1.1 Pickling passivation treatment method

There are various methods of pickling passivation for stainless steel equipment and parts depending on the operation.

The impregnation method is used for parts that can be put into pickling tank or passivation tank, but it is not suitable for large equipment. The pickling solution can be used for a long time, with high production efficiency and low cost.Large volume equipment full of acid immersion liquid consumption is too large.

Brushing method is suitable for large equipment surface and local treatment of material operation, poor working conditions, acid can not be recovered.

Paste method is used for installation or maintenance of the site, especially for the welding part processing manual operation, poor working conditions, high production cost.Spray method is used in the installation site, the inner wall of large container has low liquid amount, low cost and fast speed, but it needs to be equipped with spray gun and circulation system.The circulation method is used for large equipment, such as heat exchanger, shell and tube treatment construction is convenient, the acid can be reused, it needs to be connected with the circulation system of pipe and pump.

Electrochemical method can be used for both parts and surface treatment of field equipment using brush method. The technology is more complex, requiring DC power supply or potentiostat.

1.2 Examples of acid washing passivation treatment formula

1.2.1 General treatment

According to ASTMA380-1999, just take 300 series stainless steel as an example,

(1) the pickling

Reagents HNO3 6% ~ 25% +HF 0.5% ~ 8% (volume fraction);

Temperature: 21 ~ 60℃;Time as required;

Or agent ammonium citrate 5% ~ 10% (mass fraction);

Temperature 49 ~ 71℃;The time is 10-60min.

(2) passivation

Agent HNO3 20% ~ 50% (volume fraction);

Temperature 49 ~ 71℃;The time was 10-30min.

Or 2L ~ 38℃;The time is 30 ~ 60min.

Or HNO3 20% ~ 50% +Na2Cr207H202 2% ~ 6% (mass fraction);

Temperature 49 ~ 54℃;The time was 15-30min.

Or the temperature is 21 ~ 38℃;The time is 30 ~ 60min.

(3) Descaling pickling

H2so48-11% (volume fraction);

Temperature 66 ~ 82℃;6 time 5 ~ 45min;

And HNO3 6% ~ 25% +HF 0.5% ~ 8% (volume fraction);

Temperature: 21 ~ 60℃;

Or HNO3 15% ~ 25% +HF L % - 8% (volume fraction).

1.2.2 Paste treatment

(1) Take the internal surface weld and base material passivation of the new guangzhou petrochemical Urea stainless steel equipment and the local passivation of the polishing weld on the maintenance surface as an example. Pickling paste:

25% HNO~+ 4% HF+ 7L % condensed water (volume fraction) with BaSO, adjust to paste.

Passivation paste:

30% HNO3 or 25% HNO3+ 1% (mass fraction)K2Cr207 and BaSO7 were adjusted to paste.

The coating surface should be washed with condensed water until pH=7 for 5 ~ 30min. Chemical passivation method of hydrogen peroxide spraying can also be used for a single device.

(2) Take Shanghai Daming Iron Works * * as an example.

Pickling passivation paste:

HN03 8% ~ 14% (as a passivator);

HF L0 % ~ 15% (as etchant);

Magnesium stearate (thickener)

Magnesium nitrate 60% ~ 70% (as filler, improve adhesion and permeability);

Sodium polyphosphate 2.3% ~ 2.8% (as corrosion inhibitor);

Water (regulates viscosity).

1.2.3 Electrochemical treatment

In xiamen university, * *, for example, its processing method is: will stay handle of stainless steel workpiece as the anode, the control of constant potential anodized, or stainless steel workpiece first as cathode, constant potential control of cathode, and stainless steel workpiece as the anode, the control of constant potential anodized, and continue to change its constant potential passivation treatment, adopt HN03 electrolyte solution.After such treatment, stainless steel passivation film properties have been improved, corrosion resistance greatly improved.The pitting critical potential (Eb) was increased by about 1000mV(in 3% NaCl), and the resistance to uniform corrosion was increased by three orders of magnitude (at 20%-30% H2S04 at 45℃).