After oxide removal by mechanical milling or chemical treatment prior to welding, the surface will almost instantly re-oxidize in dry air.

After oxide removal by mechanical milling or chemical treatment prior to welding, the surface will almost instantly re-oxidize in dry air.

• A. True
• B. False
• C. It re-oxidizes only in moist air
• D. It never re-oxidizes

Answer: (A)

Freshly cleaned metal presents a highly reactive surface. When this exposed metal meets air, oxygen readily interacts with the surface atoms and an oxide layer starts to form almost immediately. This re-oxidation happens quickly even in dry air, so delaying welding after surface cleaning allows oxide to reform and hamper weld quality. That’s why the statement is true: you should weld promptly after cleaning or protect the surface with shielding gas to prevent re-oxidation. Moisture can accelerate corrosion, but oxidation begins with dry air as well, so it does not require moist conditions to occur.

Freshly cleaned metal presents a highly reactive surface. When this exposed metal meets air, oxygen readily interacts with the surface atoms and an oxide layer starts to form almost immediately. This re-oxidation happens quickly even in dry air, so delaying welding after surface cleaning allows oxide to reform and hamper weld quality. That’s why the statement is true: you should weld promptly after cleaning or protect the surface with shielding gas to prevent re-oxidation. Moisture can accelerate corrosion, but oxidation begins with dry air as well, so it does not require moist conditions to occur.