Stainless Steel Coil Tube (盘管) — Internal Heat Exchanger for Agitated Vessels

1. Product Overview

The Stainless Steel Coil Tube (盘管, Coiltube) is a precision-engineered helical heat exchange element designed for integration into agitated reactor vessels, mixing tanks, and process vessels where controlled thermal management is critical. Manufactured by Wenzhou Jixing Metal Materials Co., Ltd., this product serves as an internal heat transfer surface within stirred tanks, enabling efficient heating or cooling of process fluids through the annular space between the coil and the vessel wall or through direct immersion in the working medium.

The coil tube design is particularly significant in the context of improved frame-type combined paddle internal coil stirred tanks, where numerical simulation studies have demonstrated that the coexistence of coil heat exchange elements and complex impeller geometries creates intricate flow field interactions. These interactions directly influence mixing efficiency, heat transfer coefficients, and overall process performance. Understanding these coupled phenomena is essential for optimizing reactor design in pharmaceutical, chemical, and food processing industries.

Key Design Principle: The coil tube functions as both a thermal management component and a flow-modifying element within the vessel. Its helical geometry enhances turbulence near the vessel wall, promoting radial mixing and reducing dead zones — a finding validated through Computational Fluid Dynamics (CFD) numerical simulation of flow fields inside frame-type combined paddle stirred tanks with internal coils.

2. Material & Properties

The coil tubes are fabricated from high-grade austenitic stainless steels selected for their exceptional corrosion resistance, thermal conductivity, and mechanical integrity under cyclic thermal loading conditions.

2.1 Primary Alloy Grades

SAE 304 / AISI 304 (1.4301): General-purpose austenitic stainless steel with 18% Chromium (Cr) and 8% Nickel (Ni). Suitable for moderate corrosion environments, food-grade applications, and temperatures up to 870°C.
SAE 316 / AISI 316 (1.4401): Enhanced corrosion resistance due to 2–3% Molybdenum (Mo) addition. Preferred for chemical processing, pharmaceutical, and marine environments where chloride-induced pitting must be prevented.
SAE 321 / AISI 321 (1.4541): Titanium-stabilized grade with excellent resistance to intergranular corrosion at elevated temperatures (up to 870°C). Ideal for high-temperature heat exchange applications.
SAE 316L / AISI 316L (1.4404): Low-carbon variant of 316L with carbon content ≤ 0.03%, providing superior weldability and resistance to sensitization during welding operations.

2.2 Mechanical and Thermal Properties (Typical — AISI 316L)

Property	Symbol	Value	Unit
Tensile Strength (抗拉强度)	σ_b	≥ 515	MPa
Yield Strength (屈服强度)	σ_0.2	≥ 205	MPa
Elongation (延伸率)	A₅₀	≥ 40	%
Thermal Conductivity (导热系数)	λ	16.3	W/(m·K)
Thermal Expansion Coefficient (热膨胀系数)	α	17.1	× 10^-6 /K
Density (密度)	ρ	8.00	g/cm³
Specific Heat Capacity (比热容)	c_p	500	J/(kg·K)
Maximum Service Temperature (最高使用温度)	T_max	870	°C
Corrosion Potential in HCl 1% (25°C) (耐蚀电位)	E_corr	−45	mV vs. SCE

3. Specifications

The following table summarizes the dimensional and performance specifications for the stainless steel coil tube product line. Custom configurations are available upon request to meet specific reactor vessel geometries and process requirements.

Parameter	Specification	Notes
Outer Diameter (OD, 外径)	Φ12 mm – Φ108 mm	Standard sizes; custom OD available
Wall Thickness (壁厚)	0.5 mm – 6.0 mm	Selected based on pressure rating and thermal duty
Coil Pitch (螺距)	15 mm – 200 mm	Determined by vessel diameter and desired heat transfer area
Coil Diameter (盘管直径)	Φ200 mm – Φ3000 mm	Matched to vessel internal diameter (typically 70–80% of vessel ID)
Coil Length / Turns (盘管长度/圈数)	5 m – 500 m (up to 500+ turns)	Custom length per thermal load calculation
Surface Finish (表面光洁度)	Ra 0.4 μm – Ra 1.6 μm (electropolished available: Ra ≤ 0.2 μm)	Electropolishing enhances corrosion resistance and reduces fouling
Working Pressure (工作压力)	0.6 MPa – 6.4 MPa (6 bar – 64 bar)	Pressure-tested to 1.5× working pressure
Design Temperature Range (设计温度范围)	−196°C to +870°C	Dependent on alloy grade selected
Connection Types (连接方式)	Flanged (法兰), Threaded (螺纹), Welded (焊接), Tri-Clamp (快装)	ASME B16.5 / EN 1092-1 flange standards
Heat Transfer Coefficient (传热系数)	U = 800 – 2,500 W/(m²·K)	Depends on fluid properties, flow velocity, and fouling factor
Applicable Standards (适用标准)	ASTM A213, ASTM A269, EN 10216-5, GB/T 14976	Tube material and fabrication standards

4. Manufacturing Process

The production of stainless steel coil tubes follows a rigorous multi-stage manufacturing workflow to ensure dimensional accuracy, metallurgical integrity, and long-term service reliability.

