If you’ve ever dealt with industrial piping systems—whether for oil and gas, chemical processing, or even heavy water treatment—you’ve probably come across GOST flanges at some point. As someone who’s 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: “What’s the difference between all these GOST flange pressure classes?” Let’s be real, it’s not like ASME classes where the numbers line up neatly, and it’s way more specific to post-Soviet industry standards. Skip the boring textbook jargon for a sec—this is the stuff I actually use every day to make sure my clients don’t order the wrong flange and end up with a leak that costs them thousands (not to mention stress). GOST Flanges
First, let’s cut through the confusion: GOST flanges don’t 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 “nominal pressure” or Ру (that’s the Cyrillic letter R, pronounced “rood”)—I just call them “Ru ratings” 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’s designed for, especially in hot pipes.
Let’s 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—they’re 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’t spike. Don’t get me wrong, they work, but I never recommend them for anything that gets over 250°F, 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—cost them $12k in downtime. Never again, man.
Next up is 10 Ru. This is probably the sweet spot for most general industrial use, right around 160 psi or 16 bar. It’s 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—DN50, DN100, DN200 (that’s nominal diameter, another thing people mix up)—because every factory needs spares. The temperature limit here is around 300°F, so don’t use this for super hot oil or gas, but it’s perfect for the 80% of piping that’s not extreme.
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—you don’t have to splurge on a high Ru rating if you don’t need it.
Wait, hold on—there’s 25 Ru too, right? 400 psi or 40 bar. That’s 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°F, which is key for hot industrial processes. I always make sure to tell clients that 25 Ru flanges aren’t just “stronger”—they’re also made to resist more wear, so if you’re installing flanges in a remote area that’s hard to access, investing in these will save you from replacing them every couple of years.
Now, the higher Ru ratings—these are for when you’re 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°F for 63 Ru). I don’t stock a ton of these because not every project needs them, but when I do, they’re for things like nuclear power plant piping, high-pressure refinery lines, or large-scale LNG transfer systems. The thing about these is that they’re not cheap—so I always make sure clients double-check their pressure and temperature specs before ordering, because ordering the wrong Ru here isn’t just a cost mistake, it’s a safety hazard.
Wait, but let’s get one thing straight: the Ru rating doesn’t directly equal bar or psi. It’s tied to GOST’s specific temperature-pressure curve. For example, a 16 Ru flange might be rated for 25 bar at 20°C, but at 300°C, that drops to like 12 bar. That’s why I never just tell a client “10 Ru is 10 bar”—I always ask for their operating temperature, fluid type, and pressure, because that’s how you pick the right rating. I’ve had clients come to me thinking “Ru is pressure, full stop” and they end up with flanges that can’t handle their hot oil. Lesson learned: always cross-check with the specs, not just the Ru number.
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.
Now, why does this matter for you, if you’re a plant manager or piping engineer ordering these? Let’s 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’t just sell you a flange— I ask questions: what’s the fluid? What’s the max operating pressure? What’s the temperature? Where is this flange being installed? (Is it underground? In a corrosive environment?) That’s how I make sure you get the right one the first time. I don’t cut corners or upsell you a higher Ru than you need, because I know that’s a waste of your money.
Here’s a quick cheat sheet I keep for my clients, because I get tired of answering the same questions:
- 6 Ru: 100 psi / 10 bar, low pressure, <250°F, HVAC, water supply
- 10 Ru: 160 psi / 16 bar, medium light, <300°F, compressed air, general water lines
- 16 Ru: 250 psi / 25 bar, medium heavy, <400°F, steam, natural gas gathering
- 25 Ru: 400 psi / 40 bar, heavy duty, <500°F, high-pressure steam, chemical lines
- 40 Ru: 630 psi / 63 bar, extreme heavy, <650°F, refinery piping, power plants
- 63 Ru: 1000 psi / 100 bar, ultra extreme, <750°F, LNG, nuclear, high-pressure process
Wait, but I should mention GOST 33259-2015, right? That’s the newer standard that replaced a lot of the old GOST 12815 specs. It aligns GOST flanges more with DIN and ASME, so a lot of clients prefer it because it’s easier to cross-reference with Western standards. The pressure classes are mostly the same, but the dimensions are updated, so I always clarify which standard my flanges are to avoid mix-ups for clients who work with international projects.
Now, if you’re reading this and thinking “Okay, I need GOST flanges for my project, but I’m not sure which Ru rating is right?” that’s what I’m here for. I’ve worked with hundreds of clients—from small local factories to large energy companies—and I can help you pick exactly what you need, no pressure, no jargon, just straight talk. I don’t hide behind technical manuals, I’ll walk you through it step by step, because I’ve been in your shoes (well, next to your piping) and I know how frustrating it is to order the wrong part.
If you’ve got questions about specific pressure classes, dimensions, or face types, just reach out for a consultation. We can talk through your project specs, send you samples if you need them, and make sure you get the right GOST flanges at a fair price. Don’t risk a bad flange ruining your next project—hit me up to talk details, and let’s get your piping sorted right.
BW Pipe Fittings REFERENCES
GOST 12815-80: Flat and Weld-Neck Flanges for Pipes and Fittings. Basic Dimensions.
GOST 33259-2015: Flanges for Pipes, Fittings and Accessories. Standards of Pressure.
Kern, R. (2019). Industrial Piping Design and Installation for Post-Soviet Facilities. Process Engineering Press.
European Pipe Fitting Association (EPFA). (2021). Comparison of GOST and International Flange Standards.
Zhejiang Chengjiu Pipeline Co., Ltd.
Zhejiang Chengjiu Pipeline Co., Ltd. is one of the most professional gost flanges manufacturers and suppliers in China, specialized in providing high quality customized service. We warmly welcome you to buy high-grade gost flanges from our factory. For price consultation, contact us.
Address: NO.9-1 Hengsheng Road, Jinchuan Street, Changshan Prefecture, Quzhou, Zhejiang Province, China
E-mail: sale@cncjflange.com
WebSite: https://www.cncjflange.com/
