NZ741172B2 - Power cable of aluminium coated with a tetrazole compound corrosion inhibitor - Google Patents

Abstract

The present invention relates to a power cable comprising a metallic electric conductor surrounded by one or more semiconductive layer and one or more insulating layer, said cable having at least one metallic element made of aluminium, wherein a corrosion inhibitor is provided in direct contact with said at least one metallic element made of aluminium, and wherein said corrosion inhibitor is a corrosion inhibitor of formula (I).

Description

Power Cable Comprising an Aluminium Corrosion Inhibitor Field of the invention The present invention s to cable for power transmission/ distribution. In particular, the t invention relates to a power cable comprising at least one aluminium element.

Background of the invention Power cables may be used for both direct current (DC) or ating current (AC) transmission or distribution.

Cables for power transmission or bution at medium voltage (MV) or high voltage (HV) generally are provided with a cable core comprising a metallic electric conductor (usually aluminium or copper) surrounded by - from the radially innermost layer to the radially outermost layer - an inner semiconductive layer and an insulating layer.

The cable core is further surrounded by an outer semiconductive layer, a metal screen (usually aluminium or copper) and an outer sheath.

In the t description, the term "medium voltage" is used to refer to a voltage typically from about 1 kV to about 30 kV and the term "high voltage" refers to a voltage above 30 kV.

Aluminium has the advantage of being r and r than copper, but it is prone to oxidation and corrosion in the presence of moisture, thus cables comprising aluminium ts should be endowed with a moisture or water barrier to prevent water penetrating and reaching the aluminium element/s.

As a moisture or water barrier, a longitudinally sealed sheet of metal or plastic/metal laminate can be provided around the core/s. The metal can be aluminium. In the case of a laminate, the plastic layer is generally positioned facing towards the outer jacket of the cable and in contact thereto.

Diverse problems can arise due to water contacting the cable core, and then the penetration of water into cables, and stagnation therein, is an event that should be avoided. After manufacturing, cables are usually stored and shipped with protection caps on their heads.

However, the penetration and stagnation of water within the cable core can occur despite the above precautions. In particular, water penetration and stagnation cannot be excluded during installation, for example due to negligence of the installing personnel, but also through any defect in the polymeric sheath of the power cable which exposes the cable aluminium parts to the environment.

Components involved in the ion issue depend on cable type. A non exhaustive list can include: screen wires, equalizing tape , water barrier, sheets, etc.

In the presence of water, ium is known to form a protective oxide film stable within a wide pH range, from about 4 to 8 (see, e.g., Aluminium Corrosion, UK Aluminium Industry Fact Sheet 2 by ALFED, www.alfed.org.uk).

As reported by Khaled et al., "The inhibitive effect of some ole derivatives towards Al corrosion in acid solution: Chemical, electrochemical and theoretical studies", Materials try and Physics, 113, 2009, pp. 8, ium protective oxide film is amphoteric and dissolves substantially when the metal is exposed to high concentrations of acids or bases. Under these circumstances, corrosion inhibitors should be used e the solubility of the oxide film increases above and below pH range of from 4 to 8 and aluminium exhibits uniform attack. Inhibitors are used to prevent metal dissolution.

Khaled et al. relates to ion inhibition of aluminium in a solution of hydrochloric acid 1.0M in the absence and presence of different trations of tetrazole derivatives namely, 1-phenyl-1H-tetrazole thiol (A), 1-phenyl-1H-tetrazole (B), 1H-tetrazolamine (C), 1H- tetrazole (D). The reduction in the ution of aluminium in the presence of these tested compounds was attributed to the sulphur atom present in the thio group found in compound A as well as to the amino group and the heterocyclic rings.

Tetrazole compounds have been reported in other literature and patent references to have inhibiting action on the corrosion of other non-ferrous metals, such as silver and copper.

Among them, F. Zucchi et al., "Tetrazole Derivatives as Corrosion Inhibitors for Copper in Chloride Solutions", Corrosion Science, Vol. 38, No. 11, pp. 2019-2029, 1996 relates to the inhibiting action of some tetrazole derivatives on the copper corrosion in chloride solutions.

Among the tested derivatives, 5-phenyl-tetrazole (5Ph-T) and 5- mercaptophenyl-tetrazole (5Mc-1Ph-T) decrease their inhibiting ability at 80°C. The polarisation conductance data demonstrate that only 5Mc-1Ph-T is able to maintain its protective characteristics for almost 60’ at 40°C.

