Cleaning Stainless Steel

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The final operation after fabrication or heat treatment is cleaning to remove surface
contamination and restore corrosion resistance of the exposed surfaces. Degreasing to remove
cutting oils, grease, crayon markings, fingerprints, dirt, grime and other organic residues is the
first step.

Degreasing: Non-chlorinated solvents should be used in order to avoid leaving residues of
chloride ions in crevices and other locations where they can initiate crevice attack, pitting,
and/or stress corrosion later on when the equipment is placed in service.
Machined components: After degreasing, machined components are sometimes "passivated"
in 10% nitric acid. Nitric acid enhances the natural oxide surface film.
Fabrications: After degreasing, metallic surface contaminants such as iron embedded in
fabrication shop forming and handling, weld splatter, heat tint, inclusions and other metallic
particles must be removed in order to restore the inherent corrosion resistance of the stainless
steel surface.

Nitric-HF pickling, (10% HNO3, 2% HF at 49C to 60C (120 to 140F), is the most widely used
and effective method removing metallic surface contamination. Pickling may be done by
immersion or locally using a pickling paste.
Electro polishing, using oxalic or phosphoric acid for the electrolyte and a copper bar or plate
for the cathode can be equally effective. Electro-polishing may be done locally to remove heat
tint alongside of welds or over the whole surface.
Both pickling and electro polishing remove a layer several atoms deep from the surface.
Removal of the surface layer has the further benefit of removing surface layers that may have
become somewhat impoverished in chromium during the final heat treatment operation.
Glass bead or walnut shell blasting are very effective in removing metallic surface
contamination without damaging the surface. It is sometimes necessary to resort to blasting with
clean sand to restore heavily contaminated surfaces such as tank bottoms, but care must be
taken to be certain the sand is truly clean, is not recycled and does not roughen the surface.
Steel shot blasting should not be used as it will contaminate the stainless steel with an iron
deposit.

Stainless steel wire brushing or light grinding with clean aluminum oxide abrasive discs or
flapper wheels are helpful. Grinding or polishing with grinding wheels or continuous belt sanders
tend to overheat the surface layers to the point where resistance cannot be fully restored even
with subsequent pickling.