Acid passivation pre-treatment

If surface dirt and other stainless steel parts pickling passivation should be by mechanical cleaning, and degreasing. Acid lotion and passivation solution to remove grease, surface oil will affect the quality of pickling passivation, this degreasing can not be omitted, can be used such as lye, emulsifiers, organic solvents and steam.
Acid wash and rinse water Cl-control
 

Certain stainless steel pickling solution or pickling paste by adding hydrochloric acid, perchloric acid, ferric chloride and sodium chloride and other chlorine ion erosion of media to remove the surface oxide layer as the main agents or additives, in addition to the grease with triclosan ethylene and chlorinated organic solvents, it is not appropriate to prevent stress corrosion cracking for. In addition, the initial wash water can be used industrial water, but the final rinse water requires strict control of the halide content. Usually with deionized water. Hydrostatic test water, such as petrochemicals austenitic stainless steel pressure vessels, control of the C1-content does not exceed 25 mg / L, If you can not meet this requirement, sodium nitrate in water can be added to make it meet the requirements of C1-content exceeded will the passive film of the destruction of stainless steel, pitting corrosion, crevice corrosion, stress corrosion rupture of the root.

Process control operation 3. Pickling passivation

Nitric acid solution alone is used to remove free iron and other metal contaminants is effective, but to remove oxide scale thick corrosion products, tempering the film is invalid, and should generally be using HNO3 + HF solution, in order to facilitate the safe operation of available fluoride compounds instead of HF [2]. HNO3 solution alone is not added to the inhibitor, HNO3 + HF pickling, and needs Lan-826. HNO3 + HF pickling, to prevent corrosion, the concentration ratio of 5:1 should be maintained. Temperature should be below 49 ℃, such as too high, HF will be volatile.



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