Patent Grant
9305469
The present invention relates to a subsea antifouling sign, and to a method of mounting a subsea antifouling sign on a structure to be located subsea. Aspects of the invention relate to methods of forming a subsea antifouling sign and subsea structures having such signs mounted thereon.
Signs incorporating visual characters such as numerals, letters, words, phrases, sentences or other indicia are utilised in offshore aquatic environments such as subsea locations, for marking or providing information about an object located below the surface or on the seabed. Such signs have particular utility in the oil and gas exploration and production industry. Aquatic growth, such as barnacles, algae and other aquatic vegetation is a problem in these environments, and can cause fouling of the signs so that they become illegible.
In an effort to overcome these problems, polymeric anti-fouling silicone-based compositions were developed in the 1980s which resist such aquatic growth, as disclosed for example in European Patent Publication No. 0171110. Signs manufactured from or incorporating these materials comprise a semi-compatible lubricant, which has a tendency to leach out from the surface of the sign in use, thereby preventing aquatic growth and fouling of the sign.
International Patent Publication No. WO 2005/042220 discloses a moulding method and apparatus used in the manufacture of anti-fouling signs. In general terms, the signs are manufactured by constructing a mould; forming a character template on a surface of the mould; pouring a silicone material into the mould to form visual characters defined by the template; partially curing the characters; removing the template; coupling a backing sheet to the mould; inclining the mould from the horizontal; pouring a relief, substrate silicone material (of a different colour) into the mould through a small aperture; curing the sign; and then releasing the completed sign from the mould. Whilst signs manufactured according to this method function well in terms of resisting aquatic growth, there are various disadvantages or problems associated with the moulding method and the resultant signs.
In particular, the nature of the materials used to manufacture the signs creates difficulties in bonding the signs to a subsea object. To address this, the signs incorporate a backing layer with an irregular surface. A preferred sheet is of a type including loops, such as those provided on hook-and-loop fastener sheets, sold under the VELCRO® Trade Mark. During manufacture of the sign, the silicone material forms a mechanical connection with the loops on the backing layer. The completed sign may then be attached to an object to be located subsea using a suitable adhesive which bonds to the backing layer. However, a thin layer of a plastic material is provided on the backing sheet on the surface opposite that bearing the loops, to prevent uncured silicone from seeping through the VELCRO® sheet during manufacture.
This thin layer of plastics material can be easily detached from the backing sheet, reducing mechanical strength of the sign, in use. Furthermore, the backing layer adds to the manufacturing time and cost of the sign, and reduces flexibility.
Employing an adhesive to mount polymeric antifouling markers can provide satisfactory results if carried out correctly. However, the success of the bond depends upon the skill and knowledge of the individual carrying out the process. If the methods are not carried out correctly then a weaker than expected bond forms between the marker and the subsea structure which can result in the marker becoming detached from the subsea structure such that the associated information contained on the marker is lost. Adhesives for subsea use are often formed by mixing two components, for example a two-part polyurethane-based adhesives. The adhesive bonding system commercially available from Champion Environmental Techologies under the trade mark AQUAHESIVE™ is an example of such a system, and has an accepted operational lifetime subsea of around 50 years.
With two-part adhesive systems incorrect mixing can compromise the effectiveness of the adhesive. Even if correctly mixed, the adhesive has a limited useful period during which it can be applied, which may not be more than thirty or forty minutes. This means that individuals may attempt to use the subsea adhesives at the end of their useful lifetimes, which results in poor adhesion of the subsea markers. The adhesive needs to be carefully applied, with incorrect application resulting in a deficient bond. Furthermore, if the adhesion process is carried out on land then a number of factors have been found to weaken the bond, e.g. heat and humidity.
These adhesion issues are exacerbated due to the harsh conditions in which the markers operate. Accessing the subsea structures, e.g. for intervention or maintenance purposes, typically requires the use of divers and/or remotely operated vehicles (ROV). It is common for the diver or the ROV to come into contact with the marker when trying to read the information carried by the marker. This can act to damage the marker or completely dislodge the marker if not properly bonded with the subsea structure. In practice, it is found that if the edge of a polymeric antifouling marker is damaged then this acts as a point of weakness within the marker which can result in further tearing or disintegration of the marker.
The subsea structures and markers are also required to be cleaned during their operating lifetimes. Typically this is achieved by the employment of high pressure (5000 psi) water jet cleaning systems. A marker can be damaged by such a process or, if incorrectly bonded, the marker can be dislodged as a result of the jet washing process.
