Purpose of the dimples in a condenser is for?

Hello, I am curious as to what the purpose of the dimples in a condenser is for?

Here is an accompanying photo to show what I am talking about

 

[SteamKing]

Without knowing what kind of service this condenser is in, I would speculate that the dimples serve as an expansion joint for the shell, to relieve stresses due to high temperatures when in operation.