Abstract:
A weld seam monitoring apparatus includes a layer of sealant applied to the area surrounding the weld seam; a first layer of sheet material adapted to provide an air space and overlying the weld seam; a second layer of sheet material overlying the first layer of sheet material; and a fluid impermeable sealant overlying the second layer of sheet material. An air tight space is formed between the second layer of sheet material and the weld seam. The apparatus further includes a vacuum source, and the air tight space is in fluid communication with the vacuum source. The apparatus further includes vacuum monitoring means configured to monitor the status of a vacuum created in the air tight space.

Description:
FIELD OF THE INVENTION 
       [0001]    The present disclosure relates to an apparatus and method for monitoring a weld seam, and in particular to an apparatus and method for continuously monitoring a weld seam. 
       BACKGROUND OF THE INVENTION 
       [0002]    Weld seams are known to be a possible source of weakness in a welded structure. It is therefore common practice to inspect welds for signs of fatigue in order that any deterioration in the weld may be repaired before the weld, and possibly the structure of which the weld forms a part, fails. 
         [0003]    Typically, welds are monitored for fatigue and signs of failure by carrying out manual inspections of the welds at pre-determined time intervals. 
         [0004]    In some environments carrying out such inspections can be a costly exercise. For example, in the case of wind turbine towers, and in the case of offshore wind turbines the mono-piles on which they stand, it is necessary for personnel to enter the turbine tower and/or mono-pile. For off-shore wind turbines a special service vessel must be deployed to take the personnel out to sea. Further, personnel may only be deployed onto off-shore wind turbines when the sea conditions are favourable. 
         [0005]    In an off-shore wind turbine the mono-pile is intended to be sealed against ingress of water. However, in practice water is found to penetrate the mono-pile. In such a scenario the mono-pile must be pumped free of water before inspection of the welds may begin or inspection must be performed by and ROV with the water in situ, or a diver inspecting visually from outside the mono-pile. 
         [0006]    Whilst periodic inspection of welds may be adequate, the mono-piles and towers upon which wind turbines are mounted are subject to varying loads causing the mono-pile and tower to repeatedly bend. It is well understood that structures subject to cyclic loading are more likely to fail over time than structures subject only to static loads. 
         [0007]    It would therefore be desirable to provide an apparatus and method that allows weld seams to be monitored constantly, rather than periodically. Further, it would be desirable to provide an apparatus and method that allows the weld seams of a structure to be monitored remotely. 
         [0008]    It would also be desirable to provide an apparatus that not only provides for monitoring of the integrity of a weld seam, but also will protect the structure against ingress of matter through a failed weld seam. 
         [0009]    The apparatus and method described herein will be useful not only in relation to wind turbine towers and mono-piles. There are many structures which have critical welds and which require monitoring, either due to their remote location or because they are older than their expected service life. For example, parts of oil rigs, pressure vessels, platform structures, etc. 
       SUMMARY 
       [0010]    According to one aspect of the invention, there is provided a weld seam monitoring apparatus as specified in claim  1 . 
         [0011]    According to another aspect of the invention, there is provided a structure as specified in claim  16 . 
         [0012]    According to an additional aspect of the invention, there is provided a method of fabricating a weld seam monitoring apparatus as specified in claim  18 . 
         [0013]    Features of the invention are set out in the claims dependent on claims  1 ,  16  and  18  and in the description and drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    In the drawings, which illustrate preferred embodiments of a weld monitoring apparatus: 
           [0015]      FIG. 1  is a side view of an off-shore wind turbine mono-pile and tower; 
           [0016]      FIG. 2  is an exploded view of a part of the mono-pile illustrated in  FIG. 1 ; 
           [0017]      FIG. 3  is a cross-section through a part of the weld seam monitoring apparatus; 
           [0018]      FIG. 4  is an exploded view of the components of the weld seam monitoring apparatus shown in  FIG. 3 ; 
           [0019]      FIG. 5  is a plan view of a weld seam with some of the components of the weld seam monitoring apparatus attached thereto; and 
           [0020]      FIG. 6 a    illustrates another embodiment of the weld seam monitoring apparatus; and 
           [0021]      FIG. 6 b    illustrates a derivative of the embodiment illustrated in  FIG. 6   a.    
