Design thickness as minimum plate thickness 2

[KentCaudill]

Good Morning All:
The tank is Type 316L stainless steel. In the API 650 calculations the design thickness is a decimal. Corrosion allowance is not a factor. I intend to order the plate from the plate mill based on the design decimal thickness. Do I have to add the allowable mill rolling tolerances to the design thickness to arrive at the purchased thickness? In other words is the design thickness to be read as an absolute minimum thickness under the API 650 rules? Thanks for your help,

Thanks for your help, Kent.

 

[jlcochran1]

API-650 paragraph 2.2.1.2.1 states that the edge thickness ordered shall not be less than the computed design thickness or mimimum permitted thickness.

Par. 2.2.1.2.3 states that whether edge or weight basis is used for ordering an underrun not more than 0.25mm (0.01 in) from the computed design thickness or minimum permitted thickness is acceptable.

S.3.2 will send you back to 3.6.1.1 for minimum shell thickness to compare to calculated design thickness.

As long as your calculated thickness exceeds the minimum permitted thickness you should be able to order to the calculated thickness without having to add 0.010" mill undertolerance.

On a side note ASME Section VIII has a similar provision in UG-16(c).

 

[KentCaudill]

Good Morning jlcochran1:
Thanks for the help. Please clarify the definition of "minimum permitted thickness". Is the minimum permitted thickness a minimum thicknes specified by the purchaser or how is it determined?

Thanks for your help, Kent.

 

[jlcochran1]

I interpret minimum permitted thickness as the minimum thickness allowed per code. Since you are dealing with 316L SS Appendix S would apply. For shell plates paragraph S.3.2 referenced in my previous post applies. It states than the shell thickness cannot be less than the nominal plate thickness listed in 3.6.1.1. There you will find a table based on diameter. 3/16" is the minimum for tanks with a bottom course centerline diameter less than 50'.

 

[KentCaudill]

Thanks again. You have been a great help.

Thanks for your help, Kent.

 

[LSThill]

KentCaudill (Industrial)

http://www.coade.com

API650/653 TANK PROGRAM
OR E-TANK PROGRAM

 

[JeffcoatSmitt]

ETank2000 can be found at

http://www.etank.com