Abstract:
The present invention cleans contaminants from pipes. The first step may be pulling a vacuum on the pipe to be cleaned. The pipe is then filled with a solvent, which is preferably a fluorocarbon solvent. After the pipe is filled with solvent, a cleaning solution is pumped at a high velocity through the pipe. The cleaning solution preferably comprises the fluorocarbon solvent, and a fluorosurfactant. The pipe is then rinsed with solvent. A particle counter is used to determine whether the solvent rinse contains an acceptably low number of particles. The solvent is then blown out of the pipe by a gas, such as dry air. A vacuum is then pulled on the pipe. Subsequently, a hot dry gas is pumped through the pipe to evaporate and remove any remaining solvent. The gas is preferably hot, dry air. The gas exiting from the pipe is then checked to confirm that it contains an acceptably low level of solvent vapor.

Description:
This application claims the benefit of provisional application No. 60/196,296 filed Apr. 12, 2000. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to the field of cleaning the surfaces within pipes. The surfaces may be metal, including stainless steel. The restricted points of entry may prevent these surfaces from being cleaned by application of mechanical force or sonic energy. The contaminants to be cleaned from the surfaces include organic matter and particulates. 
     BACKGROUND OF THE INVENTION 
     The oxygen supply systems on aircraft may comprise oxygen converters, oxygen regulators, molecular sieve oxygen generators (MSOG units), oxygen pipes which are more commonly referred to as oxygen lines, and other apparatus. The cleaning of these oxygen supply systems is required primarily to remove two types of contamination. The first type of contamination arises from organic compounds. These organic compounds include jet fuel, compounds that result from the incomplete combustion of jet fuel, hydraulic oil and special types of greases that are used in these oxygen systems. The second type of contamination arises from particles of dust and dirt, as well as particles of Teflon that are found in the greases that may be used in these oxygen systems, and from Teflon tape which may be used in the threaded connections of these oxygen systems. The particulates may be in a size range of about one to 300 microns, and more commonly, in a size range of about 2 to about 150 microns. 
     The prior art attempts to clean oxygen lines have involved the use of chlorofluorocarbons, and have generally had unsatisfactory results. Aqueous solvents are unsatisfactory because they are difficult to remove completely and residual water may freeze and create a dangerous buildup of pressure. 
     There are certain requirements for methods, compositions and apparatus for cleaning the surfaces within aircraft oxygen lines to remove such contaminants. The methods should be able to be carried out in a relatively short period of time. Preferably, the cleaning should be carried out with the minimum removal of components of the oxygen system from the aircraft. The cleaning compositions should be non-aqueous, non-flammable, non-toxic, and environmentally friendly. The solvent of the cleaning compositions should be able to be used as a verification fluid that is circulated through the cleaned components in order to verify cleaning. The apparatus for cleaning should preferably be transportable to the location of the aircraft. The cleaning should achieve at least a level B of ASTM standard G93-96, which may be stated as less than 3 mg/ft 2  (11 mg/m 2 ), or less than about 3 mg. of contaminants per square foot of interior surface of the components, or less than about 11 mg. of contaminants per square meter of interior surface of the components. The method of ASTM standard G93-96 may not accurately determine the level of cleanliness in vessels with restricted entry. 
     There are other installations where clean oxygen lines are required. These include hospitals and physical science research facilities. 
     SUMMARY OF THE INVENTION 
     The present invention comprises methods, compositions and apparatus for cleaning the interior surfaces of pipes, and particularly, oxygen lines. These methods, compositions and apparatus have certain features in common, and other features that may be varied depending on the nature of the surfaces to be cleaned. 
     The present invention achieves the satisfactory cleaning of contaminants from pipes by first pulling a vacuum on the pipe to be cleaned. The pipe is then filled with a solvent, which is preferably a fluorocarbon solvent. After the pipe is filled with solvent, a cleaning solution is pumped at a high velocity through the pipe. The cleaning solution preferably comprises the fluorocarbon solvent, and a fluorosurfactant. The pipe is then rinsed with solvent. A particle counter is used to determine whether the solvent rinse contains an acceptably low number of particles. The solvent is then blown out of the pipe by a gas, such as dry air. A vacuum is then pulled on the pipe to evaporate the solvent. Subsequently, a hot dry gas is pumped through the pipe to remove any remaining solvent. The gas is preferably hot, dry air. The gas exiting from the pipe is then checked with a halogen detector to confirm that it contains an acceptably low level of solvent vapor. 
