Stainless Steel Coil Tube for Floating Coil Heat Exchanger Series
Product Overview
The Stainless Steel Coil Tube (盘管 / Coil Tube) is a precision-engineered tubular component manufactured by Wenzhou Jixing Metal Materials Co., Ltd., specifically designed for integration into Fluid-Induced Vibration (FIV) Resistant Floating Coil Heat Exchanger Series. These coil tubes serve as the primary heat transfer elements in floating coil heat exchangers, where they are arranged in a helical or serpentine configuration within a shell-and-coil arrangement. The floating coil design allows the tube bundle to expand and contract freely in response to thermal cycling, thereby mitigating thermal stress accumulation and enhancing long-term mechanical integrity.
Unlike conventional fixed-tube-sheet heat exchangers, the floating coil architecture enables the coil tube assembly to act as a self-supporting, thermally flexible element. This is particularly critical in applications involving high-temperature differentials, aggressive process fluids, or environments where Fluid-Induced Vibration (FIV) — including vortex-induced vibration (VIV), turbulent buffeting, and flow-induced acoustic resonance — poses a risk of fatigue failure. The coil geometry inherently provides superior vibration damping characteristics compared to straight-tube bundles, reducing the amplitude of fluid-excited oscillations by leveraging the natural flexibility of the helical configuration.
Material & Properties
The coil tubes are fabricated from high-performance austenitic and super-austenitic stainless steel grades, selected to ensure optimal combinations of corrosion resistance, mechanical strength, thermal conductivity, and formability for coil winding operations.
Primary Alloy Grades
- AISI 304 / UNS S30400 — General-purpose austenitic stainless steel offering excellent corrosion resistance in oxidizing environments, good weldability, and superior cold-forming characteristics essential for coil winding.
- AISI 316 / UNS S31600 — Molybdenum-enhanced austenitic grade providing enhanced resistance to pitting and crevice corrosion, particularly in chloride-containing process fluids.
- AISI 316L / UNS S31603 — Low-carbon variant of 316L suitable for welded assemblies where sensitization resistance is critical.
- AISI 321 / UNS S32100 — Titanium-stabilized grade offering superior resistance to intergranular corrosion and thermal stress cracking at elevated operating temperatures (up to 870°C).
- AISI 347 / UNS S34700 — Niobium-stabilized alternative to 321, providing comparable high-temperature stability with improved weldability.
- AISI 904L / UNS N08904 — Super-austenitic grade with high nickel and molybdenum content, delivering exceptional resistance to reducing acids and high-temperature sulfuric acid environments.
Mechanical Properties (Annealed Condition, Representative Values)
| Property | 304 | 316L | 321 | 904L |
|---|---|---|---|---|
| Tensile Strength (MPa) | ≥ 520 | ≥ 485 | ≥ 515 | ≥ 550 |
| Yield Strength (0.2% Proof Stress, MPa) | ≥ 205 | ≥ 170 | ≥ 205 | ≥ 220 |
| Elongation (%) | ≥ 40 | ≥ 45 | ≥ 40 | ≥ 35 |
| Thermal Conductivity at 100°C (W/m·K) | 16.3 | 16.3 | 16.3 | 14.6 |
| Thermal Expansion Coefficient (×10⁻⁶/K, 20–100°C) | 17.3 | 17.3 | 17.3 | 18.0 |
| Maximum Operating Temperature (°C) | 870 | 870 | 980 | 1050 |
| Minimum Operating Temperature (°C) | −196 | −196 | −196 | −196 |
Corrosion Resistance Characteristics
- Excellent resistance to atmospheric corrosion, dilute and concentrated nitric acid, and organic acids
- Strong resistance to pitting and crevice corrosion in chloride environments (316L and 904L grades)
- Outstanding resistance to stress corrosion cracking (SCC) in warm chloride solutions
- High resistance to intergranular corrosion following welding operations (stabilized grades 321 and 347)
Specifications
| Parameter | Specification |
|---|---|
| Product Name | Stainless Steel Coil Tube (盘管 / Coil Tube) |
| Item No. | 1323 |
| Manufacturer | Wenzhou Jixing Metal Materials Co., Ltd. |
| Outer Diameter (OD) | Φ6.0 mm – Φ50.8 mm (customizable) |
| Wall Thickness | 0.5 mm – 3.0 mm (customizable) |
| Coil Diameter (Helix Mean Diameter) | Φ100 mm – Φ2000 mm (application-dependent) |
| Coil Pitch (Turn Spacing) | 2.0 mm – 25.0 mm (customizable) |
| Number of Turns | 2 – 200+ turns |
| Coil Length (Developed Length) | 1 m – 100+ m (customizable) |
| Surface Finish | 2B (Mill Annealed), BA (Bright Annealed), No. 4 Brushed, No. 8 Mirror |
| Tube End Condition | Plain, Flared, Grooved, Threaded, or Custom Fitting |
| Manufacturing Standard | ASTM A213 / A269, GB/T 12771, EN 10216-5 |
| Material Standard | ASTM A270, ASTM B906, GB/T 12770 |
| Applicable Heat Exchanger Standard | TEMA (Tubular Exchanger Manufacturers Association), ASME VIII Div. 1 |
| Operating Pressure | Up to 25 MPa (design-dependent) |
| Operating Temperature Range | −196°C to +980°C (grade-dependent) |
| Minimum Bend Radius | ≥ 3D (D = tube outer diameter) for cold forming |
| Coil Tolerance | ±0.5 mm on coil diameter; ±0.05 mm on wall thickness |
Manufacturing Process
The manufacturing of high-precision stainless steel coil tubes for floating coil heat exchangers involves a rigorous multi-stage process chain, each stage subject to strict quality control protocols:
- Raw Material Procurement and Inspection — Certified stainless steel seamless tubes or welded tubes are sourced from approved mills. Incoming material undergoes chemical composition analysis (spectrometric verification), mechanical property testing (tensile, hardness), and dimensional inspection to ensure conformance to specified grades and standards.
- Tube Straightening and Cutting — Straightening eliminates residual curvature from the mill coil or tube mill. Tubes are cut to precise developed lengths using CNC-controlled plasma or laser cutting systems, ensuring square end faces within ±0.1 mm tolerance.
- Pipe End Preparation — End deburring, chamfering, or forming of custom fittings (flared ends, grooved ends, threaded connections) is performed to facilitate seamless integration into the heat exchanger header assembly.
- Coil Winding (Helical Forming) — The core forming operation is executed using a precision CNC coil winding machine (also referred to as a tube coiler or helical former). The tube is fed through a set of forming rollers and guides while rotating around a mandrel of the specified coil diameter. The winding parameters — coil pitch, number of turns, and winding speed — are controlled by a programmable logic controller (PLC) to maintain dimensional accuracy. The process is performed in a cold-forming configuration, which preserves the metallurgical integrity of the annealed tube while imparting the desired helical geometry.
- Stress Relief and Annealing (if applicable) — For applications requiring elimination of cold-work-induced residual stresses, the formed coil tubes may undergo a controlled solid solution annealing treatment (typically at 1050–1150°C with rapid water quenching) followed by a stress-relief anneal at 400–500°C.
- Surface Treatment and Passivation — Post-forming surface cleaning involves pickling (removal of oxidation scale) and passivation (formation of a protective chromium oxide layer) in accordance with ASTM A967. Bright annealing in a hydrogen or vacuum atmosphere may be applied to achieve a superior mirror finish without introducing contamination.
- Non-Destructive Testing (NDT) — Each coil tube undergoes comprehensive inspection including:
- Visual Inspection — Examination of coil geometry, surface finish, and absence of defects such as wrinkles, kinks, or cold-work cracks.
- Dimensional Verification — Measurement of coil diameter, pitch, turn count, and tube OD/wall thickness using laser scanning or coordinate measuring machines (CMM).
- Pressure Testing — Hydrostatic or pneumatic pressure testing at 1.5× the maximum design pressure to verify weld integrity and absence of leaks.
- Eddy Current Testing (ECT) — For welded tubes, automated eddy current probes traverse the coil surface to detect wall thickness variations, subsurface cracks, and seam weld defects.
- Packaging and Shipping — Finished coil tubes are individually wrapped in protective film or paper, bundled with cushioning material, and secured in wooden crates or export-grade containers to prevent mechanical damage during transit.
Applications
The floating coil heat exchanger series utilizing these stainless steel coil tubes finds extensive application across multiple industrial sectors:
- Chemical and Petrochemical Processing — Heat exchange in aggressive chemical environments including sulfuric acid, hydrochloric acid, and caustic soda processing. The 904L and 316L grades provide superior resistance to corrosive media.
- Pharmaceutical and Biotechnology — Sanitary heat exchange for CIP (Clean-In-Place) and SIP (Steam-In-Place) processes. Mirror-finish BA (Bright Annealed) surface treatment ensures compliance with FDA 21 CFR and EU GMP requirements.
- Food and Beverage Processing — Pasteurization, sterilization, and heat recovery in dairy, brewing, and juice processing industries. High thermal conductivity and sanitary-grade materials ensure efficient and safe operation.
- Power Generation — Economizers, feedwater heaters, and condenser tube bundles in steam turbine cycles. The floating coil design accommodates large thermal expansion differentials between shell and tube sides.
- Cryogenic Applications — Liquefied natural gas (LNG) processing, cryogenic air separation, and superconducting magnet cooling systems. Austenitic stainless steels retain full ductility and toughness at temperatures as low as −196°C (77 K).
- Marine and Offshore — Seawater cooling systems, ballast water heat exchangers, and offshore platform heating systems where chloride-induced corrosion and vibration are persistent concerns.
- Environmental and Waste Treatment — Flue gas desulfurization (FGD) systems, wastewater heat recovery, and landfill gas processing where both corrosive and thermally variable conditions prevail.
Quality Certifications and Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management framework ensuring that every coil tube product meets or exceeds international standards:
- ISO 9001:2015 — Quality Management Systems certification demonstrating a commitment to consistent product quality and continuous improvement.
- ISO 14001:2015 — Environmental Management Systems certification for sustainable manufacturing practices.
- ASME "S" Stamp — Authorization for the manufacture of pressure-containing heat exchanger components in compliance with ASME Boiler and Pressure Vessel Code, Section VIII, Division 1.
- TEMA Compliance — Conformance with the Tubular Exchanger Manufacturers Association standards for design, materials, fabrication, and testing of shell-and-tube heat exchangers.
- EN 10204 Type 3.1 — Independent inspection body certification of material conformity and test results.
- CE Marking — Conformity with European Union Pressure Equipment Directive (PED 2014/68/EU) and Machinery Directive (2006/42/EC).
- Material Traceability — Full heat number traceability from mill certificate through to final product, enabling complete supply chain accountability.
- NACE MR0175 / ISO 15156 — Compliance for materials used in sour service (H₂S-containing environments) where sulfide stress cracking resistance is required.
Unique Selling Points
The floating coil heat exchanger series from Wenzhou Jixing Metal Materials Co., Ltd. represents a convergence of advanced metallurgy, precision manufacturing, and innovative thermal-hydraulic design. Key differentiators include:
- Superior Vibration Damping — The helical coil geometry inherently absorbs and dissipates fluid-induced vibration energy, significantly extending the fatigue life of the heat exchanger compared to straight-tube alternatives. This is achieved through the natural frequency tuning of the coil structure, which shifts the first-mode natural frequency away from the vortex shedding frequency of the cross-flow.
- Thermal Stress Accommodation — The floating coil design eliminates the need for expansion joints or floating heads, as the coil tube assembly freely expands and contracts along its helical axis. This reduces mechanical complexity, lowers manufacturing cost, and improves long-term reliability.
- Customizable Geometry — Coil diameter, pitch, number of turns, and tube dimensions are fully customizable to optimize the heat transfer surface area, pressure