The reason for the visible turtle cracking pattern on the surface of galvanized steel pipes after water cooling

The reason for the visible turtle cracking pattern on the surface of galvanized steel pipes after water cooling is primarily due to the fact that the galvanized steel pipes have not undergone sufficient air cooling and are still relatively hot, while the temperature of the cooling water is quite low. This results in a large temperature difference. Once the galvanized steel pipes are immersed in water, due to the difference in linear expansion coefficients between zinc and iron, the galvanized layer on the surface cools and contracts first, while the steel pipe substrate inside cools and contracts later. This causes cracks to form in the galvanized layer. Such cracks are not visible to the naked eye when the pipes are cooled in clear water. However, if the turbidity and chroma of the cooling water are high, the cooling water that penetrates into the cracks will, after drying, make the turtle cracking pattern on the zinc layer surface visible.