What is scale in a boiler and what causes it?

Scale in a boiler refers to the buildup of mineral solids on the heating surfaces, which can significantly affect the efficiency and operation of the boiler. This buildup is primarily caused by water with high total dissolved solids (TDS), which includes minerals such as calcium, magnesium, and silica. When the water is heated, these minerals precipitate out and form deposits on the surfaces of the boiler, leading to reduced heat transfer efficiency and potentially causing overheating and damage to the boiler components.

The presence of high TDS indicates that the water contains more dissolved minerals than is ideal for efficient boiler operation, which is why maintaining appropriate water treatment and management is crucial in preventing scale formation. Proper water conditioning methods can help minimize TDS levels and the risk of scale development.

Other options relate to different issues that may affect a boiler but do not define what scale is or its specific cause. For instance, excessive water flow and high temperatures relate more to operational challenges rather than mineral deposits. Corrosion typically stems from chemical reactions involving oxygen and water, not specifically from mineral deposits. Similarly, free oxygen in water can lead to corrosion issues rather than scale formation.