According to GB/T20801.1-2025, flat welding flanges with necks cannot be used for flammable and explosive media. Which standard specifies this requirement?
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This post was last edited by gwd1988 on 2026-5-29 17:41. According to GB/T20801.1-2025, flanges with necks for butt welding cannot be used for flammable and explosive media. Which standard specifies this requirement?
Flat welding flanges with a neck are prohibited from use in high-risk media (such as those that are flammable, explosive, or highly toxic) because they utilize fillet welds (Type C welds), their sealing surfaces are prone to thermal deformation, and their strength and sealing reliability are lower than those of butt welding flanges. This prohibition is not specified directly in GB/T 20801.1–2025, but rather it is a clear requirement outlined in the subordinate standard GB/T 20801.3–2025.
For 20801.1 – 2025, when 6.3.8.4 specifies the use of flat welding flanges with a neck, the nominal pressure should not exceed PN40 (Class300); the operating temperature ranges from -46 ℃ to 200 ℃, and such flanges are intended for transporting non-flammable and non-explosive media only
That means that as long as it is a flammable and explosive medium and relates to GC-class pressure pipelines covered by GB20801, whether it has a neck or not, any flat-welded flange is prohibited.