Pitting corrosion cannot be reversed. Once it has started you can only deal with the consequences, not return the metal to its original state. Where a component is still structurally sound, pits can be mechanically removed and the lost metal replaced by weld build-up.
Designing for corrosion loss
Because corrosion is common in aggressive environments, a corrosion allowance, permissible weight loss or thickness reduction is often built into the original design. If a component is expected to run for 10 years and corrode at up to 0.5mm per year, then 5mm of extra metal is added to the standard design.
This pragmatic approach serves many applications well where they are not safety-critical. But the allowance assumes a uniform, predictable rate of corrosion. Changes in operating conditions, or severe pitting or crevice corrosion, can cut the anticipated working life significantly, so regular inspection is required.
The excess metal and the cost of inspection both add up. Limiting the likelihood and incidence of corrosion through better material specification, process design and operating conditions is often the more valuable exercise.
Repairing a sound component
If the component is still structurally sound, the pitting can be ground or polished out and the missing metal replaced by weld build-up. The welding must be prepared and carried out carefully to avoid reducing the properties of the surrounding metal.