Wild, kinda off the wall question here ..... WHAT IS YOUR CODE OF RECORD FOR THE DESIGN THIS TANK ?
... or are you just kinda messin around in the back yard with some scrap sheet metal seein what you can build.
You are not doing this for a client or anything like that ?.... Right ??
I can't see the difference between 0.2% and 1% strain being significant enough to make any difference??
Strain based design is used where you get rare but very high loads. The issue is that once strained it doesn't go back so then what do you do? Scrap the vessel?
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
Considering that virtually none of the alloys that we use actually have a linear section to the tensile curve, and that yield strength is an engineering construct and not a material property this is a minor issue.
Read the rules (Code).