It has been proven to be more cost effective to impregnate rather than scrap castings.  If a casting has had expensive machining there is no way to recover that cost if the casting is scrapped.

It has been calculated by engineers that impregnation is a small cost when recovering expensive components.

A few components that are good candidates for impregnation are cylinder heads and blocks, engine crankcases, aerospace components, hydraulic and pneumatic components, fire fighting components, food processing equipment and welded and braised parts.