10K API 6A 6BX Flanges

[RangerBill]

I am looking for a bit of advice regarding how to 'modify', within the API 6A guidelines, a 10K 6BX flange out of the spec. to fit commercially available pipe sizes.

i.e a 2-1/6" 10K flange doesn't fit a 2" NB pipe od (60.3mm) as the minimum dimension of the flange hub is larger than this. I can't find an unambiguous detail within the standard as to how you can detail and add a transition to the standard hub to reduce down to the O.D of the pipe and the weld prep. concerned. Bore matching/tapering is easy, but this hub OD problem usually foxes me!

It is possible to fit these flanges to usually two NB sizes. A lot of design outfits I have come accross simply ignor the API hub dimensions and 'modify' them to make the weld neck exactly match the pipe OD and live with a non-standard weld neck taper just because its neet looking. (dangerous) Some flange vendors do this also, but usually do their own FEA on the 'modified' design to prove fit for purpose.

If you can't help, can you point me in the correct direction?

 

[Hush]

What we usually do is supply it with an 8" transition nipple welded on. Two reasons; the sizes don't match and the materials don't match.

BX flanges require 60K material, usually 4130 which requires stress relief. In your example we would take a 2-1/2" XXH nipple, bore it out to 2-1/16, weld it on, and stress relieve it.

 

[ashleyg]

Although the history seems lost, careful reading of API Spec 6A will lead the reader to conclude that the writers of API Spec 6A never intended 6BX flanges to join to standard pipe. The 14th edition of 6A did mention transition pieces, but they do not appear in the latest edition. The dimensions shown for weld neck 6BX flanges exactly match the dimensions of the integral flanges shown. Manufacturers making equipment units of 10M or 15M (I use M in place of K) working pressure that do not otherwise appear in API 6A may use these flanges as shown to fabricate end and outlet connectors onto this equipment. API 6A provides stress allowables, etc. to design the bodies of these various forms of equipment. API 6A also specifies “Other End Connectors” which allows users of the specification to follow the design guidelines and make entirely new types of end and outlet connectors, or modify existing connectors, and still satisfy the requirements of the document.

Users of API documents that find them lacking should address suggested additions or changes to, American Petroleum Institute, 1220 L Street, NW, Washington, D.C. 20005-4070, USA, (202) 962-4791.

You can find a good deal of useful information about API flanges, their history and their use, at

http://www.woodcousa.com/online.htm.

 

[platvoet]

Non-matching 6BX flange hub OD and standard Pipe OD:
For standardization purposes I tried to collect basic design rules for this problem.

Info can be found in:

-Mayar piping handbook, 6th ed. Mc Graw&Hill
-API RP14E
-ASME B31.3
-ASME B16.25
-ASME B16.5
-API 6A

Info has'nt been studied yet. Standardization will take place in the coming months.

 

[RangerBill]

Thanks platvoet,

Forgive me but, Are you saying that in the 6th edition of 'Nayyar - Pipng Handbook' that there are some basic design rules covering this?

 

[platvoet]

Reference : Piping Handbook, 6th ed. Chapter A6, page A323.
Regards.
Theo Platvoet