Method for repairing wind turbine blades

Abstract

The invention relates to method repairing defect regions (401) which have developed during manufacturing of a wind turbine blade component (599). The method involves the steps of preparing a layered fiber material structure (600) for the wind turbine blade component; arranging a vacuum bag (402) over the layered fiber material structure; applying a vacuum assisted resin infusion process; recognizing a defect region below the vacuum bag which has not been sufficiently infused with resin; placing a piercing device on the vacuum bag; sealing an area covering the piercing device (501) and at least a part of the defect region with a repair bag (502) so that the repair bag forms an airtight envelope over the piercing device; piercing the vacuum bag with the piercing device; and extracting air out of the repair bag to force the resin from locations surrounding the defect region to flow into the insufficiently resin infused part of the layered fiber material structure.

Description

[0001] Method for Repairing Wind Turbine Blades

[0002] Technical Field

[0003] The present invention relates generally to the manufacture of wind turbine blades.

[0004] Background

[0005] Wind turbine blades may be manufactured using a vacuum assisted resin infusion process for forming the shells of the blade.

[0006] The blades may be manufactured from half shells which are bonded together along their leading and trailing edges using an adhesive. The process involves forming a blade shell layup in the mould by arranging fibrous reinforcing material in a mould together with other blade materials and components. The moulds are then covered with a vacuum bag, which may be sealed against a flange of the mould to form a sealed region encapsulating the blade shell layup. Air is evacuated from the sealed region and resin is admitted into the sealed region in order to fill the fibrous material with resin.

[0007] The resin infuses the fibrous reinforcing material and infiltrates between the various blade components. The resin is then cured such that it hardens and integrates the fibrous reinforcing material and other blade materials and components into a single structure, e.g. a half shell.

[0008] During the infusion process it may occur that the resin does not fill a region of the fibrous material or does fill the region sufficiently. Such regions may result in reduced structural strength. Consequently, it is important that the final wind turbine blades does not suffer from such defects due to dry spots which has not been sufficiently filed with resin.

[0009] EP3394430A1 refers to a vacuum infusion technique employing a rigid mould part and a resilient mould part in the form of a vacuum bag. Dry spots can be repaired after the process of filling the mould by puncturing the bag in the respective location and by drawing out air for example by means of a syringe needle. Liquid polymer can optionally be injected in the respective location, and this can for example be done by means of a syringe needle as well. EP3274159A1 discloses a method of repairing a subsurface defect comprising a void in a composite wind turbine component. The method comprises forming an inlet passage extending between the surface of the component and the void, forming an outlet passage extending between the surface of the component and the void, administering resin through the inlet and causing the resin to flow from the inlet towards the outlet such that the resin substantially fills the void. The inlet and outlet passages are each formed as a respective groove that extends longitudinally between first and second ends defined at the surface of the component.

[0010] Summary

[0011] It is an object of the invention to improve repair methods for repairing defects in wind turbine blades resulting from a vacuum assisted resin transfer moulding (VARTM) process, particularly to repair dry spots where the resin has not filled the fibrous material sufficiently.

[0012] In a first aspect of the invention there is provided a method for manufacturing a wind turbine blade component, the method comprises

[0013] - preparing a layered fibre material structure for the wind turbine blade component,

[0014] - arranging a vacuum bag in a vacuum tight manner over the layered fibre material structure,

[0015] - applying a vacuum assisted resin infusion process for infusing the layered fibre material structure with a resin,

[0016] - during or after the vacuum assisted resin infusion process, recognizing a defect region below the vacuum bag which is not sufficiently infused with resin,

[0017] - arranging a piercing device on the vacuum bag over the defect region, wherein the piercing device has a sharp part for piercing the vacuum bag,

[0018] - sealing an area covering the piercing device and at least a part of the defect region with a repair bag,

[0019] - extracting air out of the repair bag, and

[0020] - piercing the vacuum bag with the piercing device thereby enabling the resin to flow into the insufficiently resin infused part of the layered fibre material structure.

[0021] The term vacuum should be understood broader than the scientific understanding wherein vacuum may refer to a space which is substantially void of any matter. Herein the vacuum bag is understood as a bag or foil capable of maintaining an air pressure which is lower that the surrounding air pressure or lower than the surrounding atmospheric pressure. That is, the air pressure of the vacuum assisted resin infusion process should be low enough to make the resin flow through the layered fibre material structure. Similarly, by extracting air out of the vacuum bag, a low pressure is created under the repair bag to force the resin to flow to the defect region. Arranging a vacuum bag in a vacuum tight manner is intended to mean that the vacuum bag is e.g. sealed against a mould so that the sealing is capable of maintaining an air pressure which is lower that the surrounding air pressure. Thus, the sealing of the area covering the piercing device implies an airtight sealing so that a low pressure, lower than the surrounding pressure, or vacuum, can be created by extracting air out of the repair bag.

