Why is strict control necessary for the temperature of the cooling water used to cool galvanized steel pipes?

In the process of water cooling galvanized steel pipes, it is stipulated that the temperature of the cooling water should be strictly controlled within the range of 50～80°C. This is to minimize the temperature difference between the galvanized steel pipes after air cooling on the cooling bed and the cooling water, thereby avoiding significant differences in contraction due to the different coefficients of linear expansion between zinc and iron. By doing so, cracking in the galvanized layer can be prevented. Otherwise, the quality of the galvanized layer would be compromised, and its corrosion resistance would be reduced.