How to choose valve material under high temperature condition?

DataTime:[2020-9-13]

The high temperature valve has good quenching property and can be deeply quenched instead of the surface quenching of anti saw lock on the market. In general information, the valve with working temperature T > 450 ℃ is called high temperature valve. However, there is no unified standard for the classification of high temperature grade of high temperature valves.

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 are respectively introduced below.

Sub high temperature

Sub high temperature refers to the valve working temperature in the 325 ~ 425 ℃ region. If the medium is water and steam, WCB, WCC, A105, wc6 and wc9 are mainly used. If the medium is sulfur-containing oil, C5, CF8, CF3, CF8M and cf3m are mainly used. At this time, the valves made of CF8, CF8M, CF3 and cf3m are not used to resist the corrosion of acid solution, but are used in sour oil products and oil and gas pipelines. In this condition, the upper limit of the maximum operating temperature of CF8, CF8M, CF3 and cf3m is 450 ℃.

High temperature grade I

When the working temperature of the valve is 425 ~ 550 ℃, it is high temperature class I (referred to as PI). The main material of PI valve is CF8 in astma351 standard, which is "high temperature grade I medium carbon chromium nickel rare earth titanium high quality heat resistant steel". 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, while high temperature steel C5 (zg1cr5mo) can also be used for sour oil, but they can not be called PI grade here.

High temperature grade II

The working temperature of the valve is 550 ~ 650 ℃, which is designated as high temperature class II (referred to as P Ⅱ). Grade 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 swirl nozzle and other parts. The main material of P Ⅱ valve is CF8 in astma351 standard, which is "high temperature grade II medium carbon chromium nickel rare earth titanium tantalum strengthened heat resistant steel".

High temperature grade III

The working temperature of the valve is 650 ～ 730 ℃, which is designated as high temperature class III (referred to as P Ⅲ). The P Ⅲ high temperature valve is mainly used in heavy oil catalytic cracking unit of refinery. The main material of P Ⅲ high temperature valve is CF8M in astma351 standard, which is "high temperature grade III medium carbon chromium nickel molybdenum rare earth titanium tantalum strengthened heat resistant steel".

High temperature grade IV

The operating temperature of the valve is 730 ~ 816 ℃, which is designated as high temperature grade IV (referred to as P Ⅳ). The upper limit of operating temperature for class P IV valves is set at 816 ℃ because the maximum temperature provided in the standard asmeb16134 pressure temperature class selected for valve design is 816 ℃ (1500 V). In addition, when the working temperature exceeds 816 ℃, 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 bear high working pressure and impact force without deformation. The main material of P IV valve is CF8M in astma351 standard, which is "high temperature grade 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.

High temperature grade V

If the working temperature of the valve is higher than 816 ℃, it is referred to as p-v. the P-V high-temperature valve (used as cut-off valve instead of regulating butterfly valve) must adopt special design means, such as lining insulation lining or water or air cooling, etc., to ensure the normal operation of the valve. Therefore, there is no stipulation on the upper limit of the operating temperature of the p V class high temperature valve. This is because the control of the working temperature of the valve is not only based on the material, but also solved 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 which can meet the valve can be selected. In P V class high temperature valve, the insert plate or butterfly plate of flue gate valve or butterfly valve is usually made of hk-30 and HK-40 superalloys in astma297 standard. They can resist corrosion in oxidation resistance and reducing gas below 1150 ℃, but can not bear impact and high pressure load.

Source: China Valves Manufacturer – Yaang Pipe Industry Co., Limited (www.yaang.com)

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