As the owner and lead sales contact for a JIS and KS flanges supply business, I get at least a dozen calls a week from engineers, plant managers, and fabricators asking the same question: “What pressure ratings do JIS flanges actually have?” Most of these callers aren’t just curious—they’re staring down a tight deadline for a chemical plant expansion, a marine engine overhaul, or a water treatment upgrade, and they need to pick flanges that won’t blow mid-operation. I’ve learned over the years that pressure ratings aren’t just arbitrary numbers; they’re the backbone of safe, long-running industrial systems, and cutting corners here can end up costing way more than saving a few dollars on the wrong flanges. JIS & KS Flanges
First, I need to clarify what JIS flanges even are, because a lot of folks mix them up with ANSI flanges (the North American standard) or DIN flanges (the European one). JIS stands for Japanese Industrial Standards, and it’s a set of standards developed to match Japan’s unique industrial landscape—from coastal marine industries to high-temperature petrochemical facilities. Unlike ANSI, which uses pressure classes like 150, 300, and 600, JIS uses MPa (megapascals) and bar as its primary pressure units, which is a key difference that trips up a lot of new people working with JIS specs. It also uses different face types too—raise face (RF), flat face (FF), and ring joint (RJ) are common, but their pressure ratings tie directly to both the material and the size of the flange, which is where most mistakes happen.
Let’s break down the core pressure ratings for JIS flanges, starting with the most common series: JIS 10K, JIS 20K, JIS 30K, JIS 40K, and the less common JIS 5K (usually for low-pressure water or air systems). Wait, I should note that K here isn’t kelvin—it’s the Japanese term for pressure classes, short for “kilo.” JIS 10K is the workhorse, right? That translates roughly to 1.0 MPa, or about 145 psi, for smaller sizes. But here’s the catch that I’ve seen so many engineers get wrong: that rating only applies to smaller diameters. For example, a JIS 10K flange with a nominal pipe size (NPS) of 2 inches (DN 50) is rated for 1.0 MPa, but a JIS 10K flange at DN 600 (24 inches) drops down to 0.6 MPa, or 87 psi. Why? Because as the flange gets larger, the pressure load spreads over a bigger circumference, but the clamping force from the bolts has to be calibrated to handle that. If you use a DN 600 JIS 10K flange rated for 1.0 MPa on a large water main, it’s going to leak or fail, plain and simple. That’s why at my supply business, we always ask for both the K class and the pipe size before quoting anything—we don’t want to sell someone the wrong flange, because bad flanges lead to bad reputations, and we’ve built this business on repeat customers, not one-off mistakes.
Next up is JIS 20K, which is the next step up in pressure. JIS 20K translates to roughly 2.0 MPa (290 psi) for small sizes, again at DN 50. But same size penalty applies here: a DN 600 JIS 20K flange is only rated for 1.2 MPa, or 174 psi. This is the go-to for medium-pressure systems, like small chemical processing lines, marine fuel lines, or high-pressure steam for low-to-medium temperature operations. I remember a call we got last year from a shipyard in Osaka—they were repairing a cargo vessel’s fuel system, and they needed JIS 20K flanges for the 6-inch lines. The engineer initially ordered 1.0 MPa flanges, but once we checked the pressure of their fuel system (which runs at around 1.8 MPa, almost 260 psi), we corrected him. If he’d gone with the 10K flanges, they would’ve cracked within a few months at sea, which would’ve cost the ship thousands in downtime. That’s the kind of hands-on, specification check we do for every customer, because we know the difference between a flange that meets specs and one that keeps a project on track.
Then we have JIS 30K and JIS 40K, the high-pressure JIS flanges for heavy-duty applications. JIS 30K starts at 3.0 MPa (435 psi) for DN 50, and drops to 2.0 MPa at DN 600. JIS 40K is the heavy hitter, going up to 4.0 MPa (580 psi) at small sizes, down to 2.5 MPa at DN 600. These are used for things like high-pressure hydraulic systems, petrochemical reactors, large marine process lines, and underground pipeline systems where pressure is consistently high. We rarely stock JIS 40K flanges off the shelf, because they’re a custom order for most projects, but we work with a network of certified Japanese and Korean manufacturers (hence KS flanges, Korean Industrial Standards, which we also supply) to get them in within 10 business days for urgent jobs. I should mention that KS flanges, while separate standards, often align closely with JIS ratings for common sizes, so many of our customers use them interchangeably when their project allows, which is a bonus we highlight.
