What is a protrusion on a tube referred to as?

A protrusion on a tube is referred to as a "bag," which typically signifies a localized deformation in a tube where the material has expanded outward. In the context of boiler operations and maintenance, identifying and understanding flaws such as bags is vital, as they can indicate underlying issues related to pressure, corrosion, or material fatigue. Ensuring that tubes remain structurally sound is crucial for the effective and safe operation of a boiler.

In contrast to a "bag," terms like "blister" are more commonly used to describe a separation within the tube wall often associated with issues like overheating or improper water chemistry, while "bulge" refers to a more general outward expansion that can happen due to pressure but is not as specific as the term "bag." Finally, "fitting" pertains to components that are used to connect sections of piping or tubing, and does not relate to a deformation or protrusion on the tube itself.