Generally, stainless steel (such as SS 316) has own corrosion resistance against atmosphere, except for marine environment or insulated pipe. Actually, the definition of stainless steel is the steel which is having more than 11.5% Cr (SS 316 --> 18% Cr) and it is to form own protective oxide film(ex., Cr2O3) on the surface and does not require any coating at all against atmospheric corrosion, generally.
Lee SiHyoung,