What is Swelling and shrinking effect in boiler drum?

The swelling and shrinking effect in a boiler drum refers to the physical changes in the drum's volume due to temperature variations and pressure changes during operation. When the boiler is heated, the water inside converts to steam, causing the drum to swell as the pressure increases and the water expands. Conversely, when the boiler cools down or experiences a drop in pressure, the drum may shrink as the steam condenses back into water. This phenomenon is important to consider for the structural integrity and safety of the boiler system.