The operating temperature of the valve is 425 to 550°C and it is a high temperature class I (referred to as PI grade). The main material of the PI valve is the "high temperature grade I carbon chromium nickel rare earth titanium heat resistant steel" based on the CF8 in the ASTM A351 standard. Because the PI grade is a specific name, the concept of high-temperature stainless steel (P) is included here. Therefore, if the working medium is water or steam, although high-temperature steel WC6 (t≤540°C) or WC9(t≤570°C) may also be used, although high-temperature steel C5(ZG1Cr5Mo) may be used in the sulfur-containing oil, it is We cannot call them PI levels here.