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Application of SLM 3D-Printed TA2 Commercially Pure Titanium Micro-Channel Heat Exchange Modules for Seawater Desalination: A Comparison with Ti6Al4V and Refractory Metals (Tantalum, Molybdenum, C103)
Core heat exchange modules for large-scale island reverse osmosis desalination systems and multi-stage flash (MSF) condensers must operate while continuously immersed in high-temperature (90°C), high-salinity seawater. They are subjected to severe chloride ion corrosion, cavitation erosion, and high-pressure fluid impacts (up to 10 MPa). Traditional stainless steel and copper alloy heat exchangers typically suffer from corrosion-induced leakage within one to two years, leading to frequent shutdowns and high maintenance costs. SLM 3D printing enables the monolithic fabrication of TA2 commercially pure titanium components featuring intricate, millimeter-scale staggered micro-channel heat exchange cavities—overcoming the manufacturing limitations of traditional machining regarding dense, complex flow paths. In the field of marine heat exchange equipment, TA2 titanium has emerged as the premier material choice for system upgrades. Compared to Ti6Al4V alloys and refractory metals (such as tantalum, molybdenum, and niobium), TA2 offers key advantages: a uniform and stable passivation layer, immunity to selective alloying-element corrosion, and lower residual printing stresses.
3D-printed heat exchange components made from standard industrial metals face significant service-life failures. 316L stainless steel heat exchangers exhibit a critical pitting temperature of only 15°C; in chloride-rich seawater environments, they rapidly develop crevice corrosion and perforation leaks, resulting in a service life of less than 24 months. While 3D-printed copper alloys offer high thermal conductivity, their seawater corrosion resistance is extremely poor; electrochemical corrosion in seawater causes continuous thinning of tube walls, making them highly prone to bursting under high-pressure conditions. Aluminum alloy components suffer from severe oxidation and spalling in high-temperature seawater, with rapidly declining pressure-bearing strength, limiting their use to low-pressure auxiliary piping. Carbon steel components undergo rapid, widespread rusting, rendering them completely unsuitable for marine desalination environments. Conventional metals fail to achieve long-term, maintenance-free operation; in contrast, TA2 pure titanium—relying on its naturally formed, dense titanium dioxide passivation layer—maintains an annual corrosion rate of less than 0.0025 mm/year, offering corrosion resistance that vastly outperforms all standard structural metals. Comparative analyses were repeatedly conducted against rare metal systems such as Ti6Al4V, tantalum, molybdenum, and C103 niobium alloy. Ti6Al4V alloy, containing aluminum and vanadium, is susceptible to selective corrosion of minor alloy phases during long-term exposure to high-temperature, high-salinity environments; its passivation film integrity is inferior to that of unalloyed TA2 pure titanium, posing a risk of localized pitting during long-term service. While tantalum offers industry-leading resistance to seawater corrosion—remaining virtually unaffected by saline media—its powder costs eight times that of pure titanium, making material expenses for large heat-exchange chambers prohibitively high; furthermore, shrinkage during printing is difficult to control, making large modules highly prone to deformation and warping. Molybdenum exhibits outstanding high-temperature resistance but undergoes continuous dissolution via soluble molybdate formation in chloride-rich environments, resulting in corrosion rates far exceeding those of pure titanium; additionally, its inherent low-temperature brittleness makes it prone to cracking under thermal cycling. C103 niobium alloy offers distinct advantages in radiation and high-temperature resistance; however, its passivation film is susceptible to damage from marine microorganism attachment during prolonged immersion in concentrated seawater—resulting in poorer biofouling resistance compared to TA2 pure titanium—and the scarcity of raw materials limits its large-scale engineering application. Overall, for heat exchange applications involving highly corrosive seawater at temperatures ranging from ambient to 100°C, 3D-printed TA2 pure titanium offers a superior balance of cost-effectiveness and operational stability compared to the aforementioned rare metals and titanium alloys.
Compared to other titanium-based additive manufacturing materials, SLM-printed TA2 pure titanium offers unique advantages: extremely low residual printing stress, excellent ductility, and a uniform, single-composition passivation film. In its as-printed state, the material achieves a density exceeding 99.7% and can be deployed in corrosive environments without complex heat treatment. It enables the precise design of ultra-fine, interconnected micro-channels (0.5–1 mm), increasing heat exchange surface area by 45% and heat transfer efficiency by 15% compared to traditional tube-bundle structures, while withstanding high-pressure (10 MPa) seawater circulation without leakage. TA2 does not release aluminum or vanadium ions, ensuring the desalinated water remains free from heavy-metal contamination and fully complies with sanitary standards for island drinking water—a key advantage over Ti6Al4V alloy.
Currently, 3D-printed TA2 heat exchange modules have been deployed in large numbers for fixed seawater desalination projects on islands in the South China Sea. These modules have extended the maintenance-free operational lifespan to over 15 years, reduced the frequency of downtime for inspections and repairs by 70%, and lowered overall operation and maintenance costs by 55%. Existing limitations include a lower tensile strength compared to Ti6Al4V—necessitating thicker structural walls for ultra-high-pressure applications—and a lower high-temperature limit than C103 or molybdenum-based refractory metals. Future developments will focus on enhancing the fouling resistance of the passivation layer through surface anodization and improving the forming efficiency of large cavities by optimizing powder-bed printing processes. TA2 is poised to gradually replace stainless steel and copper alloy heat exchange components, as well as expensive tantalum-based tes.
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