There are mechanical, chemical, and electrochemical methods to remove the oxide scale of sanitary stainless steel pipes.
Because of the complexity of the oxide scale composition of sanitary stainless steel pipes, it is not easy to remove the oxide scale on the surface, but also to make the surface high to a high degree of cleanliness and smoothness. The removal of oxide scale on sanitary stainless steel pipes usually takes two steps, one is pretreatment, and the second step is to remove ash and slag.
The oxide scale pretreatment of sanitary stainless steel pipe makes the oxide scale lose, and then it is easy to remove by pickling. Pretreatment can be divided into the following methods: alkaline nitrate melting treatment method. Alkaline melt contains 87% hydroxide and 13% nitrate. The ratio of the two in the molten salt should be carefully controlled so that the molten salt has the strongest oxidizing power, melting point, and minimum viscosity. In the manufacturing process, only the sodium nitrate content is not less than 8% (wt). The treatment is carried out in a salt bath furnace, the temperature is 450~470℃, and the time is 5 minutes for ferritic stainless steel and 30 minutes for austenitic stainless steel. Similarly, iron oxides and spinels can also be oxidized by nitrates and become lose trivalent iron oxides, which are easily removed by pickling. Due to the high-temperature effect, the oxides that appear are partly peeled off and sink into the bath in the form of sludge. The bottom of the furnace.
Alkaline nitrate melting pretreatment process: steam degreasing→preheating (150~250℃, time 20~30min)→molten salt treatment→water quenching→hot water washing. Molten salt treatment is not suitable for assemblies with weld gaps or crimping. When the parts are taken out of the molten salt furnace and water quenched, a pungent alkali and salt mist will be splashed, so the deep don type should be adopted for water quenching. Splash-proof water quenching tank. When water quenching, first hoist the parts basket into the tank, stop above the horizontal surface, close the tank cover, and then lower the parts basket into the water until it is submerged.
Alkaline potassium permanganate pretreatment: the treatment solution contains sodium hydroxide 100→125g/L, sodium carbonate 100→125g/L, potassium permanganate 50g/L, solution temperature 95~105℃, treatment time 2~4 hour. Although alkaline potassium permanganate treatment is not as good as molten salt treatment, its advantage is that it is suitable for assemblies with welded seams or crimping.
To loosen the oxide scale, the following strong acid is directly adopted for pretreatment by the dipping method.
To prevent the acid from dissolving the base metal, the immersion time and acid temperature must be carefully controlled.
Post time: Jun-18-2021