Max allowed flange machining

[Jeff_A]

After welding 2x slip-on flange 18", CL 150 on both straight end of a 18" Tee, there will be misalignment. Normally this is not a problem but for the current project it is problematic. To correct the misalignment, the flanges would be machined (see image in attachment).

My question is, what would be the maximum amount of material that can be removed from the flanges ? Does anyone have any idea of which ASME standard might give pointers about this ?

So far the best info I have is ASME B16.10-2017 which does give a face to face tolerance of about +/- 0.12" for this size. However this does not tell me what I'm looking for : how much material I am allowed to remove from the flanges.

Any help would be greatly appreciated.

 

[MJCronin]

WOW ... Can you post pictures of the problematic weldment ?

How much material do you intend on removing ?

Will you be removing material on the face of the flanges or elsewhere ?

MJCronin
Sr. Process Engineer

 

[bcd]

ASME B16.5 gives flange dimensions and tolerances. Not that several dimensions in B16.5, such as flange thickness, are given as a minimum. You can machine whatever you want up to the minimum value, then, once below that, the flange no longer complies.

 

[Jeff_A]

＠MJCronin : The weldment has not begun yet but from experience I'm expecting this will be a problematic assembly due to severe alignment tolerances.

＠bcd : thanks a lot, that was exactly what I was looking for. ASME B16.5-2013 - paragraph 7.4 had the info you mentionned : Flange Thickness for NPS 0 to 18 = -0", +0.12". It seems flanges are manufactured with approx 1/16" extra material which gives me 1/16" machinable material max (To be verified per actual flange dimension).

 

[Nick_Gray_88]

Why not use tongue and groove flange faces? From memory I think they’re covered in ASME B16.5? Standard flanges with alignment built into them?

 

[HitokiriAoshi]

how desperate are you?

ultimately, the thickness of the flange is dictated by the material and the required bolting and gasket seating stress. ASME B16.5 flange dimension and ASME B16.10 dimensions are there to allow ease of calculation, procurement, and piping assembly and design. in desperate situation you can always fall back to the basic.

which is, with a given required pressure, calculate the required sealing stress based on the values provided by the specific gasket manufacture (not ASME code), you can than use the equations to optimize for minimal flange thickness. note that this will require specific bolting torque values, if you go this route to minimize flange thickness.

if that still don't get you to the require thinness, you can use FEA simulation, as even the ASME BPV flange calcs are technically conservative.

basically, how desperate are you?

Luke | Valve Hax |

https://valvehax.com/