To identify hot-dip galvanized pipes for firefighting, you first need to have an in-depth understanding of the difference between hot-dip galvanized pipes and cold-dip galvanized pipes for firefighting. Both types of pipes differ significantly in appearance and intrinsic quality.
1. Difference in principle
Hot-dip galvanizing pipes are made by immersing steel pipes in molten zinc at high temperatures, forming a dense zinc layer on its surface. This zinc layer has high corrosion resistance and can effectively protect the steel pipe from corrosion and damage.
The manufacturing process of cold galvanized pipes is relatively simple, mainly by electroplating to separate the zinc alloy into zinc ions, and cover a thin zinc layer on the surface of the steel pipe, so that the surface texture of the material is uniform, anti-corrosion and wear-resistant. 
2. Appearance difference
The surface color of hot-dip galvanized pipes is a whitish gold, which is darker than the common metallic color. A closer look at its surface and inner walls reveals that it has a rough texture, mixed with texture and zinc slag. The main reason is that in the production process, the hot-dip galvanized pipe is first heat treated to make its surface rougher, and this rough surface structure makes the zinc layer better attached to the pipe and enhances the anti-corrosion performance of the pipe.
The surface of the cold galvanized pipe is very smooth and bright, with a strong metallic luster, free of texture and zinc slag. If it is a welded steel pipe, a clear "black line" can be seen if you look closely at the weld on the inner wall of the cold-dip galvanized pipe, while the hot-dip galvanized welded steel pipe is a rough weld.
3. Internal differences
The weight of hot-dip galvanized pipes is significantly higher than that of cold-dip galvanized pipes, which is mainly due to the greater thickness of the zinc layer in the hot-dip galvanizing process. This increase in thickness allows the zinc layer to be more tightly bonded to the substrate, which gives the pipe greater corrosion and weathering resistance.
The zinc layer of the cold galvanized pipe is relatively thin, and the binding force of the zinc layer to the substrate is relatively weak. Pipes have relatively poor corrosion resistance and weather resistance. However, cold-dip galvanized pipes also have good aesthetics and wear resistance, so they are still widely used in some specific fields.
In general, in order to identify hot-dip galvanized pipes for fire protection, it is necessary to make a comprehensive judgment from many aspects such as appearance, internal quality and professional testing methods. Only by in-depth understanding of the difference between the two can we accurately identify the real fire-fighting hot-dip galvanized pipes and ensure the safety and reliability of fire-fighting facilities.