PRODUCTS FOR THE PREVENTIVE TREATMENT OF STAINLESS STEEL AND RELATED METHODS

Abstract

Provided herein is a reductive solution for preventing rouge formation on stainless steel, said solution comprising complexing anions, Fe.sup.2+, and, optionally, one or more pH modifiers. Further provided are methods for manufacturing said solution, methods for prevention of rouge formation on stainless steel surfaces, and related uses of the aforementioned reductive solution.

Claims

1. A reductive solution for preventing rouge formation on surfaces of stainless steel, said solution comprising: from 5.0×10.sup.−3 to 1.0×10.sup.−1 mol/l of one or more complexing anions; from 1.35×10.sup.−5 to 9.0×10.sup.−5 mol/l of Fe.sup.2+; and, wherein the reductive solution has a pH value from 0.0 to 6.0.

2. The reductive solution of claim 1, wherein said one or more complexing anions comprise oxalate.

3. The reductive solution of claim 1, wherein the solution has a pH value from 2.0 to 4.5.

4. The reductive solution of claim 1, wherein the solution has a pH value from 2.0 to 4.0.

5. The reductive solution of claim 1, wherein the solution has a pH value from 2.8 to 3.2.

6. The reductive solution of claim 1, wherein the solution further comprises one or more pH modifiers.

7. The reductive solution of claim 6, wherein the one or more pH modifiers are selected from the list comprising NH.sub.3 and NH.sub.4OH.

8. The reductive solution of claim 1, wherein the solution does not comprise citric acid.

9. A method for manufacturing a reductive solution of claim 1, comprising the step of: mixing water, a complexing acid and/or salts thereof, a water-soluble ferrous salt.

10. The method of claim 9, wherein the complexing acid and/or salts thereof comprise oxalic acid and/or salts thereof.

11. The method of claim 9, wherein the method further comprises mixing one or more pH modifiers.

12. A process for preventing rouge formation on surfaces of stainless steel substrates, comprising the step of: contacting the stainless steel substrate with a reductive solution of claim 1.

13. The process of claim 12, wherein the reductive solution and/or the substrate has a temperature of 50 to 95° C. during contacting.

14. The process of claim 12, wherein the reductive solution and/or the substrate has a temperature of 80 to 90° C. during contacting.

15. The process of claim 12, wherein the contact time of the substrate with the reductive solution is from 0.50 hours to 8 hours.

16. The process of claim 12, wherein the contact time of the substrate with the reductive solution is from 0.75 hours to 1.5 hours.

17. The process of claim 12, comprising the step of contacting the stainless steel substrate with the reductive solution on a recurring basis; the frequency of contacting preferably being between one contacting step per process cycle and one contacting step every 20 process cycles.

18. The process of claim 12, comprising the step of contacting the stainless steel substrate with the reductive solution on a recurring basis; the frequency of contacting preferably being between one contacting step every 5 process cycle and one contacting step every 10 process cycles.

19. The process of claim 12 wherein, in between the successive contacting events, the stainless steel substrate is exposed to an aqueous fluid having a conductivity less than 1 μS/cm.sup.2.

20. The process of claim 12 wherein the step of contacting is performed by dipping, flushing, or spraying.

Description

EXAMPLES

Example 1

[0079] In a first example, an exemplary reductive solution is provided. The reductive solution is an aqueous solution comprising oxalate ions in a concentration of 2.0×10.sup.−2 mol/l, Fe.sup.2+ ions in a concentration of 5.0×10.sup.−5 mol/l, and a quantity of NH.sub.4OH adapted to bring the pH of the reductive solution to 2.9.

Example 2

[0080] In a further example, a process for preventive maintenance of stainless steel equipment for batch manufacturing of vaccines is discussed. After each batch process, the manufacturing equipment, which includes vessels and transfer lines, is cleaned using water and detergents. Every ten batch processes, the equipment is preventively treated using a reductive solution according to example 1. After treatment with the reductive solution, the equipment's vessels and transfer lines are rinsed using water.