Question 196Steam Plants - 1st Asst/Chief

The correct answer is D) the tube metal acts as an anode. The formation of a pit in the surface of a boiler tube is most likely to occur when the tube metal acts as an anode in an electrochemical corrosion process. This happens when there are differences in the electrical potential between the tube metal and other materials, causing the tube metal to be preferentially corroded. This type of localized corrosion, known as pitting, can lead to the formation of pits or holes in the tube surface. The other options are incorrect because, while dissolved minerals, waterside deposits, and sludge can contribute to overall corrosion, they do not directly cause the formation of pits in the same way as electrochemical corrosion with the tube metal acting as an anode.