Hotrodpaint, you are kind of correct, we have parts powder coated weekly without sandblasting......we do sandblast the welded steel tubes that have mill scale and rust on them. The structural steel has a lot of dirt, oil, and grease on it too that the sand blast removes.

For the parts that are relatively clean to begin with and for sheet metal parts, they dip them in a cleaner/degreaser. IF a block has been hot tanked, it may be powder coated EXCEPT that, if there is any amount of oil on it, the powder coating will bubble where the oil outgasses. This especially happens at threaded holes and crevices where the oil is trapped. One helpful step is to pre bake the item in the oven for several hours before applying the powder. This either vaporizes the oil or boils it out where you can see it and wipe it off with solvent. Some items with mass need to be preheated and then coated hot since heating a cold part would result in uneven powder reflow.

Touchup on powder coat is a bitch.