Porcelain Coated Cooking Grates for Grill
In my experience there is no way to avoid damaging the porcelain coated cooking grids. The use of a heavy duty ScotchBrite instead of any metal brush may lenghten the time that they go undamaged, but eventually use will cause the surface to break down. Of course you can only use the ScocthBrite on a cold grill.
The problem is that in preheating the cooking surface it is doomed to fail -- the application of cold food to hot grates is unavoidable...