Question 51 3AE02 - Third Assistant Engineer (Alt)

The Correct Answer is C. **Explanation for C being correct:** Option C describes the simplest and most effective initial method for locating a tube leak in this type of heat exchanger, where the cooling medium (salt water, often referred to as sea water) is typically on the tube side, and the cooled medium (jacket water) is on the shell side. 1. **Isolate, drain, and dry the salt water side:** This removes the high-pressure fluid from the tubes. 2. **Remove the waterbox inspection plates:** This exposes the tube sheets (the ends of the tubes) on the salt water side. 3. **The core principle:** Since the jacket water (shell side) is now at a higher pressure than the isolated, drained tube side, any leak in a tube or at a tube-to-sheet joint will cause the jacket water to weep or drip out of the specific tube end(s) exposed in the waterbox. This provides a direct visual indication of the faulty tube without needing complex equipment or complete disassembly. **Explanation of why other options are incorrect:** **A) Isolate, drain, and dry the salt water side of the heat exchanger. Pressurize the sea water side with compressed air. Visually inspect the jacket water expansion tank for bubbles.** This method reverses the logical pressure application. If the sea water side (tubes) is pressurized with air, the air will escape into the jacket water (shell side). While bubbles might appear in the expansion tank, this only confirms a leak exists; it does *not* locate the specific leaking tube, which is the goal of the inspection. Furthermore, pressurizing the high-pressure side with a compressible gas like air can be less safe and less sensitive for detecting a minor weep than using the existing jacket water pressure to force liquid out. **B) Isolate, drain, and dry the jacket water side of the heat exchanger. Remove the shell inspection plates. Visually inspect the tubes along the tube lengths for seepage.** This method is impractical and often unnecessary. Accessing the tubes along their length by removing shell inspection plates is time-consuming and difficult (the tubes are closely packed). While a severe leak might be visible, minor leaks are often missed, and the entire shell side volume must be drained and opened, involving significantly more labor than simply removing waterbox plates. **D) Isolate, drain, and dry both the salt water and jacket water sides of the heat exchanger. Remove the waterbox inspection plates. Visually inspect the tube sheets for signs of seepage at each of the tube ends.** If both sides are drained and dried, there is no differential pressure to force water through the leak, making a visual inspection for seepage impossible. To make a leak visible, one side must remain pressurized (or contain liquid under pressure) while the other side is exposed to atmospheric pressure. This option neglects the necessary pressure differential required for leak detection.