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37° formed flares, allowable wall thicknesses for tubing

37° formed flares, allowable wall thicknesses for tubing

37° formed flares, allowable wall thicknesses for tubing

(OP)
Hopefully I posted in the best place, pressure systems have not really been my area of focus but I do have a need for reworking one currently.
We have an older drawing calling out a 1/4" OD, .035" wall tube that is flared (via SAE AS4330) and connects via sleeve and coupling nut to an AN-type 37° flare fitting.
Due to material shortages, we can't find any vendors with that tubing in stock (the application requires a less common material) and are having to look at alternates.

I have had a hard time finding a definitive answer of what wall thicknesses can be used for a given OD tube to produce a proper flare. I looked through SAE J514 and J533, and all I found was a table in J533 with a "max wall thickness" = .065" for a 1/4" OD tube. Suggesting to me that anything with a thinner wall would also be OK. However, I have also come across some specs that have charts showing OD and wall combinations, and several of those listed .035" as the only option for 1/4" OD tube. An example of this is KSC-SPEC-Z-0008, which is one of the documents the company has used. These charts often reference proof or allowable working pressures, and I am thinking maybe the .035" and table pressure values were supposed to represent the minimums when considering a welded-on flare (since .035" is the thinnest wall I see called out for a welded tube connection, probably for weldability reasons).

I have also found vendor information that suggested .020-.065" wall thickness is the typical acceptable range for 1/4" OD tube, but haven't been able to confirm that.
I located some 1/4" OD tube with a .020" wall in the same material, which would work fine for the application if the flare will form and seal properly. The working pressure is trivial here, I believe it's only 10-15psi.

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