WO2016038475A1

WO2016038475A1 - Anode construction and method for deploying anode construction

Info

Publication number: WO2016038475A1
Application number: PCT/IB2015/055029
Authority: WO
Inventors: Christian Peter THOMSEN
Original assignee: Bac Corrosion Control A/S
Priority date: 2014-09-12
Filing date: 2015-07-03
Publication date: 2016-03-17
Also published as: EP3191618B1; DK3191618T3; EP3191618A1; US20170241023A1

Abstract

The invention relates to an anode construction comprising a frame with two or more anodes and being adapted to be used with an offshore installation for remote connection with the offshore installation through cable connections between anodes and offshore installation. The frame comprises a main part and at least one movable part mounted on the main part and adapted to be pivotable or slidable in relation to the main part, where one or more anodes are mounted in a fixed position on the main part and one or more anodes are mounted on the movable part. The main part has a bottom frame part and a top frame part and further at least two anode mounting columns between the bottom frame part and the top frame part, and where the fixed anodes are mounted on the anode mounting columns.

Description

Anode construction and method for deploying anode construction

Field of the invention The present invention relates to the field of cathodic protection of metal constructions by use of sacrificial anodes.

Background of the invention Cathodic protection using sacrificial anodes is a well-known area within a number of areas including ships, vessels and offshore constructions, e.g. oil exploitation rigs a.o.

The electrochemical process taking place is generally along the following scheme for a ferrous material :

Fe→ Fe²⁺ + 2e^~

0₂ + 2H₂0 + 4e^~→ 40H^"

2H₂0 + 2e^"→ H₂ + 20H^"

In most environments, the hydroxide ions and ferrous ions combine to form ferroushydroxide, also known as rust:

Fe²⁺ + 20H^"→ Fe(OH)₂

It is desired to prevent or at least reduce the deterioration of the ferrous material, as this is the main structural material of the construction in question.

Therefore a sacrificial metal ranking lower in the electrochemical scheme, and therefore being more prone to the electrochemical reaction, is placed in electrical connection with the main construction and protecting this from deterioration. The most often used anode materials are aluminium or zinc or alloys comprising aluminium or zinc as the main component, but other materials may be used as alternatives to zinc and aluminium, such as magnesium as well as al- loys containing magnesium. Relevant areas of deployment are numerous; however, constructions in operation in seawater are in particular prone to corrosion and will almost always be protected from such corrosion by means of cathodic protection using sacrificial anodes. Ships, vessels and offshore oil exploitation constructions are well- known examples of such.

The sacrificial anodes should be of a type suitable to the environment of operation, i.e. taking into consideration the chemical composition of the environment and also the temperature. Further a size of the anode(s) as well as their mutual positioning of these is relevant to consider in order to provide a satisfactory protection.

Many offshore oil exploitation constructions, pipelines or other equipment are from their very first installation provided with a cathodic protection system us- ing sacrificial anodes and most often the dimensioning of the anodes is designed for the design life time of the oil exploitation construction, meaning that no further exchange of the sacrificial anodes is foreseen. The oil exploitation constructions, pipelines or other equipment are however in many cases kept in operation well beyond the initial design life time, meaning that the cathodic protection obtained through the sacrificial anodes, will disappear when the anodes are consumed after a certain time. For this situation there is a need for exchange or retrofitting the anodes of the offshore oil exploitation construction, pipelines or other equipment with new functional anodes to ensure the cathodic protection for a further life extension of the oil exploitation construction, pipe- lines or other equipment.

There are a number of ways of ensuring the cathodic protection of the construction. Most often the anodes are mounted directly on the construction with a mutual distance ensuring the most efficient protection according to the design criteria as mentioned above. Another way of ensuring the correct function is by placing the anodes remotely from the construction to be protected and connecting each anode electrically to the designed connection position of the construction, pipelines or other equipment. When retrofitting anodes to an offshore construction, pipelines or other equipment the remote positioning of the anodes is often the most effective way of doing this and therefore the preferred way of ensuring the continued cathodic protection.

It is known in the art to provide an anode construction for the purpose of retrofitting anodes to an offshore construction, pipelines or other equipment where the previously known construction comprises a framework with the anodes placed in mutually distanced positions to ensure the proper functioning of the cathodic protection. The anodes are connected to suitable connection points of the construction to be protected by means of suitable wiring. Such previously known anode construction is relatively bulky and therefore difficult to transport from the production site to the actual operational site.

From US 7138038 a collapsible and expandable construction is known, where a number of anode carrying elements are mutually hingedly joined. In a transport position the anodes are collapsed and folded at the hinges to form a relatively flat structure, and upon expanding by pulling a central connection upwards the anode carrying elements are brought into mutually aligned positions, where these may be fixed by means of brackets. Although this previously known construction makes the transportation and deployment more convenient than a totally fixed construction, it is still a somewhat cumbersome and labour intensive process to fixate the joints of the anode carrying elements after alignment of these.

