Overpressured Vessel

[loilfan]

A vessel overpressured and blew out a gasket. I am attempting to determine what minimum pressure the vessel must have seen using the formulas in Div 1 App 2.

To determine Wm1, do I use the total area of bolts, or just one bolt since each bolt is torqued individually?

If I have a flange with 4 bolts on it, do I increase the compressive load on the gasket if I add 2 more bolts (using the same torque)? Or is the flange just more evenly distributed since adding the extra bolts wouldn't compress the flange more than the 4 already have?

 

[loilfan]

The gasket blew out, so we need to treat it as an overpressured event since the vessel MAWP is limited by the B16.5 flange rating. There is a pressure transducer upstream of the vessel, but since this was a transient event, there is no way to trust what the pressure actually was.

 

[LittleInch]

Would be interesting to know what figure you come up based on assumption it was torqued up "properly".



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

 

[loilfan]

Assuming 30% loss in bolt preload, the Code says that it shouldn't leak below 971.3 psig. This is the pressure that the Code says that it can operate below assuming its tightened properly. This does not tell us what it failed it, and would have been higher since it doesn't include any consideration for the safety factors, hydrotesting or that the gasket 'blew-out' instead of leaked.

The vessel MAWP is 285 psig, which is about 3.5x smaller than my calculation. If the flanged joint was tightened properly, I would expect failure (or at least yielding and permanent strain) of the vessel before the gasket were to leak.

It's been an interesting exercise.

 

[curtis2004]

What kind of transient condition was antisipated? Water hammer?
Do you have a picture of blown out gasket and flanged connection? What kind of gasket was used?

Curtis

 

[r6155]

Is only one flange connection?
Regards
r6155

 

[loilfan]

r6155, two identical flanges blew out, but the rest of the flanges in the system have been visually inspected as well.

Curtis, Flexitallic 304 SS Spiralwound. I can't share pictures.