The flametamers are an important part of your BBQ, and are being used every time you BBQ. Therefor it is normal for the flametamers to create some surface corrosion on them. This is normal. Only when the flametamers start to get holes in them they need to be replaced.
To clean them it is best to first start your BBQ and let it heat for about 20 minutes on the maximum heat. This way it will get rid of most of the residue on your grids and flametamers.
Then you will have to wait untill your BBQ is cooled off completely. After it has cooled down you can use a brass brush to brush of all the remaining residue on your grids, and if you remove your grids off of your flametamers.
If your flametamers are really dirty you can take them out of your (cooled down!) BBQ and put them in a sink with some soapy water, and clean them with a steel wool soap pad.
After your flametamers have been cleaned it will be best to hand dry them with a towel (if you let them drip dry they can rust prematurely).