{"id":3609,"date":"2026-10-27T15:09:42","date_gmt":"2026-10-27T07:09:42","guid":{"rendered":"http:\/\/www.expressvelachery.com\/blog\/?p=3609"},"modified":"2026-10-27T15:09:42","modified_gmt":"2026-10-27T07:09:42","slug":"what-is-the-difference-between-pn-and-ansi-flanges-45bd-6b9df5","status":"publish","type":"post","link":"http:\/\/www.expressvelachery.com\/blog\/2026\/10\/27\/what-is-the-difference-between-pn-and-ansi-flanges-45bd-6b9df5\/","title":{"rendered":"What is the difference between PN and ANSI flanges?"},"content":{"rendered":"

If you\u2019ve ever worked with industrial piping\u2014whether you\u2019re a plumber, pipeline engineer, or someone who just orders parts for a manufacturing plant\u2014you\u2019ve probably run across flanges. And when you did, you definitely saw those two abbreviations: PN and ANSI. I know, I used to mix \u2019em up too, back when I first started selling PN flanges. I\u2019d get calls from people asking for \u201cANSI PN flanges\u201d like they were the same thing, and man, I had to correct that so many times. So today, let\u2019s break this down like we\u2019re chatting over a coffee (and no boring textbook stuff, promise). PN Flanges<\/a><\/p>\n

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First off, let\u2019s start with what a flange even does, just to set the scene. A flange is basically a metal ring that connects pipes, valves, pumps, or other equipment together. It\u2019s got holes around the edge for bolts, so you can clamp two flanges tight, make a leak-proof seal. The number on a flange\u2014like PN16 or ANSI 150\u2014is its pressure rating. That\u2019s super important, right? If you use the wrong one, say a low-pressure flange on a pipeline carrying hot, high-pressure gas, you\u2019re gonna have a bad time. Leaks, downtime, maybe even safety issues. That\u2019s why knowing the difference between PN and ANSI isn\u2019t just technical\u2014it\u2019s practical.<\/p>\n

Let\u2019s tackle PN first, since that\u2019s what I sell every day. PN stands for \u201cPressure Nominal\u201d (though sometimes folks say \u201cNominal Pressure\u201d and it means the same thing). PN is a metric system rating, used mostly in Europe, Asia, Africa, and a lot of places outside North America. The number next to it? That\u2019s the maximum working pressure the flange can handle at a specific temperature\u2014usually 20\u00b0C (68\u00b0F), which is like room temperature. Wait, important caveat here: PN isn\u2019t in psi (pounds per square inch), it\u2019s in bar. So PN16 is 16 bar, which converts to roughly 232 psi. Got that? Metric pressure, metric unit, tied to 20\u00b0C. Another thing about PN: it\u2019s standardized by the International Organization for Standardization (ISO), so PN10, PN16, PN25, PN40 are all common sizes. And here\u2019s a key point for my customers: PN flanges also tie to metric pipe sizes. So a PN16 flange for a 100mm pipe is gonna have different bolt hole spacing than an ANSI flange for a 4-inch pipe. No mixing those up\u2014you can\u2019t just swap a PN flange for an ANSI one on the same pipe, even if they look similar. That\u2019s a mistake I\u2019ve seen way too many new guys make.<\/p>\n

Now ANSI flanges. That\u2019s North America\u2019s go-to standard, right? ANSI stands for American National Standards Institute. Their rating system uses psi, and the numbers are like ANSI 150, ANSI 300, ANSI 600. ANSI 150 is about 150 psi at 20\u00b0C, which is way lower than PN16 (232 psi) \u2014 that\u2019s a big difference! Another thing: ANSI\u2019s pressure rating is actually for a higher temperature, wait\u2014let me double-check that. Yeah, ANSI flanges are rated for their maximum pressure at a higher temp, like 100\u00b0F or sometimes 200\u00b0F, depending on the material. So as temperature goes up, the pressure rating of both PN and ANSI goes down, but ANSI\u2019s curve is a bit different. Also, ANSI uses imperial pipe sizes\u20144 inches, 6 inches, etc.\u2014so flange dimensions are in inches, not millimeters. Bolt hole sizes, the distance between bolt centers, the outer diameter of the flange\u2014all imperial for ANSI, metric for PN. That\u2019s why when you order, you have to know which standard your system uses first. I\u2019ve had a customer call once, he thought he needed PN25 (25 bar, ~362 psi) but his pipeline was set up for ANSI 300 (300 psi, ~20.7 bar). Total mix-up, almost cost him a wrong order and a headache.<\/p>\n

Wait, let\u2019s talk about materials too, because that ties into the rating. PN flanges are usually made from carbon steel, stainless steel, or alloy steel, same as ANSI, but the way they\u2019re tested? ISO for PN, ANSI\/ASME for ANSI. ASME is the American Society of Mechanical Engineers, they work hand-in-hand with ANSI on flange standards. So when a flange is ANSI-rated, it\u2019s tested to ASME B16.5, which is the standard for pipe flanges and flanged fittings. PN flanges follow ISO 7005, that\u2019s the main one for metallic flanges. So those are two different testing bodies, which is why their pressure ratings don\u2019t line up one-to-one. Like, PN16 \u2260 ANSI 150, even though their numbers are close. PN16 is higher pressure, so you can\u2019t use an ANSI 150 flange if your system calls for PN16\u2014same vice versa, don\u2019t use a PN16 on a system rated for ANSI 300. That\u2019s a common misconception because the numbers look similar, but they\u2019re totally different units and standards.<\/p>\n