US 5,744,069 relates to a water soluble metal anticorrosive agent comprising certain tetrazole nds for non-ferrous metals such as , copper alloys and super-hard alloys. The water soluble metal anticorrosive agent comprising a ole nd is represented by the following formula (A): R1 N R2 (A) n R1 and R2 each indicate hydrogen, an alkyl group having 1 to 20 carbon atoms, a cycloalkyl group, a phenyl group, an alkylphenyl group, an amino group, a mercapto group or an alkylmercapto group.

US 4,873,139 relates to a technique for ing corrosion ance to silver and copper surfaces by contacting such surfaces with yl-1H-tetrazolethiol.

Description of the invention The ant has observed that in cable applications corrosion phenomena of aluminium can occur even within the above mentioned pH range of from 4 to 8. In particular, the Applicant has observed that these corrosion phenomena are as serious as to jeopardize the integrity of the aluminium component(s). Furthermore, the development of en due to the corrosion of the aluminium can give rise to dangerous situations, in addition to compromising the functionality of the power cable.

Without wishing to be bound by a theory, the Applicant hypothesized that this corrosion phenomenon of the aluminium may be mainly due to three redox isms, caused by the peculiar construction of the power cables.

Such redox mechanisms are (i) a reaction of oxidation-reduction, in the event of water penetration, at the air/water interface on the surface of the aluminium, (ii) a reaction of ion-reduction due to a galvanic coupling between aluminium and carbon black from an adjacent nductive layer or a carbon black loaded water absorbing tape, where ium behaves as a sacrificial anode, and (iii ) a reaction of oxidation-reduction due to a galvanic coupling between aluminium and copper, where the aluminium still behaves like a sacrificial anode.

The Applicant also observed that in the presence of a ntial lack of oxygen within the cable a sufficient ion of the protective layer of aluminium oxide cannot be obtained.

The Applicant faced the problem of avoiding the phenomena of aluminium corrosion in power cable, in particular within the above ned pH range of from 4 to 8.

In addition, taking into t the operation conditions of a power cable, a suitable inhibitors of the aluminium corrosion in a power cable should exert its function for ged time period (in the order of, at least, months) and at temperatures greater than 30°C.

Summary of the invention The Applicant found that the above problem can be solved by providing power cables comprising an aluminium component with a corrosion inhibitor in direct contact with the aluminium component, the corrosion inhibitor having at least one hydroxyl-tetrazole moiety linked to a cycloaromatic moiety.

A possible theoretical interpretation is that while hydroxyl-tetrazole moiety appears suitable for interacting with metallic ium, a cycloaromatic group could provide a hydrophobic shield against water.

The combination of the two moieties can impart the compound of formula (I) with a corrosion inhibiting capacity le for protecting the aluminium parts of a power cable for prolonged period and at temperatures substantially greater than the room one.

Accordingly, in a first aspect, the present invention relates to a power cable comprising a metallic element made of aluminium, wherein a corrosion inhibitor is provided in direct t with the metallic element, the corrosion inhibitor having the general formula (I): R1-Ar-R2 (I) wherein R1 is a 1-hydroxy-tetrazolyl group a 2-hydroxy-tetrazol yl group, 1-acryloxy-tetrazolyl group or 1-(2-carboxyethenyl)-tetrazol- -yl group; Ar is a clic or bicyclic aromatic moiety; and R2 is a hydrogen atom (H) or a 1-hydroxy-tetrazolyl group, a 2- hydroxy-tetrazolyl group, a hydroxyl group (OH), a vinyl group, an allyl group or a -O-CO-R4 group, where R4 is an alkenyl group having from 2 to 6 carbon atoms.

When Ar is a clic aromatic moiety and R2 is different from hydrogen atom, R1 and R2 are in ortho, meta, or para position with respect to each other.

When Ar is a ic aromatic moiety and R2 is different from hydrogen atom, R1 and R2 can be in peri position with respect to each other, or, ably, can be substituents of the same cycle.

Ar is advantageously selected from benzene and alene moiety.

Preferably, the corrosion inhibitor for the cable of the present invention has the following general formula (Ia) R1 (Ia) n R1 and R2 have the same meanings as defined in a Preferably, R1 is a 1-hydroxy-tetrazolyl group.

