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Overview of the JIS steel flange<\/h2>\n
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.<\/p>\n
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.<\/p>\n
Advantages of the JIS steel flange<\/h3>\n
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.<\/p>\n
Applications and installation locations<\/h3>\n
JIS steel flanges are commonly used to connect valves, pumps, and other equipment in these systems:<\/p>\n
- \n
- Water supply and drainage systems, buildings, and industrial parks<\/li>\n
- Pump stations, and the suction and discharge ends of pumps<\/li>\n
- HVAC systems, chilled water lines, and chiller cooling water lines<\/li>\n
- Fire protection and sprinkler systems<\/li>\n
- Plants using equipment and production lines imported from Japan, Korea, and Taiwan<\/li>\n
- Steam, thermal oil, and high-pressure compressed air lines at the 20K, 30K, and 40K ratings according to the design<\/li>\n<\/ul>\n
Flanges<\/a> 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\u2026 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.<\/p>\n
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JIS steel flanges are commonly used to connect valves, pumps, and other equipment in these systems<\/figcaption><\/figure>\n Classification of JIS flanges by working pressure<\/h2>\n
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.<\/p>\n
\n\n\n
\n \nK rating<\/th>\n Nominal pressure<\/th>\n Typical context (for reference)<\/th>\n<\/tr>\n<\/thead>\n \n 5K<\/td>\n 5 kgf\/cm\u00b2 (about 4.9 bar)<\/td>\n Low-pressure pipelines: process water, drainage, ventilation<\/td>\n<\/tr>\n \n 10K<\/td>\n 10 kgf\/cm\u00b2 (about 9.8 bar)<\/td>\n Water supply and drainage, pumps, HVAC, chillers, building systems<\/td>\n<\/tr>\n \n 16K<\/td>\n 16 kgf\/cm\u00b2 (about 15.7 bar)<\/td>\n Pump discharge lines, higher-pressure water lines<\/td>\n<\/tr>\n \n 20K<\/td>\n 20 kgf\/cm\u00b2 (about 19.6 bar)<\/td>\n High-pressure lines in industry<\/td>\n<\/tr>\n \n 30K<\/td>\n 30 kgf\/cm\u00b2 (about 29.4 bar)<\/td>\n Steam, thermal oil, high-pressure systems according to the design<\/td>\n<\/tr>\n \n 40K<\/td>\n 40 kgf\/cm\u00b2 (about 39.2 bar)<\/td>\n High pressure: power plants, chemicals according to the design<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n 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.<\/p>\n
JIS 5K and 10K flanges<\/h3>\n
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.<\/p>\n
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JIS 5K and 10K flanges<\/figcaption><\/figure>\n JIS 16K and 20K flanges<\/h3>\n
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.<\/p>\n
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JIS 16K and 20K flanges<\/figcaption><\/figure>\n JIS 30K and 40K flanges<\/h3>\n
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.<\/p>\n
Choosing the right K rating and notes when ordering JIS flanges<\/h2>\n
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.<\/p>\n
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.<\/p>\n
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.<\/p>\n
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.<\/p>\n
An Phu Thanh \u2013 A reputable distributor of JIS steel flanges in Vietnam<\/h2>\n
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.<\/p>\n