DD244572A1 - ANODE ARRANGEMENT FOR CATODIC INTERNAL CORROSION PROTECTION, IN PARTICULAR PIPING - Google Patents

Abstract

The invention relates to an above-mentioned arrangement of inert or active anodes in elongated hollow bodies of arbitrary diameter. The aim of the invention is the development of an easily assembled anode assembly also for non-accessible pipelines using available anode materials from own resources with high utility value properties. The object of the invention is the possibility of saving a high protection current by reducing the propagation resistance of the anode assembly and the Vergösser the Schutzbereichslaengen by reducing the voltage drop in the power supply cable. According to the invention, the individual hydrodynamically favorably designed anodes, preferably of iron-silicon alloy, are form-fitting and liquid-tight, enveloping the electrically conductive core, preferably strung on an aluminum cable at certain distances, whereby direct contact of the anodes with the protected object is prevented by insulating spacers. Possible fields of application are water-conducting steel pipes of any cross-section and other electrolyte-filled hollow bodies, preferably for the rehabilitation of pipelines with defective internal insulation. Fig. 1

Description

For this 4 pages drawings

Field of application of the invention

The invention relates to an arrangement of inert or active anodes for cathodic internal corrosion protection of electrolyte-filled metallic hollow bodies, in particular of water-bearing steel pipelines, consisting of a highly electrically conductive core with Isoiationsüberzug on the surface, such as power supply cable and the like, and a plurality of the length in certain Spaced apart and with the core in metallic connection standing individual anodes. This anode assembly is retracted during or after the pipeline assembly in the pipeline and also allows easy retrofitting.

Characteristic of the known technical solutions

For the cathodic corrosion internal protection of pipes and other elongated hollow bodies, various anode arrangements are known, by means of which the cathodic protection current with sufficient uniformity to be placed on the inner surface to be protected cathodically. Both inert anodes and active anodes can be used for this purpose. When using inert anodes, the power supply cable is passed through the pipeline in isolation and connected to the positive pole of a DC voltage source.

When using active anodes, the power supply cable is connected directly to the pipeline. An anode arrangement using inert anode materials is described in "Handbook of Catodic Corrosion Protection", Hersg. W. von Baeckmann and W. Schwenk, Verlag Chemie Weinheim, Bergstrasse, 1971, pages 349-350.

It consists of an approximately 3 mm thick titanium wire, which is provided at intervals of about 1 m to a length of 3 to 10 cm with a thin platinum layer of a few microns thick. By a helically wound around the partially platinum-plated titanium wire copper cable, the short circuit between the anode and the pipe to be protected is prevented. In the case of anodic stress, the titanium surface is passivated and the resulting thin titanium oxide layers are largely impermeable in the passivation region for the protective current. The protective current can therefore only enter through the platinum-plated areas of the titanium wire into the electrolyte and flow via this to the pipeline. In this case, a certain distance between the cathodically active platinum-plated titanium wire and the cathode wall connected as a cathode is maintained by the insulated copper conductor, which prevents an electrical short circuit. In DE-OS No. 2019148 another anode arrangement is proposed, consisting of an isolated, electron-conducting core and a plurality of this electronically connected anode pins made of titanium, niobium or tantalum, whose precious metal coated heads are in contact with the electrolyte, but by a the entire anode assembly covering electrically insulating plastic mesh can not directly touch the pipe inner wall, so that a short circuit is avoided.

Due to the relatively small anode surfaces, both known anode arrangements are suitable only for electrolytes of low resistivity, such as brine or seawater, and then only for pipelines of small diameter or low protection power demand. For electrolytes high resistivity, such as drinking water, and then especially for pipelines of large diameter or high protection requirements, these anode arrangements are not suitable because of the excessive total resistance in the protection circuit, in particular because of the large propagation resistance anode-electrolyte protection object. Namely, if the applied voltage is increased to the breakdown potential of the noble metal coating supporting base metal titanium, niobium or tantalum, these can be corrosion-resistant metals, especially in chloride-containing electrolytes, subject to corrosion, and the noble metal coating can be detached, so that the anode assembly ineffective or even destroyed. In addition, the noble metals of the platinum group used for anode coating are deficient and so expensive that economic reasons speak against the use of the known anode arrangements. The platinum-plated titanium anode described first has the disadvantages that - due to the small cross-section and the low electrical conductivity compared to copper - the titanium wire is a poor electrical conductor. In order to keep the voltage drop in the passage of current still within the allowable limits (about 0.3V), therefore, a good conductor in the form of an insulated copper cable must be performed in parallel and contacted in relatively short longitudinal distances with the titanium wire. These contact points must be isolated liquid-tight, otherwise the copper conductor is electrolytically dissolved at anodic load. Contacting and subsequent insulation increase the assembly effort considerably. Another disadvantage is that the cross-section of the copper conductor is limited to about 100 mm ² Cu for reasons of desired flexibility of the spiraled into the pipe anodized anode assembly. This results, depending on the protection power requirements, only relatively short protection ranges of 100m with bare pipe and up to 1000m with very well insulated pipe, that is at these intervals must be introduced from the outside each isolated from the pipe power supply cable into the pipeline and the anode assembly elktronenleidend connected and liquid-tight isolated from the pipeline.