[0022] The repair method provides a simple but effective and reliable method for repairing dry spots in fibre material structures such as wind turbine blades or components for wind turbine blades.

[0023] According to an embodiment the piercing device is shaped to stand on the vacuum bag with the sharp part facing the vacuum bag and where the piercing device further comprises a smooth part opposite to the sharp part. The smooth part, e.g. a plane or curved surface is intended to face the inner side of the repair bag and to receive a pressing force to pierce the vacuum bag but without piercing the repair bag.

[0024] According to an embodiment, the piercing device is placed on the vacuum bag at a location where a resin permeable mesh is located between the vacuum bag and the layered fibre material structure. Thereby, the piercing device is located on the vacuum bag at a location where a resin permeable mesh is arranged below the vacuum bag or at least at a location, e.g. at an edge of the resin permeable mesh, so that at least a part of the piercing device is in contact with the resin permeable mesh. Thus, when the vacuum bag has been pierced the low pressure under the repair bag is in direct contact with the resin permeable mesh below the vacuum bag to provide an efficient air-passageway to force resin into the dry spot.

[0025] In an example, the piecing device is located approximately at the center of the defect region, but the piecing device may also be located near an edge of the defect region.

[0026] The repair bag may comprise a repair mesh and an airtight film. The repair mesh may be made from the same material as the resin permeable mesh or other material with similar properties. The airtight film may be arranged on top of the repair mesh and sized so that it extends beyond an outer perimeter of the repair mesh. According to an embodiment, the repair mesh is arranged so that it at least partially covers the piercing device. Advantageously, when the repair mesh covers the air suction opening and / or the piercing device, the air passageway from the envelope under the repair bag to air suction opening and thereby the resin permeable mesh is improved.

[0027] According to an embodiment, the sealing comprises applying a flexible adhesive material, such as an airtight material, which surrounds the piercing device and an air suction location where air is extracted out of the repair bag. The flexible adhesive material may further surround the repair mesh.

[0028] The low pressure or vacuum under the repair bag is obtained by use of an air extraction system which is connected to an air extraction pump to extract air out of the repair bag, e.g. via an air suction opening, such as an air extraction tube, arranged between the repair bag and the vacuum bag. Further, the air suction opening may be arranged below the repair mesh of the repair bag.

[0029] To prevent the repair bag to close around the air suction opening when air suction is applied a breather material, such as an air permeable material, may be arranged around the air suction opening.

[0030] To avoid that the resin reaches the air suction opening too soon when the air extraction is applied, the air suction opening may be arranged a distance from the piercing device. For example, the air suction opening and the piercing device may be arranged at opposite edges of the repair mesh.

[0031] A second aspect of the invention relates to a kit for repairing a defect region of a wind turbine blade component which has not been sufficiently infused with resin at the defect region, wherein the wind turbine blade component has been obtained by a process involving the steps of:

[0032] - preparing a layered fibre material structure for the wind turbine blade component,

[0033] - arranging a vacuum bag in a vacuum tight manner over the layered fibre material structure,

[0034] - applying a vacuum assisted resin infusion process for infusing the layered fibre material structure with a resin, wherein the kit comprises

[0035] - a piercing device having a sharp part for piercing the vacuum bag,

[0036] - a repair bag, - a flexible adhesive material configured to be applied between the repair bag and the vacuum bag to provide an airtight sealing,

[0037] - an air extraction system such as an air extraction hose configured to extract air out of the repair bag, wherein the kit is configured to be used in a method of the first aspect.

[0038] In general the various aspects of the invention may be combined and coupled in any way possible within the scope of the invention. These and other aspects, features and / or advantages of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

[0039] Brief description of the drawings

[0040] The present invention will now be described in further detail, by way of non-limiting example only, with reference to the following figures, in which:

[0041] Fig. 1 shows a horizontal axis wind turbine,

[0042] Fig. 2 shows one of the wind turbine blades,

[0043] Fig. 3 shows a mould for forming one of the half shells of a wind turbine blade,

[0044] Fig. 4 shows a portion of a vacuum bag sealed blade shell formed in a mould,

[0045] Fig. 5 shows a top view of a defect region in a layered fibre material structure of a wind turbine blade component, and

[0046] Figs. 6 and 7 show cross-sectional views of a defect region in the layered fibre material structure.

