Method for precision-cleaning propellant tanks

• US 6,308,720 B1
• Filed: 04/08/1999
• Issued: 10/30/2001
• Est. Priority Date: 04/08/1998
• Status: Expired due to Fees

• Current Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Original Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Inventors: Modi, Paresh R.
• Primary Examiner(s): Gulakowski, Randy
• Assistant Examiner(s): CHAUDHRY, SAEED T
• Application Number:
  US09/289,372
• Time in Patent Office: 936 Days
• Field of Search: 134/22.14, 134/22.19, 134/26, 134/40, 134/29, 134/22.1, 134/27
• US Class Current: 134/22.1
• CPC Class Codes: C11D 2111/20 Industrial or commercial equipment, e.g. reactors, tubes or engines
• CPC Class Codes: C11D 3/046 Salts
• CPC Class Codes: C11D 3/1266 in liquid compositions
• CPC Class Codes: C11D 7/10 Salts
• CPC Class Codes: C11D 7/14 Silicates

Abstract

A method for precision-cleaning the aluminum alloy inner wall surface of a tank is disclosed. In one embodiment, the inner wall surface is cleaned by a method including the steps of washing the inner wall surface with a first portion of water, applying an aqueous cleaning solution comprising sodium silicate, sodium tetrafluoroborate and sodium molybdate, and rinsing the inner wall surface with a second portion of water. In a second embodiment, the method is directed to precision-cleaning a launch vehicle booster propellant tank. In this embodiment, the method includes the steps of applying washes of water and aqueous cleaning solution on at least upper and lower sections of the inner wall surface of the tank, washing such sections with water, and analyzing samples of effluent cleaning solution and water collected from the effluent drain of the tank for hydrocarbon and particulate contaminants. In a third embodiment, the method further includes drying the tank and verification of hydrocarbons and nonvolatile residues and then further drying the tank to the system level requirement.

Claims

1. A method for cleaning an inner wall surface of a tank, the inner wall surface comprising a metal, said method comprising the steps of:

applying an aqueous cleaning solution comprising sodium silicate, sodium tetrafluoroborate, and sodium molybdate to at least a first portion of the inner wall surface and a second portion of the inner wall;

wherein during the applying, the first portion of the inner wall surface is vertically higher than the second portion of the inner wall surface, and the applying comprises first spraying the second portion of the inner wall surface with the aqueous cleaning solution and, after the first spraying, second spraying the first portion of the inner wall surface with the aqueous cleaning solution.

2. The method of claim 1, further comprising, prior to the applying:

washing at least the first portion of the inner wall surface and the second portion of the inner wall surface with rinse water;

wherein, the washing comprises first spraying the first portion of the inner wall surface with the rinse water and, after the first spraying, second spraying the second portion of the inner wall surface with the rinse water.

3. The method of claim 2, wherein the washing comprises spraying the rinse water from a spraying device disposed inside of the tank;

wherein the spraying device is at a first elevation opposite the first portion of the wall surface during the first spraying of the first portion of the inner wall surface with the rinse water and, after the first spraying of the first portion of the inner wall surface with the rinse water, the spraying device is lowered to a second elevation opposite the second portion of the inner wall surface for the second spraying of the second portion of the inner wall surface with the rinse water.

4. The method of claim 1, wherein the aqueous cleaning solution comprises about 10% sodium silicate, about 1.5% sodium tetrafluoroborate, about 0.5% sodium molybdate, and about 88% water, by weight.

5. The method of claim 1, wherein said first portion of the inner wall surface and said second portion of the inner wall surface each comprise an aluminum alloy selected from the group consisting of the 2000, 6000 and 7000 aluminum series.

6. The method of claim 1, wherein the applying comprises spraying the cleaning solution from a spraying device disposed inside of the tank;

wherein the spraying device is at a first elevation opposite the second portion of the wall surface during the first spraying and, after the first spraying, the spraying device is raised to a second elevation opposite the first portion of the inner wall surface for the second spraying.

7. The method of claim 6, wherein during each of the first spraying and the second spraying, the cleaning solution is sprayed from the spraying device at a rate of at least about 55 gallons per minute.

8. The method of claim 7, wherein during each of the first spraying and the second spraying, the spraying device is operated at a pressure of at least about 35 psig.

9. The method of claim 7, wherein the spraying device comprises an orbital sprayer rotating at a rate of from about 1 revolution per minute to about 2 revolutions per minute during each of the first spraying and the second spraying.

10. The method of claim 6, wherein the method further comprises, after the rinsing, drying the inner wall surface.

11. The method of claim 10, wherein the interior of the tank, after the drying, contains:

no more than 1 mg of nonvolatile residue per square foot of internal surface area in the tank;

hydrocarbons at a level no greater than 10 parts per million by volume as methane per liter of the fluid capacity of the tank; and

total filterable solids of no greater than 0.1 mg per square foot of internal surface area in the tank.

12. The method of claim 1, further comprising, after the applying, rinsing at least the first and second portions of the inner wall surface with rinse water;

wherein the rinsing comprises first spraying the first portion of the inner wall surface with the rinse water and, after the first spraying, second spraying the second portion of the inner wall surface with the rinse water.

13. The method of claim 12, further comprising the steps of:

sampling and analyzing effluent cleaning solution from the applying to determine at least a level of hydrocarbon contaminants in the effluent cleaning solution; and

commencing the rinsing only after the hydrocarbon contaminants in the effluent cleaning solution do not exceed a preselected standard.

