B31.3 - Openings in blind flanges 3

[bdcan]

Hello, did a quick search and found a few threads relevant to what I am working on, but still have a few questions.

We will be pressure testing a number of different pipes designed to B31.3. At each end, the site superintendent wants a blind flange with two nozzles. One nozzle on each end will have a pressure gauge. The remaining two nozzles will be fill/pressurize and vent. The lines vary in size from 3" to 10", with the nozzles anywhere from 1/2" to 1.5" NPS.

Reading 304.4 of B31.3, I believe a blind flange falls under "closures". We have flexibility in the size of the nozzles so that openings are not larger than one-half the ID of the closure. Here is what is throwing me off:

304.4.2 suggests that the opening has adequate reinforcement if the outlet connection meets the requirements of para. 304.3.2(b) or (c). I belive that we can satisfy 304.3.2(b) with our design. However, there is no indication as to whether this can be applied to two openings in one closure. Furthermore, when I read farther down to 304.4.2(f), I notice that they are referring to two or more openings.

So, the questions I have are:
1) Can I rely on 304.3.2(b) for two openings on a blind flange?
2) If the answer to question 1 is "no", can I use 304.3.3 to calculate the amount of reinforcing required, or should I refer to the BPV?


Thanks in advance for any advice. I've been going around in circles all day and am hoping someone can straighten me out!

Brian

 

[vesselfab]

how about a reducing flange

allready reinforced

 

[bdcan]

Hi vesselfab...

Thanks for your suggestion. Yes, a reducing flange would be an excellent option. In fact, I tried getting our superintendent to agree to using these. He's adament that there has to be two nozzles coming out of the flange. My power of pursuasion needs work!!

Brian

 

[vesselfab]

big opening into reducing flange with small opening reducing tee or olet out of the other opening

 

[prex]

My answer to 1) is no. 304.3.2 refers to branch connections, so typically not having in mind the possibility of multiple openings. Then 304.4.2 refers to the former, but clearly implies a single opening (though not explicitly).
I'll maintain this position, though one could also argument that 304.3.2 assumes the reinforcing is entirely given by the coupling, so that two openings would not overlap their compensations.
As to your question 2), it seems to me that 304.3.3 is too conservative for a closure. In UG-39 the required reinforcement for a flat head is 50% the one required in a shell, so you would calculate the compensation in excess. However, as these are temporary closures for hydrotest only and with small diameters, it is possible that you'll anyway have sufficient excess thickness in the head to satisfy 304.3.3.
I assume of course that you are aware that, for hydrotest, you can calculate with higher allowable stresses.

prex

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[pennpiper]

I suggest that you introduce your "Super" to Bleed Rings. Then you do not have the problem with modifying a BF.

Look here:

http://www.mac-weld.com/FlushRing-BleedRing/index.html

 

[bdcan]

Thank you all for your valuable input. I'll be able to go back and talk to the guys on site with some more ammo!

 

[IFRs]

I'm not a pipe engineer, but isn't small bore extra-strong pipe essentially self-reinforcing by virtue of the extra wall thickness of the pipe?