Two Stage Process

For the most part Passivation of Stainless Steel in Ireland and indeed across Europe uses a two stage process.

STAGE NO. 1

This is a De-Greasing stage and usually consists of circulating either Caustic Soda or Tri-Sodium Phosphate at approx 5% at 60 - 80 degrees centigrade for 2 - 4 hours.
The waste is usually held for certified disposal.
The system is then rinsed to a neutral pH.

STAGE NO. 2

This is the Passivation stage and uses a mineral acid, either Nitric or Phosphoric circulated through the system at 10% for two hours at 35 degrees centigrade.
The waste is usually held for certified disposal.
The system is then rinsed using D.I. water until the conductivity of the effluent is below 10 microsiemens.

TESTING

The following tests are usually carried out:
pH.
Conductivity.
Verification of chemical concentrations.
Temperature measurement.
Some facilities also require a Ferroxile test for free iron.
Note: This test is highly sensitive and should be made only by personnel familiar with its limitations.
The test solution must be made prior to each use.
This test should not be performed for process surfaces of equipment that will be used for processing food, beverages, pharamaceuticals or other products for human consumption unless all traces of the test solution can be thoroughly removed.

As can be seen from the above procedure it is simply a "one size fits all" approach to passivation and does not take into consideration the many contaminates that may be encountered with Stainless Steel.

We do provide this procedure when required by the client but we cannot guarantee good results. Proof of this is the fact that if a tank/vessel is wiped using a wipe wetted with IPA post this procedure almost always the wipe will show a black residue. Mineral acids can only remove some free iron. They can damage the stainless steel substrate, be a hazard to personnel and create considerable waste that may need certified disposal. Some standards even call

for the addition of Sodium Dichromate and Hydrofluoric acid, these do little to enhance the process and only increase the chances of damage to the substrate and risk to personnel.

Clarwick is the only company in Ireland, U.K. and Europe to be able to offer Chelant technology for the passivation of Stainless Steel and is due to our association with R.W.EVANS and associates