Overpressured Vessel
Overpressured Vessel
(OP)
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?
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?





RE: Overpressured Vessel
Also, if by "blew out" you mean the gasket exited the joint, I don't think this method will get you there.
Regards,
Mike
The problem with sloppy work is that the supply FAR EXCEEDS the demand
RE: Overpressured Vessel
You DON'T KNOW the previous torque on those 4x bolts, nor the actual tension in the bolts (studs ?) clamping that particular flange set together. Merely that that flange was clamped the least of any other flange in the system. Are you trying to estimate acvtual failure pressure using some assumed strength of the four studs and the strength of the gasket?
RE: Overpressured Vessel
RE: Overpressured Vessel
If the pressure got so high that you blew a gasket out, then it's beyond 150% of the flange rating minimum and possibly up to 200% or more, but there will be too many unknowns and assumptions to make the calculation any more accurate that that - IMHO.
How come a pressure vessel got to that level of overpressure without relief systems kicking in??
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Overpressured Vessel
The flange was in operation without leaks, so I'm not looking at Wm2.
Nobody answered my question in the last paragraph, but after sleeping on it, I've come to the conclusion of using the total bolt area. Although I can use the torquing of a single bolt to determine what my compressive force is (where adding more bolts wouldn't increase the force if torqued the same), I need the total bolt area to determine what pressure is required to separate the flange and cause leakage.
RE: Overpressured Vessel
The problem with sloppy work is that the supply FAR EXCEEDS the demand
RE: Overpressured Vessel
you also don't really know how much stretch you needed on the bolts to get sufficient reduction of pressure on the gasket face.
The min pressure is basically just a few percent above whatever that joint was pressure tested to.
Anything else is pure supposition and the minimum pressure could be double that pressure.
BTW, how can you add two more bolts? Were some bolts removed??
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Overpressured Vessel
Remember, Appendix 2 is for designing FLANGES, not for designing the bolted flange joint system.
RE: Overpressured Vessel
I asked that hypothetically.
Keep in mind everyone, I am not doing this to give me an exact solution. I want to see what the flange should start to leak at with the known information that I have.
RE: Overpressured Vessel
Regards
r6155
RE: Overpressured Vessel
If so great,but otherwise you will generate a figure which could be put by a factor of 2
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Overpressured Vessel
Could be out by a factor of greater than 2. Too many parameters to get a sensible answer!!!
RE: Overpressured Vessel
RE: Overpressured Vessel
So I can't figure out why you're bothering.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Overpressured Vessel
RE: Overpressured Vessel
The problem with sloppy work is that the supply FAR EXCEEDS the demand
RE: Overpressured Vessel
I can't understand why you're having to go to that extent, but if it helps then go for it assuming the bolts were all originally tightened to the correct torque. I wouldn't be surprised to find the pressure is x2 of the MAWP of the flange, never mind what the MAWP of the pressure vessel is.
Some sort of severe transient event could be enough to allow enough fluid out to destroy the gasket before the relief valve had even had the chance to lift properly - if you don't have good recording or the event was so sudden the DCS didn't properly capture it then you are running blind.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Overpressured Vessel
RE: Overpressured Vessel
RE: Overpressured Vessel
RE: Overpressured Vessel
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Overpressured Vessel
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.
RE: Overpressured Vessel
Do you have a picture of blown out gasket and flanged connection? What kind of gasket was used?
Curtis
RE: Overpressured Vessel
Regards
r6155
RE: Overpressured Vessel
Curtis, Flexitallic 304 SS Spiralwound. I can't share pictures.