Hot Tap Calculation

[jstrom9]

I am working on an external pressure calculation for a hot tap. The equation is from ASME Sec. VIII, Div. 1, UG-28. Ultimately, I need to get factor B from figure CS-2 in Sec. II, Part D, pg. 797. To get factor B I first need Factor A from figure G on pg. 795. To get factor A I have to enter the figure with a value for L/Do and Do/t. The intersection of these two values falls off the lower right side of the figure. I can't get an A factor from the tables either because extrapolation is not allowed.

Has anyone encountered this before? What do I do? My supervisor checked my work and is having the same issue.

 

[SnTMan]

jstrom9,I think you should be able to get there. What are your ratios, Do/t, L/Do?

Regards,

Mike

 

[jstrom9]

There is a case for Do/t < 10 that allows you to calculate Factor A, however we are getting ~43 for our case.


L=1.4375 in
Do=16 in
t=.373 in - thickness is from client UT readings

L/Do = .0898

Do/t = 42.895

 

[jstrom9]

I forgot to mention we are using 16" diameter STD WT. pipe with a 1" sockolet branch connection, which is where the L dimension comes from.

Regards,

Justin

 

[GenB]

Why mixing values. 16in x length of this pipe and not the coupling. There is your mistake.

 

[SnTMan]

Yeah, you trying to calculate branch or run? In any case I think you would be justified to take A = 0.1, end of the chart.

Regards,

Mike

 

[jstrom9]

I don't understand the comment about mixing values. I am calculating the maximum external pressure to not collapse the header. The method I am using has been used at my firm for decades. The oldest guy in my department suggested the same thing. Just use A = 0.1.

Regards,

Justin

 

[SnTMan]

If you are calculating for the 16" run, you should use the OD of it and its unsupported length. UG-28 methods are for uniform external pressure, not a concentrated load.

Regards,

Mike

 

[jte]

Do I understand the situation properly?

You have a NPS 1 'olet on an NPS 16 Std. weight pipe. You plan to hydrotest the 'olet and valve (and hot tap cutting machine). You are concerned about external pressure over the perhaps 1.5" diameter area on the NPS 16 pipe collapsing it.

Is that correct?

 

[jstrom9]

@ jte

That is what the calculation is for, you are correct. We did a 2" tap on the same header on a separate project. So we know that is safe to perform the tap with a 1" sockolet due to the smaller hole. We just have to provide supporting documentation for the client's records. We just used A = 0.1. Which gave us a B factor of 18000. I think the pressure came out to be about 550 psig. Thanks for the assisstance.


Regards,

justin