The difference between Z41Y-16PI and Z41Y-16PII
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I would like to ask fellow sailors: in the chapter on valves in \"Design and Installation of Process Piping in Petrochemical Plants\", there are Z41Y-16PI and Z41Y-16PII. What is the difference between these two and the regular 16P type?
When the operating temperature of the valve is 425–550°C, it is classified as High Temperature Class I (abbreviated as PI class). The main material of PI-class valves is a high-temperature Class I medium-carbon chromium-nickel-rare earth-titanium high-quality heat-resistant steel based on CF8 as specified in ASTM A351. The operating temperature of the valve is 550–650°C, classified as High Temperature Class II (abbreviated as PⅡ class). Class PⅡ high-temperature valves are primarily used in the heavy oil catalytic cracking units of refineries; they include wear-resistant gate valves with high-temperature linings that are employed in components such as three-spin nozzles. The main material of PⅡ-class valves is a \"high-temperature Class II medium-carbon chromium-nickel rare-earth titanium tantalum strengthened heat-resistant steel\" based on CF8 as specified in ASTM A351.