🔍 Key Concepts

• Boiler tube metal failure mechanisms such as blistering, pitting, and grooving • The effect of oxygen and gases in feedwater on internal tube surfaces • How scale or deposits on the waterside change heat transfer and metal temperature

💭 Think About

• Think about which condition would most likely trap gases or impurities at the metal surface and weaken the tube wall from the inside. • Consider how each choice (scale, air, cold water, hot water) would affect tube metal temperature and stress during operation. • Ask yourself: which option is most directly linked to internal corrosion and separation of tube metal layers that could create a blister-like defect?

✅ Before You Answer

• Verify which factor is known to cause localized overheating or concentrated corrosion at the tube surface. • Check which choice is specifically associated with internal pressure pockets forming beneath the tube’s inner surface. • Confirm from your steam plant or boiler theory notes which condition is most often cited as a cause of tube blistering, not just general corrosion.