Flange thickness calculations

[Nichyin]

Good morning,

I have been tasked to calculate a flange thickness design check for the following procedure:

We will be tapping a 1/4" NPTF onto a 2" 150# WNRF flange rim, after which we will drill a 1/8" hole through.

I would like to know where I can go and look for the calculations to determine if this flange thickness is sufficient for a 150 line.

I've looked through ASME Section VIII, B16.5 and trawled through forums, but to no avail.

Thank you all for your help in advance!

 

[SnTMan]

Nichyin, there is not likely to be any standard calculation for proving this. You'd be left to come up if something from Roarke (if it exists) or FEA, would be my guess.

There are standard orifice flanges, but they seem to start at 300# rating.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[XL83NL]

You might consider the hole tapping as an external pressure and check if it has any negative impact on the area/volume around the bolt holes where bolt stresses occur, but you then still have to do this using mechancs (like Roarke) or FEA. For FEA, using rules from VIII-2 might be a good place to find out how the stresses need to be evaluated, amongst others.

 

[SnTMan]

If I were in a guessing mood, I'd guess the effect of a 1/8" radial hole would be negligible. Couldn't prove it though..

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[BJI]

Essentially you are removing material between the bolt holes, so you could treat it like ligament efficiency. Under VIII-1 App2, 2-6, equation (7) is for bolt spacing correction factor. You could increase your value of 'a' based on the increased area of material removed, check to see if 2a+t exceeds the bolt spacing, and if it does, calculate and apply a bolt spacing correction factor. This should also be conservative based on the location where the material is removed.

As SbTMan suggested it will likely have negligible effect but the above method should allow you to qualitatively address it.

 

[KevinNZ]

Have look at ASME B16.36. Your tapping maybe close this standard and therefore not require calculations.

 

[BJI]

Kevin, I don't think the orifice flanges are covered in class 150 as mentioned by SnTMan. Is there provision in ASME B16.5 to modify flanges and still have them covered the pressure and temperature ratings (except for reducing blind flanges specifically addressed in the code)?

 

[XL83NL]

No provivion in B16.5 on that matter

 

[racookpe1978]

9 Jul 17 20:35
If I were in a guessing mood, I'd guess the effect of a 1/8" radial hole would be negligible. Couldn't prove it though..

No, if the 1/4 inch NPT is tapped "radially" (???) into a small 2 inch low pressure flange, then the actual hole is the OD of the 1/4 inch PNOM pipe that will be threaded into the NPT tapped hole. The configuration is NOT clear from the words, and must be accurately sketched to scale.

 

[SnTMan]

Well, as I picture it the 1/4" NPT would be 1/2" - 3/4" deep, or roughly from the flange OD to bolt circle CL, with the 1/8" drilled thru from there. I'd stand by my guess. That is, if I were guessing....

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[Nichyin]

Hi all,

Sorry I couldn't access this forum in the past few days, but thanks for all the input.

I am going to plan a FEA for this just to be on the safe side, because there is no guidelines at all in ASME for these kind of calculations.