Sometimes in winter, water tanks and water pipes freeze and crack. What's this about?

First, let's talk about the physics of water at 4℃. When the density is the highest, the volume of water will increase obviously after freezing, which is called volume expansion. It is easy to accept that water will expand when it freezes, which will cause the water pipe to freeze and crack. The water tank will freeze and crack. Why? Simply explaining that the frozen volume of water will expand cannot be fully explained. Because the water tank is open, why does the volume expansion burst the water tank in a container with variable volume? It is observed that the main reason is that when the weather gets cold, the surface of the water tank will freeze first and gradually form a hard ice film downward. This ice film and the wall of the water tank form a container with a fixed volume. This limits the volume of water that will not freeze in the future. The unfrozen water will slowly release heat and continue to expand after freezing. Because the wall of the water tank is not as thick and firm as the surface ice, it will eventually burst and release the stress caused by expansion.