Passivation is the final cleaning step that lets stainless steel be stainless. Machining, forming, welding and handling leave traces of free iron on the surface; those specks rust, stain the part and can start pitting. Passivation dissolves them in a controlled acid bath — without removing base metal — and lets the chromium-oxide film re-form thicker and more evenly than it would on its own. The part looks the same as it went in; it simply behaves like the grade it is made of.
What gets passivated
- Machined and turned stainless parts — fittings, shafts, fasteners and inserts — after machining.
- Welded assemblies, spools and vessels after pickling, before they enter service.
- Food, beverage and pharmaceutical equipment to the surface condition the specification names.
- Architectural stainless steel exposed to coastal and industrial atmospheres.
Why passivate
A stainless steel part that shows rust spots after a few weeks outside has usually not corroded itself: iron picked up from tooling, grinding dust or a steel bench has rusted on its surface. Passivation removes that iron before it can, and restores the passive film that cutting and forming disturbed. It is inexpensive relative to the fabrication it protects, and for hygienic and coastal work it is the difference between a surface that stays clean and one that is cleaned repeatedly.
Where the specification names a passivation method or a test, the process is run to it and recorded.
From your parts to a passive surface
- Send the parts or the drawing with the grade and any specification clause that names the passivation method.
- We confirm the bath, the process time and whether pickling is needed first for welded or scaled surfaces.
- Parts are degreased, passivated, rinsed and dried, then checked for a clean, even surface.
- Parts are packed in clean protection — or move to assembly, polishing or PVD in the same order.