EP 2 241 676 Al discloses a corrosion inhibiting anode assembly for use with an underwater structure and comprising a generally planar main frame for lying on the bed of a body of water, a plurality of spaced-apart elongate anode bars fixedly secured by respective stand-off supports to the main frame and extending in one or more planes that are generally parallel to that of the main frame, and at least one wing frame pivotally attached to the main frame. The wing frame comprises a plurality of spaced-apart elongate anode bars and is capable of being pivoted from a folded condition suitable for transport to an extended condition for underwater employment in which the anode bars of the wing frame are generally more remote from those of the main frame than in said folded condition. In order to bring the wing frame to its extended position for underwater employment, a plurality of wing frame supports are connected to the wing frame and arranged to support the wing frame in said extended condition. However, although this previously known construction also makes the transportation and deployment more convenient than a totally fixed construction, it is still a somewhat cumbersome and labour intensive process to bring the wing frame to its extended position and connect the plurality of wing frame supports to the wing frame in order to support the wing frame in its extended condition.

The purpose of the present invention is to provide an anode construction suita- ble for retrofitting an offshore construction, pipelines or other equipment with a cathodic protection system for a further period of time where the transportation and deployment of the anode construction is further facilitated while maintaining a long life extension of the construction to be protected.

Summary of the invention

According to the invention the objective is achieved through an anode construction comprising a frame with two or more anodes and being adapted to be used with an offshore installation, pipelines or other equipment for remote connection with the offshore installation through cable connections between anodes and offshore installation, where at least one anode is mounted in a fixed position in the frame of the anode construction and where at least one anode is mounted in the frame of the anode construction to be movable from a transport position into a deployment position, where the frame comprises a main part and at least one movable part mounted on the main part and adapted to be pivotable or slidable in relation to the main part, where one or more anodes are mounted in a fixed position on the main part and one or more anodes are mounted on the movable part, where the main part has a bottom frame part and a top frame part and further at least two anode mounting columns between the bottom frame part and the top frame part, and where the fixed anodes are mounted on the anode mounting columns.

By providing an anode construction where one or more anodes may be pivota- bly or slidably movable in relation to other anode(s) of the anode construction, it may be ensured that the anode construction may be a compact unit during transportation, and upon deployment may be a fully functional anode construc- tion with the designed distance between the anodes. By further providing a bottom frame part and a top frame part and further at least two anode mounting columns between the bottom frame part and the top frame part, where the fixed anodes are mounted on the anode mounting columns, an even more compact unit may be obtained during transportation.

As will be explained in more detail below, depending on the degree of cathodic protection required, a number of such compact units may be interconnected to form a larger unit. Preferably at least one anode is a longitudinal element with an axis extending through the anode and where the axis of pivoting the pivotable frame part is essentially parallel with the axis of the anode. Hereby the at least one anode is preferably a longitudinal element with an axis extending through the anode and where the axis of pivoting the pivotable frame part is essentially perpendicular the axis of the anode. A further option exists in that the at least one anode is a longitudinal element with an axis extending through the anode and where the direction of sliding the slidable frame part is essentially parallel with the axis of the anode. A still further option is that the at least one anode is a longitudinal element with an axis extending through the anode and where the direction of sliding the slidable frame part is essentially perpendicular the axis of the anode.

The anode construction may advantageously be assembled from a number of units to form a larger anode construction. The assembly of anode units may take place through welding of the frames or through providing assembly brackets connecting the frame constructions. At least the bottom frame parts of two neighbouring anode constructions need to be connected.

The anode units are each advantageously provided with engagement means allowing use of standard container handling equipment. When a larger assembly of anode units is provided, the engagement means at the outermost corners of the assembly is used for the handling procedure.

The invention also relates to a method for deploying an anode construction according to the invention. According to the invention the method for deploying a retrofit anode construction to an off-shore installation comprises:

Providing an anode construction with anode configuration according to the invention;

Transporting the anode construction with the movable carrying elements in their transportation position;

Moving the movable elements to the deployment position for the anode construction;

Positioning the anode construction on its deployment site proximal the offshore construction, pipelines or other equipment to be protected;

Connecting the anodes of the anode construction to the relevant parts of the offshore construction through electrical connections.

The deployment or use position of the anode construction involves folding the side elements of the anode frame to their use position or in other ways of movement foreseen for the positioning of the movable anodes into their use position. Further embodiments and advantageous effects of the invention are presented in the following description of preferred embodiments of the invention.

Throughout this document the terms "comprising" or "comprises" do not ex- elude other possible elements or steps. Also, the mentioning of references such as "a" or "an" etc. should not be construed as excluding a plurality.

