ASME VIII Bolted cover calculation

[vitalis77]

Hi folks,
Here's a good one and rather strange query from the project management department.
They are about to perform a hydraulic test on venturi meters and since they are not willing to purchase blind flanges for the procedure, they are proposing to machine them so as to match the ASME B 16.47 dimensions-requirements. One of them asked me if I can perform a calculation on bolted covers acc. to ASME VIII div.1 and then try to minimize the calculated thickness using an external reinforcing for this above mentioned cover (i.e stiffener e.t.c) (P.S.Vessel IS NOT subjected to external pressure!!). I'm trying to come up with a solution but as far as I know there is no reference for such action throughout this code. I'm I right? Instead I proposed a finite element analysis to achieve that.
Could any of you vessel experts direct me to an applied
approach that indicates a good engineering practice.

 

[SnTMan]

http://www.eng-tips.com/viewthread.cfm?qid=163859&page=5

 

[dtn6770]

I wont' even go into a rant about the mentality of the manager you're dealing with...

Anyway, in a previouse life (job) at petroleum refinery we would use fantail blinds/blanks for isolation purposed included pressure testing, at times. The blinds were either standard (full) thickness or non-standard (less than full thickness) if the pressures of interest allowed it. In piping, the flanged joint would be parted, the fantail blind inserted, and the bolts retightened sandwiching the blind between them (appropriate gaskets).

The charts and tables we used to determin the thicknesses referenced B31.3 and that they be built out of SA-516-70 plate. As an example, a standard blind for a 4" 300 class system was 3/8" thick (good to 815 psig) but a 1/8" thick non-standard blind shows to be good for 90 psig.

Long story even longer, consider using B31.3 to establish a plate thickness, have it fabricated, and and secure it to your meter flanges using another unused flange of equivalent size and rating (of the meter flang).

 

[dcasto]

The equation goes like this:

d = (ID pipe + Diameter of outside raised face)/2
C = Safety factor (.25 for skillets)
KIPS = allowable stress (17,500)
P = absolute design pressure

thickness = d * (P*C/KIPS/2)^.5

 

[gr2vessels]

I hope to correctly understand the question;- can any cheaper test rig be designed and used safely for a hydrotest, assuming flanges over 26" NPS?
Short answer is yes. How to work it out is not complex and is based on the assumption that you are testing the vessel / pipe, not the closure. That is, set yourself some maximum deflections for the cover, use 90-95% of yield and treat it as a beam supported at both ends. Use stays extended radially, welded on the cover on their edge, to provide sufficient resistance to achieve the maximum allowed deflection for your given diameter. Obviously, the interface with the vessel / piping flange must be done with the corect machining of the cover. However, you can use a gasket which require less seating force, check with the gasket material supplier for the actual values, which tend to be smaller than the listed generic values.

Please understand that whilst this is a valid advice, it's still a rather vague description of the principle of how to save a buck on the other ways expensive hydrotest. I don't know your design and fabrication circumstances, so I would advise to have your calcs checked by the structural guys and reviewed by the vessel engineer.

cheers,

gr2vessels

 

[vitalis77]

Thanks everybody for your valuable advise.
My query still remains unsolved.I will try to simulate the model using the Ansys software. Will this reinforcing idea lead to a calculation of bolts with greater diameter than those used in a typical ASME B16.47 blind flange? Is this irrelevant?

 

[Shmulik]

vitalis77:
I suppose that you may reduce bl. flg thickness using external reinforcing for your working conditions, but I think you still going to remain with a problem at bolting-up conditions.
What I would suggest is using of SO. or WN. ASME B 16.47 flange, or a custom thickness ring flg designed acc. to VIII-1 app. 2 . You may weld standard or formed head on it for getting reduced weight cover.
In case you deal with high-cost material cover you may consider using of a head welded to a stub-end + LJ loose flg.