The company I worked at for several years provided the service on units we had under maintenance contracts. The results varied so much it became pretty much a money loser and we finally got out of it.
Problems, different masking debris requires different cleaning methods. Severe oil masking, like from a turbo failure never came back to be able to make compliance (at least not in CALIF)
The in and out handleing caused a lot of physical damage to catalyst, face it it's a lousy job and most techs doing it just want to get it done and weren't too careful doing it.
We got very poor support from catalyst manufacturers in how to properly clean their catalysts, and when we did follow their instructions and recommendations, then didn't pass a compliance test is was always our fault anyway.
To be fair, we were in a very tough market, everything had to be in near perfect condition to maintain compliance levels.
We had some sites that had been problem children (older models engines or low load factors causing higher oil consumption) that by installing "guard beds" basically untreated catalyst substrates to act as filters, we had better success.
On oxidation catalysts we tried quarterly vacuuming and blowouts, worked well if somebody checked after guy doing work, problem was no one wanted to give us the time to let the catalyst cool completely to do a proper cleaning.
We tried several companies in California, Arizona and Nevada and never rerally had very good results with any of them, although two of the companies we used in Arizona would take out catalysts that wouldn't pass in SOCAL and sell them into other markets with less stringent requirements.
The primary method we used to determine when a catalyst needed cleaning was a differential pressure gauge. Different manufacturers had varying recommended numbers, overall we used twice the "new" reading to start to schedule, get it out before actual reading got to 4X of the new reading. Our experience on the engines we dealt with, mostly power generation units and some oil field applications was that if you let delta pressure exceed 4 times original reading you likely wouldn't recover the catalyst at all.
Some of our power gen customers watched the delta temp on three way catalysts and compared to other parameters, as soon as they noted a drop in reductions they pulled them and dropped in their spares, costly but cheaper than a fine and associated trouble from APCD.
Hope that helps
