What is the dwell time window for the phosphoric acid/water corrosion removal process?

What is the dwell time window for the phosphoric acid/water corrosion removal process?

• A. 2-10 minutes
• B. 30-60 minutes
• C. 1-2 seconds
• D. 24 hours

Answer: (A)

The key idea is that dwell time is the exact period the part stays in the phosphoric acid/water solution to remove corrosion products without attacking the base metal. For this process, the safe and effective window is a short interval of roughly two to ten minutes. Within this time, the acid dissolves corrosion scales and converts oxides so they can be rinsed away cleanly. If you stay in the solution longer than this window, the acid can start to attack the underlying metal, causing over-etching, thinning, or surface damage. If you’re in for too short a time, corrosion products may not be fully removed, leaving residues that can continue to promote corrosion. The other options are impractical: too long could cause damage, too short won’t remove the corrosion, and an excessively long duration like hours is unnecessary. After this dwell, rinse thoroughly and inspect the surface.

The key idea is that dwell time is the exact period the part stays in the phosphoric acid/water solution to remove corrosion products without attacking the base metal. For this process, the safe and effective window is a short interval of roughly two to ten minutes. Within this time, the acid dissolves corrosion scales and converts oxides so they can be rinsed away cleanly. If you stay in the solution longer than this window, the acid can start to attack the underlying metal, causing over-etching, thinning, or surface damage. If you’re in for too short a time, corrosion products may not be fully removed, leaving residues that can continue to promote corrosion. The other options are impractical: too long could cause damage, too short won’t remove the corrosion, and an excessively long duration like hours is unnecessary. After this dwell, rinse thoroughly and inspect the surface.