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Pickling passivation ensures corrosion resistance to components of stainless steel and thus considerably
influences their life and usefulness.
The corrosion resistance of stainess steel is due to the presence of atleast thirteen percent chromium
in the alloy. With oxygen, the chromium forms a dense chemically resistant passive layer of chromic
oxide protecting the surface of the component against corrosion. The passive layer usually forms again
after abrasion. The precondition to corrosion resistance and passive layer is a metallically pure surface
with a sufficiently high percentage of chromium.
Every mechanical treatment damages the top layer of components i.e.
-contamination with Ferritic matter,
-change in the structure of the layers,
-development of inbuilt stress,
-reduction of chromium content.
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Heat treatment like
annealing and welding leads to scaling and
discolouration. This not only deteriorates
the appearance of the component but also its
corrosion resistance due to the presence of
ferric oxides. A continuous passive layer of
chromium oxide cannot form here. Hence it is a
must to have a metalically
clean and pure surface by pickling before
passivation. Corrosive strain on insufficiently
passivated stainless steel leads to ;
- pitting corrosion,
- crevice corrosion,
- stress corrosion cracking,
- intercrystalling corrosion and
- corrosion resulting from contact with foreign
metals.
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| Grinding |
Polishing |
K-2 Pickling |
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A dense passive layer can only form on
metallically pure surfaces. Professionally
pickled passivated stainless steel surfaces and
welding seams;
- are metallically pure, free of scales and
discolouration,
- have the full corrosion resistance of the
component and
- have a decorative metallic appearance.
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