[0047] Detailed description

[0048] Fig. 1 shows a horizontal axis wind turbine 100. The wind turbine comprises a tower 101 a nacelle 102 on top of the tower and a rotor 103 arranged with nacelle. The rotor 103 comprises a plurality of wind turbine blades 104 that extend radially from a central hub 105. In this example, the rotor 103 comprises three blades 104.

[0049] Fig. 2 shows one of the wind turbine blades 104. The blade extends from a generally circular root end 201 to a tip end 202 in a longitudinal 'spanwise' direction, and between a leading edge 203 and a trailing edge 204 in a transverse 'chordwise' direction. The blade 104 comprises a shell 205 formed primarily of fibre-reinforced plastic (FRP). The shell 205 comprises a pressure surface 206 on a pressure side of the blade and a suction surface 207 on a suction side of the blade. In this example, the blade transitions from the root end circular profile to an airfoil profile moving from the root end of the blade towards a shoulder 208 of the blade, which is the widest part of the blade where the blade has its maximum chord. However, other blades may be designed differently e.g. without a shoulder part or a less pronounced shoulder part.

[0050] It should be noted that the proportions of the blade are exemplary illustrations and not necessarily representative of the shape of a blade produced in practice.

[0051] The shell 205 of the blade is fabricated from first and second half shells 210, 211. The first and second half shells 210, 211 are adhesively joined together along the leading edge 203 and the trailing edge 204. The half shells 210, 211 are laminated structures that are moulded from fibre reinforced plastic (FRP) including glass fibres and possibly carbon fibres.

[0052] The half shells 210, 211 are moulded in separate moulds of a blade body manufacturing system. Once each half shell 210, 211 has been moulded, the two half shells are brought together by bringing the two mould halves together, and the half shells 210, 211 are bonded together to form the complete blade 104. Structural elements, such as webs or spars, may be provided between the half shells.

[0053] Fig. 3 shows a mould 301 for forming one of the half shells 210, 211. The mould 301 comprises a mould root end 302 and a mould tip end 303. The half shell is formed on the mould surface 304 having a shape corresponding to the shape of the half shell to be formed. The mould surface extends substantially from the mould root end 302 to the mould tip end 303.

[0054] The mould 301 has flanges 310 which extend from the mould root end 302 to the tip end 303 along the sides of the mould corresponding the leading and trailing edges 203, 204. The mould surface 304 forms a recess between the mould flanges 310.

[0055] To form a half shell, one or more layers of fibre fabric sheets such as dry glass fibre sheets and possibly carbon fibre sheets are placed on the mould surface 304 of the mould 301 . These layers will later form an outer skin of the blade 104. Structural elements, including spar caps and sandwich core panels may be arranged on top of the outer fabric layers. One or more further layers of glass-fibre fabric sheets are then placed over the structural elements and will later form an inner skin of the blade 104. The fibre layers forms a layered fibre material structure 600. The fibre material structure is then impregnated with a resin, which is subsequently hardened to form a solid plastic material. Such an impregnation can be done with a vacuum assisted resin transfer moulding (VARTM) process.

[0056] It is understood that alternatives for forming the blade shell are possible. For example, layers of pre-preg glass fibres, i.e. glass fabric sheets impregnated with polymer resin, may be used. Further, instead of forming the blade from two half shells, it is also known to form wind turbine blades in a single piece which avoids adhesive bonds between blade shells.

[0057] Fig. 4 principally illustrates a portion of the vacuum bag sealed blade shell 211 formed on the mould surface 304 in the mould 301. The vacuum assisted resin transfer moulding process involves the steps of arranging a vacuum bag 402 over the layered fibre material structure 600 so that the vacuum bag forms a vacuum tight enclosure of the entire layered fibre material structure 600.

[0058] The vacuum bag 402 which may be a plastic film may be sealed against surfaces of the mould such as against the flange 310 and end surfaces of the mould root end 302 to define a sealed region encapsulating the fibre material structure. In order to improve the flow of the resin, a resin permeable mesh 601 may be arranged between the vacuum bag and the upper layer of the fibre material 600. The resin permeable mesh 601 allows the low air pressure to be distributed and improves the distribution of resin.

