The working temperature of the valve is 550 ~ 650 °C, is designated as high temperature II grade (referred to as PII grade).

The PII high temperature valve is mainly used in the heavy oil catalytic cracking unit of a refinery, and it contains a high temperature lining wear-resistant gate valve used in a three-rotation nozzle and the like.

The main material of the PII valve is CF8 based on ASTM A351 standard "High temperature grade II carbon chromium nickel rare earth titanium crucible reinforced heat-resistant steel."

The working temperature of the high-temperature class III valve is 650-730°C, which is rated as high-temperature class III (abbreviated as PIII class). PIII high-temperature valves are mainly used in large-scale heavy oil catalytic cracking units in refineries. The main material of PIII high-temperature valve is CF8M based on ASTM A351 standard. It is a “high-temperature III grade medium carbon chromium nickel-molybdenum rare earth titanium-titanium reinforced heat-resistant steel”.

The operating temperature of the high-temperature class IV valve is 730 ~ 816 °C, which is rated as high temperature IV grade (referred to as PIV grade). Limiting the operating temperature of the PIV class valve to 816°C is due to the standard ASMEB16134 pressure-temperature rating used in the valve design that provides a maximum temperature of 816°C (1500°F). In addition, after the working temperature exceeds 816°C, the steel is close to entering the forging temperature zone. At this time, the metal is in the plastic deformation zone. The metal has good plasticity, and it is difficult to withstand high working pressure and impact force without being deformed. The main material of the PIV valve is the CF8M in the ASTM A351 standard, which is based on the "high-temperature grade IV medium-carbon chromium nickel nickel molybdenum rare earth titanium-titanium reinforced heat-resistant steel." CK-20 and ASTM A182 standard F310 (where C content ≥ 01050%) and F310H and other heat-resistant stainless steel.

The operating temperature of the high-temperature class V valve is more than 816°C. For example, the 6000 series ultra-high temperature butterfly valve produced by the source valve industry is called the high temperature class V (abbreviated as the PV class). PV-type high-temperature valves (valves for shut-off, and valves for non-adjustable butterfly valves) must use special design methods, such as lining the insulation lining or water or gas cooling, to ensure proper operation of the valve. Therefore, there is no provision for the upper working temperature limit of the PV-stage high-temperature valve. This is because the operating temperature of the control valve is not solely based on material, but is solved by special design means. The basic principle of the design means is the same. PV grade high temperature valve can choose reasonable material that can satisfy the valve according to its working medium, working pressure and special design method. In the PV high temperature valve, usually the flue or butterfly plate of the flue plug valve or butterfly valve is often selected from HK-30, HK-40 superalloy in ASTM A297 standards, which can be in the oxidation and reducing gas below 1150°C. Corrosion, but can not withstand the impact and high pressure load.

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