Valve Flange Standards Explained: ASME B16.5, PN/DIN, JIS and Interchangeability

Why Flange Standard Compatibility Matters

Flanged end valves account for the majority of industrial valve connections in process plants, and three distinct flange standard families are in global use: ASME B16.5 (North American and most international EPC projects), EN 1092 / DIN (European and former European-standard countries), and JIS B 2220 (Japan, South Korea and Southeast Asia). These standards differ in bolt hole pattern, gasket contact face dimensions and pressure-temperature ratings — even where the nominal pipe size (DN or NPS) and nominal pressure class appear numerically similar. A valve supplied to ASME Class 150 cannot reliably bolt directly to a PN 16 DIN pipe flange without careful checking of bolt circle diameter and face geometry.

ASME B16.5 Pressure Classes

ASME B16.5 covers steel pipe flanges from NPS 1/2 (DN 15) to NPS 24 (DN 600) in seven pressure classes: Class 150, 300, 600, 900, 1500 and 2500. The class number originally referred to the allowable pressure in psi at a reference temperature, but the actual allowable pressure varies with temperature and material group. For example, a Class 300 flange in ASTM A105 carbon steel is rated 51.1 bar (740 psi) at 38 °C but only 13.8 bar (200 psi) at 400 °C. ASME B16.47 extends coverage to large bore flanges NPS 26 to NPS 60 in Series A (MSS SP-44 legacy) and Series B (API 605 legacy).

EN 1092 / DIN Flange PN Ratings

European flanges are standardised under EN 1092 (which replaced DIN 2501 and related DIN standards). The PN (Pression Nominale or Pressure Nominale) rating designates a nominal pressure in bar at 20 °C for the reference material grade. Standard PN ratings are PN 6, 10, 16, 25, 40, 63, 100, 160, 250, 320 and 400. The actual allowable pressure at elevated temperatures follows a de-rating curve similar to ASME — a PN 40 carbon steel flange (P265GH per EN 10028) is rated 40 bar at 20 °C but approximately 22 bar at 300 °C. One key dimensional difference from ASME: PN flanges typically use metric bolt sizes (M16, M20, M24 etc.) while ASME flanges use imperial bolts (3/4 inch, 7/8 inch, 1 inch UNC).

JIS B 2220 Flange Standard

JIS B 2220 covers steel pipe flanges used in Japan and widely adopted in South Korea, Taiwan and the ASEAN region (especially for Japanese-EPC-constructed plants). JIS uses a different pressure class notation: 5K, 10K, 16K, 20K, 30K, 40K and 63K (where K represents kgf/cm²). JIS 10K is approximately equivalent to PN 10 / ASME Class 150 in pressure rating but differs in bolt hole dimensions — JIS flanges typically have 8 bolt holes on NPS 4 / DN 100 at a different bolt circle diameter than either ASME or EN. When replacing valves in Japanese-built plants, specifying JIS flanges is essential to avoid bolt-hole misalignment.

Flange Face Types

• Raised Face (RF): Standard face for ASME Class 150 and 300 — 1.6 mm raised seating surface; gasket seats on the raised face only. ASME Class 600 and above also use RF or RTJ
• Flat Face (FF): Flange face is flush with the bolt circle — mandatory when mating with cast iron or non-metallic flanged equipment to avoid applying bending stress to the brittle flange
• Ring-Type Joint (RTJ): Oval or octagonal metal ring gasket seated in a machined groove — used for ASME Class 600 and above, high-pressure and high-temperature service in oil and gas
• Tongue and Groove (T&G): Interlocking male tongue seats into female groove — used on heat exchangers and older plant designs; provides self-centring and full gasket confinement
• Male and Female (M&F): Similar to T&G but with a full-width raised face on one flange — used on pump and equipment nozzles paired with vessel nozzles
• Large Male Face (LMF) / Large Female Face (LFF): Full-face equivalent used on low-pressure large diameter flanges

Interchangeability Rules: Can You Mix Standards?

ASME Class 150 and PN 20 flanges appear numerically similar but should NOT be mixed without engineering verification. For NPS 4 / DN 100, the ASME Class 150 flange has 8 bolt holes on a 127.0 mm bolt circle, while the PN 20 EN 1092 flange also has 8 holes on a 125.0 mm bolt circle — close but not identical. At smaller sizes the discrepancy is larger. The definitive check is to compare the bolt hole diameter, bolt circle diameter and outer diameter of both flanges from the applicable standard drawing. In general, Class 150 valves can be mated to PN 16 or PN 20 flanges only if a detailed dimensional check confirms compatibility — they must never be assumed interchangeable.