An additional problem with many of the prior art mounting arrangements is that corrosion of the subsea structure may be caused or accelerated by a volume of static or stagnant salt water between the subsea structure and the subsea antifouling sign.
One approach to mounting polymeric antifouling signs is to manufacture them in the form of a tag wherein apertures are formed in the backing substrate of the sign (
Mountings of the type in
Another method of using polymeric antifouling signs is described in UK patent publication number GB 2473526. The method provides a backing member and a fixing frame which attaches to the backing member to secure the perimeter of the antifouling marker between the fixing frame and the backing member. Whilst this method is convenient to protect the antifouling marker and the identification tag from physical damage, it has other drawbacks such as involving multiple fabrication and assembly steps, the need of skilled labour to weld the fixing frame to the backing member, and the additional cost of the mount. In addition, the system of GB 2473526 uses bolts. There is a perception that the bolts may become loose over time and potentially damage paints or coatings on the structure. There may also be concerns about the long term effects caused by the inside of bolt holes not being protected by corrosion resistant coatings or paint schemes.
GB 2434022 describes an alternative mounting method for subsea antifouling signs wherein a silicone-based adhesive compatible with the material of the subsea antifouling sign is used.
It is an object of an aspect of the present invention to obviate or at least mitigate the foregoing disadvantages of previous methods of mounting a subsea antifouling sign to a subsea structure. Another object of the invention is to provide an easy, reliable and fast method of mounting a subsea antifouling sign to a subsea structure. A further object of the invention is to provide a subsea antifouling sign mounted on a subsea structure which is securely attached to the subsea structure for extended periods of time in the harsh conditions encountered in subsea environments. Further aims of the invention will become apparent from the following description.
According to a first aspect of the invention, there is provided a method of mounting a subsea antifouling sign to a structure to be deployed subsea, the method comprising the steps of:
providing a subsea antifouling sign, the sign comprising:
The above-described method simplifies the mounting of the sign compared with the methods known in the art. It reduces the time needed to mount the sign, and does not rely on additional mounting components. The method uses a sign in which the adhesive is applied (and protected) in a controlled manner before the installation of the sign. The method does not rely on application of an adhesive by installation personnel, and therefore problems with inconsistent or inadequate use of adhesives are avoided. Health and safety concerns associated with the handling and use of adhesives are mitigated or avoided by the application of the adhesive in an earlier manufacturing step.
The method provides mounting which is likely to be more consistent (and therefore more reliable), and may also be more resistant to forces acting to detach the mounted subsea antifouling sign from the subsea structure or equipment than the signs mounted using methods known in the prior art.
The subsea antifouling sign may comprise a backing layer, which may be moulded with the antifouling material or may be bonded to the antifouling material. The backing layer may be water impermeable. Alternatively, the backing layer may be water permeable. The backing layer may be a polyethyleneterephthalate (PET) backing layer. Alternatively the backing layer may be solid plastic, steel, rubber or a multipart backing layer. The backing layer (if present) may provide a suitable interface for the antifouling material of the sign and the adhesive layer or coating. Suitable backing layers for the sign include nylon, high density polyethylene (HDPE), a hook and loop fastener material such as VELCRO™, or other plastic or fabric layers capable of withstanding the harsh environments found in subsea locations.
Preferably, the subsea antifouling sign is made of a silicone-based polymeric antifouling material. Preferably the subsea antifouling sign is manufactured by a moulding method. Alternatively the subsea antifouling may be produced by an extrusion or a calendering process.
Preferably the adhesive layer or coating is a part of a double-sided adhesive sheet or tape. The adhesive layer or coating may comprise an acrylic adhesive layer. For example, the adhesive layer may be one commercially available from Champion Environmental Technologies under product designation KISS™. Alternatively or in addition the adhesive layer may comprise a silicone adhesive, a polyurethane adhesive, or an epoxy material.
The adhesive layer or coating may be selected to be compatible with the antifouling material of the sign or the backing layer of the sign to forming a chemical bond with the antifouling material.
In the case of acrylic adhesive layers, over extended periods of time, additional polymer crosslinking is favoured over scission. This implies that, rather than being degraded, the acrylic material may increase its mechanical strength slightly over extended periods of time. This means that a stronger, long lasting attachment may be produced. KISS™ acrylic adhesive layers exhibit a good fatigue resistance because of their viscoelasticity. The acrylic material absorbs energy and redistributes stresses internally, thus helping protect the adhesive attachment on the subsea structure and on the subsea antifouling sign.
