Very few codes speak to oxide color.
That silence is important.
Eggheads have spent countless hours and grant dollars defining exactly when service conditions merit treatment/passivation of that kind of thing.
Unless you are the egghead assigned to make the call, I would't worry too much :)
On the other hand it takes very little effort to add a wire brushing step into the WPS..
Hi Kix
Not sure what heresite coating you will be applying, but as a general rule you need a specific surface profile for the coating to adhere well. Chances are that the coating may not adhere that well on the oxidised surfaces. Not sure on the application, but words like "turbine inlet coil" makes it sound relatively critical. The type of thing you want to do once and leave for 30 years before having to mess around with again. If that is the case, then it is worth doing well. If this requires more than you quoted for, then obviously the client must pay for it, because he will be getting the benefit.
A couple of things to remember:
1) A coating that is not well applied can have a significantly reduced life. (Includes surface preperation.)
2) Coatings are often damaged, leaving the substrate exposed.
3) Stainless steel with a compromised surface can corrode substantially faster than ordinary carbon steel under many circumstances.
Put these together, and it can result in a very short service life, and excessive maintenance and down-time costs.
Just something else to consider: Power brushing of stainless is fraught with dangers. After a while the brush will start to "flare" and will scrape along the inside of the guard. This will result in iron contamination of the stainless part you are brushing. (Not to mention other sources of contamination of the wire brush.)
Regards
Niekie