How should the tendency toward graphitization be considered?
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When using carbon steel at 425 degrees, the tendency toward graphitization needs to be taken into account; are there any preventive measures? Except for changing the material.
If the materials are not changed, the only option is to reduce the designed service life and monitor usage
When the material type remains unchanged, the following measures should be taken to improve the material’s high-temperature performance: 1. All pressure-bearing components must undergo high-temperature mechanical property tests at the design temperature in accordance with GBT150.2. 2. When ordering the material, it is necessary to ensure that the contents of impurities such as carbon, sulfur, phosphorus, and manganese are within the lower limits specified by the material standards. 3. The material should be subjected to low-temperature impact tests at -20 degrees Celsius to evaluate its toughness and plasticity. 4. Each sheet of material used for pressure-bearing components must pass ultrasonic testing at grade 1; forgings should be tested using magnetic particle inspection before and after processing, and ultrasonic testing again after shaping. For steel pipes, grades 10 or 20 according to standard 9948, or Q345D or higher according to standard 6479 should be used； Preheating should be carried out before welding; overall stress relief heat treatment should be performed after the equipment is manufactured. The heat treatment temperature should be set at a minimum of 4 degrees Celsius. 100% magnetic particle testing must be conducted on the welded joints of the material before and after heat treatment, as well as before and after hydrostatic testing. The wall temperature of the equipment during hydrostatic testing should be maintained at no less than 15 degrees Celsius. Users are required to follow strict operating procedures during start-up and shutdown processes, such as raising the temperature and pressure first, and then lowering them again.
Furthermore, for elliptical heads, attention should be paid to conducting additional surface crack inspections in their transition zones
Personally, I think for high temperatures, chromium-molybdenum steel and stainless steel are the best choices
The post is highly targeted and packed with useful information. It covers the entire process, from the chemical composition of the raw materials, to their (high-temperature) mechanical properties, and to the control of subsequent manufacturing processes. Learned it :)