First of all, I don't see much corrosion in that picture. The dark goo is plumber's putty - a sealant which was torn off when the lid was lifted, it will be replaced before putting the lid back.
But even if there is corrosion caused by hot steam ... is that really a problem in the 21st century? I think we managed to build huge steam engines quite a few years ago, and all is known about corrosion of every construction material on this planet.
You can say that Rossi didn't pick the proper aluminum alloy or the proper plating or whatever, but that has nothing to do with production of heat. *That* part may be a fraud, or maybe it isn't - that would be a valid point to discuss. But corrosion ... who cares? Any competent chemical engineer will tell you exactly how to properly build anything that works with corrosive materials. Such materials are widely used in the industry exactly because they are active; not much can be done with an inert material. Even fluorine is used - an element in which water burns.
It's impressive because the ecat has only operated for a few hours. It might be deposits, too. And when the guy comes out to replace Rossi's homemade isotopes every six months, what is he going to see? And is he going to have to scrape off the putty every time and replace it?