Alloy steel pipes are a type of seamless steel pipe that offer significantly improved performance compared to standard seamless steel pipes. This is mainly due to the higher chromium content, which enhances their resistance to high and low temperatures as well as corrosion. As a result, alloy steel pipes are widely used in industries such as petroleum, chemical processing, power generation, and boiler systems.
The process of purifying hydrogen using 15CrMoG alloy steel pipes involves introducing hydrogen into one side of the pipe at temperatures between 300°C and 500°C. Once inside, hydrogen is adsorbed onto the inner surface of the pipe. Palladium, which is often used in these applications, has a 4d electron layer that lacks two electrons, allowing it to form unstable bonds with hydrogen. This reversible reaction enables hydrogen to be ionized into protons with a radius of 1.5×10â»Â¹âµ m. The lattice constant of palladium is 3.88×10â»Â¹â° m at 20°C. Under the influence of palladium, the hydrogen ions combine with electrons within the 15CrMoG alloy pipe to re-form hydrogen molecules, which then escape from the other side of the pipe. Non-dissociated gases remain on the surface and cannot pass through, resulting in the production of high-purity hydrogen.
In terms of steel designation, the first two digits in the steel number indicate the average carbon content, expressed in tenths of a percent. For example, 40Cr indicates a carbon content of 0.4%. The main alloying elements are typically listed in percentages, with numbers like 2, 3, or 4 representing the average content. For instance, 18Cr2Ni4WA indicates 18% chromium, 2% nickel, and 4% tungsten. Microalloying elements such as vanadium (V), titanium (Ti), aluminum (Al), boron (B), and rare earth elements (RE) are also included in the steel designation, even though they are present in small amounts. An example is 20MnVB, where vanadium is between 0.07% and 0.12%, and boron is between 0.001% and 0.005%.
High-quality steels are marked with an "A" at the end of the designation to distinguish them from ordinary quality steels. Special-purpose alloy structural steels may have suffixes indicating their intended use, such as ML30CrMnSi for rivet screws. It's important to note that alloy pipes and seamless pipes are not the same. Alloy pipes refer to the material used, while seamless pipes refer to the manufacturing process, which results in a pipe without a seam. Other types of pipes, such as welded pipes, have seams and are different from seamless ones.
Common materials used for alloy steel pipes include 35CrMo, 16-50Mn, 27SiMn, 40Cr, Cr5Mo, 12Cr1MoV, 12Cr1MovG, 15CrMo, 15CrMoG, 15CrMoV, 13CrMo44, T91, 27SiMn, 25CrMo, 30CrMo, 35CrMoV, 40CrMo, 45CrMo, Cr9Mo, 10CrMo910, 15Mo3, A335P11, P22, P91, T91, and others.
To calculate the weight per meter of a steel pipe, you can use the formula:
[(Outer Diameter - Wall Thickness) × Wall Thickness] × 0.02466 = kg/m.
The mechanical properties of 15CrMoG high-pressure alloy steel pipes are influenced by various factors. When the hardenability is the same, the tensile strength remains consistent, and hardness is approximately linearly related to tensile strength. Tempering to different hardness values affects the yield ratio and microstructure. Adjusting the alloying elements that enhance hardenability allows for achieving the desired mechanical properties. Elements like boron, manganese, and chromium are preferred due to their cost-effectiveness and significant impact on hardenability.
The relationship between hardness and fatigue limit varies depending on the composition of the alloy. Below 35HRC, the fatigue limit increases linearly with hardness, but above 35HRC, the fluctuation becomes more pronounced. At 55HRC, the fatigue limit range can increase up to 380MPa.
Structural strengthening in 15CrMoG alloy steel pipes is influenced by the microstructure. Cold rolling changes the structure, leading to variations in bainite and martensite, which affect the mechanical properties. Structural strengthening requires the presence of a parent phase, and the process includes deformation and diffusion. Depending on the cooling environment, the microstructure may change either through diffusion or without it. These changes impact the overall performance of the pipe, making it possible to produce pipes with varying strengths for different applications.
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