    
    
     DESCRIPTION OF THE DRAWING 
     FIG. 1 is a schematic illustration of apparatus embodying the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The solvent may be selected from a number of fluorocarbons. A preferred solvent is HFE301 which is a hydrofluoroether available from 3M, and which comprises methyl heptafluoropropyl ether (C 3 F 7 OCH 3 ). A more preferred solvent is HFE-7100, which is a mixture of methyl nonafluorobutyl ether, Chemical Abstracts Service No. 163702-08-7, and methyl nonafluoroisobutyl ether, Chemical Abstract Service No. 163702-07-06. HFE-7100 generally comprises about 30-50 percent of methyl nonafluorobutyl ether and about 50-70 percent of the methyl nonafluoroisobutyl ether. A third solvent is FC-72, which is Chemical Abstract Service No. 865-42-1, and comprises a mixture of fluorinated compounds with six carbons. A fourth solvent is FC-77 which is Chemical Abstract Service No. 86508-42-1, and comprises a mixture of perfluorocompounds with 8 carbons. A preferred group of solvents comprises segregated ethers which comprise a hydrocarbon group on one side of the ether oxygen (—O—) and a fluorocarbon group on the other side. 
     The surfactant of the present invention may be selected from the following fluorosurfactants, or similar fluorosurfactants. The preferred surfactant is L11412 which is available from 3M, and which is a perfluorocarbon alcohol, 100% volatile, and a clear, colorless liquid, with a boiling point in the range of from about 80° C. to about 90° C. and a specific gravity of about 1.8 g./ml. A second surfactant is Krytox alcohol, which is a nonionic fluorosurfactant that comprises hexafluoropropylene oxide homopolymer. A third surfactant is Zonyl UR, which is an anionic flurosurfactant. It comprises Telomer B phosphate, which is known by Chemical Abstracts Service No. 6550-61-2. A fourth surfactant is Krytox 157FS, which is a perfluoropolyether carboxylic acid, Chemical Abstracts Service No. 51798-33-5-100. 
     A preferred cleaning composition comprises from about 0.001% to about 5% by weight surfactant, and more preferably from about 0.05% to about 0.5% by weight surfactant. In a preferred embodiment, there is about 0.05% by weight of the surfactant in the cleaning composition of the present invention. 
     The methods and apparatus of the present invention are more fully disclosed in FIG.  1  and the following description. 
     The apparatus of the present invention is preferably housed in a trailer or other vehicle which is parked adjacent the aircraft. An aircraft may have one or more oxygen lines. In some aircraft, there is one oxygen line for each oxygen mask that is worn by a crew member. Each aircraft oxygen line may be provided with an oxygen regulator. In practicing the invention, the oxygen regulator is typically removed from each aircraft oxygen line before it is connected to the apparatus of the present invention. 
     In FIG. 1, aircraft  1  is shown comprising eight oxygen lines  5 ,  6 ,  7 ,  8 ,  9 ,  10 ,  11  and  12 . The apparatus of the present invention comprises hose  71  which is adapted to be attached to line  72  which is the main terminus of all of the oxygen lines. Manifold  4  is provided with hoses  73 ,  74 ,  75 ,  76 ,  77 ,  78 ,  79  and  80 , which are adapted to be attached to the terminus of oxygen lines  5 ,  6 ,  7 ,  8 ,  9 ,  10 ,  11  and  12 , respectively. Manifold  4  is provided with valves  2 ,  3 ,  33 ,  34 ,  67 ,  68 ,  69  and  70  to allow selective communication between oxygen lines  5 ,  6 ,  7 ,  8 ,  9 ,  10 ,  11  and  12 , respectively, on the one hand, and line  39  on the other hand. 
     In a method according to the present invention, valve  13  in line  14  is opened. This allows concentrated surfactant from surfactant tank  15  to flow through line  14  to surfactant proportioner  16 . The concentrated surfactant may be from about 8% to about 15% by weight of the solvent. After surfactant proportioner  16  is filled with a fixed volume of concentrated surfactant, valve  13  is closed. Valve  17  in line  18  is opened, and valve  19  in line  20  is opened. A fixed volume of solvent from solvent tank  21  is pumped by a pump (not shown) through line  18  to surfactant proportioner  16 . The fixed volume of concentrated surfactant from surfactant proportioner  16  and the fixed volume of solvent from solvent tank  21 , flow through line  20 , through desiccant  22 , through filter  23  and into cleaning solution tank  24 . Valves  17  and  19  are closed. The foregoing steps may be repeated until a predetermined amount of cleaning solution is present in cleaning solution tank  24 . 
