Question 154Steam Plants - 1st Asst/Chief

The correct answer is B) sudden cooling of tubes after being overheated. Warping of superheater screen tubes is typically caused by sudden cooling of the tubes after they have been overheated. When the superheater tubes are exposed to high temperatures, the metal expands. If the tubes are then rapidly cooled, the uneven contraction of the metal can lead to warping or deformation of the tubes. This is why sudden cooling after overheating is the primary cause of superheater screen tube warping. The other options are incorrect because high superheater temperatures (A) and high furnace temperatures (C) can contribute to overheating the tubes, but do not directly cause the warping. Installing baffles of excessive length (D) may restrict airflow and contribute to overheating, but is not the direct cause of the warping.