Nozzle Loads - Directions Applied 5

[bman289]

I'm new, obviously, and I would like to ask a basic question. I have been given allowable nozzle loads with the following terminology. Radial Reaction, Tangential Reaction, Longitudinal Bending Moment, Circumferential Bending Moment, Rotational/Twisting Moment. I am a little lost as to the direction these loads are applied in. I think they are being applied at the flange. I come from HVAC, so pressure vessel design is new to me. Any help will be appreciated. Also, what book(s) would anybody reccommend for a good, all-around pressure vessel design manual.

 

[jte]

bman-

With a vertical vessel let's assume the x-z plane is horizontal at the elevation of the nozzle and the y axis is vertical. I have a nozzle coming directly from the centerline of the vessel on the x axis. Radial load is a load on the x axis. You'll need to check with your piping guy to verify whether a positive radial load pushes or pulls on the vessel (typ for all loadings). Conventions may vary. Radial loads tend to be difficult since they cause local bending of the shell. A tangential load will parallel to the z axis. Typically easy to deal with (causes shear in the shell). A longitudinal load is parallel to the y (long) axis. Also easy - shear. A radial moment is a moment about the nozzle (x) axis (torsion in the nozzle). Easy to deal with. A circ. moment wants to twist the vessel about the y axis. This is often difficult: It causes local bending on the shell at the sides of the nozzle (which adds to the local bending caused by the radial load). A long moment wants to tip the vessel over and causes local bending in the shell at the top and bottom of the nozzle. Also can be difficult to deal with.

The loadings may be applied at the flange. In that case you'll have to translate them to the shell unless your analysis software will do that for you. Or are you being good and doing a few hand calc's using WRC-107 first? Usually its easiest to have the piping stress engineer just provide the loadings a the nozzle-shell junction.

As for books: Do a search on this forum for recommendations. You'll find plenty.

Anyone out there willing to write a FAQ on book recommendations?

jt

 

[TomBarsh]

Radial Reaction = radial to the shell surface.

Tangential Reaction = tangential to shell surface; could be in longitudinal or circumferential direction (or anywhere in-between), important to distinguish which. It is likely that by saying "tangential reaction" the author of that specification intended this reaction to apply in any direction.


It is simpler to describe the Longitudinal Bending Moment and Circumferential Bending Moment in terms of vectorial arrows. A vector arrow describing a "moment" has two arrow heads (to distinguish from the single-headed "force" vector arrow). The vector arrow follows the "right hand rule"; the direction of the moment is indicated by the direction of the fingers of a right hand as wrapped around the vector arrow with the thumb pointing in the direction of the arrow.

Longitudinal Bending Moment = bends the shell thickness in its longitudinal direction. The vector arrow points at 90° to the shell axis and at 90° to the nozzle axis.

Circumferential Bending Moment = bends the shell thickness in its circumferential direction. The vector arrow points parallel to the shell axis.

Rotational/Twisting Moment = twists the nozzle (or other attachment) about its own axis. Generally creates only shearing stresses through the shell thickness. The vector arrow points at 90° to the shell axis and extends through the nozzle axis.


The loads may or may not be applied at the flange; they may be specified at the nozzle-shell surface. It is important to know which is intended. If applied at the flange face then the tangential reaction will add an additional bending moment term at the shell surface.


The sense or direction of the loads and moments is important also. The stresses in the shell resulting from these loads may add to or diminish the stresses in the shell due to pressure.

Generally, the stresses in the shell resulting from the applied loads and moments will be calculated using Welding Research Council (WRC) bulletins 107, 297, or 497, or will be analyzed using finite element analysis, or some other means. The WRC bulletins provide a 3-D sketch of the standard load/moment orientations to be used when determining the shell stress per the bulletin (note that these orientations don’t follow what I would take as a right-hand rule, nor even a left-hand rule); this sketch is reproduced in a number of standard pressure vessel design references.

 

[TomBarsh]

jt, again "good timing"!

 

[jte]

Tom-

We work well together!

jt

 

[bman289]

TomBarsh and jte,

Thanks for the info, much appreciated. I have a question poised to the spec writer now to determine where the loads are applied, flange or nozzle connection.

Thanks again,

Brad

 

[arto]

Get Bednar's "Pressure Vessel Design Handbook"

& Harvey's "Pressure Component Construction"

 

[LSThill]

Team Members

Tom Barsh (Structural), Codeware Technical Support Engineer: " The Home of COMPRESS ASME PRESSURE VESSEL SOFTWARE" HIT THE NAIL ON THE HEAD!

Also, include the new "WRC 497"

 

[JStephen]

Hey, bman, one thing I have run into with tank (not vessel) nozzle loads- the applicable code in that case calls for the tank designer to furnish nozzle stiffness to the pipe designer, who then analyzes pipe and reports loads back to tank designer. If no one furnishes that stiffness, then the loads may be exaggerated, based on "fixed" nozzle. So if you go to analyze the loads and they seem inordinately high, don't just assume you're stuck with them- check and see where they came from.

I have noticed also that pipe people normally don't take nozzle movement due to tank stresses into account- which makes you wonder about the design.

I recall seeing a fairly useful PV book from Gulf Publishing a while back, try a web search for them. The PV books tend to furnish design methods for use with ASME, they don't just explain the code itself.

ASME does have week long PV design classes, check their website.

 

[bman289]

To all,

Many thanks for the input. I am heading to Houston in October for the ASME Sect VIII Div I class. Also, found a book, "Pressure Vessel Design Manual" Moss, that looks pretty good.

Regards,

Brad