Question 22Steam Plants - 1st Asst/Chief

The correct answer is D) rapid cooling. Boiler refractory, which is the insulating material lining the interior of a boiler, is most sensitive to rapid cooling after it has been previously baked out and fired. This is because the refractory material has been thermally conditioned and can be prone to cracking or spalling if it is subjected to sudden temperature changes, especially rapid cooling. Sustained high furnace temperatures or rapid heating are not as damaging to the integrity of the refractory as rapid cooling. The other options, A) radiant heat of the burner, B) rapid heating, and C) sustained high furnace temperature, are not as detrimental to the boiler refractory as rapid cooling, which can lead to structural damage and failure of the refractory lining.