When acrylic adhesive layers are used, it may be possible to correct errors committed during the mounting of the subsea antifouling sign. Acrylic adhesive layers are slow curing and permit to remove the subsea antifouling sign after it has been attached to the subsea structure, in order to modify its position or to replace it by another sign, without damaging the subsea structure.
When acrylic adhesive layers are used, a reduced amount of adhesive may be needed compared to mounting methods of subsea antifouling signs described in the prior art.
Additionally, when acrylic adhesive layers are used, the adhesive bonds thereby achieved exhibit an intermediate flexibility between adhesive bonds based on polyurethane adhesives, which are too rigid, and adhesive bonds based on silicone adhesives, which are too flexible. This is due to the viscoelastic nature of the acrylic adhesive bonds.
Preferably the protective lining comprises fluoro-silicone coated paper, although other suitable protective linings may be used.
Preferably the sign has a portion of the adhesive layer or coating close to every edge of its lower surface. Every portion of the adhesive layer or coating may have an edge substantially parallel to an edge of the back side of the lower surface of the sign. The adhesive layer or coating (which may be a part of a sheet or tape) may be provided in a plurality of discrete portions.
By having portions of adhesive layer close to the edges and/or substantially parallel to the edges of the sign, the resistance of the mounted sign to forces acting to detach it from the subsea structure or equipment may be increased.
Removing the protective lining of the adhesive layer may be carried out immediately before attaching the sign to the structure.
The method may comprise preparing a surface of the structure before mounting the subsea antifouling sign. This may comprise applying a primer on the subsea structure. Alternatively or additionally, it may comprise applying a cleaning product to the subsea structure. Alternatively or additionally, it may comprise applying surface treatment to the subsea structure to promote roughness on its surface in order to improve the adhesion of the subsea antifouling sign on the subsea structure.
The subsea antifouling sign may be attached to the subsea structure or equipment by application of pressure to the sign. For example, in embodiments of the invention, a force may be exerted on the subsea antifouling sign using a roller, press, clamp or the like.
The application of pressure to the sign improves the adhesion of the adhesive layer to the subsea structure.
Alternatively or in addition, the method may comprise applying heat to the subsea antifouling sign or to the subsea structure or equipment following the attachment of the subsea antifouling sign on the subsea structure or equipment, which may facilitate curing of the adhesive layer.
Preferably a gap between the perimeter of the subsea antifouling sign and the subsea structure or equipment surface is sealed with a bead of adhesive material. Preferably the adhesive material is water impermeable. Suitable adhesive materials for sealing a gap between the perimeter of the subsea antifouling sign and the subsea structure or equipment surface include acrylic cement, polyurethane (PU) materials, epoxy materials and/or RTV silicones.
A bead of adhesive material sealing a gap between the perimeter of the subsea antifouling sign and the subsea structure or equipment provides protection to the antifouling sign edge, making it more resistant to tearing by marine currents or water jets during routine cleaning. The bead of adhesive material may create a chamfered edge, in contrast with the right angle edge of the subsea antifouling sign, which softens the profile of the sign/material making it less likely to be caught or snagged.
By applying a bead of adhesive material for sealing a gap between the perimeter of the subsea antifouling sign and the subsea structure or equipment, the adhesive bond between the subsea structure and the subsea antifouling sign may be approximately 30% (or more) stronger than in a case when the bead of adhesive material is omitted.
By sealing a gap between the perimeter of the subsea antifouling sign and the subsea structure or equipment surface with a bead of water impermeable adhesive material, the adhesive layer may be completely or partially isolated from water, thus preventing or retarding the deterioration of its adhesive properties. Additionally stagnation of salty water between the subsea antifouling sign and the subsea structure or equipment's surface near the adhesive layer may be reduced, thus reducing the corrosion rate of the subsea structure or equipment next to the adhesive layer.
Additionally, by sealing a gap between the perimeter of the subsea antifouling sign and the subsea structure or equipment surface with a bead of adhesive material, it is possible to use adhesive materials which would not otherwise be expected to maintain a bond for the typical working lifetime specifications required for a subsea antifouling sign. Oilfield projects for example are typically specified to have 20 to 50 year service lives. In contrast, the service life of an acrylic adhesive layer is typically 10 years. However, with embodiments of the invention which seal the perimeter of the sign, it is possible to attach a subsea antifouling sign to a subsea structure and obtain a significantly prolonged lifespan. Performance tests have revealed that the service life of a sign mounted according to this embodiment of the invention can be at least six times longer than that of a conventionally mounted sign (typically 10 years) in the same conditions. In particular, the lifespan may be prolonged over the full service life of a subsea structure (i.e. typically from 20 to 50 years).
