annular plate thickness using elastic analysis method of bob long book 2

[inammanj123]

Dear ALL,

I am working on a tank with design height of 18.4 m and with a liquid having S.G of 1.5. Product of design height and S.G came out to be greater than 23, so i had to perform elastic analysis in finding annular plate thickness.

Now one option is to use find out thickness using ANSYS, but there is a procuder given in BOB LONG'S book. I have prepared an excel sheet using those formulas. Has any one gone through that example in bob long's book??

After preparing the sheet i found out basically you make sure that
1) fatigue stress comes out to be less than 75000 lbs/in2.
2) at the same time you have make sure that θs is equal but with opposite sign to θc and θb is zero

i am confused at one thing that for a given thickness say 8 mm by iteration i found out that 480.55 mm is the width where all conditions are satisfied, but when i increase the width to 700 mm so that the api 650 minimum width requirement of 600 mm is met, fatigue stress becomes greater than 75000 lbs/in2.

so i found out that at 14 mm thickness i can use annular plate of 659.013 mm and the same time fatigue stress is within limit.i cannot go for lower thickness otherwise 600 mm minimum requirement of api 650 and fatigue stress less than 75000 cannot be met.Even at the end of the example in bob long it says that API 650 minimum width of 600 mm is conservative

please share you opinion.

Regards,
Inam

 

[desertfox]

Hi

Not sure from your post whether the tank your talking about rectangular or circular.
I have no idea who Bob Long is but it might be a good idea to copy and scan the example that you mention and then we can all understand your problem a little better.

 

[IFRs]

Would you also share your excel sheet?

 

[inammanj123]

Hi,

attach are the pages from storage tank book "guide to storage tank". Question is whether the attached formulation can be used in deciding annular plate thickness or not?

 

[inammanj123]

attached is the excel file i have prepared

 

[IFRs]

I don't quite follow all the theory behind the worksheet calculations and it is unclear to me how you arrived at some of the values in the worksheet since some are not formulas and I would be glad to pursue this for my own interest but nonetheless I believe that your results suggest that it only takes an annular plate width of 18.92 inches to satisfy the design calculations. Using a wider annular plate only helps since the object is to create a plastic hinge in the annular plate before overstressing the corner weld. If you increase the annular plate to 30 inches, which gets you 24 inches inside the tank ( the API minimum ), you should be OK. Other references that may help you are: Comparison of design methods for a tank-bottom annular plate and concrete ringwall by T.Y. Wu, G.R. Liu at the Department of Mechanical and Production Engineering, The National University of Singapore, 10 Kent Ridge Crescent, Singapore, Singapore 119260 Received 7 March 2000; revised 27 June 2000; accepted 3 August 2000. Also an article titled More accurate method devised for tank-bottom annular plate design by Tianyun Wu of the University of Petroleum in Dongying, Shandong, China published in the Oil and Gas Journal May 20, 1966