The solution according to DE-OS No. 2019148 moreover has the disadvantage that the electrically conductive core used is weakened by the penetrating anode pins in the mechanical tensile strength, so that also for this reason, the length of the anode assembly is limited by the reduced tensile strength. Another disadvantage of this solution is that the insulating plastic net covering the assembly can be easily damaged when pulled into pipes by always present roughness in the field of assembly welds and the like. An anode arrangement using active anode materials is described in DE-OS No. 1696133. It comprises a bare strip of aluminum, zinc, magnesium or another alloy suitable for the metal to be protected and is intended to be welded directly or indirectly to the pipeline via a suitable carrier material become. A variant provides an adhesive connection between anode and tube.

The disadvantages of this solution are that it is technically difficult, if not impossible, to produce an electrically good conductive and mechanically strong connection between the anode material and the pipe wall, especially in non-accessible pipelines. This solution is not applicable for the retrofitting of already installed pipelines.

Object of the invention

The object of the invention is an extension of the life of exposed to electrolytes in the form of aqueous solutions pipes or other metallic hollow bodies. Furthermore, it should be possible to save on deficient materials, such as platinized titanium, niobium or tantalum, by using domestic raw materials, preferably iron-silicon cast alloys. Also, the assembly of the anodes in the pipelines and the like should be facilitated, a high degree of prefabrication should be made possible while reducing the maintenance occur and the possibility of easy replacement of spent anodes are created.

The production of the anode assembly should be possible with less effort on material and working time. In particular, the flexible copper cable should be replaced by a relatively rigid aluminum cable. The risk of tearing insulation network is to be replaced by a mechanically more stable solution that allows the retraction of the anode assembly in pipelines with a large inner roughness without the risk of damage.

Explanation of the essence of the invention

The invention has for its object to develop an anode assembly, which ensures a higher electrical conductivity and a lower voltage drop in the passage of current through the anodes in comparison with the known solutions. The contacting and subsequent isolation of the anodes on the core should be much easier and thus the assembly costs are significantly reduced. Furthermore, the anode assembly is a lesser obstacle in the

Drawing also in curved piping represent and high abrasion resistance of the insulation against the pipe inner wall can be achieved. It should also be virtually no restriction of the core cross section necessary, so that a use of conventional aluminum plastic sheath cable larger cross-section is possible. The protected area lengths between the individual power supply points should be significantly increased. By using inexpensive materials, it should be possible to increase the anode surfaces so that the propagation resistance is substantially lower than known anode arrays, so that any desired protection current can be imparted to the inner wall of the pipe, even with large diameter pipes having poorly conducting electrolytes. Finally, it should still be possible, if necessary zu.arbeiten work with higher DC voltages without the anode materials, such as when using placed titanium, are destroyed. According to the invention, each of the anodes is a form-fitting and liquid-tight enveloping the core, with its surface in ellektronenleitendem contact. This is the case in which the individual anodes are arranged at intervals from one another on the core, for example similar to a string of pearls, and are provided with a surface thereof which produces a good electron-conducting and liquid-tight connection.

The anode assembly according to the invention allows the use of conventional aluminum plastic sheath cable large cross-section, which now the supply of high protection currents with low voltage drop is possible and the core has a high mechanical strength. Such a power supply cable also ensures a good fixation of the anode assembly in the protected object, even at high flow velocities, so that reliable wear of the spacers is prevented by unwanted vibrations. Nevertheless, the anode assembly is still so far deformable that it can be wound both for transport on drums, as well as having sufficient adaptability to changes in direction of the object to be protected, which inevitably occurs when pulling the anode strand in curved pipes or other protective objects.

The hydrodynamic favorable design of the spacers thereby reduces the frictional resistance and certainly facilitates the overcoming of the inner wall of the pipe frequently existing obstacles.

