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Alloy pipes are a type of seamless steel pipe that offer significantly better performance compared to standard seamless steel pipes. This is due to their higher chromium content, which enhances their high-temperature resistance, low-temperature resistance, and corrosion resistance. These properties make them far superior to seam steel pipes, and as a result, alloy pipes are widely used in industries such as petroleum, aerospace, chemical processing, power generation, boiler systems, and military applications.
In terms of theoretical weight calculation for alloy pipes, the formula is: (outer diameter - wall thickness) × wall thickness × 0.02483 = weight per meter. Common materials used for alloy tubes include grades like 16-50Mn, 27SiMn, 20-40Cr, 12-42CrMo, 16Mn, 12Cr1MoV, T91, 27SiMn, 30CrMo, 15CrMo, 20G, Cr9Mo, 10CrMo910, 15Mo3, 15CrMoV, 35CrMoV, and 45CrMo.
Palladium alloy tubes are specifically designed for hydrogen purification. The process involves passing impure hydrogen into one side of the palladium tube at temperatures between 300°C and 500°C. Hydrogen molecules are adsorbed on the surface of the palladium, where they dissociate into protons under the influence of the metal. Palladium has a unique ability to form unstable bonds with hydrogen due to its incomplete 4d electron layer. These protons then diffuse through the palladium lattice and recombine on the other side to form pure hydrogen gas.
Although palladium has excellent hydrogen permeation properties, pure palladium is not suitable for use as a membrane due to its poor mechanical strength, tendency to oxidize at high temperatures, and low recrystallization temperature, which can lead to deformation and embrittlement. To overcome these issues, palladium alloys are created by adding small amounts of elements from Group IB and Group VIII, such as silver. In high-quality carbon structural steel and alloy structural steel hot-rolled seamless pipes, silver typically constitutes 20–30% of the composition, while other elements like gold make up less than 5%.
The hydrogen permeation rate through palladium alloys depends on several factors, including temperature, membrane thickness, and the pressure difference between the feed and purified hydrogen sides. Increasing the temperature or the pressure difference and reducing the membrane thickness can enhance the permeation rate. However, higher temperatures may reduce the tensile strength of the membrane. Therefore, the operating temperature is usually kept around 450°C. Certain impurities—such as mercury, arsenic, halides, oil vapor, sulfur compounds, ammonia, and dust—can poison the palladium, leading to reduced gas permeability or even membrane failure. Palladium alloys can be manufactured into either tubes (palladium tubes) or membranes (palladium membranes).
In addition to industrial applications, alloy pipes also find use in construction and automotive sectors. For example, ABS alloy pipes combined with special cold-melt adhesives are commonly used in building water supply systems and central air conditioning. PC/ABS alloys are also utilized in manufacturing car exterior parts like wheel covers, mirror housings, and taillight covers. These materials offer good formability and are ideal for producing large automotive components such as fenders.
As an essential part of steel products, alloy pipes are generally classified into two types based on their manufacturing processes: seamless steel pipes (made from round billets) and welded steel pipes (produced from plates or strips). This classification helps in selecting the most appropriate type depending on the application requirements.