According to a second aspect of the invention, there is provided a subsea antifouling sign, comprising:
a body of an antifouling material comprising a first surface and a second opposing surface, indicia or markings visible from the first surface; an adhesive layer or coating on the second opposing surface; and a protective lining for the adhesive layer or coating.
The subsea antifouling sign may comprise a backing layer. The backing layer may be water impermeable. Alternatively, the backing layer may be water permeable. Preferably the backing layer is a polyethylenterephthalate (PET) backing layer. Alternatively the backing layer may be solid plastic, steel, rubber or may be a multipart or composite backing layer.
Preferably, the subsea antifouling sign is made of a silicone-based polymeric antifouling material. Preferably the subsea antifouling sign is manufactured by a moulding method. Alternatively the subsea antifouling may be produced by an extrusion or a calendering process. Preferably the adhesive layer or coating comprises a double-sided adhesive sheet or tape. The adhesive layer or coating may comprise an acrylic adhesive layer. For example, the adhesive layer may be one commercially available from Champion Environmental Technologies under product designation KISS™. Alternatively or in addition the adhesive layer may comprise a silicone adhesive, a polyurethane adhesive, or an epoxy material.
The adhesive layer or coating may be selected to be compatible with the antifouling material of the sign or the backing layer of the sign to forming a chemical bond with the antifouling material.
Preferably the double-sided adhesive sheet or tape has two adhesive layers which are applied to an intermediate carrier layer. In this embodiment the carrier layer adds rigidity to the double-sided adhesive sheet or tape, and improves ease of handling and application.
In embodiments of the invention the adhesive layer may comprise a double-sided adhesive sheet or tape comprising a carrier layer and two adhesive layers of different composition. Each adhesive layer may be formulated to maximise the adhesion between the adhesive layer and the surface to which the tape is to be adhered. For example, an adhesive layer which is a double-sided adhesive tape wherein one side of the adhesive tape is formulated to adhere to a plastic substrate and the other side of the adhesive tape is formulated to adhere to a metal substrate.
Preferably the protective lining comprises fluoro-silicone coated paper.
Embodiments of the second aspect of the invention may include one or more features of the first aspect of the invention or its embodiments, or vice versa.
According to a third aspect of the invention, there is provided a subsea structure comprising a subsea antifouling sign mounted on a surface thereof, wherein the subsea antifouling sign is attached to the surface of the subsea structure or equipment by the method of the first aspect of the invention.
Embodiments of the third aspect of the invention may include one or more features of the first or second aspect of the invention or its embodiments, or vice versa.
According to a fourth aspect of the invention, there is provided a subsea structure comprising a subsea antifouling sign mounted on a surface thereof, wherein the subsea antifouling sign is according to the second aspect of the invention.
Embodiments of the fourth aspect of the invention may include one or more features of the first to third aspects of the invention or its embodiments, or vice versa.
According to a fifth aspect of the invention, there is provided a method of forming a subsea antifouling sign, the method comprising:
forming a body of an antifouling material comprising a first surface and a second opposing surface, and indicia or markings visible from the first surface;
disposing an adhesive layer or coating on the second opposing surface; and
disposing a protective lining over the adhesive layer or coating.
Embodiments of the fifth aspect of the invention may include one or more features of the first to fourth aspects of the invention or its embodiments, or vice versa.
According to a sixth aspect of the invention, there is provided a method of forming a subsea antifouling sign, the method comprising:
forming a body of an antifouling material comprising a first surface and a second opposing surface, and indicia or markings visible from the first surface;
disposing a double-sided adhesive sheet or tape on the second opposing surface comprising an adhesive layer or coating and a protective lining.
Embodiments of the sixth aspect of the invention may include one or more features of the first to fifth aspects of the invention or its embodiments, or vice versa.
There will now be described, by way of example only, various embodiments of the invention with reference to the drawings, of which:
As described above,
The resulting sign 20 is a planar moulded body bearing integrated silicone alphanumeric characters 27 which are visible from its front surface 28. The sign has good anti-fouling properties suitable for subsea use over a long working lifetime. The sign has a pre-formed adhesive layer which can be used to install the sign on an item of marine or subsea equipment as described below.