4.1 Process Flow

Raw Material Selection & Inspection (原材料检验):
Stainless steel seamless tubes or welded tubes conforming to ASTM A213 / A269 / EN 10216-5 are procured. Each batch undergoes chemical composition analysis (spectrometry), mechanical property testing (tensile, hardness, impact), and ultrasonic flaw detection (UT) to verify compliance with material specifications.
Cold Bending / Coil Forming (冷弯成型):
Tubes are cold-formed into helical coil shapes using precision CNC-controlled bending machines. The bending process is carefully controlled to avoid excessive work hardening, plastic deformation, or cross-sectional ovality. Bending dies are selected to minimize wall thinning at the inner bend radius, maintaining a minimum wall thickness ratio of ≥ 90% of the original wall thickness.
Solution Annealing (固溶退火):
Following cold bending, the formed coil is subjected to solution annealing at 1050°C – 1150°C followed by rapid water quenching. This process relieves residual stresses introduced during forming, restores full austenitic microstructure, and maximizes corrosion resistance by dissolving any carbide precipitation at grain boundaries.
Surface Treatment & Cleaning (表面处理与清洗):
The annealed coil undergoes acid pickling (酸洗) to remove oxide scale, followed by optional electropolishing (电解抛光) for critical applications. Electropolishing removes the outer 25–75 μm of material, resulting in a smooth, passive, and highly corrosion-resistant surface with Ra values as low as 0.2 μm.
Assembly & Welding (组装与焊接):
Support rings, inlet/outlet headers, and mounting brackets are welded to the coil using Gas Tungsten Arc Welding (GTAW / TIG) or Orbital Welding (自动轨道焊) techniques. Weld seams are inspected via Radiographic Testing (RT) or Penetrant Testing (PT) to ensure full penetration and absence of defects.
Pressure Testing & Leak Detection (压力试验与泄漏检测):
Each completed coil assembly is hydrostatically pressure-tested to 1.5× the maximum working pressure for a minimum hold time of 30 minutes. Leak testing is performed using Helium Mass Spectrometry (氦质谱检漏) for high-integrity applications, achieving leak rates below 1 × 10^-9 Pa·m³/s.
Final Inspection & Documentation (最终检验与文档):
Dimensional verification, visual inspection, and material traceability documentation are compiled. A complete Material Test Certificate (MTC, 材质证明书) in accordance with EN 10204 3.1 / 3.2 is issued with each shipment.

4.2 Key Quality Control Measures

Online monitoring of bending radius, pitch accuracy (±0.5 mm tolerance), and coil concentricity (≤ 1% of coil diameter)
Spectroscopic verification of weld chemistry matching base material
100% visual inspection of all weld seams; 100% RT for critical service coils
Post-weld stress relief annealing where thermal cycling fatigue is a concern

5. Applications

The stainless steel coil tube is a versatile heat exchange component deployed across a wide range of industrial sectors. Its integration into stirred tanks and reactor vessels is particularly well-documented in the context of improved frame-type combined paddle internal coil stirred tank designs, where CFD numerical simulations have validated the synergistic effects between coil geometry and impeller-induced flow fields.

5.1 Primary Application Areas

Pharmaceutical Manufacturing (制药行业):
Internal heating/cooling coils in stainless steel reactor vessels for drug synthesis, crystallization, fermentation, and sterilization-in-place (SIP) processes. Electropolished surfaces (Ra ≤ 0.2 μm) meet FDA and EU GMP requirements for sanitary processing.
Chemical Processing (化工行业):
Heat management in polymerization reactors, esterification vessels, and continuous stirred-tank reactors (CSTRs). AISI 316L coils withstand aggressive chemical media including acids, alkalis, and organic solvents.
Food & Beverage Industry (食品饮料行业):
Temperature control in mixing tanks for dairy processing, juice concentration, beer brewing, and confectionery production. Sanitary design with tri-clamp connections facilitates CIP (Clean-in-Place) operations.
Petrochemical & Refining (石油化工行业):
Heat exchange in crude oil fractionation, catalytic cracking, and hydrotreating reactor feed preheating systems. High-pressure rated coils (up to 64 bar) handle demanding process conditions.
Biotechnology & Bioengineering (生物技术):
Precision temperature control in bioreactors for cell culture, enzyme production, and vaccine manufacturing. Tight thermal uniformity (±0.5°C) is achieved through optimized coil pitch and flow distribution.
Environmental & Wastewater Treatment (环保与污水处理):
Thermal management in anaerobic digestion reactors and biochemical treatment vessels where temperature control is essential for microbial activity optimization.

5.2 Flow Field Enhancement in Stirred Tanks

As demonstrated in numerical simulation studies of improved frame-type combined paddle internal coil stirred tanks, the presence of the coil tube significantly modifies the internal flow field:

The helical coil geometry acts as a flow guide, promoting radial mixing and reducing stagnant zones near the vessel wall and bottom
Interaction between the coil and impeller-generated vortices enhances turbulence intensity, increasing the overall heat transfer coefficient by 15–35%
The coil provides additional surface area for heat exchange while simultaneously serving as a structural element that improves vessel rigidity
Optimal coil pitch-to-diameter ratio (typically 0.15–0.30) minimizes flow obstruction while maximizing thermal performance

6. Quality Certifications & Standards Compliance

All products manufactured by Wenzhou Jixing Metal Materials Co., Ltd. conform to international quality management and industry-specific standards, ensuring traceability, reliability, and regulatory compliance.

6.1 Management System Certifications

ISO 9001:2015 — Quality Management System (