The quality inspection of the pickling passivation effect of stainless steel can refer to the ship standard "Stainless steel pickling passivation paste" CB / T3595-94, the international standard "Stainless steel electrolytic polishing and grinding and polishing and pickling passivation surface passivation film formation" ISO15730, etc., can be generally divided into: appearance inspection, chemical test, chemical test mainly includes artificial seawater coupon corrosion test, copper sulfate titration test, potassium ferricyanide titration test (blue point test), etc. "The passivation effect of round pickling is tested in the following three ways:
Appearance inspection: The surface of stainless steel pickling and passivation should be uniformly silver-white, smooth and beautiful, no obvious signs of corrosion, welding seams and heat-affected zone must not have oxidized color, and there should be no uneven color marks.
Residual liquid test: use phenolphthalein test paper to check the flushing degree of residual liquid on the surface of stainless steel. The neutral PH value is qualified.
Blue dot test: The basic principle of the blue dot test method is that if the surface passivation film is incomplete or contaminated with iron ions, there will be free iron ions. The potassium ferricyanide solution will react with iron ions and generate a blue precipitate. , The reaction formula is as follows:
K ++ Fe + 2 + [Fe (CN) 6] -3 → KFe [Fe (CN) 6] ↓
Use a 100mL beaker to dissolve 10g of potassium ferricyanide in 50ml of distilled water, add 30ml of concentrated nitric acid after dissolution, and then transfer to a 1000ml volumetric flask and dilute with distilled water to the mark, which is the blue dot test solution, and the storage period is one week. Test method: Drop the blue dot test drop on the test paper attached to the surface of stainless steel. After 30 seconds, the test paper shows that the blue dot is unqualified. It should be noted that the chemical test will destroy the passivation film of stainless steel. Usually, the test plate and the product can be pickled and passivated at the same time, and then the above test is performed on the test plate.
