What is the high-chromium-nickel-molybdenum austenitic stainless steel specified in GB/T20801.5-2020?
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When classifying pressure pipeline inspection levels according to GB/T20801.5-2020, how should high-chromium-nickel-molybdenum austenitic stainless steel be understood? Let’s explain it together. Introduction 6.1.2 Pressure pipelines that meet one of the following conditions are classified as Class I: a pipelines specified in the design documents as being under severe cyclic operating conditions ； b GC1 grade pipeline ； c Pipes used under high-temperature creep conditions (as specified in 3.2 of GB/T20801.3-2020) ； d Titanium and titanium alloys, nickel and nickel-based alloys, high-chromium-nickel-molybdenum austenitic stainless steels, zirconium and zirconium-based alloy pipes ； e Pipes with a nominal pressure greater than P ； f Inner tube of the bushing ； g Pipes that may be exempted from pressure testing in accordance with the provisions of 9.1.7 ； h) Piping for which design requirements dictate 100% non-destructive testing of weld joints. Explanation from the General Administration: Response from the General Administration: 316L does not belong to the category of high-chromium-nickel-molybdenum austenitic stainless steels. High-chromium-nickel-molybdenum austenitic stainless steel (high-performance corrosion-resistant stainless steel) refers to stainless steels with excellent corrosion resistance that are not listed in the GB/T20801.2 stress table and have an alloy content higher than that of 316 and 310 grades; typical examples include 904L.
It usually refers to super austenitic stainless steel
Is there the original reply from the headquarters? This part has always been unclear
【Q&A on Tubes】As explained in Master Yingdaoyan’s Q&A on tube-related issues: High-chromium-nickel-molybdenum austenitic stainless steels refer to austenitic stainless steels with nickel, chromium, and molybdenum contents higher than those of the 300 series (such as 304, 316, 317, 309, 310), including materials like 904L, 254SMO, 6MO stainless steel, and 20 alloy. High-chromium-nickel-molybdenum austenitic stainless steel is also known as super austenitic stainless steel; it contains 14.0–18.0% Cr, 24.0–26.0% Ni, and 4.5% Mo. Conventional austenitic chromium-nickel stainless steels include the well-known 18Cr-8Ni steel (304 series) and 17-12-2 type austenitic stainless steels (316 series). Based on these, high-Cr-Ni series steels were developed by increasing the contents of Cr and Ni and adding elements such as Mo, Cu, Si, Nb, and Ti; examples of such steels are 904L, 254SMo (corresponding to S31252 in the national standard GB/T4237-2015), 654SMo, etc. The contents of chromium, nickel, and molybdenum in these stainless steels are higher than those in the 304 and 316 series, which is why they are also known as super austenitic stainless steels, or high-chromium-nickel-molybdenum austenitic stainless steels. It turns out that this term was present in GB/T 20801.5-2020 in the initial draft, but it was omitted during several subsequent revisions.