Off-center Blind Flange Tap, B31.4

[MechEngMSU]

I am designing a short 24" class 150 piping section to ASME B31.4 with blind flanged ends that will be used for liquid hold-up of NGL test samples to be intermittently pumped backed into the process stream. (The client doesn't want an ASME vessel and this is open to the flare with CSO valves).

Am i justified in tapping the blind flange off center with a 2" NPT tap or welding a flat weldolet to the blind flange? I read the code and believe I am required to design the closure to ASME Section VIII appendix II per B31.4 408.1.(d) but this requires a thicker than standard blind flange.

I have considered putting ASME section VIII heads with a nozzle. Is adding the nozzle designed to ASME Section VIII allowed per b31.4 406.6.3?

 

[LittleInch]

MechEng,

This comes up regularly. See

http://www.eng-tips.com/viewthread.cfm?qid=371342

In essence if you tap a flange off centre, it ceases to be a B 16.5 flange.

Whilst I understand the use of pipe as a pressure vessel, it could easily be seen as one(i.e. a PV) and in the event of failure, this could be a serious issue. The client might not want a pressure vessel, but you might need to point out that the regulations require it and failure to put one in might invalidate his insurance and open the door to lots of pesky lawyers.

What is CSO valves by the way? It is always best to assume no one else knows your abbreviations....

as ketch of this thing so we can see what it looks like and what is vertical / horizontal would help a lot.

You seem to be using a very old version of B 31.4 - 2006 or earlier as the latest doesn't have 406.x.x.. now 404.7.3

Generally if it's allowed under ASME VIII then you can use it.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[marty007]

Agree with LittleInch...

CSO: I'm guessing this stands for Car Seal Open valve. Basically a valve that is locked-open with a physical lock that operators have to get a key for or some such safety protocol.

 

[LittleInch]

I'm used to LO - Locked Open.

other questions - Why off centre? and could you use eccentric reducers, flat bottom or concentric to get you to where you want? might look a bit odd, but then they are standard components

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[MechEngMSU]

Thanks for the responses. CSO is car-seal open, same thing as LO - locked open. it is horizontal with a 2" drain line sloping to it, a vent line going to the flare coming off the top and a 2" line going to a pump coming off the bottom.

Off-center because the elevation of the drain line does not allow us to come in the top if we want to avoid burying the pot and putting a sump pump. I offered the idea eccentric reducers or coming in on-center and reducing the liquid hold up time (turn the pump on twice a day rather than once) but got shot down. I think it takes 4 reducers to get from 24" to 2" (but feels a lot more like pipe than what we're doing). I am either going to analyze the blind flange as a flat head per ASME sec. VIII div. 1 or make a non-radial type branch on the pipe and analyze it with NozzlePRO.