       
    
    
     DETAILED DESCRIPTION 
       [0022]    Referring now to  FIG. 1 , there is shown an off-shore wind turbine support structure comprising a mono-pile structure  3  attached to the sea bed  1  and extending above the water line  2 . A turbine mounting tower  4  is mounted on the mono-pile above the water line  2 . 
         [0023]    In the illustrated example, both the mono-pile and the turbine are constructed in a similar manner. In the case of the mono-pile  3 , this is made up of a number (four in the illustrated example) of steel rings  3   a,  formed by rolling a sheet of flat steel into a ring and welding the abutting faces of the sheet along weld seam  3   c.  The steel rings  3   a  are stacked one on top of the other, with the weld seam  3   c  of one steel ring  3   a  out of line with the weld seam  3   c  of the weld seams  3   c  of the adjacent steel rings. 
         [0024]    Adjacent steel rings  3   a  are welded together along weld seams  3   b.    
         [0025]    The tower  4  is constructed in a similar fashion, with steel rings  4   a  being formed by rolling a flat sheet of steel and welding the ends thereof along weld seam  4   c,  with the weld seam  4   c  of one steel ring  4   a  out of line with the weld seams  4   c  of adjacent steel rings  4   a.  Adjacent steel rings  4   a  are welded together along weld seams  4   b.    
         [0026]    The lower most steel ring  4   a  of the tower  4  is attached to the upper most ring  3   a  of the mono-pile. This may be achieved by welding the two components together, or by attaching each component to and intermediate structure. 
         [0027]    As can be seen from  FIG. 1 , most of the mono-pile  4  lies below the water line  2 . The inside of the mono-pile is supposed to be free of water. However, in practice, many mono-piles leak and fill with water. Leakage may begin to occur immediately from installation due to welds seams  3   c  being porous. The porosity may not be noticeable by visual inspection. Alternatively, the weld seams may be impervious upon installation of the mono-pile and may become porous due to corrosion or due to the loads imposed upon the mono-pile during use. For example: the salt water to which the mono-pile is exposed may cause the weld seams  3   c  to corrode; or the cyclic loading experienced by the mono-pile may cause weld seams  3   c  to crack. 
         [0028]    The same can be said of the tower  4 , save that if the weld seams become porous the tower  4  will not fill with water since it sits above the water line. However, if the weld seams  4   c  become porous, atmospheric moisture which in the case of an off shore wind turbine will be salt laden may enter the inside of the tower  4 , and in very heavy seas, sea water itself may enter the tower via porous weld seams  4   c.    
         [0029]    As explained above, inspecting weld seams is a costly exercise, and further, using a monitoring programme comprising periodic visual inspections, deterioration in a weld seam will inevitably not be noticed until some time after it has occurred. 
         [0030]    The apparatus provides for the continuous monitoring of weld seams. This is achieved by creating a monitorable interstitial space over the weld seam and exerting that space to a vacuum. If the weld seam becomes porous, the vacuum will not be held and an alarm will sound. The alarm may be located on shore. The advantage of this system is that the failure in the weld seam is noticed immediately that it occurs, so a maintenance team can be deployed to the wind turbine as soon as possible to repair the weld. Also, the manual inspection programme may be significantly reduced or eliminated, thereby reducing maintenance costs. Since it is only possible to board the wind turbine structures in seas below a certain swell threshold, any reduction in the requirement to board the structures is advantageous. 
         [0031]    In order to create a space which may be subject to a vacuum, the area of and around the weld seam must be covered and sealed, whilst providing a space between the inner surface of the weld seam and the material covering the weld seam. 
         [0032]    In  FIG. 2 , the weld seams  3   b  and  3   c  are covered by a structure  10 ,  10 ′ respectively. 
         [0033]      FIG. 3  illustrates the construction of the structures  10 ,  10 ′, and the method of forming the structures  10 ,  10 ′ will be described with reference to this Figure. 
