I am designing a pressure vessel which will sustain a pressure of 17000 psi before the safety factor.  I am having trouble determing the wall thickness.  I have seen the calculators that are available at this site but do not know what some of the variables stand for.

What is:

(S) = Maximum Allowable Stress value   (psi)?

(E) Joint Efficiency  (80% = .80)?

It would seem that these variables are a property of the material itself.  Is (S) perhaps the yield strength of the material?  Is (E) only applicable for welded parts?

Thank you for your help.