Pickling is used to remove oxide scale and the chromium-depleted layer, while passivation is used to rebuild a dense oxide film. The two serve different purposes and cannot substitute for each other.

Key control points: follow the supplier's instructions for acid concentration and temperature; pickling time is judged by a uniform silvery-white surface (over-pickling will corrode the base metal); after pickling, the surface must be thoroughly rinsed with clean water to avoid residual acid; after passivation, allow to dry naturally—never rinse with chlorine-containing water.

Common mistakes: continuing to use pickling solution after it is saturated with iron ions (causing yellow stains), incomplete rinsing, residual acid near weld seams, and using carbon steel tools that contact the stainless steel surface.