Another big difference: flange faces. The face is the part of the flange that touches the gasket between the two flanges. PN flanges often use a flat face (FF) or raised face (RF), same as ANSI, but sometimes the finish is different? Wait, no\u2014actually, the key here is that the gasket size depends on the flange\u2019s nominal size, which is metric for PN, imperial for ANSI. So a PN16 flange for 100mm pipe needs a metric gasket, while an ANSI 150 flange for 4-inch pipe needs an imperial gasket. If you get the wrong gasket, you\u2019ll get a leak, no question. I always tell my customers: don\u2019t just buy a flange, bring your pipe spec\u2014whether it\u2019s metric (mm, bar) or imperial (inches, psi)\u2014that\u2019s the first thing to confirm.<\/p>\n

Let\u2019s throw in a real-world example to make this concrete. Suppose you\u2019re building a new water pipeline in Germany (they use PN standards mostly). You need a flange for a 50mm pipe, operating at 16 bar. You\u2019d order a PN16 50mm flange. Now, if that same pipeline was in Houston, Texas, you\u2019d need an ANSI flange: 2-inch pipe, ANSI 150. If you tried to use the PN16 flange there, it\u2019s not just that the pressure is different (16 bar = ~232 psi vs 150 psi), but the bolt holes would be the wrong size (metric vs imperial), the outer diameter would be off, and the gasket wouldn\u2019t fit. It\u2019d be like trying to put a European car tire on an American rim\u2014doesn\u2019t work, even if they\u2019re both rated for similar weight.<\/p>\n

Wait, what about when someone says \u201cPN vs ANSI for high pressure\u201d? Let\u2019s see: the highest common PN is like PN100, right? That\u2019s 100 bar (~1450 psi). The highest common ANSI is ANSI 2500, which is 2500 psi (~172 bar). So at the super high end, ANSI goes higher in psi, PN goes higher in bar. But again, that\u2019s different units, so you can\u2019t just convert them directly. You have to look at the actual spec sheet, not just do a quick math conversion.<\/p>\n

Now, why does this matter for you, especially if you\u2019re ordering flanges? Let\u2019s say you\u2019re a maintenance manager at a chemical plant. Your equipment was installed in 2010, and the old flanges are PN25. If you replace one, you can\u2019t just buy a PN16 thinking \u201cclose enough\u201d\u2014PN25 is higher pressure, so it\u2019s thicker, the bolts are stronger, and the bolt holes are spaced for higher stress. If you use a PN16 replacement, it might bend or crack under the chemical\u2019s pressure, leading to a shutdown. Or if you\u2019re expanding a pipeline in a country that uses both standards (some places mix metric and imperial), you have to make sure every connection is on the same standard. I\u2019ve had customers who work on international projects\u2014they\u2019ll ask me, \u201cCan you ship PN flanges that fit an ANSI 6-inch pipe?\u201d The short answer is no, because the nominal sizes don\u2019t match. So always, always confirm: is your system metric or imperial? What\u2019s its pressure rating in bar or psi? That\u2019s non-negotiable.<\/p>\n

I sell PN flanges, so let me add a bit of context from my side. A lot of people come to me because they\u2019re working on projects that follow ISO standards\u2014whether it\u2019s in Europe, Southeast Asia, or parts of South America. They don\u2019t have to deal with the conversion mess between metric and imperial, so they stick with PN. But sometimes, those same customers have to connect to ANSI equipment when they import a pump from the US or a valve from Canada. For those cases, I can help them find transition flanges\u2014flanges that are one side PN, one side ANSI, so you can bridge the two standards. But I always warn them: transition flanges are temporary fixes, not long-term solutions. It\u2019s better to design your system entirely on one standard if you can, to avoid leaks and delays.<\/p>\n

Wait, let\u2019s clear up another myth: some people think PN is only for carbon steel, and ANSI is for stainless steel. No, that\u2019s not true. I sell PN stainless steel flanges just as much as carbon steel, and ANSI flanges come in both materials too. The material is separate from the standard\u2014it\u2019s about the pressure and size, not the metal. So that\u2019s a mistake a lot of new buyers make, assuming material ties to PN\/ANSI, but it doesn\u2019t.<\/p>\n

Let\u2019s recap the key differences to make sure it\u2019s all stuck:<\/p>\n

    \n
  1. Units: PN uses bar (metric), ANSI uses psi (imperial)<\/li>\n
  2. Origin: PN is ISO\/metric (global mostly outside US\/Canada), ANSI is ASME\/imperial (US\/Canada)<\/li>\n
  3. Size labels: PN numbers (PN10, PN16) don\u2019t convert directly to ANSI numbers (ANSI 150, 300)<\/li>\n
  4. Dimensions: Metric bolt holes, pipe sizes for PN; imperial for ANSI<\/li>\n
  5. Temperature rating: Both go down as temp rises, but their base ratings are at different temps (usually 20\u00b0C for PN, higher for ANSI)<\/li>\n<\/ol>\n

    Now, if you\u2019re reading this and thinking, \u201cOkay, so I need flanges\u2014how do I get the right ones?\u201d Don\u2019t stress. All you need is a few quick specs from your system:<\/p>\n