Stainless Steel Tanks and Piping Typical Guidelines for SS 316L Pickling & Passivation/عملية غسيل وتخليل وصقل خزانات استانلس استيل درجة 316

Stainless Steel Tanks and Piping
Typical Guidelines for SS 316L Pickling & Passivation

We attempt to follow these broad guidelines.

Deviations are permitted due to operational circumstances as long as the end result of the chemical cleaning/metal surface treatment is not affected.

Such deviations will only be decided by experienced (TECHNOLAB) supervisory staff on site (unless extraordinary circumstances dictate otherwise). A project can be divided into the following sections :

1. A pre-inspection of the system(s) to be treated.

2. Preparation of the supplied and vessel's own equipment necessary for the project.

3. Preparation of a degreasing solution, followed by the application of this solution to each of the tanks and their associated piping systems.

4. Rinsing and evacuation of the tanks prior to chemical treatment.

5. Preparation of a pickling solution in one tank. This can usually be used for all tanks in question.

6. The chemical pickling of all tanks and their associated piping.

7. The rinsing of all tanks and their associated piping by means of the vessel's own tank cleaning system, using fresh water.

8. The preparation and use of a passivation solution in one tank. This can be used for all tanks, and can be supplemented with extra oxidizing agent.

After passivation, the tanks are stripped of solution.

9. A final rinse with low chloride water of the tanks, followed by evacuation and stripping.

This stage can often be omitted if the vessel has taken sufficient high quality shore-water on board for the whole process.

The chloride content of this water can be checked for example, it is generally of 60ppm or even less.

10. The inspection of the treated system(s) and determination of passivity.

11. The completion of formalities and repatriation of personnel and equipment.

The steps listed above will be described hereunder in more detail:

1. Pre-inspection

The tanks and piping will be inspected to ensure that they are in a state conforming to readiness for the chemical surface treatment.

A check will be made that any tankcleaning operations which may be necessary to remove solid particles and old cargo residues are complete, and that no incompatible materials are in the system to be wetted by corrosive media.

2. Preparation and initial testing

The tankcleaning equipment will be set up ready for the cleaning of the first tank.
Fresh water will be added to the tank of a sufficient quantity to ensure recirculation through the discharge manifold, equipment and back to the tank.

3. Preparation and use of light degreasing solution

The volume of fresh water in the tank will be adjusted.

A water-based degreaser will be added. Recirculation will be re-established, and continued for a prescribed period.

The tankcleaning machines will be transferred to the next tank, and the solution transferred to that tank using first tank's cargo pump.

When the first tank is empty, the equipment will be moved to the discharge manifold of the tank containing the degreasing solution.

Using the cargo pump of this tank, re-circulation will be established.

This process will be repeated in the form of transfer of solution to the next tank, movement of equipment to that tank's discharge manifold and recirculation over that tank, until all tanks have been treated by the degreasing solution.

4. Rinsing of the tanks prior to subsequent chemical treatment

Using the vessel's own tankcleaning equipment, each tank will be washed with fresh water.

5. Preparation of pickling solution.

The solution will be prepared in the first tank.

The equipment for pickling will be transferred back to that tank's discharge manifold, with the tank cleaning machines inside the tank, ensuring full coverage.

6. Chemical Pickling

With the prepared solution, continue circulation over the first tank for a prescribed period.

The solution is transferred and re-circulated in the same way as for the degreasing phase, with the following exceptions :

a) During circulation, extra care is taken that all connections are tight and that tank openings are covered to minimize chemical spatter.

b) A sample is drawn at the beginning of the pickling of each tank to determine dissolved iron concentration.

7. The rinsing of the tanks after pickling.

After the above operation, the tanks will be virtually empty.

They are then rinsed, one at a time, using fresh water and the vessel's own tankcleaning system until all remaining acidic residue is removed.

Samples of the washings are checked for pH, and rinsing continues till it is established that the pH of the washings are neutral.

At the end of this operation, the tanks will be virtually empty.

8. The preparation and use of a passivation solution

The tankcleaning equipment will be attached, if it is not already the case to the discharge manifold of the first tank .

The tankcleaning machines will be lowered to the correct heights into the tank.
Fresh water is added to the tank and circulation established with the cargo pumping system.

After checking for function and tightness, an aqueous oxidizing agent is added while circulating.

The solution is transferred and passivation of all tanks is done in a similar way as for the light degreasing and pickling,

9. Final rinse of nine tanks with low chloride water ( if necessary)
After the passivation phase, above, all tanks will be virtually empty.

The tankcleaning equipment will probably be attached to the discharge manifold of the final tank passivated.

The tankcleaning machines will be lowered correctly into that tank.
Low-chloride water is added to the tank to which the tankcleaning equipment is attached.

This is circulated for 45 minutes, following which it is discharged.
This process is repeated for all tanks .

Following this, all the tanks will be stripped and their respective pipelines drained.

10. Testing for the passivity of the steel

Prior to the commencement of the chemical treatment of the tanks, a test piece of stainless steel 316L will have been placed into each tank, near to the tank top.
It will be attached to the deck by a nylon cord for easy removal. Upon completion of all operations, these test pieces will be removed to a convenient location for testing (e.g. ship's office).
The following tests will be performed:

a) Measurement of passivity using electronic passivation meter.

b) Palladium chloride test for passivity.

The results of these tests will determine the passivity of the tanks. If necessary, further checks can be done in the tanks themselves.

11. Completion of documentary formalities and demobilisation.

After successful completion of all the above, the necessary work completion documentation will be signed by all parties, indicating acceptance of the work done according to the agreed scope.

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