Technical Analysis of ASME SB-338 Grade 2 Titanium Extruded Finned Tube with Aluminum 1060 Fin
Technical Analysis of ASME SB-338 Grade 2 Titanium Base Tube with Aluminum 1060 Extruded Finned Tube
1. Introduction
Under heat exchange working conditions with corrosive media and high thermal load, the selection of tube materials directly determines the service life and operational efficiency of heat exchange equipment. The extruded finned tube (DR type) is integrally formed by mechanical compounding and rolling of fin material and base tube, achieving a seamless combination between fins and the base tube. Adopting ASME SB-338 Grade 2 titanium tube as the base tube and aluminum 1060 extruded finned tube as the fin material gives full play to the excellent corrosion resistance of titanium and the superior thermal conductivity of pure aluminum. It serves as an ideal heat transfer component for seawater cooling, chemical processing, and air-cooled heat exchangers.
2. Base Material Standards and Core Properties
2.1 ASME SB-338 Grade 2 Titanium Base Tube (Pressure-bearing and Corrosion-resistant Layer for Process Media)
ASME SB-338 is an international standard for seamless titanium tubes dedicated to heat exchangers and condensers. Grade 2 commercially pure titanium is the most widely used titanium grade in heat exchange applications, with a titanium content (balance) of ≥99.0% and strictly controlled impurities: O ≤0.25%, Fe ≤0.30%, N ≤0.03%, H ≤0.015%.
Corrosion Resistance: A dense and stable TiO₂ passivation film forms spontaneously on the titanium surface, providing reliable resistance to seawater, brine, dilute hydrochloric acid, weak acid, sulfur-containing media, and salt spray. It fundamentally eliminates pitting corrosion and crevice corrosion commonly found in 304/316 stainless steel, enabling long-term service in high-chloride fluid environments.
Mechanical and Pressure Resistance: The tube features a tensile strength ≥345 MPa, yield strength ≥275 MPa, and elongation after fracture ≥20%. With excellent plasticity, it supports U-bending and coiling processing. The applicable temperature range is from -50℃ to 300℃, allowing stable operation under medium and high-pressure process fluids without strength attenuation under thermal cycling conditions.
Fluid Flow Performance: The seamless titanium tube has a smooth inner wall that resists fouling deposition and reduces medium pressure drop, effectively extending equipment cleaning cycles. The seamless structure eliminates leakage risks and meets safety specifications for chemical and marine equipment.
2.2 Aluminum 1060 High-purity Aluminum Extruded Fins (High-efficiency Heat Dissipation Layer for Air Side)
Aluminum 1060 is a high-purity industrial aluminum with an aluminum content ≥99.6%. Free of alloying strengthening elements, it possesses excellent plasticity and is highly suitable for cold extrusion forming of integral fins.
Superior Thermal Conductivity: With a thermal conductivity of 230~237 W/(m·K), it far exceeds that of titanium, carbon steel, and stainless steel, effectively compensating for the low thermal conductivity of titanium and maximizing air-side heat transfer efficiency.
Excellent Cold Extrudability: Its superior ductility prevents cracking and springback during cold plastic deformation. Continuous spiral fins can be integrally formed in one pass, with fin roots and the outer aluminum sleeve forming a monolithic metal structure.
Lightweight and Weather Resistance: With a density of only 2.71 g/cm³, it reduces the overall weight of heat exchangers by approximately 60% compared with copper or copper-nickel finned tubes. The in-situ alumina film provides reliable resistance to atmospheric and coastal salt spray corrosion. The recommended long-term continuous operating temperature is ≤200℃, fully matching the service temperature limit of extruded fins.
Economic Advantages: Virgin 1060 aluminum raw materials are sufficiently supplied with mature extrusion manufacturing processes, significantly reducing the production cost of heat exchange equipment compared with titanium or copper fins.
3. Forming Principle of Titanium-Aluminum Bimetallic Cold Extrusion Process
The ASME SB-338 Gr.2 / 1060 aluminum extruded finned tube adopts an integrated bimetallic sleeve cold extrusion process, which is fundamentally different from conventional single-metal extrusion, wrapped fin, and high-frequency welded finned tubes. The complete manufacturing procedure is as follows:
| Process Step | Process Description |
|---|---|
| Pre-treatment and Assembly | Qualified seamless titanium tubes complying with ASME SB-338 standards are cut and sleeved with thick-walled 1060 aluminum sleeves for concentric positioning. The outer titanium tube surface and inner aluminum sleeve surface are degreased and polished to remove interface impurities and ensure tight bonding. |
| Three-roll Cold Extrusion Forming | The assembled bimetallic sleeve is fed into a dedicated three-roll extrusion unit. High-pressure cold plastic deformation is applied by rotating rolls, forcing the outer 1060 aluminum material to flow outward along the mold channel and form continuous spiral fins in one integral forming process. The aluminum sleeve fully covers the outer surface of the titanium base tube, with bare titanium tube ends reserved for tube sheet welding. |
| Sizing, Straightening and Finishing | The extruded tubes are online-straightened to eliminate bending deformation, cut to fixed lengths, and deburred at fin edges. The exposed titanium tube ends are polished to meet welding and tube expansion requirements. |
After the assembly of titanium and aluminum sleeves to form smooth bimetallic billets, low-temperature combined stress-relief annealing is mandatory before rolling, and direct rolling without annealing is prohibited. Only fully soft-state raw materials with minimal deformation and sufficient process verification are exempted for experimental samples; pre-annealing is strictly enforced for mass production. The annealing purposes are to soften the outer 1060 aluminum layer, eliminate assembly residual stress, and reduce interfacial stress between titanium and aluminum, so as to avoid rolling cracking, fin root tearing, and interface delamination. High-temperature annealing above 450℃ is strictly prohibited, as excessive temperature induces the formation of brittle intermetallic TiAl₃ phases at the titanium-aluminum interface, sharply reducing interfacial shear strength and causing unqualified fin pull-off strength.
