coil heat exchangers, and transfer lines in plants handling aggressive chemicals, acids, and corrosive media (particularly 316L, 904L, and duplex grades).
- Pharmaceutical & Food Processing: Hygienic-grade coil tubes (BA/Mirror finish) used in pasteurizers, CIP (Clean-in-Place) systems, and sterile fluid transfer where surface cleanliness and corrosion resistance are paramount.
- Petroleum & Natural Gas: Subsea umbilicals, oil well tubing, and platform heat exchangers where duplex and super duplex stainless steels provide the necessary combination of strength and corrosion resistance.
- Power Generation: Boiler economizers, superheater coils, and steam generator tubes in fossil fuel and nuclear power plants.
- Marine & Offshore: Sea water cooling coils, ballast systems, and structural components exposed to chloride-rich marine environments.
- Architectural & Decorative: Coil tubing used in handrails, railings, decorative elements, and structural frameworks in modern architecture.
- Medical Equipment: Autoclave heating coils, sterilization equipment, and precision tubing for medical device manufacturing.
Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains rigorous quality management systems and product certifications to ensure full compliance with international standards: