Stainless Steel Coil Tube for Stirred Tank Heat Exchanger — Coiltube Series

1. Product Overview

The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered heat exchange component specifically designed for integration into stirred tank reactors and agitated vessels. These coil tubes serve as the primary heat transfer surface in jacketless cooling or heating systems, where fluid flows through the coiled tube while the process medium in the stirred tank is thermally conditioned through convective and conductive heat exchange across the tube wall.

Unlike conventional jacketed reactors, coil tube heat exchangers offer superior heat transfer efficiency by directly immersing the coiled element within the process fluid. The geometry of the coil — characterized by its helical winding pattern — promotes turbulent flow conditions on the tube exterior, significantly enhancing the external heat transfer coefficient (h_o) and overall thermal performance. This product line is particularly suited for applications demanding precise temperature control, high heat duty capacity, and resistance to chemical corrosion.

2. Material & Properties

2.1 Base Material

Primary Alloy: Austenitic Stainless Steel — AISI 304 (UNS S30400) / AISI 316L (UNS S31603)
Alternative Grades: 321 (UNS S32100), 316Ti (UNS S31635), and duplex 2205 (UNS S32205) available upon request
Surface Condition: Pickled and passivated (2B finish) or mirror polished (RA ≤ 0.4 μm)
Welding Quality: All welds are ground flush and passivated to prevent crevice corrosion

2.2 Key Physical Properties (AISI 316L)

Property	Value	Unit
Density	8.00	g/cm³
Thermal Conductivity (at 20°C)	16.3	W/(m·K)
Thermal Conductivity (at 500°C)	21.0	W/(m·K)
Specific Heat Capacity (at 20°C)	500	J/(kg·K)
Linear Thermal Expansion (20–100°C)	17.2	×10⁻⁶ /K
Yield Strength (0.2% offset)	≥205	MPa
Tensile Strength (UTS)	≥515	MPa
Maximum Service Temperature	870	°C
Pitting Resistance (PREN)	24–26	—

2.3 Corrosion Resistance

The coil tube material exhibits excellent resistance to a broad spectrum of corrosive media, including:

Chloride-containing solutions (up to 2000 ppm Cl⁻ at ambient temperature for 316L)
Organic acids (acetic, citric, lactic) at moderate concentrations
Aqueous alkaline solutions (pH 9–13)
Ferrous and non-ferrous salt solutions
Steam and superheated water (with appropriate grade selection)

3. Technical Specifications

Parameter	Specification
Outer Diameter (OD)	12 mm / 14 mm / 16 mm / 19 mm / 21.3 mm / 25 mm / 32 mm
Wall Thickness	0.5 mm – 3.0 mm (standard: 1.0 mm – 2.0 mm)
Coil Pitch (Helix Spacing)	15 mm – 60 mm (adjustable per thermal design requirement)
Coil Diameter (Mean)	200 mm – 2000 mm (custom fabrication available)
Tube Length (Total Developed)	3 m – 120 m
Heat Transfer Surface Area	0.5 m² – 150 m² (per unit)
Design Pressure	0.6 MPa – 4.0 MPa (gauge)
Operating Temperature Range	−196°C to +400°C (vacuum to moderate service)
End Connections	Welded stubs, flanged (ANSI/EN), threaded (BSP/NPT), or quick-disconnect fittings
Surface Finish	2B (Ra ≤ 0.8 μm) / Electropolished (Ra ≤ 0.4 μm) / Mirror (Ra ≤ 0.2 μm)
Winding Tolerance	±0.5 mm on coil diameter; ±0.3 mm on pitch
Applicable Standards	ASTM A213 / ASTM A269 / EN 10217-7 / GB/T 12771

4. Manufacturing Process

4.1 Raw Material Selection and Inspection

Only certified stainless steel seamless tubes from accredited mills (e.g., Outokumpu, Sandvik, Baosteel, or equivalent) are used. Each batch undergoes spectroscopic verification (PMI — Positive Material Identification) to confirm chemical composition compliance with the specified grade.

4.2 Coil Forming (Cold Bending)

Preparation: The straight tube is cut to the required developed length with a precision saw. End faces are deburred and chamfered.
Tooling: A CNC-controlled helical coiling machine with mandrel support is employed to ensure uniform winding geometry. The tooling radius is selected to prevent cross-sectional ovality exceeding 5%.
Forming: The tube is progressively wound around a master mandrel at a controlled feed rate. Real-time monitoring ensures pitch accuracy within ±0.3 mm tolerance.
Fixturing: After coiling, the ends are secured with temporary clamps to prevent spring-back during handling.

4.3 Welding and Assembly

End Welding: Stub pipes or flanges are TIG-welded (GTAW — Gas Tungsten Arc Welding) to the coil ends using matching filler wire (e.g., ER316L). Argon shielding on both inside and outside of the weld ensures full penetration and contamination-free fusion.
Weld Inspection: Each weld joint is visually inspected and subjected to dye penetrant testing (PT) or radiographic testing (RT) for critical applications.
Support Structure: A fabricated stainless steel support frame with vibration-damping mounts is attached to prevent fatigue-induced cracking during operation with agitated flow.

4.4 Post-Processing

Stress Relief: Solution annealing at 1050°C followed by water quenching (for full solution treatment) or low-temperature stress relief at 300–400°C (for dimensional stability).
Pickling and Passivation: Immersion in nitric/hydrofluoric acid solution to remove oxide scale, followed by passivation treatment to restore the chromium oxide protective layer.
Cleaning: Final ultrasonic cleaning and alcohol rinse to ensure the internal bore is free of particulate contamination.
Pressure Testing: Hydrostatic pressure test at 1.5× design pressure, held for a minimum of 15 minutes with no visible leakage or permanent deformation.

5. Applications

5.1 Core Application — Stirred Tank Heat Exchangers

The primary application domain for this coil tube product is as an internal heat exchange element within stirred tank reactors (STRs). The design philosophy is grounded in the well-established correlation between external heat transfer coefficient and stirring power input:

Nu = C · Reⁿ · Pr^1/3 · (μ_b/μ_w)^m

Where Nu is the Nusselt number, Re is the Reynolds number based on stirrer tip speed and coil diameter, Pr is the Prandtl number, and the viscosity ratio accounts for wall-to-bulk temperature differences.

The helical geometry of the coil tube promotes secondary flow patterns (Dean vortices) within the tube interior and enhances boundary layer disruption on the exterior surface. When combined with mechanical agitation, the external heat transfer coefficient can reach values of 800–2500 W/(m²·K) for aqueous systems, depending on impeller type, rotational speed, and coil positioning.

5.2 Industry Applications

Pharmaceutical Manufacturing: Cooling/heating of reaction mass in crystallization reactors, fermentation broths, and aseptic processing vessels.
Chemical Processing: Temperature control in polymerization reactors, esterification vessels, and epoxidation reactors.
Food and Beverage Industry: Pasteurization, sterilization, and thermal processing in mixing tanks (compliant with 3-A Sanitary Standards).
Cosmetics Industry: Emulsification and blending processes requiring precise thermal management.
Biochemical Processing: Enzymatic reactors and bioprocessing vessels where temperature stability is critical.
Waste Treatment: Neutralization reactors and chemical dosing vessels.

6. Unique Selling Points

Superior Heat Transfer Performance: The helical coil geometry inherently generates Dean vortices, increasing the effective heat transfer coefficient by 20–40% compared to straight-tube configurations of equivalent surface area.
Compact Design: High surface-area-to-volume ratio enables significant heat duty in minimal occupied space within the vessel, preserving usable reactor volume for the process medium.
Elimination of Jacket Requirements: Reduces vessel wall thickness and manufacturing cost by removing the need for a welded jacket, while providing more uniform temperature distribution.
Scalable and Modular: Coil dimensions (diameter, pitch, tube count) can be tailored to match specific thermal duty calculations, enabling custom engineering solutions.
Low Fouling Tendency: Internal turbulence within the coil tube and high-velocity external flow near the coil surface reduce deposit formation, minimizing maintenance intervals.
Full Material Traceability: Each coil tube is accompanied by a complete material certificate (EN 10204 3.1), traceable to the mill heat number, ensuring regulatory compliance in GMP and pharmaceutical environments.
Sanitary Design Option: Electropolished internal surface (Ra ≤ 0.4 μm) with crevice-free welds meets FDA 21 CFR Part 117 and EU Regulation 1935/2004 requirements.

7. Quality Certifications and Compliance

Certification / Standard	Description
ISO 9001:2015	Quality Management System certification for manufacturing processes
ISO 14001:2015	Environmental Management System certification
EN 10204 Type 3.1	Material test certificates with verified inspection data
ASME BPV Section VIII Div. 1	Pressure vessel component compliance (upon request)
CE Marking (PED 2014/68/EU)	Pressure Equipment Directive compliance for EU market
3-A Sanitary Standards	Food-grade hygienic design (optional)
NSF/ANSI 61	Drinking water system component safety (optional)
GB/T 12771	Chinese national standard for welded stainless steel tubes

7.1 Inspection and Testing Protocol

Incoming Inspection: Chemical analysis (OES), mechanical testing (tensile, hardness), and dimensional verification of raw tube material.
In-Process Inspection: Coil geometry verification using laser scanning; weld quality assessment via PT/RT; surface finish measurement (profilometry).
Final Inspection: Hydrostatic pressure testing; dimensional audit against drawing; visual and magnetic particle inspection of all welds; passivation verification via ferrite probe.
Documentation: Complete data pack including material certificates, test reports, dimensional drawings, and inspection records delivered with each shipment.

8. Technical Support and Customization

Wenzhou Jixing Metal Materials Co., Ltd. provides comprehensive engineering support including:

Thermal design calculations based on customer process parameters (heat duty, fluid properties, allowable ΔT)
CFD (Computational Fluid Dynamics) simulation of flow patterns within the stirred tank-coil system
Custom coil geometry optimization to match specific vessel dimensions and agitation configurations
Material selection guidance based on corrosion risk assessment
On-site installation guidance and commissioning support

9. Storage, Handling, and Installation Guidelines

Storage: Store in a dry, well-ventilated warehouse. Protect from contact with carbon steel and abrasive materials. Maintain ambient temperature below 40°C.
Handling: Use appropriate lifting equipment to prevent deformation of coil geometry. Avoid dropping or impact loading.
Installation: Mount coil