Core Structural Characteristics of Extrusion Process
The fins and outer aluminum sleeve form a monolithic homogeneous metal structure without welds or winding gaps, eliminating the risk of loose or falling fin roots.
High-pressure extrusion achieves interference fit between the aluminum liner and titanium tube outer wall with no air gaps at the interface, resulting in extremely low contact thermal resistance and superior heat transfer performance compared with wrapped finned tubes.
The full 1060 aluminum cladding eliminates gaps between dissimilar metals, preventing crevice corrosion induced by accumulated contaminants. It inhibits the formation of continuous electrolyte films under dew and salt spray environments, structurally mitigating the probability and severity of galvanic corrosion between titanium and aluminum.
4. Comprehensive Advantages of SB-338 Gr.2 Titanium-based 1060 Aluminum Extruded Finned Tubes
| Advantage Item | Detailed Explanation |
|---|---|
| 4.1 Complementary Material Performance and Functional Division | The Grade 2 titanium base tube undertakes the pressure bearing and anti-corrosion function for process fluids, preventing tube perforation and leakage against seawater and chemical corrosive media. The integrally extruded 1060 aluminum fins achieve high-efficiency air-side heat dissipation, compensating for the low thermal conductivity of pure titanium. Meanwhile, the lightweight structure reduces the load on heat exchanger frames and supporting structures. |
| 4.2 Integrated Extrusion Structure Eliminates Heat Transfer Bottlenecks | Different from the inevitable air-gap thermal resistance of wrapped and embedded fins, the cold extrusion process realizes 360° tight interference bonding between aluminum and titanium tube outer walls, enabling unobstructed heat conduction from the titanium tube wall to the entire fin surface. Under typical air-cooled conditions, the overall heat transfer coefficient is 25%~40% higher than that of traditional wrapped finned tubes, allowing smaller equipment footprint and higher heat exchange efficiency under equal thermal load. |
| 4.3 Structural Suppression of Galvanic Corrosion | Titanium and aluminum have significant differences in electrode potential, which easily causes galvanic corrosion when directly contacted with condensed water or salt spray. The fully cladded 1060 aluminum sleeve completely isolates the titanium substrate from external exposure, preventing electrolyte penetration at the bimetallic interface. This structure effectively avoids root perforation failure in long-term coastal and high-humidity chemical plant service. |
| 4.4 High Mechanical Strength and Excellent Resistance to Harsh Operating Conditions | The integrally extruded spiral fins feature thick root sections and high structural rigidity, resisting long-term fan vibration, airflow scouring, and high-pressure water jet cleaning. No fin warping, cracking or detachment occurs under frequent start-stop and thermal cycling conditions, adapting to 24-hour continuous industrial production. |
| 4.5 Wide Working Condition Adaptability | With titanium tube resistance to acid, alkali, chloride and sulfur-containing corrosive media, high-efficiency air cooling of aluminum fins, and vibration-resistant extrusion structure, this single product covers multiple severe working scenarios, including seawater cooling, acidic process medium cooling, sour gas air cooling, coastal power plant closed cooling, and industrial waste heat recovery, without frequent material replacement. |
5. Main Industrial Application Scenarios
5.1 Marine Engineering and Seawater Desalination Equipment
Widely applied in seawater air coolers, offshore platform lubricating oil coolers, and seawater desalination condensing units. Grade 2 titanium resists high-concentration chloride corrosion in seawater, while the lightweight extruded aluminum fins reduce platform dead load, solving the problem of rapid failure of carbon steel and stainless steel finned tubes within 1~3 years in marine environments.
5.2 Oil and Gas Desulfurization Systems
Suitable for sour gas air coolers and sulfur-containing crude oil cooling equipment. Process media containing H₂S and chloride ions easily cause sulfide stress cracking in ordinary carbon steel. The SB-338 Gr.2 titanium tube meets NACE MR0175 sulfur-resistant standards, ensuring long-term stable operation of extrusion composite structures.
5.3 Fine Chemical and Pharmaceutical Anti-corrosion Cooling
Applied in dilute acid and salt solution process coolers and pharmaceutical sterile heat exchange units. Titanium releases no heavy metal precipitates and meets sanitary standards. The seamless integral fin structure has no dead corners for contamination accumulation, facilitating cleaning and sterilization for intermittent chemical and pharmaceutical production.
5.4 Coastal Power Plants and Power Generation Units
Used for generator hydrogen coolers, turbine oil air coolers, and power plant seawater closed circulating cooling systems. The aluminum fins withstand coastal atmospheric salt spray corrosion, while the titanium base tube resists chloride-induced corrosion in circulating cooling water.
5.5 Industrial Waste Heat Recovery Equipment
Suitable for waste heat recovery heat exchangers in chemical and electroplating wastewater systems containing trace acid, alkali and salt impurities. The titanium tube provides reliable medium corrosion resistance, and the high-thermal-conductivity extruded fins significantly improve waste heat recovery efficiency and reduce system energy consumption.
6. Conclusion
The combination of ASME SB-338 Grade 2 titanium base tube and Aluminum 1060 extruded finned tube integrally extruded fins forms a high-end heat transfer solution integrating superior corrosion resistance, high heat transfer efficiency and long service life. The cold extrusion process structurally solves three core defects of traditional finned tubes: high contact thermal resistance, fin detachment, and dissimilar metal galvanic corrosion. The titanium substrate ensures safe pressure bearing and anti-corrosion performance for corrosive process media, while 1060 high-purity aluminum fins provide efficient air-side heat dissipation and lightweight advantages with perfect performance complementarity.