[0059] The vacuum assisted resin infusion process further involves arranging an air extraction system (not illustrated) such as a vacuum hose to extract air out of the envelope sealed by the vacuum bag 402, i.e. the vacuum sealed fibre material structure 600. The air extraction system is connected to a vacuum pump which is operated to extract air from the sealed air volume under the vacuum bag 402. Resin is admitted into the sealed region e.g. via supply tubes and is drawn towards the air extraction locations under the vacuum bag where air is sucked out. In this way the resin infuses throughout the fibre material aided in part by the vacuum pressure within the sealed region.

[0060] Once the resin infusion process is complete, the next stage in the process involves curing the resin. This involves a heating process by any suitable heating method whereby the infused resin is cured. During or after the vacuum assisted resin infusion process a defect region 401 which is or has not been sufficiently infused with resin, often referred to as a dry spot, may be observed below the vacuum bag.

[0061] The fibre sheet layup method and vacuum assisted resin infusion process it not limited to whole wind turbine blades or whole blade shells but may be applied to wind turbine blade components 599 in general, e.g. components such as pre-forms which are premanufactured for use in a wind turbine blade or for use in the manufacturing of a wind turbine blade.

[0062] Fig. 4 principally illustrates that the blade shell 211 has a defect region 401 which is visible through the vacuum bag 402. The defect region distinguishes from the surrounding area e.g. in terms of the darkness of the fibre material below the vacuum bag 402. Thus, the defect region 401 is caused by a lack of resin in a volume of the fibre material below the vacuum bag.

[0063] A method for repairing the defect 401 involves a local extraction of air directly from the defect region 401. The local extraction of air forces resin from the surrounding area to flow into the fibre material in the defect region 401 and thereby fills the defect region with resin.

[0064] Reference is now made to Fig. 5 and Fig. 6 for illustrating examples of the invention.

[0065] Fig. 5 shows a top view of the defect region 401 in the layered fibre material structure 600 for a wind turbine blade component 599 such as the blade shell 211 after a piercing device 501 , a repair bag 502, and an air extraction member 504 has been arranged according to the method described below.

[0066] Thus, the repair method of an embodiment involves placing a piercing device 501 on the vacuum bag 402 over the defect region 401. The piercing device may be any component which is capable of tearing or piercing through the vacuum bag. The piercing device 501 is shaped to stand on the vacuum bag, e.g. in an upright position, with the sharp part facing the vacuum bag 402. For example, the piercing device may have at least three sharp legs so that the legs can stand on the vacuum bag 402 and cut through the vacuum bag when a force is applied. The piercing device 501 may have a smooth part opposite to the sharp part where the smooth part is arranged to receive a pressing force, e.g. from the palm of a hand, without piercing the repair bag 502. Thus, the piercing device 501 , when arranged standing one the vacuum bag 402, is merely sandwiched between the vacuum bag 402 and the repair bag 502 with the smooth side facing the repair bag 502.

[0067] The piercing device 501 may be hold in place, e.g. when it is placed on steep sides, by any sticky material, e.g. sealant tape.

[0068] The air extraction member 504 may be configured as an air extraction hose 504a which is led under the repair bag 502 and airtightly sealed against the repair bag 502. For example, the air extraction hose may be led through an opening in the repair bag 502 or led under the repair bag from the edges thereof. It is also possible that the air extraction member 504 is integrated with the repair bag 502, e.g. the air extraction hose may be integrally formed with the repair bag 502. In general the air extraction member 504 is arranged to enable extraction of air from the volumed enclosed by the repair bag 502.

[0069] A breather material (not shown) may be arranged around an air suction opening 505 of the air extraction member 504 to prevent the repair bag 502 to close around the air suction opening 505, i.e. to prevent that the airtight film clogs the air passageway to the extraction hose 504a.

[0070] The repair bag 502 is sealed against the vacuum bag 402 with a flexible adhesive material 503, e.g. a self-adhesive material such as a sealant tape, having airtight properties. The sealing material 502 is arranged so that it surrounds the piercing device 501 and an air suction location 505 where air is extracted out of the repair bag 502, i.e. where air is extracted out from the volume sealed by the repair bag 502. The air suction location 505 may correspond to an end-opening of the air extraction hose 504a.

