Branch on RFWN neck

[anolan23]

Is it acceptable to drill a hole into the neck of a weld neck flange and put a branch connection if the reinforcement is sufficient? The code of construction is ASME B31.3 and the flange is ASME B16.5. I assume this isn't allowed.

 

[mk3223]

It's a good question.
IMO, it can be acceptable if one can provide an engineering proof with FEA, for example, the connection on the flange neck is a sound design mechanically.

But, why to do it like that? There are many "established" ways, quick and simple, for the branch connection design.

 

[XL83NL]

You could consider an orifice flange for, ASME B16.36.
Neverthless, Ive never seen a sound and simple approach to tacklingthis problem for B16.5 flanges, while it's done every now and then.

One way of showing compliancewith hand calcs would be to assume that the drilled hole creates an equivalent external pressure on the bolt hole, and needs to be sufficient strong acc code rules (e.g. acc. B31.3 304.1.3). However, with simple hand calcs, Im not sure if youd get all the calculations correct, as e.g. the drilled hole itself also needs to be sufficiently strong from an internal pressure point of view. FEA would then be a good resort to get all requirements in 1 calculation.

 

[LittleInch]

Is it acceptable? - Well it might be, but my guess is you would need to get an FEA done on the entire flange. This means it wouldn't be a B16.5 flange anymore and will likely fail if exposed to a full flange pressure - as you probably now need to use ASME VIII acceptance limits. Most B16.5 flanges fail when assessed against this code at their design pressure and temperature.

What you have is essentially now a lump of metal like any other lump of metal, just not a flange to B 16.5.

codes are not in the habit of listing things which aren't allowed, but list ways to do things, but always rely on good engineering practice and the application of design principles.

I struggle to see why you would want to do this - there must be an alternative.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[XL83NL]

A bleed ring is a cheap alternative, widely used in the industry. Although I’ve never see code compliant calculations for that.