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RXSOL PASSIVATION is highly conc and acidic product , It does not give Black or Yellow stain marks after washing with water. It simultaneously removes annealing colours, ferritic contamination & weld burns.
Spray is very safe & easy to use for cleaning of large equipments like S.S. vessels, dryers, agitators, dairy machinery, fermentators, internals as well as externals of pipes by pressurised spray bottle or pump. passivation proces improve the corrosion resistance of metal parts / surface.
Concentrated materials are suitable for use only on stainless steel. While diluted is suitable for cleaning aluminum.
It is used to clean weld seams and surrounding areas with brush. It is used to remove heavy scales, discolouration, annealing colours, rust particles near weld and welding affected area by heat.
Circulation method : For closed system like PIPE , use concentrated materials atleast for 1-2 Hrs . Then FLUSH the system with TECHNICAL GRADE OF DI-WATER ( which is free from , all SOLUBLE IMPURITIES )
Spray Method : For TANK PASSIVATION , this is very effective method . Directly spray on wall of TANKS atleast for 10-15 Minutes , then wash the system with cupious amout of fresh water , finally use TECH GRADE DI water for complete wash.
Procedure of Passivation
1. Isolate the exchanger and set up a circuit with an external tank with heating coil inside and a pump to circulate cleaning solution.
FLUSHING:-
2. Flush the Exchanger with fresh water to remove loose material (like dirt etc.) till such time clear water comes.
INHIBITED ACID CLEANING:-
3. Circulate inhibited Acid (5-6 % Citric Acid and 1% Rodine 213) along with non ionic wetting agent like RXSOL-T300 through Exchanger Loop for 6 to 8 hours
4. It total iron concentration reaches 5000 - 8000 PPM and concentration below 2% acid percentage then dump the cleaning solution and repeat the cycle with fresh inhibited acid.
5. Samples to be tested for pH, TDS and iron on hourly basis.
6. Normal operating temperature should be 50-60º C.
7. When iron concentration and acid concentration of solution reaches steady state and cleaning in completed. Drain the cleaning solution.
NEUTRALIZING:-
8. Circulate 1-2% solution of soda Ash for one to two for neutralization.
9. Rinse the neutralizing solution with water till pH of Inlet and Outlet is same.
PASSIVATION:-
10. Immediately fill and Circulate with 1-3% of solution of sodium Hexametaphosphate for 4-6 hours keeping operating temperature around 50-60º C. Analyze for Phosphate levels in Inlet and Outlet. (Normally maintain 30-40 PPM O-PO4 level)
11. Drain the passive solution without flushing with water.
DRYING:-
12. Dry the circuit with dry air/N2.
For Pickling This is probably the most commonly used method. Use a solution of nitric and hydrofluoric acids in water. We use ASTM A380, solution D. The formula is specified in A380 as 6 - 25% HNO3 and ½ - 8% HF in water at 70 -140 F (21 - 60 C) for about 30 minutes. This is a strong cleaning solution and may etch highly finished surfaces.
Coverage / kg : Approx. 100 meters of weld seam.
It also helps to detect pinholes after welding.
Why Passivation required ?
1. Stainless Steel owes its corrosion resistance to the formation of a chromium oxide surface layer but this happened due to presence of oxygen , And if the oxide has been stripped, perhaps by pickling, then the oxide layer takes a short time to reach its full thickness and this can be accelerated by passivation.
2. The heat tint produced by welding is not only unsightly but the thicker oxide layer includes chromium from the surface of the metal, lowering its corrosion resistance. Pickling both removes the oxide layer causing the colour tints and a thin layer of the underlying metal to restore the original properties.
3. Iron Contamination
A major cause of corrosion in service is iron contamination which can arise from a variety of sources. These include using tools made of mild or constructional steels like fork lifts being a common cause for abrasives that contain iron and any tool that has previously been used on non stainless steel. Cross contamination can also arise from grindings and debris created whilst working close by on steel, either in the workshop or on site. Iron contamination is not always obvious, if it is suspected it can be detected using the ASTM A380, ferroxyl test. This is a rapid test in which a solution turns blue in the presence of iron. Pickling is a very effective method of removing this iron contamination from the surface.