Q1: Why are 12Cr1MoVG steel pipes particularly suitable for power plant boilers?
12Cr1MoVG steel pipes offer excellent high-temperature strength and oxidation resistance, enabling stable operation at temperatures below 580°C for extended periods. The dense oxide film formed by their chromium content (1.00%-1.50%) effectively resists high-temperature steam corrosion. The addition of molybdenum and vanadium significantly improves the material's creep rupture strength, meeting the long-term strength requirements of boiler tubes. Compared to ordinary carbon steel, 12Cr1MoVG offers superior structural stability at high temperatures and a longer service life. This makes it the preferred material for superheaters and reheaters in subcritical and supercritical power plant boilers.
Q2: In the petrochemical industry, what equipment is 12Cr1MoVG steel pipe primarily used for?
In the petrochemical industry, 12Cr1MoVG steel pipes are widely used in key equipment such as hydrogenation reactors, catalytic cracking units, and high-temperature heat exchangers. Their excellent hydrogen corrosion resistance makes them particularly well-suited for hydrogenation process environments (temperatures of 450-550°C). In reforming units, it is used to manufacture reactor cylinders and connecting pipes. It is also used to manufacture furnace tubes for ethylene cracking furnaces, where it can withstand the corrosion of high-temperature cracking gas. Compared to austenitic stainless steel, 12Cr1MoVG offers superior thermal fatigue resistance and economical performance.
Q3: What structural changes occur in 12Cr1MoVG steel pipes during high-temperature service?
During long-term service at high temperatures, carbides in 12Cr1MoVG gradually aggregate and grow, causing the material to soften. Chromium carbides (Cr23C6) precipitate at grain boundaries, potentially reducing the material's toughness. Vanadium carbides (VC) maintain good stability and slow performance degradation. At temperatures exceeding 600°C, sigma phase embrittlement may occur, affecting material properties. These changes require regular metallographic examination to monitor and assess the extent of material degradation.
Q4: How can the remaining service life of 12Cr1MoVG steel pipes at high temperatures be assessed?
Common assessment methods include metallographic structure evaluation, hardness testing, and endurance testing. Regular sampling is performed to observe changes in the morphology and distribution of carbides. Hardness degradation trends should be measured; a decrease in HB exceeding 30 points is generally cause for concern. High-temperature endurance testing should be conducted to compare measured data with initial performance. Finite element analysis should be used to calculate the degree of cumulative damage. Based on the assessment results, a plan for continued use, repair, or replacement should be developed.
Q5: What are the limitations of 12Cr1MoVG steel pipe in high-temperature applications?
When temperatures exceed 600°C, its endurance strength decreases significantly, making long-term use not recommended. In sulfur-containing media, its resistance to high-temperature sulfur corrosion is inferior to that of high-chromium steels (such as 9Cr-1Mo). Thermal fatigue cracking may occur under thermal cycling conditions, requiring careful attention to structural design. Compared to austenitic stainless steel, its resistance to high-temperature oxidation is limited. Upgrading to higher-grade P91/P92 steel may be necessary for extreme operating conditions.
