What is a 'bag' in the context of boiler tubes?

In the context of boiler tubes, a 'bag' refers specifically to a bulge that occurs due to overheating of the tube material. When a boiler operates under excessive temperatures, the thermal stress can cause the metal to deform, leading to a bulging shape that resembles a bag. This deformation compromises the integrity of the boiler tube and can lead to further damage or failure if not addressed promptly.

Understanding this concept is crucial for engineers and technicians who work with boiler systems, as recognizing signs of overheating and the consequent damage is vital for maintenance and operational safety. Monitoring the temperature and pressure conditions within a boiler helps prevent the formation of bags and ensures efficient performance.