Preferably, R2 is a hydrogen atom, a 1-hydroxy-tetrazolyl group, more preferably in ortho position with respect to R1, or a hydroxyl group (OH). More preferably, R2 is a hydrogen atom.

The corrosion inhibitor of formula (I) can be synthetized according to procedures known to the skilled person. See, for example, Tselinski, I.

V. et al., Russian Journal of Organic Chemistry, Vol. 37, No. 3, 2001, pp. 430-436.

For the purpose of the present description and of the appended claims, except where otherwise indicated, all s sing amounts, ties, percentages, and so forth, are to be understood as being modified in all instances by the term "about". Also, all ranges include any combination of the m and minimum points disclosed and include any intermediate ranges therein, which may or may not be specifically enumerated herein.

The cable of the present invention is a cable for power transmission/distribution comprising one or more cable cores.

Preferably, the power cable of the invention has three cable cores.

The term of "cable core" indicates – in the present description and claims - a metallic ic conductor sequentially surrounded by an inner semiconducting layer, an insulating layer and an outer semiconducting layer, sequentially in contact with one another.

The electric conductor of the cable of the invention can be made of aluminium, copper or composites thereof. The conductor can be in form of a metal rod or of metal stranded wires.

Power cable of the present invention can further comprise a metal screen and an outer sheath.

The metal screen can be made of ium or copper in form of wires, braids, tapes, rods or longitudinally sealed foils. In a cable configuration a single metal screen encircled all of the cable cores, while in another configuration each cable core is surrounded by its screen so that the cable has as many cable cores as metal screens. ably, the corrosion inhibitor of formula (I) is associated with a supporting material to form a corrosion inhibiting element where the corrosion inhibitor is in direct contact with the metallic element made of aluminium.

For example, the corrosion inhibitor of formula (I) for the cable of the invention can be absorbed in or adsorbed on the supporting material.

Supporting materials suitable for the present invention are preferably chemically/physically inert to water.

Supporting materials suitable for the present invention are ably heat-resistant at least up to 100°C. Advantageously, the supporting material is heat-resistant up to 150°C, more preferably up to 200°C.

Supporting materials suitable for the ion are preferably polymeric material, either l or synthetic.

For example, the ting al can be cellulose, polyamide or polyesters.

The supporting material can be provided in various forms suitable for the cable construction, for example in form of threads, yarns, tapes or sheets.

The corrosion inhibitor of formula (I) can be bound onto the supporting al by means of an adhesive al, typically polyvinyl alcohol (PVA) or an te resin. In particular, the supporting material can be moistened with a solution of an adhesive material, and then the corrosion inhibitor of a (I) in form, for example, of powder, is sprinkled thereon and s ped in the solution and, after drying, in the adhesive material.

Preferably, the average amount of corrosion inhibitor of formula (I) in direct contact with the metallic element made of aluminium to be protected ranges from 1x10-3 g/cm2 to 100x10-3 g/cm2 with respect to the surface of the metallic element.

In the cable of the present invention the ion inhibitor of formula (I), optionally supported in the corrosion inhibiting element, can be present within the metal wires of the electric tor, at the interface between the conductor and the inner semiconductive layer, in contact with the metal screen, or at the interface of the metal screen and the inner semiconductive layer or the outer .

In the cable of the ion a water barrier can be present in radial external position with respect to the cable core(s) and metal screen(s).

The water barrier can be in form of a longitudinally sealed sheet of metal or plastic/metal laminate. The metal can be aluminium. In the case of a laminate, the plastic layer is generally positioned facing towards the outer jacket of the cable and in contact thereto.

In a cable according to the invention having a water barrier comprising an aluminium layer, the corrosion inhibitor of a (I), optionally supported in the corrosion ting element, can be t in contact with such aluminium layer.

