Small Hole in ASME B16.5 Blind Flange 5

[bayardwv]

I am using an 8" 150# ASME B16.5 Blind flange with a 1/2" NPT connection drilled & tapped directly into the flange 3" off center. I am being told the Flange is no longer an ASME Flange and that calculations are required. I disagree for several reasons,
1.) The Flat head formulas in UG-34 don't change when there's a hole added. The addition of the hole is addressed in UG-39, so why would the thickness of an ASME flange change?
2.) ASME B16.5 allows holes less than 3-1/2" to be added to an 8" blind flange to create a reducing flange using the published press/Temp rating. I don't see why this can't still apply to small holes that are located off center and exempt from reinf per UG-39.
3.) The design in questions is exempt from Reinforcement per UG-39 & UG-36(c)(3) which implies the material removed is not enough to affect the integrity of the part with the hole. Why would this be different on a flange?
4.) Where does Sect. VIII Div.1 or B16.5 say that a flange thickness calculations is required when a hole is added to an ASME Blind Flange.

 

[marty007]

Speaking as one fabricator, we would be supplying calcs for such a situation. If the design conditions are anywhere near the B16.5 flange ratings, then a standard B16.5 blind flange would likely fail the calcs, and we would resort to fabricating a custom blind flange from thicker plate.

Just one fabricator speaking...

 

[Spoonful]

My 2 cents,

Let's put aside what the code said, consider a flat head(blind flange), under pressure, most deflection is at the center, and stress, of course not considering bolting load around the edges. If a small opening with/without its reinforcement can be placed at the center, why can can't the same be placed off the center? where there is less stress, hence less compensation required for the removed material. Hence safer?


I do agree once flange dimension is modified, it is no longer a B16.5 flange, hence custom calculation. But I believe we all have seen vent/instrument holes drilled from the side of the flange, in between two hold holes. How would you do you calculation for this case?

 

[DekDee]

Would it not be an Auxiliary Connection as Cuemaster noted ?
If B16.5 allows you to drill & tap through the side of a fitting why would it not allow drilling & tapping through the blind flange ?
Are they not both subject to the same pressures ?

6.12.1 Pipe Thread Tapping. Holes may be
tapped in the wall of a fitting if the metal is thick
enough to allow the effective thread length specified
in Fig. 3. Where thread length is insufficient or the
tapped hole needs reinforcement, a boss shall be added.

Only problem with that is 6.12.4 requires a 3/4" connection for an 8" fitting so the 1/2" connection would not be compliant with B16.5,
Cheers,
DD

 

[TGS4]

Dekdee - different things. And no one thinks that what the OP proposed wouldn't be fine. It's a compliance issue, not a safety issue.

 

[XL83NL]

Wouldnt this be a perfect topic for an interpretation to the B16.5 committee?

 

[moltenmetal]

I'd say it's about time B16.5 addressed this issue, especially since some of the B16.5 flanges fail the Appendix 2 calc when it is used as an alternative means to determine whether or not off-centre or multiple small tappings are a problem or not.

 

[bayardwv]

I submitted an ASME interpretation request yesterday afternoon. I'll post their response. Thank you everyone for your comments and suggestions.

 

[TGS4]

bayardwv - excellent. This is how progress is made. We would all appreciate an update (even if it takes 1+ year(s)). Thanks for not succumbing to the default position of complaining but not doing anything about it - but for actually taking matters into your own hands and taking action. This is how the Codes and Standards Committees are supposed to act.

 

[jte]

I'll second TGS4's commentary. It is very easy to sit back and whine about an issue in the code. It is a far greater public service to follow up and write a coherent request to the Code Committee involved to (hopefully) provoke some action.

Well done, bayardwv!

 

[bayardwv]

UPDATE: as of today, Monday Nov.10, 2014, my ASME interpretation request status is...

Out for SC Ballot- the interpretation is currently balloted by the Subcommittee.

I was able to address my current problem by changing the spiral wound closure gasket from a CGI style to an LSI style which has a minimum seating stress ("Y") of 5,000 vs the CGI stress of 10,000. This allowed the ASME B16.5 flange to meet the required code calcs.

