How does thermal shock occur in boilers, and how can it be prevented?

How does thermal shock occur in boilers, and how can it be prevented?

• A. Thermal shock is not a concern for boilers.
• B. Thermal shock is caused by sudden pressure changes in the steam drum.
• C. Thermal shock occurs only during startup in hot climates.
• D. Thermal shock occurs from rapid temperature changes causing thermal stress; prevent with gradual heat-up, avoiding sudden load changes, and proper feedwater preheating.

Answer: (D)