In a second aspect, the present invention relates to a process for producing a power cable comprising a metallic element made of aluminium and a corrosion inhibiting element comprising a supporting material associated to a corrosion inhibitor of formula (I), R1-Ar-R2 (I) wherein R1 is a 1-hydroxy-tetrazolyl group a 2-hydroxy-tetrazol yl group, loxy-tetrazolyl group or 1-(2-carboxyethenyl)-tetrazol- -yl group; Ar is a clic or bicyclic aromatic moiety; and R2 is a hydrogen atom (H) or a 1-hydroxy-tetrazolyl group, a 2- hydroxy-tetrazolyl group, a hydroxyl group (OH), a vinyl group, an allyl group or a -O-CO-R4 group, where R4 is an alkenyl group having from 2 to 6 carbon atoms, the process comprising the steps of - ling the supporting al with said corrosion tor of formula (I) in dry form or dissolved in a polar solvent to be subsequently evaporated, to provide said corrosion inhibiting element; and - positioning the corrosion inhibiting t in direct contact with the metallic element made of aluminium.

Polar solvents particularly preferred for the process of the invention are water, acetone and hydroxyl-containing solvents such as isopropanol and ethanol.

Advantageously, the corrosion inhibitor of a (I) is dissolved in the polar solvent at a concentration of up to 250-300 ppmw (parts per million weight).

Preferably, the solution of the corrosion inhibitor of formula (I) into the solvent is a saturated solution.

Following evaporation of the organic solvent, the supporting material with the corrosion inhibitor of formula (I) enters into the cable manufacturing through paying off station ing on the desired position of the marker within the cable.

Brief description of the figures The present invention will be better tood by reading the following detailed description, given by way of e and not of limitation, to be read with the accompanying drawings, wherein: Figure 1 shows a perspective view of a power cable according to an embodiment of the present invention; Figure 2 shows a cross section of a power cable according to an embodiment of the present invention; Figure 3 shows a graph plotting the linear polarization resistance (LPR) variation over time with and without corrosion tor, as described in Example 2; and Figure 4 shows a graph plotting the corrosion rate variation over time with and without corrosion inhibitor, as described in Example 2.

Detailed description of the invention Figure 1 shows a perspective view of a power cable 11 according to an ment of the present invention.

The power cable 11 of Figure 1 is a single core cable and comprises a conductor 12, an inner semiconductive layer 13, an insulating layer 14 and an outer semiconductive layer 15, which constitute the cable core.

The cable core is surrounded by, a metal screen 16 and an outer sheath 17.

The tor 12 lly ses metal wires, which are preferably made of copper or aluminium, and which are braided together by using conventional technique.

The cross sectional area of the conductor 12 is determined in relationship with the power to be transported at the selected voltage.

Preferred cross sectional areas for power cables according to the t invention range from 16 mm2 to 1,600 mm2.

Inner semiconductive layer 13, insulating layer 14 and outer semiconductive layer 15 are made of polymeric materials.

Polymeric als le for layers 13, 14 and 15 can be selected from the group comprising: polyolefins, copolymers of different olefins, copolymers of an olefin with an ethylenically unsaturated ester, polyesters and mixtures thereof.

Examples of suitable polymers are: polyethylene (PE), in particular low density PE (LDPE), medium density PE (MDPE), high density PE (HDPE), linear low density PE ), ultra-low density polyethylene (ULDPE); polypropylene (PP) and copolymers thereof; elastomeric ethylene/propylene copolymers (EPR) or ethylene/propylene/diene terpolymers (EPDM); ethylene/vinyl ester copolymers, for example ethylene/vinyl acetate (EVA); ethylene/acrylate copolymers, in particular ethylene/methyl acrylate (EMA), ethylene/ethyl acrylate (EEA) and ethylene/butyl acrylate (EBA); ethylene/?-olefin thermoplastic copolymers or ical mixtures thereof.

In the case of inner semiconductive layer 13 and outer nductive layer 15, the above listed polymeric materials are added with an electro-conductive carbon black, for e electroconductive furnace black or acetylene black, so as to confer semiconductive properties to the r material.

The insulating layer 14, inner nductive layer 13 and outer semiconductive layer 15 can be made of polymeric a plastic al, preferably sing a thermoplastic polymer material including a predetermined amount of a dielectric liquid. Example of thermoplastic insulating layers are disclosed in WO 98, WO 02/27731, WO 04/066318, WO 07/048422 e WO 08/058572.

The metal screen 16 is made of a metal braid, made for example of aluminium, wrapped around the outer semiconductive layer 15.

The outer sheath 17 is preferably made of polymer material, such as polyvinyl chloride (PVC) or polyethylene (PE).

In the embodiment of Figure 1, a corrosion inhibiting element 18, in form of a tape of supporting material bearing, on the surface facing the metal screen 16, a corrosion inhibitor of formula (I), is provided around and in contact with the metal screen 16.

