Operating temperature of A351-CF8(PII)

This post was last edited by Liu Jiajia on 2018-2-6 09:19. 1. Classification of high-temperature valves: Valves that operate at temperatures above 450°C are considered high-temperature valves. For such valves, if the operating temperature is between 425~538°C (approximately 800~1000°F), they are classified as high-temperature Class I, abbreviated as PI class； Operating temperature >538~650°C (approximately 1000~1200°F), classified as High Temperature Class II, abbreviated as PII class ； Operating temperature >650~730°C (approximately 1200~1350°F), classified as High Temperature Class III, abbreviated as PIII class ； Operating temperature >730~816°C (approximately 1350~1500°F), classified as High Temperature Class IV, abbreviated as PIV class ； Operating temperature > 816°C (about 1500°F) is classified as High Temperature Class V, abbreviated as PV class. 2. Material selection for valves in various temperature ranges: PI grade: CF8/304/304H/321/321H, etc., can be used ； PII level: Same as PI level ； Grade PIII: CF8M/316/316H, etc. can be selected ； PIV grade: CK-20/310/310H, etc. are available ； PV class: These types of valves need to be specially designed based on the operating conditions. 3. Points that need to be clarified: ①. Materials with a higher classification level as mentioned above can be used in those with a lower classification level; for example, PIII-level materials can be used in PII-level applications, but the reverse is not possible. ②When the temperature exceeds 538°C (about 1000°F), the carbon content of the material must be above 0.04%, which means a high-carbon material should be used ； ③For .PI grade high-temperature valves, WC6 and WC9 can be selected when used with water and steam as the medium ； When used in media such as water, steam, and oils, Cr-Mo high-temperature steels such as C5 (Cr5Mo) can be selected ； ④Stainless steel for high-temperature applications should undergo thorough desulfurization and dephosphorization, slag removal and degassing refining, to refine the grain structure, purify the grain boundaries, and improve properties such as resistance to high-temperature creep. CF8 and CF8M, which are not subjected to special high-temperature treatments and are typically used for corrosion protection, are not suitable as high-temperature resistant heat-resistant stainless steels. 4. According to what you said, with a operating temperature of 720°C, the design institute designated a PII grade, and the material chosen was A351-CF8 (PII), which is inappropriate. It is recommended to upgrade the material grade.

At this temperature, 316H should be fine~~~304H won’t work~~~~~~~~~~~