Plant Operation Practice Test

The presence of impurities on the surface of the water in the boiler plays a crucial role in preventing steam from breaking through. These impurities can form a layer that disrupts the surface tension and alters the behavior of steam bubbles that form within the water. When steam bubbles attempt to escape to the surface, they encounter this layer of impurities, which inhibits their rise. This condition helps maintain stability in the boiling process and can also prevent issues such as foaming or priming, which can lead to operational inefficiencies or safety hazards.

The other options do not serve the same purpose. For example, while buildup of heat is necessary for the generation of steam, it does not directly prevent steam from breaking through the surface. An excessive water level may lead to other operational concerns but does not inherently stop steam release. Lastly, low pressure in the boiler can actually facilitate steam formation rather than inhibit it. Understanding how impurities affect the behavior of steam in a boiler is vital for maintaining safe and efficient plant operations.