A train crew was cleaning out a rail tanker that had been emptied of its contents. They rinsed the rail car out with scalding hot water through a port of the bottom of the rail car. When they were finished and had drained the water out they shut the valve of the port and went home for the day. During the night the temperature droppe d and it was very cold outside. When they came back to the work the next night something happens to the rail car!