     Vacuum pump  25  is turned on and evacuates line  26 . Hoses  71 ,  73 ,  74 ,  75 ,  76 ,  77 ,  78 ,  79  and  80  are attached to aircraft oxygen lines  72 ,  5 ,  6 ,  7 ,  8 ,  9 ,  10 ,  11  and  12 , respectively. Valve  27  is opened, while valves  2 ,  3 ,  33 ,  34 ,  67 ,  68 ,  69  and  70  are closed. Vacuum pump  25  is used to leak test aircraft oxygen lines  72 ,  5 ,  6 ,  7 ,  8 ,  9 ,  10 ,  11  and  12  through hose  71  and lines  28  and  26 . After a predetermined level of evacuation is achieved, valve  27  is closed. Vacuum pump  25  may be turned off. Valves  2 ,  3 ,  29 ,  30 ,  31 ,  33 ,  34 ,  67 ,  68 ,  69  and  70  are opened. Pump  32  is turned on. Solvent is pumped from solvent tank  21  through line  37 , through pump  32 , through lines  38  and  28 , through hose  71 , through aircraft oxygen lines  72  and  5 ,  6 ,  7 ,  8 ,  9 ,  10 ,  11  and  12 , through hoses  73 ,  74 ,  75 ,  76 ,  77 ,  78 ,  79  and  80 , and through lines  39  and  35  to distillation unit  40 . After aircraft oxygen lines  72 ,  5 ,  6 ,  7 ,  8 ,  9 ,  10 ,  11  and  12  are full of solvent, valves  3 ,  29 ,  31 ,  33 ,  34 ,  67 ,  68 ,  69  and  70  are closed, and valves  41  and  43  are opened. 
     Cleaning solution is pumped by pump  32  from cleaning solution tank  24 , through line  42 , through pump  32 , through lines  38  and  28 , through hose  71 , through aircraft oxygen lines  72  and  5 , through hose  73 , through lines  39  and  44 , through desiccant  22 , through filter  23  and into cleaning solution tank  24 . Filter  23  should remove a substantial amount of particles. The cleaning solution is pumped by pump  32  through this continuous loop for a predetermined amount of time at a relatively high velocity. The velocity through aircraft oxygen lines  72  and  5  is preferably from about 10 to about 30 feet (about 3.0 to 9.1 meters) per second, and more preferably from about 16 to about 25 feet (about 4.9 to 7.6 meters) per second. After the cleaning solution has been pumped through this loop for a predetermined amount of time, valve  3  is opened and valve  2  is closed. After the cleaning solution has been pumped through this loop for a predetermined amount of time, valve  33  is opened and valve  3  is closed. After the cleaning solution has been pumped through this loop for a predetermined amount of time, valve  34  is opened and valve  33  is closed. After the cleaning solution has been pumped through this loop for a predetermined amount of time, valve  67  is opened and valve  34  is closed. After the cleaning solution has been pumped through this loop for a predetermined amount of time, valve  68  is opened and valve  67  is closed. After the cleaning solution has been pumped through this loop for a predetermined amount of time, valve  69  is opened and valve  68  is closed. After the cleaning solution has been pumped through this loop for a predetermined amount of time, valve  70  is opened and valve  69  is closed. After the cleaning solution has been pumped through this loop for a predetermined amount of time, valves  41  and  43  are closed, and valves  2 ,  3 ,  29 ,  31 ,  33 ,  34 ,  67 ,  68 ,  69  and  70  are opened. 
     Solvent is pumped by pump  32  from solvent tank  21 , through line  37 , through pump  32 , through lines  38  and  28 , through hose  71 , through aircraft oxygen lines  72 ,  5 ,  6 ,  7 ,  8 ,  9 ,  10 ,  11  and  12 , through hoses  73 ,  74 ,  75 ,  76 ,  77 ,  78 ,  79  and  80 , through manifold  4 , and through lines  39  and  35  to distillation unit  40 . The velocity of the solvent does not have to be a relatively high velocity. After aircraft oxygen lines  72 ,  5 ,  6 ,  7 ,  8 ,  9 ,  10 ,  11  and  12  have been rinsed with solvent, valves  45  and  46  are opened. Pump  32  continues to pump solvent from solvent tank  21 , through line  37 , through pump  32 , through lines  38  and  28 , through hose  71 , through aircraft oxygen lines  72 ,  5 ,  6 ,  7 ,  8 ,  9 ,  10 ,  11  and  12 , through hoses  73 ,  74 ,  75 ,  76 ,  77 ,  78 ,  79  and  80 , to manifold  4 . Solvent is further pumped from manifold  4  through lines  39  and  47 , through particle counter  49 , and through lines  48  and  35  to distillation unit  40 . If the amount of particles in the solvent passing through particle counter  49  is below a predetermined level, then aircraft oxygen lines  72 ,  5 ,  6 ,  7 ,  8 ,  9 ,  10 ,  11  and  12  have been cleaned. On the other hand, if the amount of particles in the solvent passing through particle counter  49  is not low enough to meet a predetermined level, then the steps of pumping cleaning solution through aircraft oxygen lines  72 ,  5 ,  6 ,  7 ,  8 ,  9 ,  10 ,  11  and  12  may be repeated. 
