Guidance for the use of temperature and medium of commonly used materials for valves

5. High temperature conditions
      High temperature valves mainly refer to high temperature valves used in oil refineries.


5.1 Sub-high temperature
      Sub-high temperature means that the valve's operating temperature is in the region of 325 to 425°C. If the medium is water and steam, WCB, WCC, A105, WC6 and WC9 are mainly used. If the medium is sulfur-containing oil, mainly use C5, CF8, CF3, CF8M and CF3M which are resistant to sulfide corrosion. They are mostly used in the atmospheric and vacuum units and delayed coking units of oil refineries. At this time, valves made of CF8, CF8M, CF3 and CF3M are not used for corrosion resistance of acid solutions, but for sulfur-containing oil and oil and gas pipelines. In this working condition, the upper limit of the maximum operating temperature of CF8, CF8M, CF3 and CF3M is 450°C.


5.2 High temperature class I
      The valve's working temperature is 425～550℃, it is high temperature grade I (referred to as PI grade). The main material of the PI-level valve is "high-temperature grade I medium-carbon chromium-nickel rare-earth titanium high-quality heat-resistant steel" based on CF8 in the ASTM A351 standard. Because 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℃) or WC9 (t≤570℃) can also be used, although high-temperature steel C5 (ZG1Cr5Mo) can also be used for sulfur-containing oil, They cannot be called PI grades here.


5.3 High temperature class Ⅱ
      The working temperature of the valve is 550～650℃, which is set as high temperature level II (referred to as PII level for short). The PⅡ high temperature valve is mainly used in the heavy oil catalytic cracking unit of the refinery. It contains high temperature lining wear-resistant gate valves used in three-rotation nozzles and other parts. The main material of the PⅡ valve is the "high temperature grade Ⅱ medium carbon chromium nickel rare earth titanium tantalum reinforced heat-resistant steel" based on CF8 in the ASTM A351


5.4 High temperature Ⅲ grade
      The working temperature of the valve is 650～730℃, which is set as high temperature grade III (referred to as PⅢ grade for short). PⅢ high temperature valves are mainly used in large-scale heavy oil catalytic cracking units in refineries. The main material of the PⅢ grade high temperature valve is the "high temperature grade Ⅲ medium carbon chromium nickel molybdenum rare earth titanium tantalum reinforced heat-resistant steel" based on CF8M in the ASTM A351 standard.


5.5 High temperature grade IV
      The working temperature of the valve is 730～816℃, which is set as high temperature grade IV (referred to as PIV grade for short). The upper limit of the working temperature of the PIV valve is 816°C because the maximum temperature provided in the standard ASME B16.34 pressure-temperature grade selected for the valve design is 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, and the metal has good plasticity, and it is difficult to withstand high working pressure and impact without being deformed. The main material of the PⅣ valve is CF8M in the ASTM A351 standard, which is the basic shape "high temperature grade IV medium carbon chromium nickel molybdenum rare earth titanium tantalum reinforced heat-resistant steel". Heat-resistant stainless steels such as F310 (with C content ≥0.050%) and F310H in the CK-20 and ASTM A182 standards.


5.6 High temperature grade V
      The working temperature of the valve is above 816℃, which is called high temperature grade V (referred to as PⅤ grade). PⅤ-grade high-temperature valves (used as shut-off valves, not valves of regulating type butterfly valves) must adopt special design methods, such as lining heat insulation lining or water or air cooling, etc., to ensure the normal operation of the valve. Therefore, the upper limit of the working temperature of the PⅤ high temperature valve is not stipulated. This is because the working temperature of the control valve is not solved by materials alone, but by special design methods, and the basic principles of the design methods are the same. According to the working medium, working pressure and special design method adopted, the PⅤ high temperature valve can select reasonable materials that can meet the requirements of the valve. In the PⅤ high temperature valve, usually the flue flapper valve or the flapper or butterfly plate of the butterfly valve often use the HK-30 and HK-40 high temperature alloys in the ASTM A297 standard. They can resist oxidation and reducing gases below 1150℃ Medium corrosion resistance, but can not withstand impact and high pressure load.


6 Conclusion
      With the rapid development of technology today, the main material of the valve is becoming increasingly diversified and highly parameterized. The working medium corresponding to the valve is also more complicated, and the working temperature requirement is higher. Understanding the properties of various types of valve steels and alloys and their suitable working temperature is the knowledge that relevant scientific and technical personnel and operators who design, manufacture, purchase and use valves must master. Especially the use temperature of the material should not exceed its suitable working temperature, otherwise it will cause terrible and serious accidents.