[0071] The sealing material 503 is applied so that the sealing material forms a closed, airtight, sealing bead which surrounds the piercing device 501 and the air suction location 505 where air is extracted out of the repair bag 502. Thus, the repair bag 502, the sealing material 503, and the main vacuum bag 402 forms an airtight or substantially airtight envelope from which air can be extracted via the air extraction part member 504. The air extraction member 504 is connected to an air extraction pump 610, to extract air out of a volume under of the repair bag 502 and out of a volume under the vacuum bag 402 via a hole in the vacuum bag pierced by the piercing device 501.

[0072] The air extraction pump 610 may be the same used for extracting air out of the vacuum bag 402 as described above or it may be a different air extraction pump.

[0073] Fig. 6 shown a cross-sectional view of the defect region 401 in the layered fibre material structure 600. The upper surface of layered fibre material structure 600 is optionally covered with one or more sheets of a resin permeable mesh 601 for improving distribution of the resin. The vacuum bag 402 is arranged over a part of the resin permeable mesh 601 and the layered fibre material structure 600 in a vacuum tight manner so that an air pressure lower than the surrounding air pressure can be established in the closed envelope of the vacuum bag 402 and the mould surface 304.

[0074] Fig. 6 shows that the entire area below the repair bag 502 is covered by the resin permeable mesh 601, however, in another example the repair bag 502 may be located at an edge of the resin permeable mesh 601 so that the resin permeable mesh only covers a fraction of the area below the repair bag 502. The mould surface 304 and the sealing of the vacuum bag 402 against the mould such as the mould flanges 310 is not shown in Fig. 6 but an example is shown in Fig 4.

[0075] The piercing device 501 is placed on the vacuum bag 402 or otherwise arranged in relation to the surface of the vacuum bag 402 so that the sharp part of the piercing device can cut through the vacuum bag 402 when a pressing force is applied to the piercing device, e.g. by hand pressure.

[0076] Preferably, the piercing device 502 may is located on the vacuum bag 402 at a location where a resin permeable mesh 601 is arranged below the vacuum bag 402 or at least at a location, e.g. at an edge of the resin permeable mesh 601 , so that a part of the piercing device is in contact with the resin permeable mesh 601.

[0077] The repair bag 502 is arranged over at least a part of the of defect region 401. The repair bag 502 comprises an airtight film 602 and optionally a resin permeable mesh 603 such as a sheet of an open structured material. The resin permeable mesh 603 used for the repair bag 502 may be made from the same material as the resin permeable mesh 601 used for the vacuum bag 402. Accordingly, both resin permeable meshes 603, 601 can be named equally. The resin permeable mesh 603 used for the repair bag 502 is also referred to as the repair mesh 603.

[0078] Thus, the repair mesh 603 may be connected to the film 602 or it may be a separate mesh element which is initially arranged on the vacuum bag 402 over the defect region 401 and subsequently covered by the film 602.

[0079] The repair bag 502 may be configured so that the airtight film 602 extends beyond an outer perimeter of the repair mesh 603. Thereby, the airtight film 602 forms a rim around the repair mesh 603 onto which the flexible adhesive 503 can be attached to.

[0080] The piercing device 502 may be located on the vacuum bag 402 at a location away from the repair mesh 603 e.g. below the rim of the airtight film 602. In other example shown in Fig. 7, the piercing device 502 and the repair mesh 603 is arranged so that the repair mesh 603 at least partially covers the piercing device. In this case the repair mesh 603 overlays the smooth part of the piercing device 502 or overlays at least a part thereof, i.e. the repair mesh 603 may be arranged between the film 602 of the repair bag 502 and the piercing device 502. In this example and other examples of the invention, the air extraction hose 504a may be arranged below the repair mesh 603, i.e. so that the repair mesh also covers the air suction opening 505. Advantageously, configurations where the repair mesh covers the air suction opening 505 and / or the piercing device 502, the air passageway between the piercing device 502 and air suction opening is improved.

[0081] Illustrating examples of the repair bag 502 may have largest dimensions less than 200 cm and smallest dimensions greater than 5 cm. However, other dimensions are possible. Examples of typical dimensions include 20cmx30cm, 30cmx40cm, 40cmx50cm, 50cmx70cm, 60cmx80cm and 80cmx100c.

[0082] The flexible adhesive 503 may be arranged to that it surrounds the repair mesh 603. Thus, the repair mesh 603 may be arranged so that it is not in contact with the adhesive flexible material 503, but rather separated therefrom.

