GB2126352A

GB2126352A - Improvements in or relating to leak path detection and repair

Info

Publication number: GB2126352A
Application number: GB08319521A
Authority: GB
Inventors: Zahoor Ahmed Saifurrahman; John Gannon; John Eric Nelson
Original assignee: UK Secretary of State for Defence
Current assignee: UK Secretary of State for Defence
Priority date: 1982-07-26
Filing date: 1983-07-19
Publication date: 1984-03-21
Also published as: GB8319521D0

Abstract

A leak path detector comprises a pressurisable reservoir 10 sealably clampable over the external leak site in tank 12, the reservoir having valve means 15 for the admission of a pressurised fluid to the reservoir. Bubbles of fluid are observed emerging at the internal leak site. Sealing compound may be introduced into the reservoir and is forced along the leak path by fluid pressure. The detector may include a relief valve 16 and may be braced inside a jet engine intake duct 14 by a turnbuckle 18. <IMAGE>

Description

SPECIFICATION Improvements in or relating to leak path detection and repair The present invention relates to a method and apparatus for repairing leaks in, for example, the joints formed between panels of a fuel tank structure such as may be found in many types of aircraft.

Fuel tanks on aircraft are often formed integrally with the wings and fuselage with a fuel resistant sealant coated on internal surfaces and injected into the joint areas to prevent leakage. When a leak does occur the actual point on the exterior from where the fuel emanates is usually relatively easy to locate, however, due to the nature of the joint the origin of the leak within the tank may often be remote from the exit point, the leak path running for some distance through sealant which has cracked or become detached from the structure.

According to one aspect of the present invention, apparatus for the detection of leak paths in a tank comprises a pressuriseable reservoir sealably clampable to the tank exterior, the reservoir having valve means for the admission of a pressurised fluid to the reservoir.

The apparatus may include clamping means. For situations such as engine intake ducts the clamping means may include an axially adjustable strut or an adjustable device operating on the scissor-jack principle. Where the reservoir is required to be clamped onto an external surface where a suitable opposing surface does not exist to jack against the clamping means may include bands or straps with tightening means around the wing or fuselage.

The apparatus reservoir may also include pressure relief valve means and/or a pressure gauge.

According to a second aspect of the present invention a method for the detection of leak paths in tanks comprises positioning a pressuriseable reservoir over the external leak site of the tank, sealably clamping the reservoir to the tank, pressurising the reservoir from a pressurised fluid source, viewing the interior of the tank and determining the entry point or points of the pressurised fluid into the tank.

Preferably the pressurised fluid will be air provided from a locally available pressure regulated supply. However, in some instances where this is not available, such as when a leak is being repaired away from a well equipped service area, the pressurised fluid may comprise, for example nitrogen or carbon dioxide from a bottled supply.

Once the leak path has been identified and an assessment made of the seriousness of the sealant defect a decision may be made as to whether the leak may be repaired in situ or whether dismantling of the tank structure will be required. If the former course of action is chosen the apparatus of the invention may be utilised to facilitate, effect or enhance the repair itself. The leak path having been identified the fuel tank may then be drained, and the reservoir utilised to allow a cleaning agent (eg METHYL ETHYL KETONE) followed by compressed air to be blown along the leak path in order to clean and dry out the joint. The reservoir may be removed and sealant injected into the leak path using standard equipment.After sufficient sealant has been injected into the joint the reservoir may be reattached to the exterior leak site and the compressed air used to force the injected sealant further along the leak path thus enhancing the effectiveness of the repair.

Alternatively the reservoir may be provided with valve means such that sealant under pressure may be admitted to the reservoir and urged directly into the leak path from the reservoir. Additionally sealant may be applied directly to the flaw at the tank internal surface.

In order that the invention may be more fully understood one embodiment will now be described by way of example only with reference to the accompanying drawing which shows a section through an aircraft fuselage and jet engine air intake duct with apparatus for the detection and repair of leak paths positioned within the duct.

The apparatus shown in the drawing comprises a reservoir 10 fabricated from steel plate, the reservoir having an open face 11 positioned over the external leak site of an integrally constructed fuel tank 12. The reservoir 10 has a rubberseal 13 aroundthe periphery of the open face 11 to allow the reservoir 10 to be sealed against the structure 14 of the aircraft jet engine air intake duct. The reservoir 10 has a first valve means 15 to allow admission of compressed air into the reservoir 10 and valve means 16 to control the maximum pressure of air within the reservoir 10.On the outer surface of the reservoir face opposite the open face 11 there is a cotter pin and lug arrangement 17 to locate one end of an axially adjustable threaded turnbuckle 18 on the other end which is a second cotter pin and lug arrangement 19 retaining a contoured support foot 20 carrying a conformable rubber pad 21.

