**15CrMo Boiler Tube Overview**
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 steels are typically subjected to heat treatment such as normalization or quenching and tempering. Components made from this material often undergo additional treatments like quenching and tempering, surface chemical treatments (e.g., carburizing, nitriding), or surface hardening techniques such as induction hardening.
Due to differences in chemical composition—particularly carbon content—as well as the heat treatment process and application, this category of steel can be broadly classified into three types: **carburizing**, **quenching and tempering**, and **nitriding** steels.
**Classification of High-Pressure Boiler Tubes:**
1. **High-quality carbon structural steels** include grades such as **20G, 20MnG, and 25MnG**.
2. **Alloy structural steels** consist of grades like **15MoG, 20MoG, 12CrMoG, 15CrMoG, 12Cr2MoG, 12CrMoVG, 12Cr3MoVSiTiB**, etc.
3. **Rust and heat-resistant stainless steels**, such as **1Cr18Ni9** and **1Cr18Ni11Nb**, require additional testing beyond chemical and mechanical properties. These include hydrostatic tests, flaring, and flattening tests. The tubes are delivered in a heat-treated condition.
Moreover, the final product must meet specific requirements regarding **microstructure, grain size, and decarburization layer thickness**.
**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 between **20–70 mm**. Cold-drawn or cold-rolled tubes have smaller dimensions, with outer diameters from **10–108 mm** and wall thicknesses of **2.0–13.0 mm**.
**Hydrogen Purification Principle:**
When hydrogen is passed through a **15CrMo boiler tube** at temperatures between **300–500°C**, it adsorbs onto the inner surface. 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 is ionized into protons with a radius of **1.5 × 10â»Â¹âµ m**. Since the lattice constant of palladium is **3.88 × 10â»Â¹â° m**, these protons can pass through the tube and recombine with electrons to form pure hydrogen gas on the other side. The undissociated gas cannot permeate, allowing the tube to produce high-purity hydrogen.
**Representation of 15CrMo Steel Grades:**
- The first two digits indicate the average carbon content in **ten-thousandths**, e.g., **40Cr**.
- Main alloying elements (excluding microalloying elements) are generally denoted by their symbols. If the average content is less than 1.5%, only the symbol is shown. For example, **12CrMoV** and **12Cr1MoV** differ in chromium content.
- Microalloying elements like **V, Ti, Al, B, RE** are always marked, even in small quantities. For example, **20MnVB** contains **0.07–0.12% V** and **0.001–0.005% B**.
- High-quality steel adds **"A"** at the end of the grade to distinguish it from general quality steel.
- Special-purpose steels may include a symbol indicating their use, such as **ML30CrMnSi** for rivet screws.
**Distinction Between Alloy Pipes and Seamless Pipes:**
Although **alloy pipes** and **seamless pipes** are related, they are not interchangeable. **Alloy pipes** refer to pipes made from alloy steel, while **seamless pipes** are defined by their production method—without seams. This includes **straight seam welded pipes** and **spiral welded pipes**.
**Weight Calculation Formula for 15CrMo Boiler Tubes:**
To calculate the weight per meter of a 15CrMo boiler tube:
$$
\text{Weight (kg/m)} = \left[ (\text{Outer Diameter} - \text{Wall Thickness}) \times \text{Wall Thickness} \right] \times 0.02466
$$
This formula helps engineers and manufacturers estimate the mass of the tubes accurately, ensuring proper handling and transportation during installation.
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