ASME B31.3 - Aluminium Flanges

[Caloooomi]

Hi all,

Very quick question regarding Appendix L of B31.3. Does anyone know the reason why the pressure-temperature ratings for socket welding flanges are lower than that of welding neck?

I've looked at the EN equivalents for the aluminium flanges and well, EN 1092-4 has only WN (Type 11) / blinds (Type 05) and EN 1759-4 is the same, so that doesn't help...

 

[XL83NL]

I could imagine that their design and construction, due to the use of a fillet weld, introduces lower bearing strength opposed to the rating a WN has.

By yhe way, Ive never seen an application using aluminum flanges under B31.3. What could be it's potential use or application?

 

[Caloooomi]

It has been suggested as a use for a cryogenic installation but I am currently against due to the cyclical nature of system, but figured I would explore it before dismissing the idea...

The actual use would be on a pressure vessel nozzle (ASME VIII, Div 1), however the P/t ratings from B16.5 do not exist for 6061 and when using the same dimensions as those from B16.5 for the flanges, say class 300, the ratings are then taken from B31.3 appendix L. Then the issue would be that the ratings from appendix L are a bit more aggressive when comparing to calculated flange ratings using Div 1 or even div 2...

 

[XL83NL]

Well, technically Im not sure if you can use B31.3 ratings for aluminum flanges (acc. B31.3 appendix L) under VIII-1, since B31.3 is not a listed standard under VIII-1.
What would be more in line with VIII-1 Code requirements is to select an aluminum alloy from section II part D, and use that material as a basis for a flange calculation acc. VIII-1 appendix 2.

Why not use 304/304L material for cryo? Isnt that much simpler? Or does aluminum provide an advantage over 304/304L?

 

[Caloooomi]

Hmmm. I mean, B31.3 says that the flanges shall meet the dimensional and tolerance requirements of ASME B16.5. So it is in effect a B16.5 flange, but derated pressure ratings as it is aluminium. Typically we have not had any issues with our AI when using them and I do not want to rock the boat now...

The aluminium flanges are used a lot on the nozzles for heat exchangers. You can go for a lap joint flange with ally stub / 304/L flange, or if we wanted to be fancy, a transition joint for 6061/304. Typically though, it is just a RFWN in aluminium with a stainless mate.

 

[XL83NL]

Aluminum flanges are not in B16.5 and as such cant be cosnidered a listed standard under VIII-1. Perhaps an VIII-1 interpretation on thissubject may shed more light. Nevertheless I understand you dont want to rock your AI's boat.

Why not use aluminum B16.11 lap joint stub ends with B16.5 304 lap joint flanges? Your rating than also isnt limited.

On a side note; you can easily buy Ti flanges (from fraudulent factories), which are sold and marked as 'B16.5' standard. That doesnt mean they meet B16.5 requirements and are listed as such.