In operation the aircraft fuel tank is filled to above the level of the suspected leak area and the reservoir 10 positioned over the site of the external leak. The turnbuckle 18 is adjusted until the open face 11 of the reservoir 10 is sealed against the aircraft structure 14 by the rubber gasket 13, the support foot 20 being positioned approximately diametrally opposite the reservoir 10 in the duct. Compressed air is admitted to the reservoir 10 through the valve 15 to a maximum pressure of 5 lbf/in2 this pressure being governed by the valve 16. Compressed air escapes from the reservoir 10 via the leak path into the fuel tank 12, the emergence of air bubbles within the tank is noted thus establishing the extent of the leak and its internal location.If it is decided to repair the leak in situ without further dismantling of the airframe the following procedure is adopted.

The fuel tank 12 is drained and the apparatus of the invention removed temporarily. The area of the external leak site is thoroughly cleaned with a suitable agent such as methyl ethyl ketone. The apparatus is then repositioned and methyl ethyl ketone followed by compressed air is blown through the joint in order to clean and drythe internal surfaces of the leak path. The apparatus is again temporarily removed and sealant is injected into the joint at the external leak site. When sufficient sealant has been injected the apparatus is again repositioned and the reservoir 10 pressurised to a maximum of 3 Ibf/in2. This has the effect of urging the injected sealant further along the leak path thus enhancing the effectiveness of the repair. The apparatus is finally removed from the aircraft and the tank tested with fuel for joint integrity.

It will be apparent to the person skilled in the art reservoir itself could be modified to provide it with additional valve means. This would allow admission of sealant under pressure to be administered directly to the external leak site and directly into the leak path withoutthe need for some of the dismantling and reassembly operations. There would be some disadvantage entailed in this route due to the need to clean the reservoir of excess sealant after the operation.

Modifications to the basic apparatus may be made whereby instead of using a third valve to admit sealant to the reservoir the sealant may be loaded into the reservoir in a precharged collapsible container. Such a modification would obviate the need to clean out valves etc, reduce wastage of sealant and allow the amount and type of sealant to be varied according to the specific requirement, however, a removal/refit operation would be necessary with this approach.

It will also be apparent and although the example described above has a specific form of mechanical device used to locate the reservoir over the leak site the actual clamping means used will be chosen to suit the geometry of the area surrounding the leak site. The contour of the reservoir open face periphery will not be appropriate to effect a seal against the tank structure in all instances due to variations in the airframe contour. It may, therefore, be necessary to have a number of reservoirs of various open face contours or alternatively to have a number of different shaped skirts which are sealably attachable to a basic reservoir structure having the necessary valve means etc. It will be appreciated, however, that only a limited number of open face contours may be required since minor contour variations will be accommodated by the face sealing gasket employed.

It will further be appreciated that the apparatus and process of the present invention are not restricted only to aircraft fuel tanks. Almost any liquid containing tank having a fabricated structure containing sealant filled joints may be amenable to inspection and repair by the present invention if suitable selection of a pressurised fluid compatible with the liquid in the tank is made.

Claims

1. Apparatus for the detection of a leak path in a tank comprises a pressurisable reservoir sealably clampable to the tank exterior, the reservoir having valve means for the admission of a pressurised fluid to the reservoir.

2. Apparatus for the detection of a leak path according to claim 1 comprising clamping means to sealably attach the reservoir to the tank exterior.

3. Apparatus for the detection of a leak path according to either claim 1 or claim 2 and wherein the reservoir also includes pressure relief valve means.

4. Apparatus for the detection of a leak path according to any preceding claim and wherein the reservoir also includes a pressure gauge.

5. Apparatus for the detection of a leak path according to any preceding claim and further comprising valve means to allow admission of sealant to the reservoir.

6. Apparatus for the detection of a leak path according to any preceding claim from 1 to 4 and wherein the reservoir is adapted to receive a precharged collapsible container of sealant.

7. Apparatus for the detection of a leak path in a tank substantially as hereinbefore described with reference to the accompanying specification and drawing.

8. A process for the detection of a leak path in a tank comprises the steps of positioning a pressurisable reservoir over the external leak site on the tank, sealably clamping the reservoir to the tank, pressurising the reservoir from a pressurised fluid source, viewing the tank interior to determine the entry point or points of the pressurised fluid into the tank.

9. A process according to claim 8 and wherein the pressurised fluid is air.

10. A process for the repair of a leak path in a tank comprises the steps of injecting sealant into the leak site, sealably clamping a pressurisable reservoir over the leak site, pressurising the reservoir from a pressurised fluid source to force the sealant along the leak path.

11. A process for the repair of a leak path in a tank according to claim 10 and wherein the sealant to be injected into the leak site is contained within the pressurisable reservoir in a precharged collapsible container.

12. A process for the detection and repair of a leak path in a tank substantially as hereinbefore described with reference to the accompanying specification and drawing.