Flange Specification, BSI

Written by Matt Milbury on . Posted in Pipe Flange

The BSI specifications for flanges are:

  • BS 10 - Specification for Flanges and Bolting for Pipes, Valves, and Fittings
  • BS 3293 - Specification for Carbon Steel Pipe Flanges (over 24 inches nominal size) for the Petroleum Industry
  • BS 4504 - Specification for Steel Flanges Circular Flanges for Pipes, Valves and Fittings
  • ISO 7005-1 - Metallic Flanges - Part 1: Steel Flanges (this is substantially the same as BS 4504)


BSI Flange Materials

Standards usually specify the material from which the flange is produced.


BSI Flange Sizes

There are available flange sizes and grades for all standard pipe wall thicknesses and pressure ratings.


BSI Flange Facing Types

The typical flange faces used are flat face, raised face, tongue and groove and ring joint.


BSI Flange Finish

The flange face finish is determined by the standard used and measured as an Arithmetical Average Roughness Height (AARH). An example would be ANSI B16.5 which specifies face finishes within a range 125AARH - 500AARH (3.2 Ra to 12.5 Ra).


BSI Flange Class Rating




(ISO 7005-1)

DN 10 to

DN 4000



Blind 2.5-40 -
Lap Joint 6-40 -
Slip-On 2.5-40 150-600
Socket - -
Threaded 6-40 -
Weld Neck 2.5-40 150-600
Flat/Raised Facing As Above As Above
Ring Joint Facing 2.5-40 300-600
Other Facings 2.5-40 -