Thus, the current output is limited only to the actual anodes and the electrically conductive core can not be electrolytically dissolved by anodic load, the core remains enveloped by the insulation coating between the anodes. For the same reason, the gap between each anode and the core with electrically non-conductive material is also liquid-tight isolated. To prevent a short circuit between the anodes and the pipe inner wall, a certain distance must be maintained between each anode and the pipe inner wall. This can be done once by the anode partially enveloping insulating, for example, annular spacers or even arranged directly on the power supply cable, for example, spherical spacer body whose outer diameter but must be greater than that of the anodes to prevent electrical short circuit. The spacers may be formed as solid or hollow body.

The use of annular spacers proves to be particularly advantageous when serving as material Elstomere. By their own elasticity, these then snap immovably into a form-fitting adapted, for example, groove-shaped recess on the circumference of the anodes, which is arranged in multi-part anodes on the screw connections. This results at the same time an additional seal and securing the screw against the penetration of the electrolyte.

The insulating spacer body may be hollow and spherical, but also spherical shell-shaped, so that they are partially disposed on the anode and partly directly on the electrically conductive core or on the insulation coating. This is particularly advantageous when penetration of the electrolyte between the anode and core to the contact surface is to be prevented without using screw connections. However, the spacers may also consist of one piece and be rigid or elastic or multipart, with their parts fixed, for example, the half shells by adhesive or welded joints, or even releasably, for example by screwing each other or with the anodes and / or Power supply cables are connected. It is also advantageous with regard to the simple manufacture and assembly of the anodes on the core if the anodes consist of two or more parts, for example half-shells, which are solid and well electronically conductive with the core, for example by means of an adhesive or welded connection are connected to each other, or if they are easily detachable from the core, for example, with known rivet or screw, equipped. The screw connections offer particular advantages in the replacement of spent anodes, as these can be easily and conveniently mounted by hand on the reusable core. For easy liquid-tight contacting of the anodes with the core, it is particularly advantageous to form the anodes so that the continuous insulation coating of the core only in the region of the highest contact pressure of the half-shells of the anodes on the electrically conductive core, ie in the region of the screw connections to Exposing a contact surface is removed, the remaining parts of the half-shells of the anodes but the screw on both sides sealingly pressed onto the insulation coating, thereby achieving a reliable press seal against the advance of the electrolyte to the contact surface and thus in the long term good electron-conducting contact between the Anode and the electrically conductive core is secured. The anode arrangement according to the invention makes it possible to use both known inert material and active anode material. Economically advantageous is the use of iron-silicon casting alloys, which are both cheap and good pourable. This variant is preferably suitable for large protective objects, for which a power supply is acceptable. For smaller objects, however, the use of active anode material, in particular known magnesium-aluminum-zinc alloys is more advantageous. However, this must be taken into account that dre anodes, depending on the protection power requirement, consume more or less quickly and must be replaced more often, but this is possible without significant difficulties in the inventive solution.

embodiment

The anode arrangement will be explained in more detail below on several embodiments. In the accompanying drawings show:

Fig. 1 - the anode assembly as an anode strand in the water-bearing pipe with the longitudinally arranged on the core at intervals and the core enveloping anodes and the annular spacer body;

Fig. 2 - the anode assembly with arranged on the core anodes as shown in FIG. 1, but with between the anodes

arranged spherical spacers; Fig. 3 - the anode assembly with both on the anode and on the insulation coating of the power supply cable arranged spherical half-shell-shaped spacer bodies;

Fig. 4 - the one-piece cast around the core as a solid anode; Fig. 5 - the section along the line A-A of Figure 4;

Fig. 6 - consisting of two half-shells anode with the adhesive bonds; Figure 7 - the section along the line B-B of Fig. 6; Fig. 8 - consisting of two half-shells anode with the screw, the interrupted insulation coating

and the annular spacer body in the form-fitting adapted groove-shaped recess; 9 - the section along the line C-C of Fig. 8.

Fig. 1 and the enlarged view Fig. 8 leave the positive, liquid-tight, the core 4 enveloping arrangement of the anodes 1; 2; 3 and the electron-conducting contacts of the contact surface 5 well. In Fig. 8 is particularly well visible, as the core 4, except for the contact surface 5, wrapped by the insulation coating 17 and like the latter with each anode 1; 2; 3 is connected liquid-tight.

You can also see from Fig. 1; 2 and 3, the spacer body 6; 7; 8 and 9 and how their larger diameter D than the anode diameter prevents a short circuit of the anodes with the tube inner wall 10.

The arrangement of the annular spacer body 6 on the circumference of the anode 1 is clearly visible in Fig. 1 and 8, as well as the arrangement of the full spherical spacer body 7 and the hollow spherical spacer body 8 between the anodes 1 and 2 and 2 and 3 of FIG .2 is clearly visible.

