Where is caustic embrittlement typically found in a boiler?

Caustic embrittlement occurs primarily in areas of a boiler where high concentrations of caustic substances, such as sodium hydroxide, can accumulate, often in the presence of high temperatures and pressures. In the context of a boiler, this condition is typically found in riveted joints below the water line.

At this location, the riveted joints may be subjected to both the caustic soda in the water and the stress from high pressure. The conditions facilitate the formation of caustic soda deposits, leading to localized corrosion and the eventual failure of the boiler material. This failure mechanism is particularly insidious as it can weaken the structural integrity of the joints without much visible warning, making it critical to monitor and control the water chemistry to prevent such embrittlement.

The other options relate to different areas of the boiler where caustic embrittlement is less likely to occur due to different operational dynamics or lower concentrations of caustic elements. Hence, riveted joints below the water line emerge as the most susceptible location for this particular issue.