PROCESSING SERVICES
Pickling and passivation services
Pickling and passivation is a chemical process that provides metal protection for corrosion and pitting. No matter in which procedure, acid liquid can be used on the metal surface to remove contaminants, to help form a passivation film. Without pickling and passivation, it may cause quality problems. Although both pickling and passivation include the use of acid to treat metal surface, there's significant difference between the two procedures.
Pickling
Stainless steel welding or heating by other means will produce a discolored or oxidized layer, depleting the chromium layer, thus reducing the corrosion resistance of steel. This is a procedure that uses an acid solution to remove the heat-affected zone and the basic chromium reduction layer of stainless steel. The stainless steel surface after pickling is free of carbon steel pollution or concealed iron particles, and the surface is matte gray.
Before using the pickling procedure, it is required to state clearly why pickling is required, determine the composition of the pickling solution, and soaking time, to minimize the impact on the equipment. See the chart below, you will find the roughness changes due to the different deposition times.
Roughness change with pickling time |
|||
Soaking time (minutes) |
Before picklingRa(㎛) |
After picklingRa(㎛) |
Remarks |
20 |
0.06 |
0.05 |
Material : Super heat resistant alloy steel Hydrofluoric acid : 4.5% Nitric acid : 9.5% Temperature : 25℃ |
60 |
0.07 |
0.14 |
|
120 |
0.09 |
0.34 |
|
240 |
0.07 |
0.50 |
|
360 |
0.05 |
0.77 |
|
480 |
0.09 |
1.02 |
|
600 |
0.08 |
1.46 |
|
What are the advantages of pickling and passivation?
• Both pickling and passivation can remove surface contamination.
• Maximize corrosion resistance by passivation.
• Pickling can remove discoloration and welding sludge.
What are the methods of pickling and passivation?
Immersion in the tank: It is usually carried out at GKVAC, and it is good for treating all the manufacturing surfaces at the same time, with uniformity and best corrosion resistance for finishing.
Circulation: The chemical solution circulates through the piping system, and pipes for transporting corrosive liquids are specially recommended.
Spraying: It can be performed at GKVAC or at the customer's site. Although site disposal is more advantageous, it requires proper acidification and safety procedures.
Gluing: Use a brush to apply gel-like medicine on the surface.
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