High temperature conditions mainly include sub-high temperature, high temperature grade I, high temperature grade II, high temperature grade III, high temperature grade IV, high temperature grade V.
1. Sub-high temperature
Sub-high temperature refers to the working temperature of the valve in the range of 325-425 C. If the medium is water and steam, WCB, WCC, A105, WC6 and WC9 are mainly used. If the medium is sulfur-containing oil, it mainly has C5, CF8, CF3, CF8M and CF3M which are resistant to sulfide corrosion. They are mostly used in atmospheric and vacuum distillation units and delayed coking units in refineries. At this time, CF8, CF8M, CF3 and CF3M valves are not used for acid corrosion resistance, but for sulphur-containing oil products and oil and gas pipelines. In this condition, the maximum operating temperature of CF8, CF8M, CF3 and CF3M is 450 C.
2. High Temperature Grade I
The working temperature of the valve ranges from 425 ~550 C to Class I of high temperature (PI for short). The main material of PI class valve is CF8 in ASTM A351 standard, which is the basic form of ;high temperature grade I medium carbon chromium nickel rare earth titanium high quality heat resistant steel;. Because PI grade is a specific term, 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) can also be used in sulfur-containing oil products, although high temperature steel C5 (ZG1Cr5Mo) can also be used, they can not be called PI grade here.
3. High Temperature Grade II
The working temperature of the valve is 550-650 C, which is classified as high temperature class II (referred to as P class II). Class P II high temperature valve is mainly used in heavy oil catalytic cracking unit of refinery. It contains high temperature lining wear-resistant gate valve used in tri-rotating nozzle and other parts. The main material of class P II valve is CF8 in ASTM A351 standard, which is ;high temperature grade II medium carbon, chromium, nickel, rare earth, titanium, tantalum reinforced heat resistant steel;.
4. High Temperature Grade III
The working temperature of the valve is 650-730 C, which is classified as high temperature class III (referred to as P class III). 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 in ASTM A351 standard, which is the basic form of ;high temperature grade III medium carbon, chromium, nickel, molybdenum, rare earth, titanium and tantalum reinforced heat resistant steel;.
5. High Temperature Grade IV
The working temperature of the valve is 730-816 C, and it is classified as high temperature class IV (P class IV for short). The working temperature of the PIV valve is limited to 816 C because the highest temperature provided in the standard ASMEB16134 pressure-temperature class is 816 C (1500_). In addition, when the working temperature exceeds 816 C, the steel approaches the forging temperature region. At this time, the metal is in the plastic deformation region, and the metal has good plasticity, so it is difficult to withstand high working pressure and impact force and keep the deformation. The main material of PIV valve is CF8M in ASTM A351 standard, which is the basic form of ;high temperature grade IV medium carbon chromium nickel molybdenum rare earth titanium tantalum reinforced heat resistant steel;. In CK-20 and ASTMA182 standards, F310 (in which C content is more than 01050%) and F310H are heat-resistant stainless steel.
6. High Temperature Grade V
The working temperature of the valve is above 816 C, referred to as PV class for short. The PV class high temperature valve (as a cut-off valve, not a regulating butterfly valve) must adopt special design means, such as heat insulation lining or water or gas cooling, in order to ensure the normal operation of the valve. Therefore, the upper limit of working temperature of PV high temperature valve is not stipulated, because the working temperature of the valve is controlled not only by material, but by special design means, and the basic principle of design means is the same. Class PV high temperature valve can select reasonable material according to its working medium, working pressure and special design method. In PV class high temperature valves, the flue plug valves or butterfly valves usually use HK-30, HK-40 superalloys in ASTM A297 standard. They can resist corrosion in oxidation and reducing gases below 1150 C, but cannot withstand impact and high pressure load.