🔍 Key Concepts

• Heat transfer in boiler tubes (how tubes stay cool in normal operation) • Difference between evaporation, circulation, and combustion in a boiler • What happens to metal temperature when water flow inside tubes is reduced or stopped

💭 Think About

• Ask yourself: What keeps generating tubes from overheating when the boiler is operating normally? • Which of the choices refers to the movement of water/steam through the boiler, rather than just making steam or burning fuel? • If water stops moving properly through the tubes, what happens to the metal temperature compared to when water is flowing well?

✅ Before You Answer

• Identify which option is tied to water/steam flow inside the boiler, not steam production amount or fuel burning alone • Confirm which condition would cause loss of cooling on the inside of the tubes • Make sure the choice you select relates directly to the point where tube metal is no longer adequately cooled by water