🔍 Key Concepts

• heat transfer between combustion gases and boiler water • effect of insulating deposits (oil/scale) on metal temperature • relationship between tube metal temperature and boiler safety

💭 Think About

• Ask yourself: if you put an insulating layer on the tube wall, will heat pass into the water more easily or less easily? What happens to the tube metal temperature then? • Think about whether deposits directly raise or lower boiler pressure, or whether they mainly affect the tube itself first. • Consider what the first likely result is: does the tube condition change before overall boiler pressure or catastrophic failure?

✅ Before You Answer

• Verify that oil and scale act as insulation, not as a coolant. • Consider how reduced heat transfer affects the temperature of the metal compared to the water/steam inside. • Decide which option reflects the initial direct effect on the tubes, not a later or extreme consequence.