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**15CrMo Boiler Tube: Properties, Classification, and Applications**
The **15CrMo boiler tube** is a type of high-quality carbon structural steel that incorporates one or more alloying elements to enhance its mechanical properties, toughness, and hardenability. These tubes typically undergo heat treatment processes such as normalizing or quenching and tempering to achieve the desired performance. Components made from this material often require additional treatments like quenching and tempering, surface chemical treatments (e.g., carburizing or nitriding), or even surface hardening techniques such as induction or high-frequency hardening.
Based on chemical composition—primarily carbon content, heat treatment methods, and intended use—this type of steel can be broadly categorized into three groups: carburizing steels, quenched and tempered steels, and nitriding steels.
### Classification of High-Pressure Boiler Tubes
1. **High-quality carbon structural steel grades**: Includes 20G, 20MnG, and 25MnG.
2. **Alloy structural steel grades**: Such as 15MoG, 20MoG, 12CrMoG, 15CrMoG, 12Cr2MoG, 12CrMoVG, 12Cr3MoVSiTiB, etc.
3. **Rust and heat-resistant steels**: Commonly used grades include 1Cr18Ni9 and 1Cr18Ni11Nb. These materials must pass hydrostatic, flaring, and flattening tests in addition to meeting chemical and mechanical requirements. The steel pipes are delivered in a heat-treated condition.
In addition, there are specific standards for the microstructure, grain size, and decarburization layer of the final product to ensure quality and performance.
### Specifications and Appearance Quality
According to the standard **GB5310-95**, seamless steel tubes for high-pressure boilers have an outer diameter ranging from 22–530 mm and wall thicknesses from 20–70 mm. Cold-drawn or cold-rolled tubes have smaller dimensions, with outer diameters between 10–108 mm and wall thicknesses from 2.0–13.0 mm.
### Hydrogen Purification Principle
The **15CrMo boiler tube** plays a key role in hydrogen purification. When hydrogen gas is introduced at temperatures between 300–500°C, it adsorbs onto the inner surface of the tube. Palladium, which has a 4d electron layer lacking two electrons, forms unstable chemical bonds with hydrogen. This reaction is reversible. Under palladium’s influence, hydrogen becomes ionized into protons with a radius of 1.5 × 10â»Â¹âµ m. Since the lattice constant of palladium is 3.88 × 10â»Â¹â° m at 20°C, these protons can recombine with electrons through the tube to form pure hydrogen molecules, which then escape from the other side. The surface remains impermeable to undissociated gases, making the 15CrMo tube ideal for producing high-purity hydrogen.
### Representation of 15CrMo Steel Grades
- The first two digits in the steel grade indicate the average carbon content in ten-thousandths. For example, in 40Cr, the carbon content is 0.4%.
- Main alloying elements are usually indicated by their symbols. If the average alloy content is less than 1.5%, only the symbol is shown. For higher contents, the percentage is specified, e.g., 18Cr2Ni4WA.
- Microalloying elements like vanadium (V), titanium (Ti), aluminum (Al), boron (B), and rare earths (RE) are always included in the grade, even in small amounts.
- High-quality steel grades end with "A" to distinguish them from ordinary ones.
- Special-purpose steels may include a symbol indicating their function, such as ML30CrMnSi for rivet screw applications.
### Alloy Pipes vs. Seamless Pipes
Although **alloy pipes** and **seamless pipes** are related, they are not the same. Alloy pipes are defined by the material used—made from an alloy—while seamless pipes refer to the manufacturing process, meaning they have no weld seam. In contrast, **seamed pipes** include straight-seam and spiral-welded types.
### Weight Calculation Formula
To calculate the weight per meter of a 15CrMo boiler tube:
$$
\text{Weight (kg/m)} = [(OD - t) \times t] \times 0.02466
$$
Where:
- **OD** = Outer Diameter (mm)
- **t** = Wall Thickness (mm)
This formula helps in estimating the weight of the pipe for logistics, cost estimation, and structural planning.
By understanding the properties, classifications, and applications of 15CrMo boiler tubes, engineers and manufacturers can make informed decisions about material selection and usage in high-pressure and high-temperature environments.