Calculation of allowable loads at a shell nozzle?
Calculation of allowable loads at a shell nozzle?
(OP)
Guys I have a couple questions for you. I posted this in the vessel forum also, so please forgive me this time for cross-posting.
(1) Do any of you know a method to calculate the allowable piping reaction loads (forces and moments) on a head nozzle for a cylindrical vessel? Megyesy's book has a method based on WRC 107 but it only covers shell nozzles.
(2) Megyesy's method does not cover all six possible applied loads at a nozzle. His method only covers a radial force and a longitudinal and circumferential moment. So - what about the other three loads? E.g., the force and moment in the plane of the nozzle?
Any help would be greatly appreciated. I have not looked in Section VII yet, so I'm guilty of not doing my homework first... OK, I'm HEADing to the library now...
Thanks!
(1) Do any of you know a method to calculate the allowable piping reaction loads (forces and moments) on a head nozzle for a cylindrical vessel? Megyesy's book has a method based on WRC 107 but it only covers shell nozzles.
(2) Megyesy's method does not cover all six possible applied loads at a nozzle. His method only covers a radial force and a longitudinal and circumferential moment. So - what about the other three loads? E.g., the force and moment in the plane of the nozzle?
Any help would be greatly appreciated. I have not looked in Section VII yet, so I'm guilty of not doing my homework first... OK, I'm HEADing to the library now...
Thanks!
Thanks!
Pete
P. J. (Pete) Chandler, PE
Principal Engineer
Mechanical, Piping, Thermal, Hydraulics
Processes Unlimited International, Inc.
Bakersfield, California USA
pjchandl@prou.com





RE: Calculation of allowable loads at a shell nozzle?
RE: Calculation of allowable loads at a shell nozzle?
Good luck!
Edgar
RE: Calculation of allowable loads at a shell nozzle?
Interesting question. We sorta-kinda itteratively figured out some of the allowable load combinations for some shipboard heat exchangers and only then (of course) we found out about Paulin Research Group and NozzlePro. The NozzlePro software shows explicitly how to do exactly what you want to do - and it is cost effective.
This is not advertising, I have nothing to gain but in the interest of passing on to the community what we learned the hard way:
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There are many times when the typical beam model pipe or nozzle analysis (even with the correct stress intensification factors are applied) simply will not tell you what you need - then you must go for finite element analysis (FEA). The WRC Bulletins (107 and 297) were useful for a long time, but not always conservative.
Go to http://www.paulin.com/ to check out the FE/PIPE software (of which NozzlePro is a subset) as well as other neat things.
Best regards, John.
RE: Calculation of allowable loads at a shell nozzle?
the method suggested by John Breen, above is , of course the best way...... however we all know how cheap engineering management is these days.
Another way to approach the problem is to bracket the nozzle sizes, wall thicknesses as well as the range of vessel diameters, wall thicknesses and pressures. This was a method used by the large AE firms, (Stone & Webster... remember them !!??) in the 1980's during the big nuclear power push by the electric utilities.
If you have a tool, such as the one contained in CAESAR-II, you can iteratively solve for what will be "reasonable" stresses" for a range of nozzle sizes and vessel conditions.
For example; most nozzles will be between 2"NPS and 10"NPS and vessels will be 4 feet to 12 feet in diameter. Iterativly solve ( over a couple of afternoons) for most of the combinations and develop a general guideline ( for preliminary layouts and design)
Of course, the final piping loads should be confirmed with the final vessel design at a later date.
As I recall, for most carbon steel systems of Schedule 40 nature..... using 300 times the nominal OD would give reasonable limits for forces..... and 500 times the nominal OD gives reasonable limits for moments ( units are lbs. and foot lbs.)
So...... for example, for preliminary design loads for a 6" nozzle on a carbon steel vessel, connected to a sched 40 piping system..
Maximum forces Fx=Fy=Fz= 300x6 = 1800 lbs
Maximum moment Mx=My=Mz= 500x6 = 3000 ft-lbs
Higher & lower pressure/temperature systems can adjust the 300 and 500 factors up or down...
This should, of course be confirmed with the vendor... and gives a starting point for design.... all bets are off for atmospheric tanks or for vessels of other materials
I realize that this is not exact and many may have problems with an iterative approach that tries to bracket the problem but without the access to software designed specifically for this purpose, it seems to work..
I would like to see comments from others about this....
Regards
MJC
RE: Calculation of allowable loads at a shell nozzle?
I do need a bit of amplification here, though. I don't see how C2 will help me with this problem. Unless I'm wrong, the nozzle and vessel modeler (WRC 107/297) in C2 only models the stiffness of the nozzles and thus will more accurately (hopefully...) determine the magnitude and direction of the reactions forces transmitted BY the piping ON the vessel. This only helps me from the piping side of the system but does nothing for the vessel side. As far as I know it does nothing to tell me if the magnitude of those reactions are low enough to keep the stress magnitude developed in the vessel itself below the Sec. VIII allowables. As I see it I would need some type of vessel modeler or FEA to do that - yes?
I can develop a bracketed set of nozzle loads using C2 (great idea!) but don't I first have to know if those bracketed loads keep the vessel stresses below the Sec VIII allowables?
Thanks!
Pete
P. J. (Pete) Chandler, PE
Principal Engineer
Mechanical, Piping, Thermal, Hydraulics
Processes Unlimited International, Inc.
Bakersfield, California USA
pjchandl@prou.com
RE: Calculation of allowable loads at a shell nozzle?
You're right, CAESAR II won't do anything for you on the "vessel side". You still need to check the acceptability of the loads on the vessel.
RE: Calculation of allowable loads at a shell nozzle?
Richard Thompson, P.E.
Pipe Stress Engineer
Houston TX
S&B Engineers and Constructors, Ltd.
RE: Calculation of allowable loads at a shell nozzle?
Thanks for your reply. Let me make sure I understand your terminology:
longitudinal shear = a force applied parallel to the vessel longitudinal axis (a force in the plane of the nozzle flange face applied at the nozzle, along the vessel longitudinal axis)
circumferential shear = a force applied normal to the vessel longitudinal axis
torsion = a moment in the plane of the nozzle flange face
Yes?
Thanks!
Pete
P. J. (Pete) Chandler, PE
Principal Engineer
Mechanical, Piping, Thermal, Hydraulics
Processes Unlimited International, Inc.
Bakersfield, California USA
pjchandl@prou.com
RE: Calculation of allowable loads at a shell nozzle?
A lot of time the other two shears and torsion can be ignored, but it is important that you check the loads at the shell wall rather than the face of the nozzle flange. Obviously, a shear load at the face of flange will generate some additional bending in the nozzle when looked at from the nozzle shell. THis is why we usually evaluate nozzle loads at the shell wall.
Richard Thompson, P.E.
Pipe Stress Engineer
Houston TX
S&B Engineers and Constructors, Ltd.
RE: Calculation of allowable loads at a shell nozzle?