There are also courses offered by NACE International. Among them you will find one titled "Corrosion in the Refining Industry". Also, UOP offers a "Corrosion and Fouling" class sometimes.
As a fellow corrosion engineer in the refining industry, I highly suggest the following groups, in order of applicability: NACE, API, UOP, and then ASM. (Nothing against ASM, but you'll find more information regarding the petroleum refining industry elsewhere.)
You state you are quite versed with API 571 and that is excellent (especially since the document only premeired last year). In that case, you may want to take the "Damage Mechanisms" course offered by Equity Engineering (in part through API) which is the logical extension of that document.
~NiM