BS 4504 is the British Standard for circular flanges for pipes, valves, and fittings (PN-designated). Section 3.1 (BS 4504: Section 3.1: 1989) is the most referenced portion, specifying steel flanges. BS 4504 has been formally superseded by EN 1092-1, which was designed to be dimensionally identical for the same PN class. BS 4504 flanges may still be found on existing plant installations in the UK and Commonwealth markets. Covers sizes DN 10 to DN 3000 across PN 2.5 to PN 40.

View Other Standards:

EN 1092-1 (Replacement)   DIN 2527 Blind    JIS B2220   DIN 2543 Slip-On


BS 4504 — British Circular Flange Standard PN 2.5 – PN 40

BS 4504 is the British Standard for circular flanges. Section 3.1 specifies steel flanges. It has been formally superseded by EN 1092-1, which is dimensionally identical for the same PN class. BS 4504 flanges may still be found on existing UK and Commonwealth plant installations.


Key Specifications

Standard: BS 4504: Section 3.1: 1989
Pressure: PN 2.5 / 6 / 10 / 16 / 25 / 40
Size Range: DN 10 – DN 3000
Face Types: Flat Face (FF), Raised Face (RF), RTJ (for high PN)
Status: Superseded by EN 1092-1 (2002)
Compatibility: Dimensionally identical to EN 1092-1 for same PN class


BS 4504 Pressure Rating Summary

PN Class Max Pressure (bar)at 20°C Max Pressure (psi) Typical Bolt
Circle		 Common Sizes Notes
PN2.5 2.5 bar 36 psi Low-pressure table DN 50–DN 1000 Low-pressure process/utility
PN 6 6 bar 87 psi Table 1 DN 10–DN 2000 Water, drainage, HVAC
PN 10 10 bar 145 psi Table 2 DN 10–DN 3000 Municipal water, general industrial
PN 16 16 bar 232 psi Table 3 DN 10–DN 3000 Water, gas, light steam
PN 25 25 bar 363 psi Table 4 DN 10–DN 2000 Steam, gas, chemical
PN 40 40 bar 580 psi Table 5 DN 10–DN 600 High-pressure steam, oil & gas
Table 1: BS 4504 Section 3.1 pressure ratings. Note: BS 4504 has been withdrawn and replaced by EN 1092-1. Dimensionally compatible with EN 1092-1 for the same PN class.


BS 4504 vs. EN 1092-1 — Dimension Equivalence

Key Point: The flange OD (D), bolt circle diameter (k), bolt hole diameter, and thickness (b) for any given DN/PN combination are identical between BS 4504 and EN 1092-1. This means EN 1092-1 flanges can directly replace BS 4504 flanges in existing installations. Always verify material group compatibility when replacing.
 

BS 4504 Reference — PN 16 Dimension Table (Selected Sizes)

DN Flange OD D (mm) Bolt Circle k (mm) Bolt Holes Hole d (mm) Thickness b (mm) RF d₄ (mm)
10 90 60 4 14 12 40
15 95 65 4 14 12 45
25 115 85 4 14 14 68
50 165 125 4 18 16 102
80 200 160 8 18 18 138
100 220 180 8 18 18 158
150 285 240 8 22 20 212
200 340 295 12 22 22 268
300 460 410 12 26 26 378
400 580 525 16 30 28 490
500 715 650 20 33 30 610
600 840 770 20 36 32 725
Table 2: BS 4504 Section 3.1 — PN 16 Steel Flange reference dimensions. Dimensional tables are identical to EN 1092-1 for the same PN class.


Materials

Carbon Steel: BS 1503-161 (Gr. 261), BS 1504-161
Stainless Steel: BS EN 10088 (304, 316, 321, 347)
Duplex: BS EN 10088 (1.4462, 1.4410)
Alloy Steel: BS 1503-622 (2¼Cr-1Mo)


Applications

UK and Commonwealth industrial plant (legacy installations)
Water and wastewater treatment (historic PN 10/16 use)
North Sea offshore platforms (legacy BS specification)
Power generation and process industries in UK
Refinery and chemical processing (existing plant)
 

For new projects or replacement of BS 4504 flanges, EN 1092-1 is the recommended standard. EN 1092-1 flanges are dimensionally identical and carry current CE marking compliance for the EU market.
 

Flange Material Selection Guide

Material Grade Max Temp Key Application
Carbon Steel BS 1503-161 / A105 425°C Steam, water, air, oil
Stainless Steel 316 BS EN 10088 / A182 F316 400°C Chemical, food, pharma
Stainless Steel 316L A182 F316L 400°C Weld-intensive fabrication
Duplex 2205 BS EN 10088 / S31803 300°C Offshore, seawater
Alloy Steel F22 BS 1503-622 / A182 F22 550°C Power plant, refineries
Table 3: Material selection guide for BS 4504 / EN 1092-1 flanges.

HT PIPE supplies BS 4504-compatible flanges (EN 1092-1 replacement) in carbon steel, stainless steel, duplex, and special alloys. All flanges supplied with EN 10204 3.1 material test reports and dimensional inspection certificates.