Similarly, but not shown in figure 1, a corrosion inhibiting element can be provided, preferably in form of yarns, within the metal wires of the conductor 12 and/or between the inner semiconductive layer 14 and the conductor 12 and/or between the metal screen 16 and outer semiconductive layer 15.

Figure 2 shows another ment of the invention. Figure 2 illustrates a cable 21 comprising three cable cores. Each cable core comprises a conductor 22, an inner semiconductive layer 23, an insulating layer 24 and an outer semiconductive layer 25. Each cable core is surrounded by a metal screen 26. An outer sheath 27 surrounds all of the three screened cable cores. Conductors 22 are each made of a solid aluminium rod.

The three screened cable cores are stranded and embedded into filler (or bedding) 29 which, in turn, is surrounded by an outer sheath 27. Outer sheath 27 can be made of the same al already disclosed in connection with outer sheath 17 of Figure 1.

The materials of inner semiconductive layer 23, insulating layer 24, and outer semiconductive layer 25 can be as those already mentioned in connection with cable 11 of Figure 1 for analogous cable portions.

In the embodiment of Figure 2, a corrosion inhibiting element 28, in form of a tape supporting material bearing a ion inhibitor of formula (I) on the surface facing the conductor 22, is provided at the interface between conductor 22 and the inner nductive layer 23 of each cable core.

The corrosion inhibiting element 28 can be, alternatively or additionally, a yarn or tape wound positioned as already said in tion with cable 11 of Figure 1.

Similarly, but not shown in figure 2, a corrosion inhibiting element can be provided in direct contact with metal screen 26, either between the metal screen 26 and outer semiconductive layer 25 or between the metal screen 26 and outer sheath 27.

The cable ing to the present invention can be manufactured as disclosed above. The ion inhibiting element can be supplied using common process apparatus at a suitable step of the manufacturing process. For example, when the corrosion inhibiting t is to be positioned within the wires of an electric conductor, the inhibiting element in form of yarn(s) is stranded together with the wires. For example, when the corrosion inhibiting element is to be positioned between the electric conductor and the protecting layer (insulating layer or inner semiconducting layer), the corrosion ting element in form of yarn(s) or tape is wound around the conductor before extruding said layer.

The ing examples are intended to further illustrate the present invention, without however restricting it in any way.

Example 1 Synthesis of 5-phenylhydroxy-(1H)-tetrazole Step 1 : Preparation of N-hydroxybenzimidoyl chloride Ethanol (30 mL) was poured in a 250 mL three-necked roundbottomed flask equipped with internal temperature probe, reflux condenser and nitrogen inlet. Benzoyl chloride (19.71 mL, 23.87 g, 0.17 moles) was added via syringe and the on was stirred during the addition. Hydroxylamine hydrochloride (21.20 mL, 35.41 g, 0.51 moles) was added in one portion, followed by sodium hydroxide 97% (27.2 g, 0.68 . The on flask was placed in an oil bath and heated at 60°C with stirring for 1 hour. The reaction flask was removed from the oil bath and was left to cool to ambient temperature.

The mixture was transferred to a single-necked round-bottom flask and trated by rotary evaporation at temperature of 45°C and vacuum of 40 mbar.

The solid residue was transferred to a tory funnel and was extracted three times with ethyl acetate. The combined organic layers were dried over Na2SO4. The drying agent was removed by filtration and then the c layer was concentrated by rotary evaporation at temperature of 45°C and vacuum of 40 mbar.

The solid residue was recrystallized from 60 mL of hexane at 5°C for 2 hours to give crystals of N-hydroxybenzimidoyl chloride (20.21 g, 0.13 moles).

The resulting yield of reaction was of: 76.9% Step 2: ation of N-Hydroxybenzimidoyl azide Sodium azide (9.75 g, 0.15 moles) dissolved in 10 mL of water was charged in a 250 mL three-necked round-bottomed flask equipped with internal temperature probe and reflux condenser. A solution of N- hydroxybenzimidoyl chloride (18.65 g, 0.12 moles) in 20 mL of ol was added se. The solution was placed in an oil bath and heated at 45°C with stirring for 2.5 hours.

At the end of the reaction, the reaction flask was removed from the oil bath and was left to cool to ambient temperature.

