🔍 Key Concepts

• Blister formation on boiler tubes and what it tells you about metal thickness and heat transfer • How metal thickness and contact with water/steam affect tube metal temperature • Where the worst cooling occurs on a blister compared to the normal tube wall

💭 Think About

• Look at points A, B, C, and D and decide which locations still have good contact with the water/steam inside the tube and which are partly separated by the blister gap. • Think about where the metal is thinnest and most exposed to the furnace heat, and where it has the least ability to conduct heat away to the water. • Ask yourself: on this sketch, which point lies in the area of the blister that is directly exposed to the hot gas side but is no longer well cooled by internal fluid?

✅ Before You Answer

• Identify which labeled point is on sound tube wall and which are on or near the bulged, weakened area of the tube. • Visualize the water/steam path inside the tube: where is cooling flow in good contact with the metal, and where is it partly cut off by the blister? • Confirm which point has minimum cross‑section of solid metal between the hot gas side and the inside of the tube, as that is where temperature will be highest.