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Alloy pipes are a type of seamless steel pipe that offer significantly higher 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 alloy pipes far superior to seam steel pipes, leading to their widespread use in industries such as petroleum, aerospace, chemical processing, power generation, boilers, and military applications.
The theoretical weight calculation for an alloy pipe is as follows:
**(Outer Diameter – Wall Thickness) × Wall Thickness × 0.02483 = Weight per meter**
Common materials used in alloy tubes include: 16–50Mn, 27SiMn, 20–40Cr, 12–42CrMo, 16Mn, 12Cr1MoV, T91, 27SiMn, 30CrMo, 15CrMo, 20G, Cr9Mo, 10CrMo910, 15Mo3, 15CrMoV, 35CrMoV, and 45CrMo.
Alloy tubes can be classified based on their application. For example, palladium alloy tubes are specifically used for hydrogen purification. The principle behind this process involves passing impure hydrogen into one side of the palladium tube at temperatures between 300–500°C. Hydrogen molecules are adsorbed onto the surface of the palladium. Since palladium’s 4d electron layer is short by two electrons, it forms unstable bonds with hydrogen, allowing the gas to dissociate into protons. These protons can then pass through the palladium lattice, recombine with electrons on the other side, and form pure hydrogen gas. However, undissociated gases cannot permeate, making the palladium tube effective for obtaining high-purity hydrogen.
Despite its unique hydrogen permeation properties, pure palladium has poor mechanical strength, is prone to oxidation at high temperatures, and has a low recrystallization temperature, which can lead to deformation and embrittlement. To overcome these issues, palladium is often alloyed with elements from Group IB and Group VIII, such as silver, to improve its mechanical and thermal stability. In high-quality carbon structural steel and alloy structural steel hot-rolled seamless pipes used in shells and shafts, silver typically makes up 20–30% of the composition, while other elements like gold are present in smaller amounts (less than 5%).
The hydrogen permeation rate through palladium alloys depends on several factors, including temperature, membrane thickness, and the pressure difference between the raw hydrogen and purified hydrogen sides. Increasing temperature or pressure and reducing membrane thickness can enhance permeability. However, higher temperatures may reduce the tensile strength of the membrane, so the typical operating temperature for palladium tubes is around 450°C. Certain impurities, such as mercury, arsenic, halides, oil vapor, sulfur- and ammonia-containing compounds, and dust, can poison the palladium and damage the membrane. Palladium alloys can be manufactured into tubes or membranes for various applications.
In addition to industrial uses, alloy pipes also find applications in construction and automotive sectors. For example, ABS alloy pipes, combined with special cold-melt adhesives, are widely used in building water supply systems and central air conditioning. PC/ABS alloys are commonly used in automobile exterior parts, such as wheel covers, mirror housings, and taillight covers. These materials offer excellent formability, making them suitable for large automotive components like fenders.
As an essential part of steel products, alloy pipes are generally divided into two categories: seamless steel pipes (made from round billets) and welded steel pipes (formed from plates or strips), depending on their manufacturing processes and raw material shapes.