PV ELITE SADDLE WARNING

[shady2554]

A vessel diameter 3500mm, barrel length 9800mm, design pressure of 5.17barg, the design temperature of 90 degrees Celsius, the wall thickness of 11.11mm, with checking saddle PVelite, ** Warning: One or more Stresses Exceeded its Allowable ** alarm, Circ. Stress at Horn of Saddle -Actual is 34247.23psi Allowable is -30000.00psi.

Saddle Parameters:
Saddle Width 8.000in.
Saddle Bearing Angle 120.000 deg.
Centerline Dimension 103.346in.
Wear Pad Width 12.000in.
Wear Pad Thickness 0.375in.
Wear Pad Bearing Angle 132.000 deg.
Distance from Saddle to Tangent 36.449in.

I would like to ask what is the meaning of this alarm?
How to adjust the parameters? Thank you for help.
See attached for more details.

"Let he that thinks he is standing beware that he does not fall".

 

[fegenbush]

You need to add a stiffening ring (think vacuum ring) to the vessel at the location of the saddles. The external pressure of the saddle on the shell is what is causing the issue.

 

[jtseng123]

This is the most common failure mode.
Make the saddle wider, make the wear plate longer, wider, move saddle 3" closer to head to take the advantage of the head stiffness, increase contact angle. etc. Read Megyesy or Moss design handbook, you will know how to tackle this simple problem.

Sifffening ring is good as mentioned by fegenbush. But that is my last resort becasue you will need to check interference from nozzle/manway, re-pad, platform, how the insulation shall be done, etc. Causing me too much trouble. So I just play around the size of the saddle, wear plate and location.