The mixture was transferred to a -necked round-bottom flask and the solvent of the solution was distilled off by rotary evaporation at temperature of 25°C and vacuum of 55 mbar.

The residue was transferred to a separatory funnel and was extracted three times with diethyl ether (3x30 mL). The aqueous phase was further extracted three times with diethyl ether (3x30 mL).

The organic layers were dried with sodium sulfate filtered and evaporated to give N-hydroxybenzimidoyl azide (16.2 g, 0.10 .

The resulting yield of reaction was of: 89.9% Step 3: Preparation of N-acetoxybenzimidoyl azide N-Hydroxybenzimidoyl azide (16.2 g, 0.10 moles), dissolved in 10 mL of dichloromethane and pyridine (11.85 g, 12.12 mL, 0.15 moles) was d in a 100 mL three-necked round-bottomed flask, ed with internal temperature probe.

The solution was placed in an ice/ethanol bath and kept at 0°C while stirring, subsequently acetyl chloride (10.19 g, 9.23 mL, 0.13 moles) was added dropwise. After the addition was completed, the mixture was stirred at room temperature for 4 hours. After reaction terminated, water (20 mL) was added to the mixture and distilled off to remove methylene chloride.

The obtained solid was ed through a folded filter and left to dry overnight. The residue was extracted three times with toluene (3x10 mL) in a separatory funnel, to remove water and then the organic layer was dried with sodium e and filtered. The solution was cooled to 0°C for 2 hours to give crystals that were filtered and dried to 60°C for 7 hours, to give crystals of N-acetoxybenzimidoyl azide (18.36 g, 0.09 moles).

The resulting yield of reaction was of: 92.3% Step 4: Preparation of 5-phenylhydroxy-(1H)-tetrazole N-acetoxybenzimidoyl azide (18.36 g, 0.09 mol) dissolved in 30 mL of diethyl ether, and zinc chloride were charged in a 100 mL singlenecked round-bottomed flask. The solution was cooled to 20°C with stirring for 2 hour to give de-acetylation and intramolecular cyclization.

After reaction terminated, the solvent was removed by rotary evaporation at temperature of 30°C and vacuum of 400 mbar, to obtain crystals of 5-phenylhydroxy-(1H)-tetrazole (11.34 g, 0.07 moles).

The ing yield of reaction was of: 77.7% Example 2 tion of corrosion inhibiting property The 5-phenylhydroxy-(1H)-tetrazole corrosion inhibitor prepared in Example 1 was used to evaluate the corrosion inhibition of the aluminium shield 16 in the cable 11 of Figure 1.

The electrode linear polarization resistance (LPR) method was used for evaluating the corrosion rate in presence and absence of inhibitor, as shown, for e, in http://www.gamry.com/application- notes/corrosion-coatings/corrosion-techniques-polarization-resistance/.

The electrode system was ed by using (i) a Standard Calomel Reference ode as a reference electrode, (ii) an aluminium screen, insulated with a polyester tape, as a working electrode (WE), and (iii) an aluminium wire of 1.6 mm er and 45 cm long, insulated with a polyester tape, inserted between the aluminium screen and a polyethylene outer sheath, as a counter electrode (CE).

For comparison e, two systems were realized, with and without corrosion inhibitor.

In the system with the corrosion inhibitor, the aluminium wire ed as counter electrode was previously immersed into tap water solution containing 0.7 mmoles/L of 5-phenylhydroxy-(1H)-tetrazole as corrosion inhibitor (I). In the system without the corrosion inhibitor, the aluminium wire employed as counter electrode was previously immersed into tap water.

Using the linear polarization resistance set up the material was polarized, typically on the order of ±10mV, relative to the open circuit potential. As the potential of the working electrode was changed , a current was induced to flow n the working and counter electrodes, and the material’s resistance to polarization was found by taking the slope of the ial versus current curve. This resistance was then used to find the ion rate of the material using the Stern- Geary equation.

The results are illustrated in Figure 3, showing a graph ng the polarization resistance variation (ohm·cm2) in ordinate over time (hours) in sa with (straight line and filled marker) and without (dashed line and empty marker) corrosion inhibitor, and in Figure 4, showing a graph plotting the corrosion rate ion (as current density, µAmp/cm2) in ordinate over time (hours) in abscissa with (dashed line and rhombic markers) and without (straight line and round markers) corrosion inhibitor.

