Oxygen attacks steel at small anodic spots, digging round pits often capped with reddish-black rust mounds called tubercles. It concentrates where oxygen-rich water first meets hot metal: feedwater lines, economizers, the deaerator and tubes near the feed inlet, and in boilers left idle and wet without protection. Pits can perforate a tube while the rest of the metal looks sound, which is why deaeration and scavenger residuals are watched closely.
Tube failure was oxygen pitting, right by the feedwater inlet, the DA hasn't been venting properly for months.
Also heard as
- O2 pitting
- oxygen corrosion
Related terms
Deaerator
A pressurized feedwater heater that strips dissolved oxygen and carbon dioxide out of boiler feedwater with steam.
Oxygen scavenger
A chemical fed to boiler feedwater that reacts with and removes the last traces of dissolved oxygen.
Lay-up
Protecting an idle boiler from internal corrosion during an outage or the off season.
Makeup water
Fresh water added to a boiler system to replace water lost to leaks, blowdown, venting and unreturned condensate.