Nozzles are mostly attached to the cylindrical or torispherical
head portion of pressure vessels and tanks, whereas lugs are attached
mostly to the cylindrical portion. When the nozzle is much thicker than
the vessel, the nozzle behaves like a rigid inclusion in the vessel (i.e.,
like a lug attachment). Hence, we discuss here only the local shell behavior
at nozzles.
For radial force and lateral moments at nozzles, torispherical head is
stiffer than cylindrical shell. This is because cylindrical shell ovalizes
for such external loadings, while spherical shell does not. For example,
a cylindrical shell deforms as shown in figure below for a radial load.
For a thin shell, where R/T is large (say, R/T >>
10), the shell for nozzle loads may be as flexible as the attached piping.
In such cases, the local shell flexibility should be included in pipe
stress analysis. If, instead, the nozzle is modeled as an anchor, the
resulting pipe stresses and support reactions would be different from
those for a pipe stress model with a flexible nozzle.
To include local shell flexibility, you need to define a Nozzle data type
at the node in question. Once done, in the Layout window, use List >
Nozzle Stiffnesses to display the stiffensses.
It couldn't be easier to edit an existing material library
or create a new one in CAEPIPE.
TO EDIT:
Execute CAEPIPE, select File menu>Open>set Files of type to Material
library files (*.mat). Click on B311.mat (or B313.mat). Once the library
is opened, you can insert, delete or modify an existing material entry.
Once you insert or modify a material entry, it is necessary to press Enter
with the cursor in the left hand side table (say, with the cursor in the
Description field). This will enter the material into the database.
To add a material, simply go to the end of the table to a new row and
start typing information. Move to the right hand side subtable to enter
temperature, alpha, modulus, allowable etc. Once done on the right hand
side, move the cursor to the left hand side and press ENTER.
To edit an existing material, place highlight on the material to be edited,
and start changing information. Once done, press Enter.
After all editing and adding activites are over, save file and close.
Now, load a piping model file. The new material will be available once
you open the library from within the model (under Ctrl+Shift+M).
TO CREATE:
To create a new library file, select File menu>New. Select Material
Library file. Once inside, follow instructions above.
In CAEPIPE results, Element forces (and moments) are shown
for each element in the piping model. There are two screens that show
element forces: 1. Pipe elements, 2. All other elements (such as valves,
expansion joints, etc.). Element forces may be displayed either in local
or global coordinate system.
Except the network (piping end nodes) endpoints, intermediate pipe element
node numbers appear twice (one below the other) in the Element forces
screen. All other non-pipe elements appear under Other Element forces
(Press F6 from the Element forces screen).
Example: For pipe elements 10 to 20 and 20 to 30, element forces are reported
for two elements shown next to each other with node 20 shown twice (once
for each element).
Shouldn't forces and moments be equal and opposite at every common node?
Yes. The element forces at the common node should be equal and opposite
unless the common node has a
• Force (externally applied)
• Concentrated mass,
• Weight (e.g., from a Flange),
• a Support, among other things.
Note that different weight distribution does not cause unequal forces.
Refer to any strength of materials book, e.g., "Introduction to Mechanics
of Solids" by Egor P. Popov, Chapter 2: Axial force, Shear and Bending
moment in Beams, for more information.
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