Why do the zinc flowers differ on thin-walled and thick-walled pipes under the same process and operating conditions?

Under identical hot-dip galvanizing and cooling conditions, the zinc flowers obtained on thin-walled and thick-walled pipes after hot-dip galvanizing are not the same. The zinc flowers on the former are larger, while those on the latter are smaller. We understand that the cooling rate of the molten zinc on the steel pipe surface is related to the wall thickness of the steel pipe substrate. When hot-dip galvanizing is generally performed using the "flux method," the temperature of the steel pipe (150-230°C) entering the molten zinc is lower than the temperature of the molten zinc (470-510°C). Therefore, thin-walled pipes absorb less heat, while thick-walled pipes absorb more heat. However, under the same process conditions, after the steel pipes are immersed in molten zinc, when the temperature on the thin-walled pipe has reached uniformity between the inner and outer surfaces, the center of the thick-walled pipe may still be below the galvanizing temperature at the surface. Consequently, once removed from the molten zinc, the molten zinc on the thin-walled pipe only undergoes gradual solidification due to air cooling, whereas the molten zinc on the thick-walled pipe, apart from air cooling, also needs to dissipate heat towards the lower temperature at the pipe's center, which accelerates the solidification of the molten zinc. Therefore, the slowly cooled thin-walled pipe produces large zinc flowers, while the thick-walled pipe with a faster cooling rate forms small zinc flowers.