Which action is taken to prevent excessive stresses in boiler metal from uneven expansion?

Warming the boiler up as slowly as possible is crucial to prevent excessive stresses in the boiler metal from uneven expansion. When a boiler is heated too rapidly, different parts of the boiler can expand at different rates, leading to thermal stress due to uneven heating. This stress can cause warping, cracking, or other forms of damage to the boiler structure over time.

By gradually increasing the temperature, all parts of the boiler will expand more uniformly, minimizing the chance of these adverse effects. This slow approach allows the materials to adjust to temperature changes steadily, which is vital for maintaining the integrity and longevity of the boiler.

Routine maintenance is essential for overall performance and safety but does not directly address the issue of thermal expansion during the heating process. Similarly, reducing the water level in the boiler could lead to other operational issues. Heating the boiler rapidly is counterproductive as it directly contributes to the risks posed by uneven expansion.