Method for Removing Oxidation Scale of Anti-corrosion SSAW Steel Pipe

The removal methods of anti-corrosion sawtooth 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 difficult to remove the scale on the surface and obtain a high degree of cleanliness and smoothness. What are the cleaning methods?


It usually takes two steps to remove the scale of corroded spiral steel pipe. The first step is pretreatment and the second step is ash removal.


The anti-corrosion treatment of spiral steel pipe will make the oxide skin loose, and then it is easy to remove by pickling. Pretreatment can be divided into the following methods: basic nitrate melting treatment. The basic melt contains 87% hydroxide and 13% nitrate. The proportion of the two in the molten salt should be strictly controlled so that the molten salt has strong oxidation ability, lower melting point and lower viscosity. In the production process, only sodium nitrate content is not less than 8% (weight). It is treated 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 oxide and spinel can be oxidized by nitrate to loose ferric oxide, which can be easily removed during pickling. As a result of the high temperature, the oxide formed is partially stripped and precipitated 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 applicable to components with welding clearance or crimping. When the parts are taken out from the molten salt furnace after water quenching, the irritant alkali and salt mist will be splashed out. Therefore, deep well type waterproof measures should be used in the process of water quenching.


Water quenching bath. During water quenching, first hang the parts basket in the water tank, stop above the horizontal plane, close the water tank cover, and then lower the parts basket into the water until it is immersed.


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 components with welding or crimping.