Passivation vs Electropolishing: Two Different Jobs

Passivation and electropolishing both show up on stainless steel drawings, and both improve corrosion performance — which is exactly why they get confused for each other. They are different processes doing different jobs, and knowing which one (or both) a part actually needs avoids paying for the wrong process, or worse, missing a requirement the application depends on.

Passivation — restoring the passive layer

Passivation, per ASTM A967 or AMS 2700, is a chemical treatment (nitric or citric acid) that removes free iron contamination left on the surface by machining, without removing meaningful base material or changing the surface finish. Machining smears free iron across the surface, which interferes with the chromium-oxide passive layer stainless steel relies on for corrosion resistance; passivation strips that free iron and lets the native passive layer reform. It's verified with a water-break test, high-humidity exposure, salt spray or copper sulfate test as specified in A967 — and it's the right call whenever a machined stainless part simply needs its native corrosion resistance restored.

Electropolishing — smoothing and deburring

Electropolishing is an electrochemical material-removal process. Its primary job is smoothing the surface — reducing microscopic peaks and valleys, lowering surface roughness (Ra), removing burrs and embedded contaminants. As a byproduct, it also removes free iron and improves the passive layer, similar in effect to passivation, but that's a secondary benefit, not the reason the process is specified. Electropolishing is called out where the surface finish itself matters: medical implants and instruments, pharmaceutical and high-purity gas or fluid piping, and any application where a smoother, more cleanable surface is a functional requirement, not a cosmetic preference.

Which one does your part need

• Machined stainless fasteners, brackets, general components — passivation is usually sufficient on its own.
• Medical, pharmaceutical or high-purity process components with an explicit Ra or surface-finish requirement — electropolishing, which typically satisfies the passivation requirement as a byproduct but should still be verified against A967 if the spec calls for it separately.
• When the drawing calls out a specific Ra value or references cleanability/biofilm resistance, that's a signal electropolishing is needed, not passivation alone.

Specifying "passivate" when the application actually needs a controlled surface finish — or paying for electropolishing when passivation alone would meet the requirement — both point back to the same fix: read the functional requirement on the drawing, not just the word "stainless."