Which type of grooving that causes metal loss occurs at horizontal tubes in the boiler?

The fireside grooving refers to the erosion that occurs on the surface of tubes that are directly exposed to the heat and combustion gases within a boiler. This type of grooving results from the high temperatures and aggressive combustion environment, leading to the gradual wear and metal loss on the tube surfaces.

In the case of horizontal tubes, the fireside is particularly vulnerable because the heat concentration and the flow of hot gases can create differential temperatures and pressures that exacerbate metal loss. This degradation can significantly affect the efficiency and safety of the boiler system if not addressed.

Other types mentioned, like water side, involve corrosion due to factors such as water chemistry, which impacts the internal surfaces of the tubes rather than the fireside. Corrosion generally refers to a chemical reaction that occurs with moisture and other chemicals present in the system. External would typically indicate issues like rust or wear from exterior elements, which do not apply specifically to the metal loss caused by the direct thermal conditions experienced by horizontal tubes in the boiler.