A huge, often misunderstood factor that affects JIS flange pressure ratings is material. You can’t have a pressure rating without matching it to the material the flange is made from. A JIS 10K carbon steel flange has a completely different rating than a JIS 10K stainless steel or brass flange, for example. Carbon steel JIS flanges (the most common type, used for general-purpose industrial applications) have a temperature-pressure rating that declines as temperature rises. A carbon steel JIS 10K flange rated for 1.0 MPa at room temperature is only good for about 0.7 MPa at 400°C (752°F), which is a critical detail for high-temperature steam systems. Stainless steel JIS flanges, on the other hand, maintain their pressure ratings better at high temperatures—for example, a 304 stainless JIS 20K flange holds its 2.0 MPa rating up to around 600°C, which makes it ideal for food processing or chemical applications where high heat is a constant. We also supply JIS flanges in cast iron, bronze, and even alloy steel for specialty projects, so we always ask about operating temperature and medium (water, steam, oil, corrosive chemicals) to make sure the rating matches the job.
Another thing that confuses a lot of first-time JIS customers is the difference between working pressure and test pressure. JIS flanges aren’t just rated for working pressure—they have a hydrostatic test pressure that’s higher, usually 1.5 times the working pressure, per JIS B2220 (the main standard for JIS flanges). That means a JIS 20K flange rated for 2.0 MPa working pressure was tested to 3.0 MPa before it left the factory. But that test pressure is for initial installation; ongoing operating pressure can’t exceed the rated working pressure, even if the test was higher. I’ve had customers call us asking if they can run their system at test pressure permanently, and the answer is a hard no—testing is just to make sure the flange doesn’t fail during installation.
I should also touch on common mistakes I see customers make all the time, because that’s what makes this blog practical, not just a list of specs. First, mixing up JIS pressure classes with ANSI classes. A lot of people assume JIS 10K is the same as ANSI 150, which is close (ANSI 150 is 1.05 MPa), but JIS 20K is roughly ANSI 300, and JIS 30K is close to ANSI 400, but the size-based pressure drop is different. For example, ANSI 150 flanges at DN 600 are still rated for ~1.0 MPa, while JIS 10K drops to 0.6 MPa. That’s a critical difference that can lead to overloading if you mix standards. Second, ignoring temperature derating. Like I mentioned earlier, high temperatures lower pressure ratings, and many customers don’t account for that when designing systems. Third, buying uncertified flanges to save money. We see this all the time—someone buys a cheap off-brand JIS flange from a non-certified supplier, and it fails within a month. All the JIS flanges we supply (both JIS and KS) are certified to JIS B2220 and KS B1503 standards, with material test reports (MTRs) available for every order, so our customers never have to worry about failing inspections or safety tests.
Now, let’s talk about how to pick the right JIS flange for your project, because at the end of the day, specs are only useful if you apply them correctly. First, confirm your operating pressure: don’t just go by system design pressure, add a 10-15% safety margin for fluctuations, which is common in industrial systems. Second, note your nominal pipe size (DN) and the flange face type (RF, FF, RJ), because that ties to both connection compatibility and pressure rating. Third, confirm operating temperature and medium, so you can pick the right material. Fourth, make sure you’re working with a certified supplier who can provide MTRs and match the JIS/KS specs to your project’s requirements. That’s what we do every day here—we don’t just sell flanges; we help customers spec the right ones.
I’ve been in this business for over 12 years, and I’ve seen too many projects derail because of incorrect flange pressure ratings. One time, a pharmaceutical plant in Tokyo tried to save money by buying JIS 10K flanges for their hot water lines, which run at 1.2 MPa and 120°C. The flanges failed in three places within two weeks, leading to a shutdown that cost them over $200,000 in lost production. We supplied them with JIS 20K stainless steel flanges with a temperature-derated pressure rating for their operating conditions, and they’ve been running without issues ever since. That’s why this stuff matters—pressure ratings aren’t just numbers on a sheet; they’re the difference between a project that stays on track and a disaster.
If you’re working on a project that requires JIS or KS flanges, whether it’s new construction, repair, or an upgrade, and you’re not sure about the correct pressure rating, don’t guess. Reach out to our team for a free spec check and quote. We can walk you through the pressure ratings for any JIS/KS flange size, material, and operating condition, and provide certified products that meet all safety and industry standards. We work with clients across marine, petrochemical, water treatment, food and beverage, and construction industries, so we know how to adapt to every unique project need.
B16.47 & AWWA C207 Flanges References:
Japanese Industrial Standards Committee. JIS B2220: Steel Flanges for Pipes, 2018.
Korean Agency for Technology and Standards. KS B1503: Steel Flanges for General Use, 2020.
American Society of Mechanical Engineers. Pressure Vessel and Piping Codes, Section VIII, 2021.
National Institute of Technology and Evaluation (Japan). Technical Report on JIS Flange Pressure Rating Derating, 2019.
Zhejiang Chengjiu Pipeline Co., Ltd.
Zhejiang Chengjiu Pipeline Co., Ltd. is one of the most professional jis flanges manufacturers and suppliers in China, specialized in providing high quality customized service. We warmly welcome you to buy high-grade jis 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/
