First, the inherent factors of galvanized square tube sheet, we all know that the low nickel content in galvanized square tube, galvanized square tube passivation performance is low, so the martensite content and chromium and nickel content in galvanized square tube have a great impact on the passivation performance of galvanized square tube sheet surface.
Secondly, the passivation film of galvanized square tube belongs to the restrained metastable structure in thermodynamics, and its protective effect is related to the medium in the environment. However, no matter what kind of environment is used, in the process of use, galvanized square tube sheets should be cleaned regularly to remove harmful substances attached to the surface of galvanized square tube sheets.
3. Surface cleanliness of galvanized square tube sheets. For galvanized square tube alloys, the smoother the surface of galvanized square tube is, the lower the roughness is, the harder it is for the galvanized square tube surface to be adhered to by foreign bodies, and the foreign bodies are not easy to adhere to, so the corrosion on the galvanized square tube surface will be reduced to the lowest point, so the galvanized square tube surface should adopt the finishing surface as far as possible. In addition, the final passivation cleaning of galvanized square tube sheet should also be carried out carefully, so that the residual acid can promote the anodic reaction, protect the integrity of the film, and ensure that the corrosion resistance of the galvanized square tube sheet surface is enhanced.
4. Chloride ion and chloride ion are very harmful to galvanized square tube sheet. Therefore, we should strictly control the chloride ion content in the passivation solution during the passivation process of galvanized square tube sheet, based on the harmfulness of chloride ion to galvanized square tube sheet. Many passivation chemicals have limited requirements for chloride ions. Water for passivation solution and cleaning water also have strict water quality requirements for chloride ions to ensure that the passivation products do not contain chloride ions.
Galvanized square tubes are corroded rapidly in the presence of chloride ions, even exceeding ordinary low carbon steel. As for the steel pipes receiving fluid pressure, they should be prevented from hydraulic test to repair their pressure-resisting ability and quality. Under the specified pressure, they should not leak, soak or shrink to qualified. Some steel pipes should also be prevented from edge-rolling test, flattening test and flattening test according to scale or requirement.