{"id":653,"date":"2026-11-03T20:28:10","date_gmt":"2026-11-03T12:28:10","guid":{"rendered":"http:\/\/www.ledsscreen.com\/blog\/?p=653"},"modified":"2026-11-03T20:28:10","modified_gmt":"2026-11-03T12:28:10","slug":"what-are-the-different-pressure-classes-of-gost-flanges-4fdd-af36a4","status":"publish","type":"post","link":"http:\/\/www.ledsscreen.com\/blog\/2026\/11\/03\/what-are-the-different-pressure-classes-of-gost-flanges-4fdd-af36a4\/","title":{"rendered":"What are the different pressure classes of GOST Flanges?"},"content":{"rendered":"

If you\u2019ve ever dealt with industrial piping systems\u2014whether for oil and gas, chemical processing, or even heavy water treatment\u2014you\u2019ve probably come across GOST flanges at some point. As someone who\u2019s been sourcing and supplying these for over 8 years, I can tell you that one of the most common questions I get from new clients is: \u201cWhat\u2019s the difference between all these GOST flange pressure classes?\u201d Let\u2019s be real, it\u2019s not like ASME classes where the numbers line up neatly, and it\u2019s way more specific to post-Soviet industry standards. Skip the boring textbook jargon for a sec\u2014this is the stuff I actually use every day to make sure my clients don\u2019t order the wrong flange and end up with a leak that costs them thousands (not to mention stress). GOST Flanges<\/a><\/p>\n

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First, let\u2019s cut through the confusion: GOST flanges don\u2019t use psi or bar like a lot of Western flanges. They use a rating system tied directly to GOST 12815-80 (the main standard for flat and weld-neck flanges) and GOST 33259-2015, the newer, updated version that syncs a bit more with international norms. The pressure classes here are called \u201cnominal pressure\u201d or \u0420\u0443<\/em> (that\u2019s the Cyrillic letter R, pronounced \u201crood\u201d)\u2014I just call them \u201cRu ratings\u201d to keep it simple. Each Ru number corresponds to a maximum working pressure at a specific temperature, which is non-negotiable because a flange rated for 10 Ru will totally fail if you push it beyond what it\u2019s designed for, especially in hot pipes.<\/p>\n

Let\u2019s start with the most common ones I supply, because 90% of my orders are these, no cap. The lowest I usually sell is 6 Ru. What does that translate to? Roughly 100 psi or 10 bar. These are super basic\u2014they\u2019re the thin, lightweight flanges you see for low-pressure, non-critical stuff like HVAC lines, water supply for factories, or small chemical lines where the pressure doesn\u2019t spike. Don\u2019t get me wrong, they work, but I never recommend them for anything that gets over 250\u00b0F, because the metal starts to soften and the pressure rating drops fast. I once had a new client order 6 Ru flanges for a steam line (total rookie move) and they blew a gasket within a month\u2014cost them $12k in downtime. Never again, man.<\/p>\n

Next up is 10 Ru. This is probably the sweet spot for most general industrial use, right around 160 psi or 16 bar. It\u2019s thicker than 6 Ru, has a stiffer sealing surface, and works great for medium-pressure stuff like compressed air lines, moderate-temperature water, or low-pressure process piping. I stock these in all the common sizes\u2014DN50, DN100, DN200 (that\u2019s nominal diameter, another thing people mix up)\u2014because every factory needs spares. The temperature limit here is around 300\u00b0F, so don\u2019t use this for super hot oil or gas, but it\u2019s perfect for the 80% of piping that\u2019s not extreme.<\/p>\n

Then we hit 16 Ru, which is 250 psi or 25 bar. This is where things start getting serious. These are thicker, heavier-duty flanges, made from higher-grade steel (usually carbon steel or alloy, not just the basic stuff) for lines that carry more pressure, like medium-pressure steam, natural gas pipelines, or chemical processing lines that handle slightly corrosive materials. The sealing surface here is usually a raised face (RF) instead of the smooth flat face of lower Ru ratings, which creates a better seal when you tighten the bolts. I see a lot of oil and gas companies use 16 Ru for their wellhead gathering lines, because it balances strength and cost\u2014you don\u2019t have to splurge on a high Ru rating if you don\u2019t need it.<\/p>\n

