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Application of CB752 Alloy as Lining for High-Temperature Corrosive Chemical Cracking Furnaces and Comparison with Rare Corrosion-Resistant Refractory Metals
Linings for high-temperature cracking furnaces and gas-phase synthesis reactors in the petrochemical and fine chemical industries are subjected to prolonged exposure to temperatures of 950–1200°C and severe corrosion from hydrogen sulfide, hydrogen chloride, and high-temperature hydrocarbon media, as well as cyclic thermal shock from startups and shutdowns. Traditional stainless steels and nickel-based alloys frequently suffer from corrosion-induced perforation, while rare corrosion-resistant metals such as tantalum, zirconium, and molybdenum are prohibitively expensive and difficult to form. CB752 niobium-based alloy offers a balanced combination of high-temperature resistance, resistance to corrosion by high-temperature media, thermal shock resistance, and suitability for large-scale welded fabrication. Positioned between standard corrosion-resistant alloys and high-end rare corrosion-resistant metals, it has become the preferred cost-effective material for linings in high-end, high-temperature corrosive chemical equipment, demonstrating significant value for widespread engineering application through repeated comparisons with rare metals.
Standard industrial pure metals and conventional corrosion-resistant alloys exhibit significant shortcomings under cracking furnace operating conditions. While 310S and Hastelloy (nickel-based corrosion-resistant alloys) are traditional materials for high-temperature furnaces, they suffer from intergranular corrosion and sulfidation embrittlement in chlorine- and sulfur-containing atmospheres at 1000°C, leading to lining perforation and leakage, with maintenance intervals of less than 18 months. Ordinary carbon steel and chromium-molybdenum alloy steel undergo severe high-temperature oxidation and scaling, resulting in extremely high corrosion rates. Pure copper and pure aluminum lack sufficient high-temperature resistance and are entirely unsuitable for high-temperature cracking operations. Although pure niobium possesses excellent inherent corrosion resistance, its high-temperature strength is relatively low; it is prone to deformation and indentation under negative furnace pressure and gas flow erosion, resulting in insufficient structural stability for the lining, which prevents its use as a standalone pressure-bearing lining.
A comparison with four rare corrosion-resistant metals commonly used in the chemical industry—tantalum, zirconium, molybdenum, and hafnium—highlights the outstanding overall cost-performance advantage of the CB752 alloy. Ruthenium and tantalum offer excellent resistance to high-temperature corrosion from various strong acids and possess exceptional chemical stability; however, tantalum is a scarce metal—equipment manufacturing costs exceed five times that of CB752, and its high density results in excessive self-weight for large liners, making lifting and installation difficult. Zirconium exhibits excellent resistance to sulfur and chlorine corrosion but has an upper operating temperature limit of 900°C; it fails rapidly due to hydrogenation when overheated and suffers significant loss of high-temperature strength, rendering it unsuitable for cracking processes exceeding 1100°C. Molybdenum meets high-temperature requirements but is prone to forming volatile sulfides in sulfur-containing atmospheres, leading to continuous corrosion and severe wall thinning during long-term operation; furthermore, the corrosion resistance of molybdenum welded joints is significantly compromised, making liner welds susceptible to preferential corrosion and leakage. Hafnium offers the best overall combination of corrosion and high-temperature resistance, yet its limited production capacity and extremely high processing costs restrict its use to small-scale laboratory high-pressure reactors, making it unfeasible for large-scale industrial furnace applications. CB752 incorporates tungsten to enhance high-temperature structural strength and zirconium to inhibit intergranular corrosion and resist attack by sulfur and chlorine media; it combines corrosion resistance comparable to rare corrosion-resistant metals with the capability for large-scale welded cylinder fabrication, offering controllable costs suitable for continuous industrial production.
A comparison of niobium-based alloys highlights the distinct advantages of CB752 for chemical processing applications: Nb-1Zr offers corrosion resistance similar to CB752 but lacks sufficient high-temperature rigidity, making large liners prone to deformation and bulging; NbTa alloys provide superior corrosion resistance but entail high melting costs and poor batch-to-batch plate consistency; high-strength niobium alloys suffer from significantly reduced corrosion resistance in welded areas, turning welds into weak points vulnerable to corrosion. CB752 plates can be rolled into large, seamless cylindrical liners using mature longitudinal and circumferential welding techniques; the material exhibits an annual corrosion rate of less than 0.003 mm in sulfur- and chlorine-containing atmospheres at 1100°C and resists cracking under thermal shock from thermal cycling. Its pressure-bearing and deformation-resistance capabilities meet the requirements for cracking furnace operations involving negative and slight positive pressures, allowing for extended maintenance intervals of 8 to 10 years and significantly reduced operation and maintenance costs. Currently, CB752 liners have achieved industrial application in high-temperature cracking reactors for coal-to-olefins processes and high-temperature synthesis furnaces in the fine fluorine chemical industry. They replace nickel-based alloy liners (which require frequent maintenance) and tantalum-lined equipment (which is costly), resulting in a 45% reduction in the equipment's total lifecycle cost. A current limitation is that its corrosion resistance under the extreme conditions of ultra-high-concentration hydrofluoric acid is inferior to that of tantalum, making it unsuitable for the most severely corrosive systems. Future development trends include: first, using surface passivation and ceramic diffusion layer modification to narrow the gap in ultimate corrosion resistance compared to rare metals like tantalum and hafnium; second, reducing costs through continuous rolling of large-scale cylindrical shells and automated welding processes; and third, expanding applications to high-temperature waste gasification and hazardous waste incineration furnaces—gradually replacing traditional corrosion-resistant alloys and expensive rare-metal liners—to open up markets for high-end, corrosion-resistant chemical materials.
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