API RP 571 3.9 Boiler Water and Steam
Condensate Corrosion Exam Questions
and Answers (Latest Update 2026)
3.9.1 Description of Damage -
correct answer ✅General corrosion and pitting in the boiler
system and condensate return system. It is primarily the result of
dissolved oxygen and/or carbon dioxide, which could lead to
oxygen pitting corrosion and carbonic acid corrosion, respectively.
Flow accelerated corrosion (FAC) in these systems may occur either
as general wall thinning corrosion or localized corrosion at high
velocity, high turbulence, or change of flow direction locations.
3.9.2 Affected Materials -
correct answer ✅Carbon steel and low-alloy steels.
3.9.3 Critical Factors -
correct answer ✅a) Critical factors are the concentration of
dissolved gas (oxygen and/or carbon dioxide), pH, temperature,
quality of the feedwater, and the specific feedwater treating
system.
b) Corrosion protection in the boiler is accomplished by laying
down and continuously maintaining a layer of protective Fe3O4
(magnetite).
c) In the case of FAC, this protective oxide layer is dissolved or
prevented from forming. Carbon steel is the most affected. Alloying
, API RP 571 3.9 Boiler Water and Steam
Condensate Corrosion Exam Questions
and Answers (Latest Update 2026)
elements in low-alloy steels such as Cr, Cu, and Mo can enhance
corrosion resistance. The most critical temperature for FAC is 300°F
(150°C), and it decreases with increasing pH. Too low an oxygen
concentration increases the corrosion due to the corrosion due to
the inability to form the protective oxide layer. At least 3 ppb to 7
ppb may be required to form the oxide layer.
d) The chemical treatment for scale and deposit control must be
adjusted to coordinate with the oxygen scavenger for the specific
water service and BFW treating system.
e) Oxygen pitting can occur if the deaeration and oxygen scavenging
treatment are not working correctly.
3.9.4 Affected Units or Equipment -
correct answer ✅a) Corrosion can occur throughout the boiler
water treatment system, including the deaerating equipment,
feedwater lines, and pumps, as well as in the steam generation
system including stage heaters, economizers, and boiler tubes as
well as process unit steam generators.
b) Corrosion in the condensate return system as well as in process
unit reboilers and associated piping may be due to carbon dioxide,
although oxygen pitting from oxygen contamination is also possible
as well as FAC if the proper conditions are present.
Condensate Corrosion Exam Questions
and Answers (Latest Update 2026)
3.9.1 Description of Damage -
correct answer ✅General corrosion and pitting in the boiler
system and condensate return system. It is primarily the result of
dissolved oxygen and/or carbon dioxide, which could lead to
oxygen pitting corrosion and carbonic acid corrosion, respectively.
Flow accelerated corrosion (FAC) in these systems may occur either
as general wall thinning corrosion or localized corrosion at high
velocity, high turbulence, or change of flow direction locations.
3.9.2 Affected Materials -
correct answer ✅Carbon steel and low-alloy steels.
3.9.3 Critical Factors -
correct answer ✅a) Critical factors are the concentration of
dissolved gas (oxygen and/or carbon dioxide), pH, temperature,
quality of the feedwater, and the specific feedwater treating
system.
b) Corrosion protection in the boiler is accomplished by laying
down and continuously maintaining a layer of protective Fe3O4
(magnetite).
c) In the case of FAC, this protective oxide layer is dissolved or
prevented from forming. Carbon steel is the most affected. Alloying
, API RP 571 3.9 Boiler Water and Steam
Condensate Corrosion Exam Questions
and Answers (Latest Update 2026)
elements in low-alloy steels such as Cr, Cu, and Mo can enhance
corrosion resistance. The most critical temperature for FAC is 300°F
(150°C), and it decreases with increasing pH. Too low an oxygen
concentration increases the corrosion due to the corrosion due to
the inability to form the protective oxide layer. At least 3 ppb to 7
ppb may be required to form the oxide layer.
d) The chemical treatment for scale and deposit control must be
adjusted to coordinate with the oxygen scavenger for the specific
water service and BFW treating system.
e) Oxygen pitting can occur if the deaeration and oxygen scavenging
treatment are not working correctly.
3.9.4 Affected Units or Equipment -
correct answer ✅a) Corrosion can occur throughout the boiler
water treatment system, including the deaerating equipment,
feedwater lines, and pumps, as well as in the steam generation
system including stage heaters, economizers, and boiler tubes as
well as process unit steam generators.
b) Corrosion in the condensate return system as well as in process
unit reboilers and associated piping may be due to carbon dioxide,
although oxygen pitting from oxygen contamination is also possible
as well as FAC if the proper conditions are present.
