JIS 5K, 10K, 16K, 20K, 30K, 40K STEEL FLANGES

The JIS steel flange is a round flange made of steel to the Japanese standard JIS B2220, used to join valves, pumps, equipment, and pipe sections with bolts. Each flange is designated by pipe size (DN, or the A designation such as 100A) and the K pressure class, for example a JIS 10K DN100 flange.

The K rating is the nominal pressure in kgf/cm², so 5K corresponds to about 5 kgf/cm² and 40K to about 40 kgf/cm². The connection dimensions of JIS flanges differ from BS4504, EN 1092-1, and ASME B16.5, so when choosing a flange you must match the K rating of the valves, pumps, and equipment in use.

Overview of the JIS steel flange

The JIS flange is a round disc with a bore in the center for the fluid to pass through, surrounded by a ring of bolt holes used to bolt two opposing flanges together with a gasket in between. This joint keeps the pipeline sealed and allows it to be taken apart for maintenance or valve replacement.

The material is usually carbon steel such as SS400, S20C, S25C, or A105 for forged parts. The specific steel grade depends on the manufacturer and is stated in the Certificate of Quality (CQ) of each batch.

Advantages of the JIS steel flange

Equipment originating from Japan, Korea, and Taiwan commonly uses JIS connection ports, so JIS flanges of the same K rating fit this equipment directly without additional machining. The wide pressure range, from 5K for low-pressure pipelines to 40K for high-pressure lines, lets one standard serve many types of systems. The steel body withstands bolt tightening force and vibration well, and the detachable joint reduces system downtime during maintenance.

Applications and installation locations

JIS steel flanges are commonly used to connect valves, pumps, and other equipment in these systems:

• Water supply and drainage systems, buildings, and industrial parks
• Pump stations, and the suction and discharge ends of pumps
• HVAC systems, chilled water lines, and chiller cooling water lines
• Fire protection and sprinkler systems
• Plants using equipment and production lines imported from Japan, Korea, and Taiwan
• Steam, thermal oil, and high-pressure compressed air lines at the 20K, 30K, and 40K ratings according to the design

Flanges are usually found at both ends of valves, at the suction and discharge ports of pumps, and at the connections of Y-strainers, foot valves, flow meters, tank outlets, and heat exchangers… On long pipelines, flanges should be installed at sections that need to be removed frequently, for example before and after valves and close to the pump.

Classification of JIS flanges by working pressure

JIS steel flanges are divided into the pressure classes 5K, 10K, 16K, 20K, 30K, and 40K. The higher the class, the thicker the flange, the larger the outside diameter, and the more bolt holes there usually are at the same pipe size.

The values above are nominal pressures at normal temperature. The actual permissible working pressure depends on the material and the system temperature. The usage contexts are for reference only; the K rating for each pipeline is decided by the design.

JIS 5K and 10K flanges

The JIS 5K steel flange is the thinnest and lightest class, used for low-pressure pipelines. The JIS 10K flange is the most common on the market, used to connect most butterfly valves, gate valves, Y-strainers, and pumps built to JIS. In both classes, the small sizes have only 4 bolt holes: 5K has 4 holes up to DN80; 10K has 4 holes up to DN65 and changes to 8 holes from DN80.

JIS 16K and 20K flanges

These two classes have the same outside diameter, bolt circle, and number of bolt holes at sizes DN15 to DN200, differing only in thickness. For example, at DN100 the minimum thickness is 22 mm for 16K and 24 mm for 20K. Compared with the JIS 10K flange, the JIS 16K and 20K flanges have 8 holes from DN50 and a larger outside diameter from DN80 upward.

JIS 30K and 40K flanges

These two high-pressure classes are usually forged parts. At DN50 to DN80, the JIS 30K and 40K flanges have the same connection dimensions. From DN100 upward they differ: DN100 has an outside diameter of 240 mm for JIS 30K and 250 mm for JIS 40K, and DN150 is 325 mm and 355 mm.

Choosing the right K rating and notes when ordering JIS flanges

The first rule is to choose a flange of the same K rating and the same DN as the flange of the valve or pump it will be fitted to. Upgrading only the flange to a higher K rating does not make the whole joint withstand higher pressure, because the permissible pressure is also limited by the gasket, the bolts, and the valve body.

Do not cross-connect JIS flanges with PN flanges (BS4504, EN 1092-1) or ASME. In practice there are a few sizes where the bolt circle and number of holes coincide; for example, the JIS 10K DN150 flange and the BS4504 PN16 DN150 flange both have 8 holes on a 240 mm bolt circle. But the hole diameter and the other dimensions differ, so they should not be considered compatible, and the drawings must be checked before installation.

The gasket also changes with the K rating. At DN100, a ring gasket to JIS B2404 has an outside diameter of 149 mm for 5K, 159 mm for 10K, 165 mm for 16K and 20K, and 173 mm for 30K. Ordering the wrong gasket class easily leads to misalignment or failure to cover the full sealing face.

When ordering, please provide: the DN size, the K rating, the flange type (slip-on, weld neck, blind, threaded), the sealing face (FF or RF), the material, the surface finish (plain, hot-dip galvanized, or electro-galvanized), and the quantity. On receipt, re-measure the outside diameter, bolt circle, and number of holes, and compare the markings stamped on the flange with the CO and CQ documentation.

An Phu Thanh – A reputable distributor of JIS steel flanges in Vietnam

For industrial projects and MEP systems, choosing flanges of the right standard not only determines the construction schedule, but also ensures safe and durable operation of the entire pipeline.

Accompanying thousands of projects across the country over more than 17 years, An Phu Thanh DV TM Co., Ltd. is proud to be a reputable distributor of quality JIS 5K, 10K, 16K, 20K, 30K, and 40K steel flanges in Vietnam.

Why do partners and contractors trust An Phu Thanh?

• Large warehouse, ready stock: The full range of specifications from DN15 up to large sizes, in a variety of types (forged flanges, slip-on flanges, blind flanges, weld neck flanges).
• Transparent legal documentation: 100% of products come with full CO and CQ documents, supporting fast project acceptance.
• Complete solutions: Supply of full sets of flanges, industrial valves, fittings, sealing gaskets, and connecting bolts, saving the maximum time spent sourcing materials.
• Dedicated consultation: Our experienced team will advise on materials and industrial valves that suit your requirements.

If you need a quotation or advice on choosing JIS steel flanges, please contact Hotline 0946 729 913 or message An Phu Thanh’s Zalo OA. The experienced team at An Phu Thanh is always pleased to serve you.