Openings in blind flanges

[alex2010]

I am required to make 4 x 1/8" NPT holes in a class 150 blind flange and would like to know if the rules of UG-36 (Openings in Pressure Vessels) apply to the design.

Thank you.

 

[jte]

The rules of UG-36 in general do apply. The excemption from calculations in UG-36(c)(3) specifically does not apply. You'll have to run numbers in accordance with UG-39. This is similar to UG-37 except for requiring only half of the Area Required.

jt

 

[alex2010]

Which dimensions do the dead diameter and the shortest span refer to when it comes to a blind flange?

 

[michigander]

ANSI B16.5 Table 7 provides guidance on what size opening in what size flange can be considered inherently reinforced. See the attached scan.

Best Regards,

Michigander

 

[jte]

Michigander-

It's ASME. And you're two editions out of date. And the referenced table applies to a single, centrally located, opening. Four openings are out of the scope of ASME B16.5. Thus, the fall-back to ASME VIII-1.

Alex-

Shortest span? In what context? You have round holes, right? Although you'll technically have to run the numbers, four 1/8" NPT holes should not be terribly problematic provided they're spaced reasonably far apart.

jt

 

[alex2010]

I completed the design of the blind flange. Thank you all for your help.

I am also required to design an additional blind flange, which has a partial penetration located in the center of the flange, as shown in Sketch 1. I have read the code and I was unable to find anything that would help me register the design. Any suggestions?

Thank you,
Alex

 

[jte]

Alex-

Consider the thin spot to be a through hole. Now either check the table which Michigander provided (but check the appropriate edition per Section VIII Div. 1) or run opening reinforcement calc's. If either passes, you can reasonably argue that the design is ok.

If both fail, then either add reinforcement (still treating it as a through hole), or you might get some relief from an FEA per U-2(g) and typically evaluated per VIII Div. 2 Appendix 5.

jt

 

[alex2010]

Jt, I forgot to mention that the customer wants to have a fitting screwed onto the flange, with a weight attached to it. Is that allowed by the ASME codes?

 

[jte]

Yes, if you engineer it properly.

jt

 

[alex2010]

Is there a section which covers this type of design or would I have to do as stress analysis showing that the stresses are withing the code allowable stresses?
Thank you.

 

[jte]

You need to do some independent thinking design work.

The Code does not address all aspects of these activities and those aspects which are not specifically addressed should not be considered prohibited. The Code is not a handbook and cannot replace education, experience, and the use of engineering judgment.

jt