What must be prevented during heat up or cooldown of systems?

• A. Overpressurization
• B. Overcooling
• C. Overloading
• D. Overexpansion

Answer: (A)

The key idea here is that thermal transients can drive large pressure changes in a system. When things heat up, fluids expand and gases may generate higher vapor pressures; when they cool, volumes contract but can trap gas or steam and create gradients that stress components. In many plant and piping systems, this is most dangerous if the pressure rises above what the equipment, pipes, and safety devices are designed to handle. Overpressurization can lead to ruptures, leaks, or venting requests that disrupt operation and pose safety risks. Therefore, preventing pressure from climbing beyond design limits during both heating and cooling is the primary concern.

Other potential issues—overcooling, overloading, or overexpansion—are important in their own right, but the situation that encompasses the main risk during thermal transients is keeping pressure under control. Implementing proper venting, expansion tanks, staged heating, and correctly rated relief devices helps manage these pressure changes and keeps the system safe.