Hot-dip galvanized pipes are produced by reacting molten metal with an iron substrate to form an alloy layer, thereby bonding the substrate and the coating together. The hot-dip galvanizing process involves first pickling the steel pipe to remove iron oxide from its surface. After pickling, the pipe is cleaned in an aqueous solution of ammonium chloride or zinc chloride, or a mixed solution of both, before being immersed in a hot-dip galvanizing bath. Hot-dip galvanizing offers advantages such as a uniform coating, strong adhesion, and long service life. The steel pipe substrate undergoes complex physical and chemical reactions with the molten galvanizing solution, forming a tightly structured, corrosion-resistant zinc-iron alloy layer. This alloy layer integrates seamlessly with the pure zinc coating and the steel pipe substrate, resulting in exceptional corrosion resistance.

Uniformity of the Zinc Coating: After being immersed five times consecutively in a copper sulfate solution, the pipe sample must not turn red (copper-plated color).

Surface Quality: The surface of the galvanized steel pipe must have a complete zinc coating, with no uncoated black spots or bubbles. Minor roughness and localized zinc nodules are permissible.

Zinc Coating Weight: Upon the buyer's request, the zinc coating weight of the galvanized steel pipe can be tested. The average weight must not be less than 500g/m², with no single sample measuring below 480g/m².

The iron pipes used for gas supply, greenhouses, and heating systems are also galvanized pipes. However, when galvanized pipes are used as water pipes, significant rust buildup occurs inside, leading to yellow water that not only stains plumbing fixtures but also harbors bacteria due to the rough inner surface. The rust also increases heavy metal content in the water, posing serious health risks. In the 1960s and 1970s, developed countries began phasing out galvanized pipes in favor of new types of piping materials. China’s Ministry of Construction and three other ministries also issued a directive banning galvanized pipes starting in 2000. As a result, newly built residential areas rarely use galvanized pipes for cold water supply, though some still use them for hot water pipes.