 

[keyen]

bayardwv, thanks for taking the time to keep us up to date. Can you post a copy of the interpretation you've requested? Is the question and response available online somewhere?

 

[TGS4]

bayardwv - what's the tracking number (BC-14XXX)?

 

[XL83NL]

Any update on this interpretation?

 

[XL83NL]

No news?

 

[bayardwv]

Finally, here's the question submitted and their response,,,

Here's the question I submitted...
Are minimum thickness calculations per UG-34(c)(2) in Section VIII, Division 1 required if an ASME B16.5 or B16.47 circular blind flange, used as an unstayed flat head, otherwise conforming to the requirements of UG-34(c)(1), has a hole added off center that meets the requirements of UG-39(a) and the nozzle opening size is exempt from reinforcement per UG-36(c)(3)?

Here is the reply I received...

Question (1). If a B16.5 or B16.47 blind flange is modified in a manner that is not covered by those standards, may pressure/temperature ratings of these standards be used in accordance with UG-44?

Reply (1). No.

Question (2). In the situation described in Question 1, would calculations using the design provisions of UG-34 and UG-39 be required?

Reply (2). Yes.

 

[TGS4]

Unfortunate, that the question-answer that you received is unlike the question that you asked. However, the specific question that you asked would likely be considered to be "consulting".

This, to me, highlights the need to be attending the Code Committee meetings where these issues are going to be addressed. Frankly, if you had an interest in the answer, then you should be there when the issue is discussed.

What was the BC item number (the tracking number that you would have been provided)?

 

[keyen]

TGS4, why do you think the "question-answer was unlike the question [he] asked"? It was re-worded, yes; but it answers the original question while providing additional information for future uses (such as different modifications to B16.5 flanges).

 

[bayardwv]

The Item# for this inquiry is 14-1803. Unfortunately I wasn't aware that I could attend the meeting. I would truly enjoy seeing how this process works, as well as question the reply.

I also don't understand why they reworded my question in a way that no longer addressed my key points. I don't completely disagree with keyen's comments however I still plan on resubmitting with different wording.

 

[TGS4]

Thank you for the tracking number. Indeed, the meetings are open to the public, so anyone can attend. And it is encouraged that anyone who has such a request for interpretations to attend to present their case and be part of the solution.

See, the ASME Codes are essentially run as a consensus committee of volunteers, who work in industry just like you and me. Each individual has become involved for their own unique reason, but often got started with a single issue, such as this one. The way the system works is that everyone gets involved, makes logical, yet passionate arguments for their issue, their peers listen and respond accordingly. My experience is that the group of engineers are extremely experienced, and very open-minded and fair. They only want what is in the best interests of public safety.

To see when meetings are, go to

https://cstools.asme.org/csconnect/CommitteePages.cfm?Committee=N20110000&CommitteeErrata=yes.

The future meetings link is on the top left. The next meetings are in Atlanta in a few weeks. You can register to attend (free) via

https://www.asme.org/events/boiler-pressure-vessel-code-week/committee-meetings.

 

[moltenmetal]

The question 1 they gave you is so broad that the answer could not be anything other than "no".

To really answer your question, the committee would have to re-write the standard to define the conditions under which off-centred holes, or multiple smaller holes etc. would be considered safe modifications without requiring additional calculations or a de-rating of the blind flange. That would be a lot of work to do properly, so the easier and quicker answer is "no, read the standard as written".

Clearly it doesn't matter to the blind flange whether a small hole such as the one considered in the OP (a 1/2" NPT tapping in an 8" blind flange) is put in the dead centre of a blind flange or anywhere such that the small hole's OD is entirely within the ID of the flange's raised face. It would be easy enough for the committee to establish whether that is also true at the maximum permitted hole size which the standard permits for an on-centre hole in a standard (flat) rather than a high hub blind flange. But then there's the issue of multiple holes, and it starts to get fairly complex fairly quickly. Is it a simple matter of total hole area? I would imagine that if the total area of the holes is no larger than the area of the largest hole permitted on centre, multiple holes wouldn't matter wherever they were placed. But getting that written into the standard is a lot to ask, I guess. So instead of using engineering judgment, a lot of unnecessary calculations and work-arounds will be done. So it goes- it is the 2nd edge of the double-edged sword of codes and standards.