🔍 Key Concepts

• Boiler tube failures and how they relate to deposits on the tube surface • Difference between external corrosion/erosion and internal water-side damage • How fuel impurities (like vanadium) affect high‑temperature surfaces

💭 Think About

• Is cratering and water tracking happening on the gas side (outside) of the tube or the water/steam side (inside) of the tube? That will tell you what kind of mechanism is involved. • Which of the options is most likely to cause localized overheating or damage paths that follow where water actually flows inside the tube? • Think about which condition would cause pitting or channels that look like they were ‘etched’ by water, rather than a more uniform surface corrosion.

✅ Before You Answer

• Decide whether cratering and water tracking is typically classified as water‑side damage or fireside (gas‑side) corrosion. • Check which choices are related to fuel ash and combustion deposits versus trapped moisture and mechanical contact. • Ask: which option would most directly cause damage that follows the water circulation path inside a tube, rather than just coating the outside with corrosion or slag?