When taking a shell-and-tube heat exchanger with a removable tube bundle such as a bayonet-tube heavy fuel oil service heater out of service, to prevent water hammer what statement represents the correct operating procedure?

Correct Answer: Option C — Crack open the condensate drains first. Gradually close down and secure the steam, then close the condensate drains when no longer draining condensate. Finally, secure the heavy fuel oil.

Cracking condensate drains before securing steam prevents the accumulation of condensate in the shell, which causes water hammer as steam collapses. By gradually closing the steam valve and draining remaining moisture, you ensure the unit is safely isolated without damaging the internal components through sudden pressure or temperature changes.