[0083] As illustrated in Fig. 6 and Fig. 7, the air extraction hose 504a is arranged under the repair bag 502 such as under the airtight film 602. Preferably, the air extraction hose 504a or the air suction opening 505 of the hose is arranged at a distance from the piercing device 501 in order to maximize the delay of the resin travel time from the hole in the sealing bag 402 made by the piercing device 501 to the air suction location 505 such as the opening of the air extraction hose 504a. If an air extraction hose 504a is used it may be sealed against the vacuum bag 402 and the repair bag 502, e.g. by use of the flexible adhesive material 503.

[0084] According to the method for manufacturing a wind turbine blade component as described herein, i.e. the repair method, in an example of carrying out the method, after the piercing device has been arranged and the repair bag 502 has been sealed air is initially extracted out of the repair bag 502 using the air extraction system 504. Only after air has been extracted out from the sealed envelope of the repair bag 502, the vacuum bag 402 is pierced. This specific order avoids an air flow into the defect region 401 of the layered fibre material structure 600 when the vacuum bag 402 is pierced. However, the repair method may also be performed in the opposite order by piercing the vacuum bag 402 before the air extraction from the repair bag 502 is applied.

Claims

Claims1. A method for manufacturing a wind turbine blade component (599, 211), the method comprises- preparing a layered fibre material structure (600) for the wind turbine blade component,- arranging a vacuum bag (402) in a vacuum tight manner over the layered fibre material structure,- applying a vacuum assisted resin infusion process for infusing the layered fibre material structure with a resin,- during or after the vacuum assisted resin infusion process, recognizing a defect region (401) below the vacuum bag which is not sufficiently infused with resin,- arranging a piercing device (501) on the vacuum bag over the defect region (401), wherein the piercing device has a sharp part for piercing the vacuum bag,- sealing an area covering the piercing device (501) and at least a part of the defect region (401) with a repair bag (502),- extracting air out of the repair bag (502), and- piercing the vacuum bag with the piercing device (501) thereby enabling the resin to flow into the insufficiently resin infused part of the layered fibre material structure (600).

2. A method according to claim 1, wherein the piercing device (501) is shaped to stand on the vacuum bag (402) with the sharp part facing the vacuum bag (402) and where the piercing device further comprises a smooth part opposite to the sharp part.

3. A method according to any of the preceding claims, comprising placing the piercing device (501) on the vacuum bag (402) at a location where a resin permeable mesh (601) is located between the vacuum bag (402) and the layered fibre material structure (600).

4. A method according to any of the preceding claims, wherein the repair bag (502) comprises a repair mesh (603) and an airtight film (602).

5. A method according to claim 4, wherein the repair bag (502) is arranged so that the airtight film (602) extends beyond an outer perimeter of the repair mesh (603).

6. A method according to any of the preceding claims, wherein the repair mesh (603) is arranged so that it at least partially covers the piercing device (501).

7. A method according to any of the preceding claims, wherein the sealing comprises applying a flexible adhesive material (503) which surrounds the piercing device and an air suction location (505) where air is extracted out of the repair bag (502).

8. A method according to claim 7, wherein the adhesive flexible material (503) further surrounds the repair mesh (603).

9. A method according to any of the preceding claims, comprising arranging an air extraction system (504), which is connected to an air extraction pump (610), to extract air out of the repair bag (502).

10. A method according to claim 9, wherein an air suction opening (505) of the air extraction system (504) is arranged between the repair bag (502) and the vacuum bag (402).

11. A method according to any of claims 9-10, wherein a breather material is arranged around the air suction opening (505) to prevent the repair bag (502) to close around the air suction opening (505).

12. A method according to any of claims 9-11 , comprising placing the air suction opening (505) at a distance from the piercing device (501).

13. A kit for repairing a defect region (401) of a wind turbine blade component (599, 211) which has not been sufficiently infused with resin at the defect region, wherein the wind turbine blade component has been obtained by a process involving the steps:- preparing a layered fibre material structure (600) for the wind turbine blade component,- arranging a vacuum bag (402) in a vacuum tight manner over the layered fibre material structure,- applying a vacuum assisted resin infusion process for infusing the layered fibre material structure with a resin, wherein the kit comprises- a piercing device (501) having a sharp part for piercing the vacuum bag,- a repair bag (502),- a flexible adhesive material (503) configured to be applied between the repair bag and the vacuum bag to provide an airtight sealing,- an air extraction system (504) such as an air extraction hose (504a) configured to extract air out of the repair bag, wherein the kit is configured to be used in a method of claim 1.

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