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Application and Development Prospect of Ti6Al4V Alloy in Core Pressure-Bearing Components of Seawater Desalination

High-pressure reverse osmosis membrane shells, seawater pressurization pipelines, corrosion-resistant valve bodies, and heat exchange pressure-bearing components in seawater desalination equipment are subjected to extreme corrosive conditions such as high salinity seawater, high-pressure osmosis, microbial adhesion, and acid-base micro-alternation. These components must simultaneously possess properties such as resistance to strong seawater corrosion, high pressure resistance, anti-scaling, fatigue resistance, and long service life, which are core guarantees for stable water production in seawater desalination projects. Traditional pure metal materials have poor seawater corrosion resistance, are prone to scaling, and have short service lives, leading to frequent maintenance and increased operating costs. Ordinary titanium alloys have insufficient pressure-bearing capacity and poor formability. In contrast, Ti6Al4V titanium alloy, with its excellent seawater corrosion resistance, high pressure resistance, fatigue resistance, and low surface energy anti-scaling properties, has become a high-end key material for core pressure-bearing components in modern large-scale seawater desalination projects, significantly improving the stability and service life of seawater desalination equipment.

Various pure metals exhibit significant performance shortcomings in seawater desalination conditions. Pure carbon steel and stainless steel are the mainstream materials used in traditional seawater desalination equipment. They are inexpensive and have decent pressure resistance, but their resistance to seawater corrosion is limited. High salinity seawater and chloride ions easily cause pitting corrosion, crevice corrosion, and electrochemical corrosion. Equipment often develops rust perforations and pipeline leaks within 1 to 3 years of operation. Furthermore, the high surface roughness of these metals makes them highly susceptible to the adhesion of seawater scale and microorganisms, frequently clogging membranes and pipelines, requiring regular shutdowns for cleaning and maintenance, resulting in extremely high operating costs. Pure aluminum alloys are lightweight, but have low pressure resistance and poor salt corrosion resistance, rapidly corroding and failing under high-pressure seawater, making them only suitable for low-pressure auxiliary structures. Pure copper has good seawater corrosion resistance, but insufficient pressure resistance, high cost, and excessive weight, making it unsuitable for high-pressure components. Pure titanium (TA2) has excellent seawater corrosion resistance, but its low pressure resistance makes it unsuitable for the demands of high-pressure reverse osmosis seawater desalination, limiting its use to low-pressure pipeline fittings.

Compared to other titanium alloy materials, Ti6Al4V alloy offers irreplaceable comprehensive advantages for seawater desalination equipment. TA15 titanium alloy exhibits strong high-temperature resistance, but its resistance to seawater crevice corrosion is only average, and it is difficult to form, making it challenging to integrally mold large pressure-bearing shells. TC21 high-strength titanium alloy boasts high pressure-bearing strength, but its surface energy is relatively high, making it prone to scale and microbial adhesion, and its anti-scaling performance is weaker than Ti6Al4V. Ti3Al2.5V titanium alloy has excellent corrosion resistance, but its pressure-bearing capacity is insufficient, making it unsuitable for high-pressure reverse osmosis applications. Ti6Al4V alloy, strengthened with aluminum and vanadium composite elements, retains the extreme seawater corrosion resistance of titanium alloys while significantly improving high-pressure bearing capacity and structural rigidity. It also possesses low surface energy, is not prone to scaling, and is not easily adhered to by microorganisms, making it perfectly suited for the complex conditions of high pressure, high corrosion, and easy scaling in seawater desalination.

The core application advantages of Ti6Al4V alloy are particularly prominent. First, it exhibits exceptional resistance to seawater corrosion, capable of withstanding long-term erosion from high concentrations of chloride ions, seawater microorganisms, and alternating acid-base media. The corrosion rate is less than 0.001 mm/a, with virtually no pitting or crevice corrosion. Its corrosion resistance far surpasses that of all industrial pure metals, allowing for a service life of over 15 years. Second, it possesses excellent high-pressure bearing capacity, high tensile strength, and stable structural rigidity. It can withstand the 8-10 MPa high-pressure osmosis load of seawater desalination for extended periods without plastic deformation or the risk of bursting or leakage, making it suitable for large-scale high-pressure reverse osmosis seawater desalination equipment. Third, it exhibits excellent anti-scaling and self-cleaning properties. The dense, smooth alloy surface with low surface energy makes it difficult for seawater scale and marine microorganisms to adhere and accumulate, significantly reducing equipment clogging frequency and lowering downtime for cleaning and maintenance costs. Finally, it boasts excellent fatigue resistance, capable of withstanding the alternating impact of high-pressure water flow for extended periods without fatigue cracks, maintaining structural stability and meeting the requirements for continuous 24-hour operation.

Currently, Ti6Al4V alloy is widely used in large-scale island desalination projects, coastal industrial desalination equipment, and high-pressure membrane housings, pressurization pipelines, corrosion-resistant valve bodies, and heat exchange pressure-bearing components in marine desalination systems, completely replacing traditional stainless steel, carbon steel, and other pure metal materials. Actual test data shows that desalination equipment using Ti6Al4V alloy components reduces maintenance frequency by 70%, significantly reduces equipment downtime losses, increases overall water production efficiency by 15%, and significantly lowers long-term maintenance costs. The main drawback at present is the relatively high manufacturing cost, resulting in low adoption rates in small and medium-sized civilian desalination equipment.

Future industry development trends will mainly focus on cost reduction and efficiency improvement, as well as performance upgrades. This will be achieved through integral forging and rolling processes for large components to improve mass production efficiency and reduce manufacturing costs; through ultra-smooth surface modification technology to further enhance anti-scaling and anti-microbial adhesion properties; and through compositional fine-tuning to improve the alloy's resistance to seawater erosion fatigue. With the large-scale development of the seawater desalination industry, Ti6Al4V alloy will gradually replace traditional pure metal pressure-bearing materials and become the core material for high-end seawater desalination equipment, helping seawater desalination projects to operate stably with low cost, high efficiency and long service life, and alleviating the pressure of global freshwater resource shortage.

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