Removal methods of anti-corrosion ssaw steel pipe
include mechanical method, chemical method and electrochemical method. Due to the complexity of the scale composition of the anti-corrosion spiral steel pipe, it is not easy to remove the surface scale and achieve a high degree of cleanliness and smoothness. What are the removal methods?
Removal of the anti-corrosive spiral steel tube oxide scale generally requires two steps. The first step is pretreatment and the second step is ash removal.
Anti-corrosion spiral steel pipe pre-treatment makes the oxide scale loose, and then pickling is easy to remove. Pretreatment can be divided into the following methods: alkaline nitrate melting treatment. Alkaline melt contains 87% hydroxide and 13% nitrate. The proportion of the two in the molten salt should be strictly controlled to make the molten salt have strong oxidation power, lower melting point and lower viscosity. In the production process, only the sodium nitrate content is not less than 8% (wt). It is processed in a salt bath furnace at a temperature of 450 ~ 470 ° C. Time: 5 minutes for ferritic stainless steel and 30 minutes for austenitic stainless steel. Similarly, iron oxides and spinels can also be oxidized by nitrates to become loose trivalent iron oxides, which are easily removed during acid washing. Due to the action of high temperature, the formed oxide is partly peeled off and sinks into the bottom of the bath furnace in the form of sediment.
Basic nitrate melting pretreatment process: steam degreasing → preheating (150 ~ 250 ° C, 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 after water quenching, they will splash an irritating alkali and salt spray. Therefore, deep well type water prevention should be used during water quenching.
Water quenching bath. When water quenching, first hang the parts basket into the trough, stop above the horizontal surface, close the trough cover, and then lower the parts basket into the water until it is submerged.
Pretreatment with alkaline potassium permanganate:
The processing solution contains sodium hydroxide 100 → 125g / L, sodium carbonate 100 → 125g / L, potassium permanganate 50g / L, solution temperature 95 ~ 105 ° C, and processing time 2 ~ 4 hours.
Although the effect of alkaline potassium permanganate treatment is not as good as molten salt treatment, its advantage is that it is suitable for assemblies with welds or curling.