The quality of galvanizing has a huge impact on the function and cost of hot-dip galvanized steel pipes. If the hot-dip galvanized steel pipe has insufficient galvanizing thickness, uneven galvanized layer, insufficient zinc adhesion, and leakage of plating, it will cause corrosion of the steel pipe, reduce the physical and chemical properties of the steel pipe, shorten the life of the steel pipe, and even cause safety hazards.
The quality of galvanizing has a great relationship with the hot-dip galvanizing process: the purity of the zinc ingot, the surface treatment of the steel pipe, the temperature of the zinc bath, the time of hot dip, the post-plating treatment, etc. will all affect the quality of the galvanizing. The indicators for judging the quality of galvanizing mainly include:
1. Appearance of galvanized pipe fittings
The surface of high-quality galvanized pipe fittings should have a complete coating, consistent color, uniform transition, and no sag, dripping, or unnecessary agglomeration on the surface. There shall be no defects such as missing plating or exposed iron on the surface of the pipe fittings.
2. The thickness of the galvanized layer
The thickness of the zinc layer of the galvanized pipe is an important indicator for judging the quality of galvanization. It is generally expressed in the unit of μm, and it can also be expressed by the weight of the galvanized layer per square meter (g/m2). The conversion formula is: 1g/m2 = 0.14μm. Since zinc and steel have different magnetic properties and polarizabilities, the thickness of the zinc layer can be measured non-destructively with a galvanized layer thickness gauge. To determine the weight of the zinc layer, it is necessary to scrape the zinc layer to sample and measure it with antimony chloride method and other chemical methods.
Three, galvanized layer uniformity
Fourth, the adhesion of the galvanized layer
The adhesion of the galvanized layer is a measure of the firmness of the galvanized layer and the steel pipe. After the steel pipe is immersed in the zinc bath for a certain period of time, the surface of the steel pipe will react with the galvanizing liquid to form a zinc-iron mixed layer. The scientific and sophisticated galvanizing process will form a zinc-iron mixed layer of sufficient thickness to improve the adhesion of the zinc layer. The adhesion of the galvanized layer can be monitored by tapping with a rubber hammer. It is better that the coating does not fall off after a certain number of taps.
At present, the domestic perception of the galvanizing quality of galvanized steel pipes has a certain tendency to be wrong, and one-sided emphasis on the bright color of the galvanized surface. As mentioned earlier, the quality of galvanizing is related to many factors. In order to achieve a bright surface color, it is necessary to lower the temperature of the zinc bath and lengthen the bath time. This will reduce the adhesion of the galvanized layer. Although it is beautiful, but from the perspective of anti-corrosion and practicality, the reduction of adhesion will cause the galvanized layer to be easily damaged, which is not worth the loss. China's hot-dip galvanizing standard only stipulates that the surface color of the galvanized layer is consistent. For the sake of beauty, the color of galvanized steel pipe is required to be bright. There is no theoretical basis, and it is neither scientific nor economical.