We are currently investigating reasons for pitting on the cone of a powder drier. From reading other posts I should find out running times and temperatures, Cleaning chemicals and frequency of cleaning, as well as the nature of its operation and the materials used in manufacture. Is there anything else I should find out that would help diagnoses, we can not take samples from the drier except as a last resort. Does anyone have any experience with the dynamics of powder driers, I would assume the powder would have to be quite abrasive at high temperature on what I believe is SS316. I have found the pitting to start with a tiny pinhole which is quite clean and shiny which then seems to progress in a shotgun like pattern radiating out from the centre pinhole, which will by then have the appearance of cast alluminium dull in colour and pitted looking within itself. Pitted pitting, kind of like it has disolved. They do use a hot caustic CIP maybe they are running it too hot?? The major pitting is localised to one band within the cone area while the rest of the drier is only showing minor intermittent pitting(suggests it isnt the CIP but rather that particular metal). Does this sould familiar to anyone?

The powder is milk powder, and could these aqueous chlorides be concentrated in certain areas of the cone only.......I mean if that was the case would'nt the entire surface area be suffering a similar rate of corrosion?? There is no obstructions or anything stopping the flow of powder air or cleaning agent. Perhaps if I can get more accurate information.