Saddle Design for Horizontal Vessel 1

[MOHAMMED89]

for the existing vessel (build in 1999) having dia 3m and Length (T/T) 8m.

this vessel to be modified to meet the new process requirement.
Calculation is not available, So i tried to design using PVElite. When i run the calculation for the saddle anlaysis in operating condition the below failures are showing.:-
1. Circu. Stress at horn of saddle is failing. The actual stress is 2 time of allowable.
2. Bending stress is also failing.

Kindly advise me wat i can do in this situation, What are modification on saddle i can try. existing saddle details provided below. Kindly note that sins the vessel is already in operating condition there are some limits for the modification aswell.

Saddel width - 230mm
Saddle contact angle - 168
Wear plate width - 280mm
Wear contact angle - 180
Base plate thickness - 30mm.
Number of ribs 4Nos, Thickness 10mm.
Web plate thickness 10mm, Position center.
vessel dimension - 3m Dia and 8m length (T/T).

 

[marty007]

Take a look at adding a stiffener ring above the saddle, something like this:

What this does is essentially hang part of the vessel from the stiffener ring, thereby reducing the load acting directly at the saddle horns. I know Compress provides this functionality, I'm not sure about PVElite. This could resolve issue #1.

Regarding issue #2, where is this bending stress occurring? In the main vessel shell, or in the saddle material? If it's in the saddle material, you could look at adding more gusset plates.

 

[chicopee]

I would check other sources being Zicks' paper on horizontal pressure vessel and Bednar's handbook on pressure vessel. Bednar's work is a modified version of Zick's paper.
The hand calculations required from these two sources are in the English units and would be useful in collaborating the PVElite results.

 

[LittleInch]

What is the change of process parameter?

for such a size vessel it may be quicker cheaper and easier to just buy a new vessel purpose designed for the new conditions. If this vessel is nearly 20 years old not sure how long a life it has left. Any fatigue calcs will need to include for the fatigue life already experienced.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[JStephen]

It is possible that the saddle wasn't designed or was designed incorrectly to begin with, so that it simply won't meet the design requirements.
It is possible that it was designed using finite element methods so that it was adequate, but still doesn't satisfy the Zick procedures.
There are some variations in how the Zick procedures are used. Look at the details in two or three different vessel handbooks.
There are some variations in how ASME allowable stresses are/have been used, look into the possibilities there.
Wind and seismic loading may have changed, specific gravity of contents may have changed, design liquid depth may have changed.
Also take a close look at whether you actually NEED to re-evaluate the saddles.

 

[r6155]

My rule of thumb indicates something is not good
Careful revise input data.

Regards
r6155