         [0034]    The weld seam  3   a  is prepared back to bare metal and repaired if necessary. This may be done using any know technique. The area prepared back to bare metal extends just beyond the weld seam, for example 50 mm to each side of the edge of the weld seam. A layer of sealant  11  is then applied to the prepared area around the edge of the weld seam. The sealant may be urethane for example, or an epoxy sealant. Advantageously, the sealant is solvent free. The sealant may be a two component sealant that is mixed prior to application, and may be a sealant that requires heating prior to application in order to reduce its viscosity. 
         [0035]    The sealant is allowed to cure. A layer of adhesive is attached to the cured sealant. In the illustrated example, this is achieved by mounting sheet material  12 , such as paper, that is either coated on both sides with adhesive or impregnated with adhesive such that both sides of the sheet material have adhesive properties. The sheet material  12  has an opening  12   a,  the shape and dimension of which opening corresponds to the shape and dimension of the weld seam. 
         [0036]    For ease of use, the sheet material  12  is preferably supplied with peel off layers of material on each side of the material  12 . In this way the material  12  may be supplied on a roll without the material adhering to itself. To apply the sheet material  12  to the cured layer of sealant  11 , an appropriately sized piece of sheet material  12  is taken, an opening  12   a  corresponding in shape and dimension to the shape and dimension of the weld seam is cut out of the sheet material. Alternatively, the sheet material  12  may be supplied with the opening  12   a  pre-formed therein. For example, if the weld seams are known to be of 100 mm in width, the material  12  may be supplied with an opening of 150 mm in width. The peel off layer (if provided) is removed from one side thereof, and the material is placed onto the surface of the sealant  11 . The sheet material  12  is prepared such that it is slightly smaller than the area covered with sealant  11 . Such a pre-formed sheet material  12  is illustrated in  FIG. 5  which shows the prepared weld seam  3   c,  the prepared area around the weld seam to which sealant  11  has been applied, and the sheet material  12  attached around the weld seam  3   c  and on the sealant  11 . In this Figure a space exists between the inner edge of the opening  12   a  and the peripheral edge of the weld seam  3   c.    
         [0037]    If both sides of the sheet  12  were covered with a peel off layer, the remaining peel off layer is removed. 
         [0038]    Next a layer of mesh  13  is applied to the adhesive surface of the sheet material  12 . The mesh  13  is prepared such that its peripheral shape and dimension matches substantially the peripheral shape and dimension of the sheet  12 . It is this mesh  13  that provides the space which may be subject to a vacuum. The mesh will be described in greater detail with reference to  FIG. 4 . 
         [0039]    The mesh  13  is next covered with a layer of fluid impervious sheet material, which in the example is a layer of aluminium foil  14 . The aluminium foil  14  is prepared such that its peripheral shape and dimension is substantially the same as the shape and dimension of the mesh  13 . The aluminium foil is adhered to the mesh  13  with the each edge of the aluminium foil substantially co-terminus with the edge of the mesh  13 . 
         [0040]    In this example, the aluminium foil has adhesive on one side thereof and is this is covered with a peel off layer. Hence, the peel off layer is removed and the aluminium foil is applied and attached to the free surface of the mesh  13 . 
         [0041]    The foil  14  is then covered with a layer of cloth  15 , which is glass fibre cloth in this example. The cloth  15  is attached to the foil  14  by adhesive, which in the example is provided as a covering to the glass fibre cloth  15 . The glass fibre cloth may have a peel off layer covering the adhesive. If so, the peel off layer is removed and the adhesive face of the glass fibre cloth  15  is presented up to and pressed on to the foil  14 . The glass fibre cloth is prepared such that its shape and dimension matches the shape and dimension of the foil  14 . 
         [0042]    The final step in creating the structure  10 ,  10 ′ involves applying a sealant  16  to the glass fibre cloth  15  and around the cloth  15  over the sealant  11  around the weld seam. Where the mesh  13  sits on top of the layer of sheet material  12 , the sealant  16  seals the edges of the mesh and other layers of sheet material, such that all the components of the structure  10 ,  10 ′ are encapsulated in the sealant  16 . The sealant  16  is preferably the same as or of the same family as the sealant  11 . For example, if the sealant  11  is urethane based, it is preferred that the sealant  16  is also a urethane based, whereas if the sealant  11  is epoxy based, it is preferred that the sealant  16  is epoxy based. 
