The 15CrMo boiler tube is manufactured using high-quality carbon structural steel, with specific alloying elements added to enhance its mechanical properties, toughness, and hardenability. Products made from this steel typically require heat treatment processes like normalizing or quenching and tempering. Components produced with this steel often undergo further treatments such as quenching and tempering or surface chemical treatments like carburizing, nitriding, or surface quenching. Therefore, depending on the chemical composition (primarily carbon content), heat treatment methods, and intended use, this type of steel can be categorized into three main types: carburizing, quenching and tempering, and nitriding.
When it comes to high-pressure boiler tubes, they can be classified into different grades. These include high-quality carbon structural steels such as 20G, 20MnG, and 25MnG. There are also various alloy structural steels, such as 15MoG, 20MoG, 12CrMoG, 15CrMoG, 12Cr2MoG, 12CrMoVG, 12Cr3MoVSiTiB, among others. Additionally, commonly used rust and heat-resistant steels like 1Cr18Ni9 and 1Cr18Ni11Nb must undergo hydrostatic testing, flaring, and flattening tests, in addition to ensuring proper chemical composition and mechanical properties. These steel pipes are delivered in a heat-treated state.
There are also specific requirements for the microstructure, grain size, and decarburization layer of the finished steel pipe. In terms of specifications and appearance quality, according to GB5310-95 "Seamless Steel Tubes for High-Pressure Boilers," the outer diameter ranges from 22-530mm, with wall thicknesses varying from 20-70mm. For cold-drawn (cold-rolled) tubes, the outer diameter is 10-108mm, and the wall thickness is between 2.0-13.0mm.
The principle behind purifying hydrogen using a 15CrMo boiler tube involves passing the hydrogen to be purified through one side of the tube at temperatures between 300-500°C. Hydrogen is adsorbed onto the tube's surface, where the 4d electron layer of palladium interacts with hydrogen, forming unstable chemical bonds (a reversible reaction). Under the influence of palladium, hydrogen is ionized into protons with a radius of 1.5 × 10^-15m. Given that the lattice constant of palladium is 3.88 × 10^-10m (at 20°C), protons can combine with electrons through the tube under palladium's action to form hydrogen molecules again, escaping from the other side of the tube. Undissociated gases remain impermeable on the tube’s surface, allowing the 15CrMo boiler tube to produce high-purity hydrogen.
The representation method for 15CrMo boiler tubes works as follows: the first two digits in the steel number represent the average carbon content in ten-thousandths, such as 40Cr. Main alloying elements are generally expressed as percentages. If the average alloy content is less than 1.5%, only the element symbol is listed without specifying the exact amount, though in some cases, a "1" may follow the element symbol to clarify, such as 12CrMoV and 12Cr1MoV. The former has a chromium content of 0.4-0.6%, while the latter has 0.9-1.2%. Other elements are identical. When the average content reaches or exceeds 1.5%, 2.5%, 3.5%, etc., the content is specified after the element symbol, expressed as 2, 3, 4, etc., such as 18Cr2Ni4WA. Microalloying elements like vanadium (V), titanium (Ti), aluminum (Al), boron (B), and rare earths (RE) are always included in the steel grade, even if their amounts are low, such as in 20MnVB steel where vanadium is 0.07-0.12% and boron is 0.001-0.005%. High-quality steel adds "A" at the end of the steel number to distinguish it from standard high-quality steel. For special-purpose alloy structural steels, the steel number is prefixed or suffixed with a symbol indicating the steel's purpose, such as ML30CrMnSi for rivet bolt-specific 30CrMnSi steel.
Alloy pipes and seamless pipes are related yet distinct, and should not be confused. An alloy pipe is defined by its production material (i.e., the alloy), while a seamless pipe is defined by its manufacturing process (seamless). Seamless pipes differ from seamed pipes, which include straight-seam welded pipes and spiral pipes.
To calculate the weight of a 15CrMo boiler tube, use the following formula:
[(outer diameter - wall thickness) * wall thickness] * 0.02466 = kg/meter (weight per meter).
This comprehensive understanding ensures that these tubes meet the necessary standards and specifications for various industrial applications, particularly in high-pressure environments.
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