It depends on several operating variables such as water temperature, pH, type and amount of passivator/oxygen scavenger and mineral content of the feedwater. I don't know how long it would take for pitting problems, but there have been situations where HP boilers (>1500 psig) operated 18 mos...
I use saturation conditions +/- 3F as my rule-by-thumb for deaerator performance check. I like to check the oxygen content of the water exiting the deaerator and exiting the boiler feedwater pumps as X-checks. I like to run the oxygen test in the absence of any oxygen scavenger.