Brief description of the drawings Fig. 1 shows schematically an anode construction according to the invention in a perspective view with one side in the transport mode and the opposed side in the deployment mode;

Fig. 2 shows schematically an anode construction according to the invention in a side view with one side part in the transport mode and the other side part in the deployment mode;

Fig. 3 shows in an enlarged view the electrical connection to the anode construction;

Fig. 4 shows schematically an anode construction according to the invention in an end view with one side in the transport mode and the opposed side in the deployment mode;

Fig. 5 shows schematically and enlarged a connection part adapted for connection of two anode constructions forming a larger anode assembly; and

Fig. 6 schematically shows two anode constructions assembled to form a larger anode assembly.

Description of preferred embodiments of the invention

From Fig. 1 the anode construction 1 according to the invention appears in a perspective view. The construction comprises a frame with a rectangular bottom part 2 and a rectangular top part 3 and at four perpendicular corner posts 4 extending between the bottom part 2 and the top part 3. Between the corner posts 4 the frame defines two opposed side areas and two opposed end areas. At the end areas and between the top part and the bottom part, stationary anode carrier elements 8,9 are provided. The stationary anode carrier elements 8,9 carry six anode elements 7, three towards each side area. At each side area and connected to the bottom part 2 a pivotable side part 5 is provided, connected to the bottom part 2 through hinges 6 at each side of the pivotable side part 5. Each pivotable side part 5 carries four anode elements 10. In order to control the pivoting position chains 11 are provided between the pivotable side part 5 and the corner posts 4. This mainly serves the purpose of protecting the bottom frame part 2 from an otherwise significant momentum exerted by the pivotable side part 5 to the bottom frame part through the hinges 6.

The anode element 7,10 comprises a steel core part and an anode material comprising a sacrificial metal molded around the steel core part. The core steel part is configured with curved end areas serving the purpose of creating a distance to the frame construction when mounted on this. The distance will partly separate the anodes individually from each other and partly ensure that the anode mounted on the pivotable side parts is kept free of the sea bottom. It should be appreciated that the shape and size of the anode including the core part may vary and as such is not limited to the shape and size indicated in this example.

The anode material may be any suitable metal usable for cathodic protection. Aluminium or zinc or an alloy comprising aluminium or zinc as a main component are most often preferred but for specific purposes where other materials are more appropriate these may be used without interfering with the scope of the present invention. From Fig. 1 it further appears that one of the pivotable side parts has been pivoted into the deployment position. The chains 11 holding the pivotable side part

5 are visible in their tightened mode holding the side part and relieving the bottom frame part 2 from the torque that would otherwise be imposed to it. From Fig. 1 a view of a hinge joint 6 between a bottom frame part and the pivotable side further appears. The hinge as such comprises a stationary bearing part and a rotating or pivoting bearing shaft, where these parts obviously are dimensioned to carry the significant weight of the pivotable side part. A hinge is provided at each side of the pivotable side part 5, i .e. two hinges are provided for each side part.

From Fig. 2 a side view appears of the anode construction, where one of the pivotable side parts 5 has been pivoted into the deployment position and one side part 5 is still maintained in the transport position. It appears that the pivotable side part in deployment position is held in place by the holding chains 11 at each side of the pivotable side part 5. From Fig. 3 the area A shown in Fig. 1 is shown in enlarged form . The attachment to the anode construction of the cable 14 forming the electrical connection to the construction to be protected is shown here. The attachment to the anode construction will preferably happen through a cable shoe 15 attached to threaded support (preferably welded to the anode construction) by means of a nut 16 and with one or more clamps 17 for relief of the cable 14.

From Fig. 4 an end view appears of the anode construction with the side parts 5 in the transport mode and the deployment mode respectively. It is more clear from this view that the distance between the anodes 7 being mounted in a fixed position and the anodes 10 mounted on the pivotable side parts 5 is significantly less in the transport mode than in the deployment mode. As already emphasized, the closer positioning of the anodes in the transport mode will allow for a more compact and hence more efficient transport of the anode construction that at the deployment site has a larger capacity than otherwise possible within a limited space.

The frame construction is preferably a construction adapted to be movable and transported by means of standard container handling and transportation equipment. This means that the dimensions of the frame construction advantageously correspond to standard measures of container modules, e.g. 10, 20 and 40 foot in the length and with height and width corresponding to normal standard containers. This will significantly ease the handling of such system and will provide for a cost effective and reliable transportation of such constructions. In order to achieve the use of standard handling equipment engagement openings 12 (Fig. 1) are provided at the corners of the anode construction, where the engagement means of the standard lifting and handling equipment may engage. For stacking of several anode constructions or for stacking of an- ode constructions together with standard freight containers there may in similar way be provided means for engaging the stacked container in order to stabilize the stacked containers by preventing possible sliding of any of the containers.

