The cargo drain cooler is a heat exchanger that condenses the saturated steam generated after the steam heating service, and makes it possible to be used as the boiler feed water. In LNG carriers, saturated steam is condensed from the drain cooler and then it is collected after heating the LNG (LNG vaporizer, forcing vaporizer, gas heater, glycol heater) using steam as the heat source. This equipment is an essential item to improve the circulated energy efficiency for steam heating service.