Wait, hold on\u2014there\u2019s 25 Ru too, right? 400 psi or 40 bar. That\u2019s my go-to for more demanding applications. These are way sturdier, with a much thicker hub and heavier bolts, designed for high-pressure lines like high-temperature steam, long-distance natural gas transmission, or heavy-duty chemical lines that carry acids or other corrosive stuff. I also supply 25 Ru for mining operations, where piping has to handle both pressure and rough handling. The temperature limit here jumps up to around 500\u00b0F, which is key for hot industrial processes. I always make sure to tell clients that 25 Ru flanges aren\u2019t just \u201cstronger\u201d\u2014they\u2019re also made to resist more wear, so if you\u2019re installing flanges in a remote area that\u2019s hard to access, investing in these will save you from replacing them every couple of years.<\/p>\n

Now, the higher Ru ratings\u2014these are for when you\u2019re dealing with extreme pressure, like in power plants or heavy industrial manufacturing. We have 40 Ru, which is 630 psi or 63 bar, and 63 Ru, which is 1000 psi or 100 bar. These are the big boys, made from high-alloy steel (like chrome-moly) to handle both pressure and high temperatures (up to 750\u00b0F for 63 Ru). I don\u2019t stock a ton of these because not every project needs them, but when I do, they\u2019re for things like nuclear power plant piping, high-pressure refinery lines, or large-scale LNG transfer systems. The thing about these is that they\u2019re not cheap\u2014so I always make sure clients double-check their pressure and temperature specs before ordering, because ordering the wrong Ru here isn\u2019t just a cost mistake, it\u2019s a safety hazard.<\/p>\n

Wait, but let\u2019s get one thing straight: the Ru rating doesn\u2019t directly equal bar or psi. It\u2019s tied to GOST\u2019s specific temperature-pressure curve. For example, a 16 Ru flange might be rated for 25 bar at 20\u00b0C, but at 300\u00b0C, that drops to like 12 bar. That\u2019s why I never just tell a client \u201c10 Ru is 10 bar\u201d\u2014I always ask for their operating temperature, fluid type, and pressure, because that\u2019s how you pick the right rating. I\u2019ve had clients come to me thinking \u201cRu is pressure, full stop\u201d and they end up with flanges that can\u2019t handle their hot oil. Lesson learned: always cross-check with the specs, not just the Ru number.<\/p>\n

Another thing that trips people up: GOST flanges also have different face types depending on the Ru rating and application. Like, lower Ru (6, 10) usually have flat face (FF) or raised face (RF), while higher Ru (16, 25, 40, 63) often have male-female (MF) or tongue-and-groove (T&G) faces for better sealing under high pressure. I always break this down for new clients, because a flange with the right Ru but the wrong face is just as useless as one with the wrong Ru.<\/p>\n

Now, why does this matter for you, if you\u2019re a plant manager or piping engineer ordering these? Let\u2019s be real: ordering the wrong GOST flange is expensive. A wrong 10 Ru flange might leak and cause $10k in downtime. A wrong 25 Ru flange could burst, causing safety issues and millions in damage. As a supplier, I don\u2019t just sell you a flange\u2014 I ask questions: what\u2019s the fluid? What\u2019s the max operating pressure? What\u2019s the temperature? Where is this flange being installed? (Is it underground? In a corrosive environment?) That\u2019s how I make sure you get the right one the first time. I don\u2019t cut corners or upsell you a higher Ru than you need, because I know that\u2019s a waste of your money.<\/p>\n

Here\u2019s a quick cheat sheet I keep for my clients, because I get tired of answering the same questions:<\/p>\n