Okay, talked to the other stress engineer at my company and he pointed out that the larger shorter tank was also FRP so it to is also growing from the Bourdon effect. The other tanks are 316L, so the FRP tank is pusing up against the other two tanks.

In other news, I spoke with the client and they dropped the design pressure and temp. So with the addition of the spring cans, all is well.

Thanks Dan and Richard for the input.