14. The method of claim 12, further comprising the steps of:

sampling and analyzing for pH of effluent rinse water from the first spraying the first portion of the inner wall surface with rinse water; and

continuing the first spraying at least until the pH of the effluent rinse water is within a range of from about pH 6.5 to about pH 8.

15. The method of claim 12, wherein said rinsing step is commenced within about five minutes after completion of said applying step.

16. The method of claim 12, wherein the rinsing comprises spraying the rinse water from a spraying device disposed inside of the tank;

wherein the spraying device is at a first elevation opposite the first portion of the wall surface during the first spraying of the first portion of the inner wall surface with the rinse water and, after the first spraying of the first portion of the inner wall surface with the rinse water, the spraying device is lowered to a second elevation opposite the second portion of the inner wall surface for the second spraying of the second portion of the inner wall surface with the rinse water.

17. The method of claim 12, wherein the rinse water contains:

total organic carbon of no greater than 1 mg per square foot of internal surface area in the tank; and

total filterable solids of no greater than 0.1 mg per square foot of internal surface area in the tank.

18. The method of claim 12, further comprising, after the rinsing, final rinsing, the final rinsing comprising:

spraying a final rinse water on at least the first portion of the inner wall surface; and

sampling final rinse water effluent and determining particulate contamination in final rinse water effluent;

wherein the final rinse is continued at least until the particulate contamination in the final rinse water effluent is determined to be no larger than a preselected standard.

19. The method of claim 1, wherein the aqueous cleaning solution is at a temperature between about 65 degrees Fahrenheit and about 75 degrees Fahrenheit during the applying.

20. The method of claim 1, wherein the tank has a capacity of at least approximately 26,000 gallons.

21. The method of claim 1, wherein the tank has a height of at least 32 feet.

22. The method of claim 1, wherein the inner wall surface has an isogrid structure.

23. The method of claim 1, wherein the applying further comprises, after the second spraying, third spraying at least a third portion of the inner wall surface with the cleaning fluid, the third portion of the inner wall surface being vertically higher than the first portion of the inner wall surface.

24. The method of claim 1, wherein each of the first and second spraying last at least about 30 minutes.

25. A method for cleaning a cylindrical tank, having top and bottom ends, and an inner wall surface comprising an aluminum alloy, said method comprising steps of:

verticalizing the tank;

first washing at least a first section of the inner wall surface with a first portion of rinse water;

after the first washing, second washing at least a second section of the inner wall surface located below said first section with a second portion of rinse water;

after the second washing, first applying a first amount of an aqueous cleaning solution comprising sodium silicate, sodium tetrafluoroborate, and sodium molybdate to said second section of the inner wall surface;

after the first applying, second applying a second amount of said aqueous cleaning solution to said first section of the inner wall surface;

after the second applying, first rinsing said first section of the inner wall surface with a third portion of rinse water; and

after the first rinsing, second rinsing said second section of the inner wall surface with a fourth portion of water.

26. The method of claim 25, further comprising, following said second applying step, the steps of:

collecting a first sample of said effluent cleaning solution after said second applying step; and

analyzing said first sample for hydrocarbon contaminants.

27. The method of claim 26, wherein said first sample of said effluent cleaning solution includes a first level of hydrocarbon contaminants, said method further comprising the step of:

repeating at least said first and second applying steps.

28. The method of claim 25, wherein each of the first rinsing and the second rinsing comprise:

monitoring effluent rinse water for at least pH as an indication of the level of aqueous cleaning water in the effluent rinse water; and

wherein the first rising and the second rinsing are each continued at least until the pH of the effluent rinse water is within a range of pH 6.5 to pH 8.

29. The method of claim 25, further comprising, following said second rinsing, the steps of:

third rinsing said first section of the inner wall surface with a fifth portion of rinse water, wherein an effluent rinse water results from said third rinsing with a fifth portion of water;

collecting a sample of said effluent rinse water from said third rinsing with a fifth portion of water;

analyzing said sample of effluent rinse water from said third rinsing with a fifth portion of water to determine at least a level of particulate contaminants;

comparing the level of particulate contaminants with a preselected standard and continuing the third rinsing at least until the level of particulate contaminants is no larger than the preselected standard.

30. The method of claim 29, further comprising, following said step of analyzing said sample of effluent rinse water from said third rinsing with a fifth portion of water, the steps of:

drying said first and second sections of the inner wall surface;

analyzing a bottom area of said second section of the inner wall surface proximate to the bottom end to determine measured nonvolatile residues; and

,

repeating at least said first applying, said second applying, said first rinsing, said second rinsing, said third rinsing and said drying when the measured nonvolatile residues exceed a preselected standard.

31. The method of claim 30, wherein said analyzing step comprises applying a first amount of a first organic cleaning agent to a portion of said second section and testing effluent organic cleaning agent from said applying the first amount of the first organic cleaning agent draining off said portion for nonvolatile residues.

32. The method of claim 30, wherein said analyzing step comprises at least one swipe test with a Teflon membrane filter and Fourier transform infrared analysis of said Teflon membrane filter following said swipe test.

33. The method of claim 25, wherein said aqueous cleaning solution is comprised of about 10% sodium silicate, about 1.5% sodium tetrafluoroborate, about 0.5% sodium molybdate, and about 88% water, by weight.

34. The method of claim 25, wherein said second applying is commenced no later than about five minutes after said first applying and said first rinsing is commenced no later than about five minutes after said second applying.

35. The method of claim 25, wherein the aluminum allow is selected from the group consisting of 2000 series aluminum alloys, 6000 series aluminum alloys and 7000 series aluminum alloys.