Question 37 OSE01 - Chief Engineer - OSV

The Correct Answer is A. **Why Option A ("Measuring the outside diameter of the tubes") is correct:** Scale deposits in a boiler are typically categorized as internal (waterside) or external (fireside). Hard scale deposits are formed by combustion products (soot, sulfates, etc.) on the **outside surface** (fireside) of the fire tubes. These external deposits act as an insulator, reducing heat transfer efficiency, and crucially, they build up on the tube surface, effectively **increasing the overall outside diameter** of the tube. By measuring the outside diameter and comparing it to the original, clean diameter (or adjacent, less-affected tubes), an engineer can determine the thickness of the external scale layer and judge if it is excessive. This is a direct, practical, and non-destructive method for assessing the extent of external scaling. **Why the other options are incorrect:** * **B) Monitoring the feed pump pressures:** Feed pump pressure relates to the boiler's operating pressure and the flow of water into the steam drum. It would be primarily affected by the boiler load, steam demand, or faults in the feed system (e.g., blocked strainers or valve issues), not directly by external fireside scaling. * **C) Monitoring the circulating pump pressures:** Auxiliary fire-tube boilers typically rely on natural circulation unless they are waste-heat or complex watertube designs. Even if a circulating pump were present (e.g., to aid water treatment or rapid circulation), the pressure would relate to waterside flow dynamics, not the build-up of hard scale deposits on the fireside of the tubes. * **D) Performing a visual inspection:** While a visual inspection is required for general maintenance, determining if the scale is "excessive" and "hard" based purely on sight in the confined space of a boiler combustion chamber or smoke box is often impractical and inaccurate. Hard scale (which may appear similar to regular soot) can only be accurately quantified by measuring its thickness, which is done by measuring the overall tube diameter, making option A the most practical and reliable quantitative method.