🔍 Key Concepts

• Corrosion and marine growth inside sea water passages when equipment is idle • Role of drain valves vs. vent/air-cock valves when emptying a shell-and-tube exchanger • Difference between leaving a system full, empty, or fresh-water filled for long lay‑up

💭 Think About

• Think about what happens to stagnant sea water if it is left standing inside a metal heat exchanger for weeks or months. • Consider what must happen to allow sea water to drain completely from a low point drain – what else besides the drain valve might need to be opened? • Ask yourself whether simply draining is enough, or if there is a good reason to flush with something else before an extended lay‑up.

✅ Before You Answer

• Verify which choice prevents internal corrosion and marine growth during long idle periods. • Check which option would allow the heat exchanger to drain freely without creating a vacuum or air lock. • Confirm whether marine practice usually recommends leaving sea water systems full of sea water, completely empty, or filled with fresh/treated water for extended shutdown.