GB1603629A

GB1603629A - Sacrificial anodes

Info

Publication number: GB1603629A
Application number: GB39353/80A
Authority: GB
Original assignee: ISC Alloys Ltd
Current assignee: ISC Alloys Ltd
Priority date: 1978-04-24
Filing date: 1978-04-24
Publication date: 1981-11-25
Also published as: GB1603628A; NO781436L

Description

(54) SACRIFICIAL ANODES (71) We, ISC ALLOYS LIMITED, a British Company, of 1 Redcliffe Street, Bristol BS99 7EA, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to arrangements for use in the cathodic protection of submarine bodies and structures, for example pipelines. Submarine pipelines are subject to corrosion as a result of electrochemical action during their immersion in water and it is known to minimise the effect of this corrosion by providing on the pipeline, which is for example made of steel, a body of a more electro-chemically active metal, for example, zinc, aluminium or magnesium alloy, than the metal of the pipeline and connecting the body electrically to the pipeline. The body of material forms an anode and the more active material of the anode corrodes in preference to that of the pipeline, the electrical current associated with the corrosion process flowing from the anode via the electrolyte and back to the pipeline.

A form of anode which is suitable for this purpose is described in United States Re Issue Patent No. 27, 529, re-issued on the 12th December 1972 in the name of Gordon L. Doremus. The galvanic anode described in this United States Patent Specification consists of at least a pair of arcuate segments constructed of a suitable galvanic metal and having completely embedded within the galvanic metal a steel core or armature adapted to be connected together to join the anode sections into a bracelet about the pipe. The steel core or armature sections have end portions which project from opposite, longitudinal edges of the anode body to form joint elements for connecting one of the segments to the other in a pipeembracing relation.

Anode bodies employed in this manner for the cathodic protection of submarine pipelines are commonly known as sacrificial anodes, since the active metal is sacrificed instead of the steel of the pipeline being eaten away. Unfortunately, the sacrifical anode is not eaten away evenly and parts of the material of the anode can become dislodged or in some other way disconnected from the main body of the anode so that they are wasted.

The present invention provides an arrangement which enables a replacement anode to be introduced in a simple manner when the original anode body has been eaten away.

According to the present invention there is provided an arrangement for use in the cathodic protection of submarine bodies and structures, for example pipelines, including an anode body having a first part which is constituted by a material which is electrochemically active, a core which is constituted by a material which is less chemically active than the first part and a member which is of less electro-chemically active material than the first part and which is electrically connected to the core, the said member being concealed within the first part, whereby, when the member is exposed during the use of the body, a replacement anode body can be attached to the member.

It will be appreciated that features of the arrangements to be described can be applied in varying combinations to galvanic anodes of the type described in the above mentioned re-issued U.S. Patent Specification and to other types of sacrifical anode.

Embodiments to which the invention can easily be applied together with embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings in which: Figures 1 and 2 are end and plan views respectively of the sacrificial anode to which the invention can easily be applied.

Figure 3 is an end view of an anode arrangement embodying the invention, Figure 4 is a diagrammatic sketch of a detail of a further arrangement embodying the invention and Figures 5 and 6 are end and plan views respectively of another embodiment of sacrificial anode.

Referring to Figures 1 and 2, there are indicated by broken lines 1 and 2 the outlines of two anode bodies 3 and 4 which include a first part made of metal which is electro-chemically more active than a pipeline with which they are to be used. Suitable metals are aluminium, zinc, magnesium and alloys thereof. Cast into each of the bodies 3 and 4 is a steel supporting core structure 5 which is less chemically active and is cathodic to the first part and is constituted by a pair of straps 6 and 7 extending longitudinally of the bodies, three bars 8 extending both transversely and beyond the edges of the bodies 3 and 4, two straps 9 which extend transversely of and within the bodies 3 and 4 and a plurality of rods 10 extending both transversely and longitudinally of the structure. The bars 8, straps 9 and rods 10 are welded to the straps 6 and 7 and it will be noted that, by way of example, the angular spacing between the transversely extending rods 10 in the body 3 is different from that in the body 4. The angular spacing of the transversely extending rods 10 in the body 3 is between 4" and 5 and that of the rods in the body 4 is between 8" and 10 . The larger the number of rods 10 in the structure, the less likely is it that large portions of the bodies 3 and 4 will fall away as the bodies are consumed during use. It will be noted that the longitudinally extending rods of body 3 are closer together than are those of body 4. In fact an improvement in utilisation factor by up to 10% has been obtained with the two arrangements described. It will be appreciated that the rods 10 of the supporting structures 5 form mesh or grid structures defining rectangular apertured regions; a plurality of the rectangular regions extending both across the width of the bodies 3 and 4 and along the length of each body.

The bars 8 near to the ends of the body 3 are joined, at their respective ends, by straps 12 to the corresponding bars 8 near to the ends of the body 4, in assembling the bodies and structures about a pipeline (not shown). It will be seen that the straps 9 are ribbed at 13 in order to key them better into the bodies 3 and 4. It would, of course, be possible to include more straps than the two 6 and 7 shown in the structure 5.

Referring to Figure 3 there is shown an embodiment similar to that shown in Figures 1 and 2, but in which a right angled bracket 15 has its foot 16 welded to the underside of one of the straps 9. On the leg 17 of the bracket 15 there is a hole 18 about a centre line 20. More than one such bracket 15 can be attached to each strap 9 and, as the anode bodies 3 and 4 are eaten away during use, the legs 17 and the holes 18 are exposed, thereby enabling a replacement anode body 22 to be attached to each strap 9 by bolting to the leg 17 by means of the hole 18 a member 23 extending from the body 22.

