AWS and ASME qualification requirements are nowhere near the same - as far as certification goes.

Not sure how you do this as a hobby, but regardless, for boiler work you need to be certified in accordance with ASME sec IX.  There may be some testing labs in your area that may be able to test and certify you, for a price of course. 

To look a little deaper into the matter - if your state has pressure vessel/boiler laws, you will need a quality manual and program, and you will need and "R" stamp from the National Board (NBIC).  This is a pretty pricey thing to get certifed for repairs (the "R" stamp).  If this is the case, then you will be considered a company, and all testing and qualification requirements for welders will be spelled out in your QC Manual.

If you are working for a company, or will be, then they will more than likely have an "R" stamp and all the requirements will be in their hands.

Not all states have pressure vessel laws, but I beleive most if not all do have boiler laws.  There is so much more to it than being a "certified welder to ASME sec IX" to be able to make repairs to boilers.