When putting an exchanger in service, which side is always introduced first?

• A. Cool side
• B. Hot side
• C. Either side
• D. Both sides simultaneously

Answer: (A)

Starting with the cooler side minimizes thermal stress on the exchanger during startup. Introducing the cool stream first allows the unit to warm up gradually and helps equalize temperatures across the shell and tubes, reducing differential expansion that can damage tubes, tubesheets, or gaskets. Once the exchanger is wetted and more uniform in temperature, the hot side can be brought in more safely, controlling the rate of heat input. If the hot side were started first or both sides were started together, the large temperature difference could cause thermal shock, distortion, or seal failures. So the best practice is to introduce the cool side first.