By providing a sign with an adhesive layer and a protective film, the invention facilitates convenient attachment of a subsea antifouling sign to an item of subsea equipment. The method does not require additional equipment or fixings and does not rely on application of an adhesive layer by the installation operator. An advantage of this method is that as soon as the sign and its material are placed on the tubular it is held in place sufficiently so that it does not peel back. This avoids the use of banding or other securing means during the installation method.
In a subsequent step, shown in
In this embodiment, the sign is supplied to the installation operator with an adhesive layer located over substantially the whole lower surface of the sign, and close to the edges of the sign to provide a secure bond to the subsea equipment. Sealing the perimeter of the sign further improves the strength of the attachment, and reduces the tendency for the sign to peel from its edges. The seal also resists water ingress and provides protection against forces from cleaning operations or other subsea activity which may tend to damage the sign at its edges.
Standard and aggressive immersion tests carried out on samples representative of this embodiment show their superior performance versus other methods of mounting an antifouling sign.
The peak forces resisted by the samples can be divided by the area of the adhesive bond in order to normalise results and make them more comparable. This parameter is referred to as adhesive strength, having units of Newtons per unit area, in this case Newtons per squared millimeter.
The immersion tests consisted of submerging the samples in synthetic seawater. The temperature of the synthetic seawater bath was 70° C. in the aggressive immersion tests and 50° C. in the standard immersion tests. The lap-shear adhesive tests were carried out using samples that have undergone an immersion test, either aggressive (carried out at 70° C.) or standard (carried out at 50° C.).
After increasing amounts of time (several days or weeks) some samples were removed from the thermostatic seawater bath and a lap-shear adhesive test was carried out Every few days the lap-shear adhesive test was repeated using samples that had remained for the longer time within the seawater bath.
In a first example, the performance of samples representative of the mounting method according to
Aggressive immersion tests revealed that the adhesive bond of samples representing the conventionally mounted subsea sign using polyurethane adhesives failed after approximately 20 days of immersion in the thermostatic seawater bath. In contrast, samples made according to the method of
In another comparative test, samples representative of signs mounted with the method described in GB 2434022, were subjected to an aggressive immersion test using the experimental set-up described with reference to
It can be concluded that in the case of acrylic adhesive layers, over extended periods of time, additional polymer crosslinking is favoured over scission. This implies that, rather than being degraded, the acrylic material increases its mechanical strength slightly over extended periods of time. This means that a stronger, long lasting attachment is produced. Acrylic adhesive layers exhibit a good fatigue resistance because of their viscoelasticity. The acrylic material absorbs energy and redistributes stresses internally, thus helping protect the adhesive attachment on the subsea structure and on the subsea antifouling sign.
In another example, standard immersion tests were carried out at 50° C. according to the methodology of
This example illustrates the surprising result that a sealing bead which is applied to the edge of the subsea antifouling sign to surround it completely, protects the adhesive bond between the antifouling subsea sign and the subsea infrastructure, retards its degradation and provides additional bond strength compared to a case where the sealing bead is not applied.
The embodiment with a bead of adhesive around it has also passed environmental tests according to standard normative BS-EN-ISO 60068 and a test of 706 bar of pressure.
The invention provides a subsea antifouling sign and a method for mounting such a sign on a structure to be located subsea. The sign comprises a body of an antifouling material, and a first surface of the body has indicia or markings thereon. An adhesive layer or coating is provided on a second opposing surface, and a protective lining is located on the adhesive layer or coating. The method comprises removing the protective lining from the adhesive layer or coating; and attaching the subsea antifouling sign to the structure by adhering the adhesive layer or coating to a surface of the structure.
The process of mounting a subsea antifouling sign is performed before deploying the structure into its definitive subsea location. The method provides a more durable attachment of the subsea sign to the subsea structure and addresses issues of corrosion and other detrimental effects produced at the interface between the subsea sign and the subsea structure. Another benefit of this method is that the attachment between the subsea sign and the subsea structure may withstand higher forces due to marine currents, cleaning operations and impacts by remotely operated vehicles.
The foregoing description of the invention has been presented for the purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the precise form disclosed. The described embodiments were chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilise the invention in various embodiments and with various modifications as are suited to the particular use contemplated. Therefore, further modifications or improvements may be incorporated without departing from the scope of the invention herein intended.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1116011.6 | Sep 2011 | GB | national |
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| Number | Date | Country |
|---|---|---|
| 0171110 | Dec 1988 | EP |
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| Number | Date | Country | |
|---|---|---|---|
| 20130067783 A1 | Mar 2013 | US |