The anode construction is preferably modular, meaning that a number of base modules or anode constructions may be assembled to form larger assemblies of anode constructions as shown in Fig. 6. The connection between the base modules 1,1' may be constituted by welding or through connection means such as brackets or simply bolts extending through both anode constructions to be assembled. A combination of two or more alternative connection means may be provided. An enlarged view of the connection part 13 adapted for the connection between the two modular anode constructions 1,1' forming an anode assembly is shown in Fig. 5. Holes in the connection part allow for insertion of suitable holding means, such as bolts, allow for holding the two holding parts 13 together and thereby holding the anode constructions 1,1' together.

The modular construction will provide an overall optimization of the production as the individual size of the anode assembly may be adapted to the actual needs based on a standard anode construction. The manufacturing of the anodes with a shorter length is furthermore significantly easier than longer an- odes.

The number of anodes in an anode unit may vary dependent on a number of factors. The distance between the anodes is important in order to achieve the optimal protection effect. The anode material may also influence the choice of distance and further the environment of deployment may have an influence on the choice of anode material . In a complex three dimensional construction a simulation of the conditions is most often used to determine the optimal dis- tance. The dimensions of the unit will limit the number of anodes that may be accommodated in a unit. In the unit shown in the drawings six anodes are mounted in a fixed position in the frame construction with three anodes in each of two columns, and four anodes are mounted on each pivotable side part. The number of fixed anodes in each of the rows and the pivotable side parts may be shifted to be four and three, respectively.

Deployment of an anode construction at an offshore site will normally comprise pivoting the pivotable side parts into the deployment position and successively lifting the anode construction off the vessel and lowering the anode construc- tion into the sea until firmly resting on the seabed. In the transport position the side parts are held in position by means of bolts or other types of holding means, which are removed upon preparing the anode construction for deployment. The connection of the anode construction to the offshore construction to be protected happens after the positioning on the seabed. The electrical con- nection is ensured through a cable connection that is at one end attached to the offshore construction, pipelines or other equipment and at the opposed end attached to the anode construction. The attachment may be performed manually or may be performed by means of a ROV (Remote Operated Vehicle). The attachment to the offshore construction may be in the form of a clamp, which is well-known in the field of retrofitting cathodic protection.

The size of the anode construction will be defined by the designed lifetime extension required in relation to the construction, pipelines or other equipment to be protected. One way of varying the size of the anode constructions is through providing these as modular units that can be connected to form larger assemblies. It will be possible to connect such anode constructions and still maintain the general format of a standard container and as such be able to use existing infrastructure and handling equipment for the transport of the anode construction^) to the deployment site.

Claims

1. An anode construction comprising a frame with two or more anodes and being adapted to be used with an offshore installation, pipelines or other equipment for remote connection with the offshore installation through cable connection between anode construction and offshore installation, where at least one anode is mounted in a fixed position in the frame of the anode construction and where at least one anode is mounted to be movable from a transport position into a deployment position, where the frame comprises a main part and at least one movable part mounted on the main part and adapted to be pivotable or slidable in relation to the main part, where one or more anodes are mounted in a fixed position on the main part and one or more anodes are mounted on the movable part, where the main part has a bottom frame part and a top frame part and further at least two anode mounting columns between the bottom frame part and the top frame part, and where the fixed anodes are mounted on the anode mounting columns.

2. An anode construction according to claim 1, where at least one anode is a longitudinal element with an axis extending through the anode and where the axis of pivoting the pivotable frame part is essentially parallel with the axis of the anode.

3. An anode construction according to claim 1 or 2, where the at least one anode is a longitudinal element with an axis extending through the anode and where the axis of pivoting the pivotable frame part is essentially perpendicular the axis of the anode.

4. An anode construction according to any one of the preceding claims, where the anode columns are mounted between the bottom frame part and the top frame part between corner columns at opposed ends of the frame construction.

5. An anode construction according to any one of the preceding claims, where the anode columns are corner columns between the bottom frame part and the top frame part.

6. An anode construction according to any of the preceding claims, where the number of anodes mounted in fixed positions is at least 2 and where the number of anodes mounted to be movable is at least 2.

7. An anode assembly comprising at least two anode constructions according to any of the preceding claims, where the at least two anode constructions are mutually connected, e.g. through welding, bolting or bracket connecting or a combination of these.

8. A method for deploying a retrofit anode construction to an offshore in- stallation, the method comprising : a. Providing an anode construction with anode configuration as defined in any of the previous claims;

b. Transporting the anode construction with the movable anodes i their transportation position;

c. Moving the movable anodes to the deployment position for the ode construction;

d. Positioning the anode construction on its deployment site proximal the offshore construction;

e. Connecting the anodes of the anode construction to the relevant parts of the offshore construction through electrical connections.