I have had experience with a couple of different types. There are lots of variables. One of the things that has a big bearing i believe is the number of cycles the diffusers do where they go from no air flow to full airflow such as what they might in an SBR.
I have seen lots of failures sometimes in only a few months. I would think anything over two years between change outs would be pretty lucky in an SBR type application. Where there was always a fairly constant airflow such as in a conventional aeration tank with modest airflow per diffuser flow rates you would probably do a bit better.
Regards
Ashtree
"Any water can be made potable if you filter it through enough money"
This is a conventional plug flow aeration basin, so aside from rare anomalies they're on 24-7. They're getting something of a calcium-iron scale and we're starting to see some failures. They were installed in 2010, so wondering if these are premature and any related to the buildup or if we've already got our money's worth out of them and need to replace with like kind?