Flanges
British Standard BS 4504 : Section 3.1 : 1989 - Circular Flanges for Pipes, Valves and
Fittings (PN Designated), Specification for Steel Flanges. This covers flanges in nominal
pressure ranges PN 2.5 to PN 40 and nominal sizes up to DN 4000 (see table below).
BS 4504 substantially agrees with ISO 7005-1 : 1992 (E) Part 1 : Steel Flanges.
BS 4504 : 1969 is still commonly used. This older standard allows for manufacture from
bar, whereas the latest standard specifies that forging or plate are to be used, which can
be significantly more expensive. There are minor differences in dimensions between the
two versions. The following tables are based on the later version.
Notes
- Flanges > DN 2000, are not covered in this summary.
- Dimensions: Nominal sizes, DN followed by a numerical designation of size (a convenient round number for reference
purposes), are used as defined in ISO 6708.
- Pressure Ratings: Nominal pressures, i.e. PN followed by a numerical designation of size (a convenient round number for
reference purposes), are used as defined in ISO 7268.
1 Dimensions for these flanges are not covered in this summary.
2 The DN range for weld neck flanges extends to DN 4000 for PN 2.5, to DN 3600 for PN 6, and to DN 3000 for PN 10.
Designations/Marking
Marking. All flanges are marked with BS number, code number, PN, DN, material designation, manufacturers
name or trade mark, cast number or melt identification, thread identification, An example follows:
Summary of flanges covered by BS 4504 : Section 3.1
Code No. Description PN Range DN Range
101 Plate flange for welding
(see page 8-65)
PN 2.5 DN 10 to DN 2000
PN 6, 10, 16, 25, 40 DN 10 to DN 600
102
Loose plate flange with weld-on plate collar or
for lapped pipe end
(Weld-on plate collar = Code 1321
Lapped pipe end = Code 1331)
PN 6, 10, 16, 25, 40 DN 10 to DN 600
104 Loose plate flange with weld-neck collar (Weldneck
collar = Code 1341) PN 6, 10, 16, 25, 40 DN 10 to DN 600
105 Blank flange (see page 8-70)
PN 2.5, 6 DN 10 to DN 2000
PN 10, 16 DN 10 to DN 1200
PN 25, 40 DN 10 to DN 600
111 Weld-neck flange (see page 8-66)
PN 2.5, 6, 10, 16 DN 10 to DN 20002
PN 25 DN 10 to DN 1000
PN 40 DN 10 to DN 600
112 Hubbed slip-on flange for welding
(see page 8-68)
PN 6 DN 10 to DN 300
PN 10, 16, 25, 40 DN 10 to DN 600
113 Hubbed threaded flange (see page 8-69) PN 6, 10, 16, 25, 40 DN 10 to DN 150
121 Integral flange PN 6, 10, 16, 25 DN 10 to DN 2000
PN 40 DN 10 to DN 600
BS 4504/111/B - PN 16 - DN 400 - B4 - XXX - 12345
Cast Number or melt identification
Manufacturer’s name or trade mark
Material designation
Nominal size, DN
Nominal Pressure, PN
Flange face type (A - H)
Flange code number
British standard number