     When aircraft oxygen lines  72 ,  5 ,  6 ,  7 ,  8 ,  9 ,  10 ,  11  and  12  have been cleaned, pump  32  is turned off, valves  29 ,  30 ,  45  and  46  are closed, and valves  31  and  36  are opened. Dry air from dry air generator  50  is forced by a pump or other means (not shown) through lines  51  and  28 , and through hose  71  to aircraft oxygen line  72 . This forces the remaining solvent out of aircraft oxygen lines  72 ,  5 ,  6 ,  7 ,  8 ,  9 ,  10 ,  11  and  12 , through hoses  73 ,  74 ,  75 ,  76 ,  77 ,  78 ,  79  and  80 , through manifold  4 , and through lines  39  and  35  to distillation unit  40 . After the remaining solvent has been forced out of aircraft oxygen lines  72 ,  5 ,  6 ,  7 ,  8 ,  9 ,  10 ,  11  and  12 , valves  2 ,  3 ,  31 ,  33 ,  34 ,  36 ,  67 ,  68 ,  69  and  70  are closed. Valve  27  is opened. Vacuum pump  25  pulls a vacuum through lines  26  and  28  and through hose  71 , on aircraft oxygen lines  72 ,  5 ,  6 ,  7 ,  8 ,  9 ,  10 ,  11  and  12 . After a predetermined level of evacuation has been achieved, valve  27  is closed, and valves  2 ,  3 ,  33 ,  34 ,  67 ,  68 ,  69 ,  70 ,  52 ,  53 , and  54  are opened. 
     Dry air from dry air generator  50  is forced by a pump or other means (not shown) through line  55  to air heater  56 . Air heater  56  is turned on. Air heater  56  heats the dry air which is further forced through lines  57  and  28 , through hose  71 , through aircraft oxygen lines  72 ,  5 ,  6 ,  7 ,  8 ,  9 ,  10 ,  11  and  12 , through hoses  73 ,  74 ,  75 ,  76 ,  77 ,  78 ,  79  and  80 , through manifold  4 , and through lines  39  and  58  to vent  59 . After a predetermined amount of heated dry air has been forced through aircraft oxygen lines  72 ,  5 ,  6 ,  7 ,  8 ,  9 , 10 ,  11  and  12 , valves  60  and  61  are opened. The heated dry air exiting from manifold  4  passes through lines  39  and  62 , through halide detector  63 , and through lines  64  and  58  to vent  59 . If the amount of halide detected by halide detector  63  is below a predetermined level, then aircraft oxygen lines  72 ,  5 ,  6 ,  7 ,  8 ,  9 ,  10 ,  11  and  12  have been dried. On the other hand, if the level of halide that is detected by halide detector  63  is above a predetermined level, then additional hot dry air may be forced through aircraft oxygen lines  72 ,  5 ,  6 ,  7 ,  8 ,  9 ,  10 ,  11  and  12 , until the level of halide is below the predetermined level. 
     After the level of halide that is detected by halide detector  63  is below the predetermined level, air heater  56  is turned off and valves  2 ,  3 ,  33 ,  34 ,  52 ,  53 ,  60 ,  61 ,  67 ,  68 ,  69  and  70  are closed. Hoses  71 ,  73 ,  74 ,  75 ,  76 ,  77 ,  78 ,  79  and  80 , may now be disconnected from aircraft oxygen lines  72 ,  5 ,  6 ,  7 ,  8 ,  9 ,  10 ,  11  and  12 , respectively. 
     Solvent may be recycled before, during or after the steps that are described above, by opening valve  66  and activating distillation unit  40 . The solution within distillation unit  40  is heated to vaporize the solvent, and the condensed solvent vapor is gravity fed through line  65  to solvent tank  21 . 
     Variations of the invention may be envisioned by those skilled in the art.