Using the traditional methods of paint and galvanized, anti-corrosion effect and duration of the coating layer is generally not very good with the conditions, and a permeability rate year. In the penetration of oxygen, enough to cause corrosion of the zinc coating consumption in urban air in a year and a mix paint, galvanized surface burrs, it is difficult to achieve high purity requirements. In addition, under normal circumstances, the metal coating is damaged, the micro-cell corrosion occurs in the area, if there are metal phosphide layer, these phosphate film firmly attached to the substrate, to prevent the lateral expansion of the electrolyte, it can effectively inhibit the corrosion under the film. Acid phosphate and passivation, that is impregnated with carbon steel pipe containing manganese, iron, zinc, chromium, phosphate and chromate ions in solution, chemical processing, the pipeline surface layer of a complete needle crystal shape iron phosphate film and the chromium layer, it is compared with the coating and the zinc coating, has good resistance to water, oxygen, ion permeability and good adhesion, alkali and strong, corrosion better than other methods.
Despite the wide variety of industrial phosphating agent, all of which must contain the following a few basic ingredients ¢Ù free phosphoric acid to maintain a certain concentration of hydrogen ion generation ¢Ú phosphate salt, representatives, etc. ¢Û slower than high-temperature phosphating, the overwhelming majority phosphating agent contains at least one or more of the accelerator to increase speed and improve phosphate phosphate coating quality. Phosphating process is an electrochemical reaction. When a metal part immersed in the phosphating solution, the surface on the formation of many corrosion micro-cell, when the ferrite is a micro-anode area, and pearlite, carbon, alloy elements, and the stress concentration part of the potential than ferrite height, is the micro-cathode region. Micro-anode is oxidized and dissolved iron, micro-cathode region and reduction of hydrogen ions to be electronic.
Pipe wall wet sand-blasting treatment
In addition to the net carbon steel pipe for the complete wall surface of the burr, rust and oxidation skin, improve the quality of phosphate coating and bonding strength, to avoid dust hazards, keep blasting rust shortly after longer oxidation, using the wet sand of the sewage treatment process method to rust. The specific method is adding a small amount of trisodium phosphate in water and other blunt liquid, water, and the ratio of yellow sand to a pressure of compressed air jet.
Pickling. Taking into account the pipe wall has been carried out pre-wet sand, so the weaker phosphoric acid used for pickling, which either no or little use Cheung corrosion inhibitors, but also ensures the quality of pickling, but also in the pickling process surface of the pipe will be insoluble iron phosphate, phosphate in the next step when the nuclei from the role. Pickling time is normally at room temperature in minutes, the temperature is low, may be extended. In and. After pickling and processing to be carried out in order to avoid corrosion of pipes phosphate residues. And the liquid is generally in the sodium carbonate solution, and in time of one minute. Of water. During and after the pipe clean water required to ensure the phosphate effect. Rinse with cold water washing process for the first minute, then hot water rinse minutes.
Phosphate. Dihydrogen phosphate, zinc phosphate used to add the right amount of sodium fluoride or zinc nitrate, phosphate ¡æ low temperature for about minutes. Phosphate, the phosphate solution tank should put a coupon in order to check the control phosphate coating thickness. Of water. Phosphate treatment, rinse required ¡æ minutes to cleanse the pipe wall surface of the sediment phosphate residues. Phosphate free high acidity is slow, even on the high and low free acidity film could easily lead to partial or complete passivation of steel, parts on color film, with or without phosphate coating film is not continuous. Acid ratio and the temperature and the value should be coordinated. With increasing temperature, the ratio of acid to reduce the value to be smaller when the temperature is low contrast, acid ratio and the value should be bigger. The best choice for ¡æ.
Passivation. Carbon steel pipe, after phosphating treatment to be supporting the chromate treatment, that is, a polymer with phosphoric acid solution on the phosphate coating of chromium chromate passivation. Polymerization of chromium is trivalent chromium and hexavalent chromium polymer. Hexavalent chromium from inactivation, trivalent chromium phosphate in the formation of intergranular area closed role of chromium compounds, phosphate coating to improve corrosion resistance, especially resistance to corrosion under wet conditions can increase the times. Chromium containing chromic acid ', a phosphate and phosphoric acid solution of chromic acid chromium, passivation best. Water rinse, dry, sealed. After passivation, the minute rinse with hot water to remove impurities attached to the pipe wall, then dry with clean compressed hot air drying, and as soon as possible at both ends of the pipe with plastic film, adhesive tape pasted closed storage. Not long pipeline, the method can be taken to protect the nitrogen sealed.