saddle for a vessel 1

[MGV]

I try to decide the saddle for a vessel length 4250 mm, diameter 2800 mm. I found the right dimensions for the saddle but I don't know the separation between these saddles. If you have any idea please let me know
Thanks a lot
MGV

 

[kstaylor]

You need to do an analysis of supports for your horizontal vessel using the method of L.P. Zick (see Welding Journal Research Supplement, 1951). This method is described in detail in several of the pressure vessel texts in current publication. This method accounts for the bending stresses in the vessel shell, the increased stresses in the heads (depending on saddle location), and the stress in the saddle itself.

There are several commercial computer programs available that can do this analysis. However, for your first few times I strongly recommend you do it by hand to get a better understanding of the method and its limitations.

Good luck.

 

[torsani]

The paper above was reprinted in Welding Journal Research Supplement of 1971 with a subtle change.
Other papers was published by Z. F. Sang (Journal of Pressure Vessel technology, Nov. 1988), G. B. Moody (Hydrocarbon Processing, Nov. 1972)and others.

 

[prex]

For the proportions you mention (not a slender vessel) I would position the saddles as close as possible to tangent lines, that is with saddle pad plate at some 200 mm distance from head circumferential weld.
You might need to leave some space for a nozzle on bottom line, if vessel axis is sloped, then having saddles closer to the middle.
There are no general nor specific rules for saddle positioning. On the contrary it is necessary to check stresses as mentioned by kstaylor, especially if wall is relatively thin.
prex
motori@xcalcsREMOVE.com

http://www.xcalcs.com

Online tools for structural design

 

[fba123456]

I usually use 80% of the Shell length then do a Zick analysis to confirm it.

 

[Heyner]

Hey!
Nice to hear about your doubt!
I'm just starting to know how to use the Zick's work. You can download the text of Zick's paper from

http://www.codeware.com/papers.html

The best position of saddles is when the bending moments at saddles & midspan becomes the minimum, but after that you migth see if it is necessary to reinforce the shell at saddles. I'm building&searching for a spreadsheet for that. I'll send it to you to see some of the variables, let me know your e-mail address. Let's study the article and share to understand it well.

Regards,

Heyner.

 

[Heyner]

This thread will look better on pressure vessels forum.

 

[yup]

Length between tangents / 5 is the best for layout purposes. If the zick analysis confirms the stresses in the shell are too high move them out towards the ends to a min dimension of diameter / 4 and redo the analysis.
The position of the nozzles in the bottom of the shell also has a bearing on the position of the saddles but the above 'rule' can be generally applied and backed up by the zick stress calc.

 

[korakrit]

Heyner!

I'm interested in your saddle spreadsheet.

my email : korakrit@engineer.com

 

[meca]

There is a saddle spreadsheet at

http://www.mecaconsulting.com,

however it is not free. The cost is $75.

 

[twistobar]

Meca,
Have you considered my suggestions to be able to combine wind and seismic loads for offshore applications?
I am prepared to buy your spreadsheet as soon as this feature is adopted.
Regards,
ob

 

[meca]

ob,

It's still something I eventually plan to do, but I have not incorporated it as of yet.

There has also been an interest in designing saddles for for pipe and ducting. I have been looking for a reference for this type of design. I think it would be a modified version of the Zick method.

Thanks,

meca

 

[olmedo]

For 2800 mm diameter tank, you should consider using Ring Girders and column type instead of saddles.

 

[johnp]

meca stated that
There has also been an interest in designing saddles for for pipe and ducting. I have been looking for a reference for this type of design. I think it would be a modified version of the Zick method.

That is a big subject which would better be handled as a separate thread in the Piping section.

The pipe saddle problem is a small part of the general field of the support of thin cylindrical shells and pressure vessels. Most of the work takes tank support research and adapts it directly to pipe supports.

Two leading researchers in this field are
1 - Dr V Krupka - Vitovice, Institute of Applied Mechanics, Brno, Check Republic
2 - Prof A.S. Tooth - Dept Mech Eng, Uni Strathclyde, Glascow, Scotland.

I can send more information if you let me know your e-mail address

 

[meca]

Johnp,

Here is my email chris@mecaconsulting.com . I would appreciate any information you can send me on the subject of pipe saddles.

Thanks,

Chris

 

[MURZ]

Dear Meca,
I have downloaded the Demo to your spreadsheet for saddle design and I have two questions.

1.) On page 5 of 8 on the PDF paper you show a calculation for the variable “d” as being
B-R*sin(Theta)/Theta with a result of 49 inches. Using your numbers for this calculation I get 44.25 inches. Theta is equal to 2.097 rad and sin Theta is 0.865 rad. Therefore, the calculation is 69-60* 0.865/2.097 which is equal to 44 .25 inches. This changes the bending stress from 913 psi to 824 psi.

2.) Also on page 5 of 8 you show a bending stress in the wear plate fb = 17,624 psi. Again using your numbers for the calculation I get 121,518 psi.
(6*Q*K5*wb)/(8*tw^2*Rs) = 121,518 or 6*300,000*0.7595*24/(8*0.750^2*60) = 121,518.


Since I only have your Demo I can’t see the actual formula that was used. I was contemplating purchasing your software until I saw these discrepancies. Could you take a look at these two and let me know if it is just me or is it the spreadsheet that is incorrect.

 

[ibrahimdemir]

Hi Johnp,

I am very interested in seeing the papers that you listed. I was wondering if you can e-mail me those to the following address:

idemir@cbh.net.au

Thanks in advance.

Ibrahim Demir
Clyde Babcock Hitachi ( Australia )

 

[VDK44]

Dear Heyner,

I am interested to have your spread sheet for pressure vessel saddle design. Kindly send to my E-mail

v.dwarakakrishna@idpeltd.com

Regards
V.Dwaraka Krishna