The body 22 is considerably longer than the width of the structure 5 upon which it is mounted and it will be understood that a replacement anode or anodes of equivalent capacitor to the original bodies 3 and 4 can easily be fitted when the original bodies have been consumed without removing the structure from the pipe which it surrounds or employing any welding operation. The bracket 15 could be attached to the strap 9 in some other way, for example by being bolted to the strap. It will also be understood that the structure 5 could be different from that shown, for example the rods 10 could be omitted. By providing brackets 15 around the structure at angular intervals of up to 60 degrees it is possible to ensure that one will always appear in the upper segment of the pipeline.

In a further embodiment of the invention shown in Figure 4, a replacement anode 25 is connected, by means of a flexible lead 26 bolted to a member 27, to a strap 9 to which the member 27 is welded. The strap 9 and the member 27 may initially be concealed within the anode body 3. Alternatively, the strap 9 and the member 27 may extend transversely beyond the edges of the body 3 and the lead 26 may be bolted either directly to the strap 9 or to the member 27 at any time.

Figures 5 and 6 illustrate diagrammatically structures 30 and 31 constituted by a plurality of anode segments 32 into each of which there is cast a supporting bar 33 which extends transversely of the structure well beyond the ends of the respective segment 32. Each bar 33 is welded at its end to a strap 34 and flanges 35 on the straps 34 of the structure 30 are clamped, by means not shown, to corresponding flanges 36 on the straps 34 or the structure 31. Replacement anodes may be connected, for example, to the straps 34, as indicated by leads 37.

By arranging components of a steel supporting core structure, such as that shown at 5 in Figure 1 and consisting of straps, 6, 7 and 9 bars 8 and rods 10, to be at or near the inner face of the anode segments 32 an improvement in the utilisation factor of the anode of some 10% is obtained.

Variations modifications and combinations of the arrangements shown may be made within the scope of the invention. For example, the segmented anodes 32 of the structures 30, 31 of Figures 5 and 6 could be cast on two respective mesh or grid structures 5, in a similar way to that in which the anode bodies 3 and 4 in Figures 1 and 2 are cast. It would also be possible to incorporate brackets, similar to the brackets 15 previously described, within the segments 32 attached to the bars 33 for mounting replacement anodes on. The shape and configuration of the various parts can also be varied within the scope of the invention. For example, the grid regions defined by the rods 10 could be other than rectangular; they could be diamond shaped. It would, alternatively, be possible for the supporting core structure to define circular grid regions, for example, and be made of perforated steel sheet.

It will also be appreciated that, although the description has been made particularly with reference to the application of the arrangement described to submarine pipelines, it can be applied to other submarine bodies and structures, for example oil rigs.

Attention is drawn to our co-pending application 17579/77. Serial No. 1603628.

WHAT WE CLAIM IS: 1. An arrangement for use in the cathodic protection of submarine bodies and structures, for example pipe lines, including an anode body having a first part which is constituted by a material which is electrochemically active and a core which is constituted by a material which is less electrochemically active than the first part and a member which is of less electro-chemically active material than the first part and which is electrically connected to the core, the said member being concealed within the first part, whereby, when the member is exposed during the use of the body, a replacement anode can be attached to the member.

2. An arrangement as claimed in claim 1, wherein the core defines a plurality of apertured regions, there being a plurality of the apertured regions in a direction extending transversely of the body and a plurality of the apertured regions in a direction extending longitudinally of the body.

3. An arrangement as claimed in claim 2, wherein the core includes a plurality of rods, the said rods being arranged to extend longitudinally and transversely of the arrangement to define the apertured regions.

4. An arrangement as claimed in any one of the preceding claims, wherein the core includes a transversely extending strap, the said member being attached to the strap.

5. An arrangement as claimed in any one of the preceding claims wherein the body is in the form of an arcuate segment and wherein a strap extending transversely of the arrangement is arranged near to each end of the segment to extend beyond opposite edges of the body and provide means for coupling the said body to a further body in the form of an arcuate segment.

6. An arrangement as claimed in any one of claims 1-4, including a plurality of the said bodies, wherein the core of each body includes a strap extending transversely of the arrangement and beyond an edge of the respective body, the arrangement including a further strap attached to the part of each strap extending beyond an edge of a respective body and having a flange at each end for connection to a corresponding flange of a similar arrangement.

7. An arrangement as claimed in any one of the preceding claims wherein the core is cast into the first part of the body.

8. An arrangement as claimed in claim 1 substantially as described herein with reference to Figures 3 and Figure 4 or Figures 5 and 6 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. example, the segmented anodes 32 of the structures 30, 31 of Figures 5 and 6 could be cast on two respective mesh or grid structures 5, in a similar way to that in which the anode bodies 3 and 4 in Figures 1 and 2 are cast. It would also be possible to incorporate brackets, similar to the brackets 15 previously described, within the segments 32 attached to the bars 33 for mounting replacement anodes on. The shape and configuration of the various parts can also be varied within the scope of the invention. For example, the grid regions defined by the rods 10 could be other than rectangular; they could be diamond shaped. It would, alternatively, be possible for the supporting core structure to define circular grid regions, for example, and be made of perforated steel sheet. It will also be appreciated that, although the description has been made particularly with reference to the application of the arrangement described to submarine pipelines, it can be applied to other submarine bodies and structures, for example oil rigs. Attention is drawn to our co-pending application 17579/77. Serial No. 1603628. WHAT WE CLAIM IS:

1. An arrangement for use in the cathodic protection of submarine bodies and structures, for example pipe lines, including an anode body having a first part which is constituted by a material which is electrochemically active and a core which is constituted by a material which is less electrochemically active than the first part and a member which is of less electro-chemically active material than the first part and which is electrically connected to the core, the said member being concealed within the first part, whereby, when the member is exposed during the use of the body, a replacement anode can be attached to the member.