Angela,
I work for a brewery equipment manufacturer, and yes we build tanks to the ASME code when they are rated greater than 15 psi. Ordinarily, the tanks are exempt but occasionally a customer will ask for a 2 or 3 bar tank (typically a bright tank). Greater pressure = faster carbonation, or so I've been told. The CO2 is the tricky part, particularly for fermenters. It's difficult to claim an exemption for a fluid approximating water when a pressurized blanket is being applied using CO2.
We also have fitting designs registered for steam jackets rated greater than 15 psi.
Sean