How to choose valve material under high temperature conditions?


High temperature working conditions mainly include sub-high temperature, high temperature grade I, high temperature grade II, high temperature grade III, high temperature grade IV, and high temperature grade V, which will be introduced separately below.

1. Sub-high temperature
Sub-high temperature refers to the working temperature of the valve in the region of 325 ~ 425 ℃. If the medium is water and steam, mainly use WCB, WCC, A105, WC6 and WC9. If the medium is sulfur-containing oil, C5, CF8, CF3, CF8M and CF3M with anti-sulfide corrosion are mainly used. They are mostly used in atmospheric and vacuum units and delayed coking units in refineries. At this time, valves made of CF8, CF8M, CF3 and CF3M are not used for corrosion resistance of acid solutions, but are used for sulfur-containing oil products and oil and gas pipelines. In this case, the upper limit of the upper working temperature of CF8, CF8M, CF3 and CF3M is 450℃.
2. High temperature class I
When the working temperature of the valve is 425 ~ 550 ℃, it is high temperature class I (referred to as PI class). The main material of the PI grade valve is “high temperature grade I medium carbon chromium nickel rare earth titanium high-quality heat-resistant steel” based on CF8 in the ASTMA351 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°C) or WC9 (t≤570°C) can also be used, and high temperature steel C5 (ZG1Cr5Mo) can also be used in the case of sulfur-containing oil, but in They cannot be called PI grades here.
3. High temperature class II
The working temperature of the valve is 550 ~ 650 ℃, which is designated as high temperature grade II (referred to as PII grade). PII grade high temperature valve is mainly used in heavy oil catalytic cracking unit in oil refinery, it includes high temperature lined wear-resistant gate valve used in three-rotation nozzle and other parts. The main material of the PII grade valve is “high temperature grade II medium carbon chromium nickel rare earth titanium tantalum reinforced heat-resistant steel” based on CF8 in the ASTMA351 standard.
4. High temperature grade III
The working temperature of the valve is 650~730℃, which is designated as high temperature grade III (referred to as PIII grade). PIII grade high temperature valves are mainly used in large heavy oil catalytic cracking units in oil refineries. The main material of PIII grade high temperature valve is “high temperature grade III medium carbon chromium nickel molybdenum rare earth titanium tantalum reinforced heat-resistant steel” based on CF8M in ASTMA351 standard.
5. High temperature grade IV
The working temperature of the valve is 730 ~ 816 ℃, which is designated as high temperature grade IV (referred to as PIV grade). The upper limit of the working temperature of the PIV class valve is 816°C because the higher temperature provided in the standard ASMEB16134 pressure-temperature class selected for valve design is 816°C (1500υ). In addition, after the working temperature exceeds 816 °C, the steel is close to entering the forging temperature region. At this time, the metal is in the plastic deformation range, and the metal has good plasticity, and it is difficult to withstand high working pressure and impact force without deformation. The main material of the PIV grade valve is CF8M in the ASTMA351 standard as the base 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 (including C content ≥ 01050%) and F310H in CK-20 and ASTMA182 standards.
6. High temperature grade V
The working temperature of the valve is more than 816 ℃, abbreviated as PⅤ grade, PⅤ grade high temperature valve (for shut-off valve, not regulating butterfly valve type valve) must adopt special design means, such as lining with heat insulation lining or water or gas. Cooling, etc., can ensure the normal operation of the valve. Therefore, the upper limit of the working temperature of the PⅤ grade high temperature valve is not specified. This is because the working temperature of the control valve is not only solved by materials, but by special design methods, and the basic principles of the design methods are the same. PⅤ grade high temperature valve can choose reasonable materials that can meet the valve according to its working medium and working pressure and the special design method adopted. In the PⅤ grade high temperature valve, usually the plug or butterfly plate of the flue plug valve or butterfly valve is usually HK-30, HK-40 superalloy in the ASTMA297 standard, which can resist oxidation and reducing gases below 1150 ℃. Corrosion resistant, but cannot withstand shock and high pressure loads.

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