The values of polarization resistance obtained with the sample with corrosion inhibitor were substantially higher than those obtained with the sample t corrosion inhibitor, as from Figure 3. T he results illustrated in Figure 4 show that the calculated corrosion rate based on LPR method in the presence of inhibitor was about half the ated corrosion rate in the absence of tor.

These results confirmed that a corrosion inhibitor of formula (I) can effectively inhibit the corrosion of aluminium ts of power cables.

Claims (11)

Claims

1. Power cable comprising a metallic element made of aluminium, wherein a corrosion inhibitor is provided in direct contact with the ic t, the corrosion inhibitor having the following 5 general formula (I): R1-Ar-R2 (I) wherein R1 is a 1-hydroxy-tetrazolyl group a 2-hydroxytetrazolyl group, loxy-tetrazolyl group or 1-(2- carboxyethenyl)-tetrazolyl group; 10 Ar is a monocyclic or bicyclic aromatic ; and R2 is a hydrogen atom (H) or a 1-hydroxy-tetrazolyl group, a 2-hydroxy-tetrazolyl group, a hydroxyl group (OH), a vinyl group, an allyl group or a -O-CO-R4 group, where R4 is an alkenyl group having from 2 to 6 carbon atoms, 15 wherein the corrosion inhibitor of formula (I) is in an average amount of from 1x10-3 g/cm2 to 100x10-3 g/cm2 with respect to the surface of the metallic element.

2. Power cable according to claim 1, wherein, when Ar is a monocyclic aromatic moiety and R2 is different from hydrogen 20 atom, R1 and R2 are in ortho, meta, or para position with respect to each other.

3. Power cable according to claim 1, wherein, when Ar is a bicyclic aromatic moiety and R2 is different from hydrogen atom, R1 and R2 are in peri position with respect to each other, or are 25 substituents of the same cycle.

4. Power cable ing to any one of the preceding claims, wherein the corrosion inhibitor has the following l formula R1 (Ia) wherein R1 and R2 have the same meanings as defined in formula (I) of claim 1.

5. Power cable according to any one of the preceding claims, 5 wherein R1 is a 1-hydroxy-tetrazolyl group and R2 is a hydrogen atom.

6. Power cable according to any one of claims 1 to 4, wherein R2 is a en atom, a 1-hydroxy-tetrazolyl group, preferably in ortho position with respect to R1, or a hydroxyl group (OH). 10

7. Power cable according to any one of the preceding claims, wherein the corrosion inhibitor of formula (I) is associated with a ting material to form a corrosion inhibiting element, where the corrosion inhibitor is in direct contact with the metallic t made of aluminium. 15

8. Power cable according to claim 7, wherein the corrosion tor is absorbed in or adsorbed on the supporting al.

9. Process for producing a power cable comprising a metallic element made of aluminium and a corrosion inhibiting element comprising a supporting material ated to a corrosion 20 inhibitor of formula (I), R1-Ar-R2 (I) wherein R1 is a 1-hydroxy-tetrazolyl group or a 2-hydroxytetrazolyl group, a loxy-tetrazolyl group or a 1-(2- carboxyethenyl)-tetrazolyl group; 25 Ar is a monocyclic or bicyclic aromatic moiety; and R2 is a hydrogen atom (H) or a 1-hydroxy-tetrazolyl group, a 2-hydroxy-tetrazolyl group, a hydroxyl group (OH), a vinyl group, an allyl group or a -O-CO-R4 group, where R4 is an alkenyl group having from 2 to 6 carbon atoms; the process comprising the steps of - sprinkling the supporting material with said corrosion tor of a (I) in dry form or dissolved in a polar solvent to be 5 subsequently evaporated, to provide said corrosion inhibiting element; and - positioning the corrosion inhibiting element in direct contact with the metallic t made of aluminium, wherein said corrosion inhibitor of formula (I) is in an average 10 amount of from 1x10-3 g/cm2 to 100x10-3 g/cm2 with respect to the surface of the metallic element.

10. Process according to claim 9 wherein the polar solvent is selected from water, acetone and hydroxyl-containing solvents.

11. Process according to claims 9 or 10, wherein the ion 15 inhibitor is dissolved in the polar solvent at a concentration of up to 0 ppmw (parts per million weight).