Classification of the High Temperature Working Conditions of Valves
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 valve’s working temperature of 325 ~ 425 ℃. If the medium is water/steam, WCB, WCC, A105, wc6 and wc9 are mainly used. If the medium is sour oil, C5, CF8, CF3, CF8M and cf3m with sulfide corrosion resistance are mainly used. 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 anti-acid solution corrosion, but for sulfur-containing oil products and oil and gas pipelines. Under this condition, the upper limit of the maximum working temperature of CF8, CF8M, CF3 and cf3m is 450 ℃.
2. High Temperature Grade I
When the working temperature of the valve is 425 ~ 550 ℃, it is designated as high temperature grade I (PI grade for short). The main material of PI class valve is “high temperature grade I medium carbon chromium nickel rare earth titanium high quality heat resistant steel” with CF8 as base shape in 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, high temperature steel wc6 (t ≤ 540 ℃) or wc9 (t ≤ 570 ℃) can also be used, and high temperature steel C5 (zg1cr5mo) can also be used for sour oil. However, they cannot be called PI grade here.
3. High Temperature Class II
The working temperature of the valve is 550 ~ 650 ℃, which is defined as high temperature class II (P Class II for short). Class P Ⅱ high temperature valve is mainly used in heavy oil catalytic cracking unit of refinery. It includes high temperature lining wear-resistant gate valve used in three rotary nozzles and other parts. The main material of class P II valve is “high temperature class II medium carbon chromium nickel rare earth titanium tantalum strengthened heat resistant steel” with CF8 as base shape in ASTM a351 standard.
4. High Temperature Class III
The working temperature of the valve is 650 ~ 730 ℃, which is defined as high temperature class III (P Class III for short). The P Ⅲ high temperature valve is mainly used in the heavy oil catalytic cracking unit of refinery. The main body material of class P Ⅲ high temperature valve is “high temperature class Ⅲ medium carbon chromium nickel molybdenum rare earth titanium tantalum strengthened heat resistant steel” with CF8M as base shape in ASTM a351 standard.
5. High Temperature Grade IV
The working temperature of the valve is 730 ~ 816 ℃, which is defined as high temperature grade IV (P grade IV for short). The upper limit of working temperature for class P IV valve is set at 816 ℃ because the maximum temperature provided in the standard ASME b16134 pressure temperature class is 816 ℃ (1500 ℃) υ)。 In addition, when the working temperature exceeds 816 ℃, the steel is close to the forging temperature region. At this time, the metal is in the plastic deformation range, and the metal has good plasticity, so it is difficult to bear high working pressure and impact force without deformation. The main material of class P IV valve is CF8M in astma351 standard, which is base shape “high temperature class IV medium carbon chromium nickel molybdenum rare earth titanium tantalum strengthened heat resistant steel”. F310 (C content ≥ 01050%) and f310h in CK-20 and astma182 standards.
6. High Temperature Grade V
The working temperature of the valve is higher than 816 ℃, which is referenced as class P v. class P V high-temperature valve (used as cut-off valve, rather than regulating butterfly valve). It must adopt special design means, such as heat insulation lining or water or gas cooling, so as to ensure the normal operation of the valve. Therefore, the upper limit of the working temperature of class P V high temperature valve is not specified, because the working temperature of the valve is controlled not only by materials, but by special design means, and the basic principle of the design means is the same. According to the working medium, working pressure and special design method, the reasonable material that can meet the requirements of the valve can be selected. In class P V high temperature valves, hk-30 and HK-40 superalloys in ASTM a297 standard are usually used as the inserts or butterfly plates of flue gate valves or butterfly valves. They can resist oxidation and corrosion in reducing gas below 1150 ℃, but they can’t bear impact and high pressure load.