         [0043]    As can be seen from  FIG. 3 , the sealant  16  is taken over the edge of the sheet materials  12  to  15  so that the edges thereof are sealed. 
         [0044]    Referring now to  FIG. 4 , it can be seen that the mesh  13  is made up of strands of material  13   a  extending in one direction and strands of material  13   b  extending substantially perpendicularly to the strands  13   a.  The strands  13   a  and  13   b  lie in two different planes. Hence, and air space is formed between the lower surface of strands  13   a  and the upper surface of strands  13   b.    
         [0045]    In another embodiment, the mesh  13  is formed such that its peripheral shape and dimension corresponds to the internal shape and dimension of the opening  12   a.  The mesh  13  is then placed within the opening  12   a.  The remaining layers are applied in the same manner as described above. Hence, peripheral shape and dimension of the layer  14  corresponds to the peripheral shape and dimension of the layer  12 , and so on. 
         [0046]    If the weld seam cracks or otherwise becomes porous, the vacuum applied to the interstitial space formed between the weld seam and the layer of fluid impervious material covering the mesh layer  13  will fail and an alarm will be sounded. 
         [0047]      FIG. 6 a    illustrates another embodiment of the invention. In this embodiment, instead of the layer  16  being formed by a sealant that is applied as a liquid, the sealant provided by the layer  16   a  comprises a fluid impervious tape that has adhesive on one side thereof. The adhesive is provided on the side of the tape facing the weld that is to be monitored. 
         [0048]      FIG. 6 b    illustrates a derivative of the embodiment illustrated in  FIG. 6 a   . In the  FIG. 6 b    example the layer  15  has been omitted and the tape  16   a  applied directly over the fluid impervious layer  14 . 
         [0049]    Referring to  FIG. 2 , the interstitial spaces provided by each of the structures  10 ,  10 ′ are not inter-connected. Hence, failure of the vacuum in one of the structures does not cause the vacuum in any of the other structures  10 ,  10 ′ to fail. In this way, the location of a weld seam failure may be determined. If the interstitial spaces provided by each of the structures  10 ,  10 ′ were inter-connected, a failure in a weld seam would be connected, but the position of the failed weld seam would have to be confirmed by other means. 
         [0050]    It may be practical to inter-connect groups of structures  10 ,  10 ′. In this way, the number of interstitial spaces requiring monitoring can be kept to a minimum, but a weld seam failure could be isolated to being one of a certain group of weld seams. In this way, less inspection time would be required to confirm the particular failed weld seam. 
         [0051]    A device  20  is provided for creating a vacuum in the structures  10 ,  10 ′ and relaying sensed information to a remote monitoring station. The device  20  has a number of vacuum lines  21  extending therefrom, each attached to a respective one of the structures  10 ,  10 ′. When the device  20  is switched on a vacuum is created in the structures  10 ,  10 ′ via the vacuum lines  21 . Information as to the status of the vacuum in each line  21  and hence structure  10 ,  10 ′ to which it is connected is monitored by the device and that information is relayed to a remote monitoring station via a radio antenna  22 . Alternative means of relaying the monitored information to a remote monitoring station may be used. 
         [0052]    In addition to providing for monitoring the integrity of the weld seam, the apparatus also protects the weld seam from attack by corrosive elements. For example, in the case of the mono-pile, if there is a failure of a weld seam resulting in ingress of water to the mono-pile, the structures  10 ,  10 ′ will protect the weld seams which have not failed against the salt laden sea water, and in the case of the tower  4 , the weld seams will be protected from salt laden air which may pass through failed weld seams. 
         [0053]    The apparatus and method provide a convenient means of monitoring weld seams, which is of particular use in relation to towers and mono-piles supporting wind turbines. However, the apparatus and method is not limited to monitoring the integrity of weld seams in wind turbine supporting structures. The apparatus and method could be useful for monitoring the integrity of weld seams in many welded structures, particularly where access is restricted. For example, the legs of oil rigs, bridge components, ship hulls, etc.