Alberta Special Oilwell Boiler Practice Test

Iron in OTSG feedwater must be kept extremely low because iron ions and oxide particles readily form on heat-transfer surfaces at the high temperatures of a once-through boiler. When iron oxidizes, it tends to deposit as iron oxides on tubes and in tubesheets, reducing heat transfer efficiency and creating sites for localized corrosion. In an OTSG, where there’s vigorous flow and high heat flux, even small amounts of iron can lead to scale, fouling, and accelerated corrosion, increasing the risk of tube damage. Keeping the iron concentration at or below 0.01 ppm minimizes these deposition and corrosion risks, which is why this is the specified limit. Achieving this requires effective pretreatment and monitoring—such as filtration and deaeration—so that iron entering the boiler remains at or below this very tight threshold. The other values would permit more iron, leading to greater potential for fouling and damage, so they’re not suitable as a standard for OTSG feedwater.