Flanges – Tips for an easy life.

The Golden Rules of Stainless Steel Flange supply

Flanges are amongst the most critical components in a pipeline. They are used as connections for pumps, valves, strainers etc. and for pipework which has to be regularly dis-assembled and re-assembled.

It is critical that the correct flanges are supplied that can cope with the pressure of the system and are compatible with all the components which are connected in the pipeline. A flange is specified by the nominal pipe size and the pressure rating. However, there are distinctly different types of flanges depending on the plant design. In the offshore, petro-chemical, power and nuclear power industries they are generally designed in the USA, UK or Germany. There are of course flanges required for the paper pulp, water, brewery industries etc. but the rules of suitability remain the same.

Those who are regularly involved in the buying and selling of flanges, will be all too aware of how easy it is to supply the wrong flange if the correct questions are not asked. In this short piece we outline the do’s to supply the correct flange which will avoid delay, frustration and most importantly costly mistakes!

Listed is a short tick list of the relevant questions for the correct identification of a flange

Golden rules for flange identification

  1. Stainless Steel Grade: 304L, 316L, 1.4306, 1.4404, 31803, 254SMO, UNS 31254 etc.
  2. Pipe Size: NB (Nominal Bore), NPS (Nominal Pipe Size), DN (Diameter Nominal)
  3. Dimensional specification: ASME B16.5, EN1092-1, BS4504, BS10, API605 etc.
  4. Pressure Ratings: 150#, PN16, Table E etc.
  5. Type of Face: RF (Raise Face), FF (Flat Face), RTJ (Ring Type Joint) etc.
  6. Quantity Required


  • There is no such thing as a ‘better grade’ of steel, and a higher price does not mean better quality or performance. Instead steel is manufactured to internationally recognised specifications to fulfil a particular application. Material grades may or may not be interchangeable, but it is essential that the grade of steel is fit for purpose. You must find out exactly what grade of material is acceptable before supplying or purchasing a stainless steel flange.
  • Flanges of different dimensional specifications and pressure ratings are not interchangeable.
Image of Stock Services Chris Price puzzling over a weld neck flange.
What’s this then? I think it is written on the side Chris?

Flange manufacturing materials

Dimensions Base Material Pressure Rating
ASME B16.5 ASTM A182 (Forgings) ASTM A240 (Plate) 150#. 300#. 400#. 600#. 900#. 1500#. 2500#.
API 605 ASTM A182 (Forgings) ASTM A240 (Plate) 150#. 300#. 400#. 600#. 900#. 1500#. 2500#.
ASME B16.47series A & B ASTM A182 (Forgings) ASTM A240 (Plate) 150#. 300#. 400#. 600#. 900#. 1500#. 2500#.
EN1092-1 ASTM A182 (Forgings) PN2.5. PN6. PN10. PN16. PN25. PN40. PN63. PN100. PN160. PN250. PN320. PN400.
BS4504 BS970 (Bar)ASTM A240 (Plate) ASTM A182 (Forgings) PN2.5. PN6. PN10. PN16. PN25. PN40. PN63. PN100. PN160.
BS10 BS970 (Bar)ASTM A240 (Plate) ASTM A182 (Forgings) Table D. Table E. Table F. Table H. Table J. Table K. Table R. Table S. Table T.


Typical Stainless Steel 18/8 Grade Designations

304 304S15 X5 Cr Ni 18 10 1.4301
304L 304S11 X2 Cr Ni 18 9 1.4307
316 316S31 X5 Cr Ni Mo 17 12 2 1.4401
316L 316S11 X2 Cr Ni Mo 17 13 2 1.4404
321 321S31 X6 Cr Ni 18 10 1.4541
316Ti 320S31 X6 Cr Ni Mo Ti 17 12 2 1.4571
SMO 254SMO X1 Cr Ni Mo Cu N 20 18 7 1.4547


The information contained in this article is intended to help you to supply the correct flanges contained in the golden rules. It is not intended as a comprehensive guide to all the flanges that are available.


Should you like to send you next enquiry for stainless steel flanges to Stock Services, please send us an email.

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