The arrangement of the spherical half-shell-shaped spacer body 9 on the one hand both on the anodes 1; 2; 3 and on the other hand on the insulation cover 17 of the power supply cable 4; 17 is shown in FIG. 3.

In Figs. 4 and 5, the embodiment of the one-piece anodes 1; 2; 3 to see as a cast solid body.

There is also shown how the insulation coating 17 is liquid-tightly connected to the anode 1 by the adhesive bond 11.

The embodiment of the multi-part anodes 1; 2; 3 show FIGS. 6 and 7. The two half-shells 13; 14 are thereby the adhesive bonds 12 connected together.

The multi-part detachable embodiment of the anodes 1; 2; 3 is shown enlarged in FIGS. 8 and 9. Here are the two half shells 13 and 14 by the screw 15; 16 releasably connected together. Through these screw the highest contact pressure of the half-shells 13 takes place; 14 on the core 4 at the contact surfaces 5, so that here a good electron-conducting contact between the anodes 1; 2; 3 and the core 4 is. The liquid-tight termination of this contact surface 5 against the penetration of the electrolyte is carried out by the Preßdichtungen 18 by the insulation coating 17 by the same pressure of the screw 15; 16 there between the core 4 and the walls of the bores of the half-shells 13; 14 is compressed and still further characterized in that the elastically stretchable annular spacer body 6 due to its elastic force sealingly over the screw 15; 16 in the adapted groove-shaped recess 21 on the circumference of the anodes 1; 2; 3 is located.

To further improve the sealing of the contact surface 5 against the electrolyte also serve the seals 19; 20 between the insulation coating 17 and the anodes 1; 2; 3 and between the screw 15; 16 and the anodes 1; 2; 3 by plastic sealant, casting resin or adhesive. At the same time, the annular spacer body 6 secures the screw connections 15; 16 additionally against corrosion and falling out.

Claims (8)

Invention claim: An anode assembly for the cathodic protection of inner electrolyte-filled metallic hollow bodies, especially water-bearing pipes, with a good electrical conductivity core and an insulation coating on the surface, such as power supply cable, and a plurality of the length arranged at certain distances from each other, with the core in metallic connection standing, individual anodes, characterized in that each of the anodes form-fitting and liquid-tight enveloping the core, with the surface in electron-conductive contact, the core-except the contact surface-is coated by the insulation coating, the insulation coating is also liquid-tightly connected to each anode, and spacer bodies of a larger outer diameter than that of the anodes either on the circumference of the anodes or between the anodes on the insulation coating of the power supply cable or on the anodes and the insulation coating, al so are arranged on both. 2. Anode arrangement according to claim 1, characterized in that the anodes (1, 2, 3 ...) consisting of one piece and firmly connected to the core (4), for example consisting of a cast solid body, or more parts and solid, beispielsweie consisting of half shells (13; 14) with adhesive connections (11; 12), or consisting of several parts and detachable, for example consisting of half shells (13; 14) with clamping or screw connections (15; 16). 3. Arrangement according to claims 1 and 2, characterized in that the anodes only in the region of the highest contact pressure, for example only in the region of the screw connections (15; 16), form-fitting and liquid-tight, the core (4) are enveloping with this in electron-conductive contact and the insulation coating (17) interrupted only at these points, but with the anodes liquid-tight, for example, by press seals (18) is connected. 4. Anode arrangement according to claims 1 to 3, characterized in that the spacer body (6 to 9) in the form of hydrodynamically favorable rotationally symmetrical solid or hollow body, for example as a full annular spacer body (6), or as a full cast spherical spacer body (7 ), or as a hollow spherical spacer body (8) or as a spherical half-shell-shaped spacer body (9) are formed. 5. Anode arrangement according to claims 1 to 4, characterized in that the spacer body consist of one piece and in itself rigid or elastic,. Or multipart, similar to the anodes, formed and their parts, such as shells, solid, for example by gluing or Welded joints, or releasably, for example by screw, with each other and with the anodes and / or the power supply cable connected. 6. anode arrangement according to claims 4 and 5, characterized in that the spacer body, for example, the annular spacer body (6), are elastically deformable and by their elastic force on the circumference of the anodes (1, 2, 3 ...) in a positive fit matched groove-shaped recesses (21) on the screw (15; 16), are immovably mounted. 7. Anode arrangement according to claims 1 to 6, characterized in that as anode materials for inert anodes commonly used metals or metal oxides, such as magnetite, or metal alloys, such as iron-silicon, or non-metals, such as graphite, find use. 8. Anode arrangement according to claims 1 to 6, characterized in that as anode materials for active anodes common metals, such as zinc, or metal alloys, such as magnesium-zinc alloys, find use.