ELECTRIC CABLE WITH CORROSION RESISTANT ARMOR

Abstract

An electric cable (10) is disclosed comprising a) at least one cable core (11) comprising at least one power transmissive insulated element (12); and b) a metallic outer armor (19) containing the cable core (11); wherein the outer armor (19) comprises a carbon steel tape (20) wound according to helical interlocked windings, the tape (20) being coated with an aluminum coating layer (22) having a thickness equal to or lower than 50 m. Furthermore, a process for manufacturing such an electric cable is disclosed.

Claims

1. An electric cable comprising: a cable core comprising a power transmissive insulated element; and a metallic outer armor containing the cable core; wherein the outer armor comprises a carbon steel tape wound according to helical interlocked windings, the tape being coated with an aluminum coating layer having a thickness equal to or lower than 50 m.

2. The electric cable according to claim 1, wherein the aluminum coating layer has a thickness of from 20 m to 45 m.

3. The electric cable according to claim 1, further comprising an AlFe intermetallic compound at an interface between the steel tape and the aluminum coating layer.

4. The electric cable according to claim 1, wherein the aluminum coating layer of the carbon steel tape of the outer armor comprises silicon.

5. The electric cable according to claim 1, further comprising a FeAlSi intermetallic compound at an interface between the steel tape and the aluminum coating layer.

6. The electric cable according to claim 4, wherein the aluminum coating layer comprises from 5 to 15% by weight of Si based on a total weight of the aluminum coating layer.

7. The electric cable according to claim 5, wherein the FeAlSi intermetallic compound has the formula:
Al.sub.xSiFe.sub.y wherein x is a number of 3 to 7 and y is a number of 1 to 3.

8. The electric cable according to claim 7, wherein the FeAlSi intermetallic compound has the formula:
Al.sub.5.3SiFe.sub.1.5.

9. The electric cable according to claim 1, further comprising an intermetallic compound at an interface between the steel tape and the aluminum coating layer, the intermetallic compound being included within an interface layer having a thickness of m to 7 m.

10. The electric cable according to claim 1, wherein the carbon steel tape has a thickness of 550 m to 750 m.

11. A process for manufacturing an electric cable comprising: a cable core comprising a power transmissive insulated element; and a metallic outer armor containing the cable core; wherein the outer armor comprises a carbon steel tape wound according to helical interlocked windings, the tape being coated with an aluminum coating layer having a thickness equal to or lower than 50 m; the process comprising: producing a flat carbon steel tape; dipping the flat carbon steel tape in melted aluminum to obtain a flat aluminum coated steel tape; shaping the flat aluminum coated steel tape at room temperature; and winding and interlocking the flat aluminum coated steel tape around the cable core.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0089] Additional features and advantages of the present invention will appear more clearly from the following detailed description of a preferred embodiment thereof, such description being provided merely by way of non-limiting example and being made with reference to the annexed drawings. In such drawings:

[0090] FIG. 1 shows a schematic perspective view of an electric cable according to a first preferred embodiment of the invention;

[0091] FIG. 2 is a cross-sectional view of the electric cable of FIG. 1;

[0092] FIG. 3 shows a schematic perspective view of an electric cable according to a second preferred embodiment of the invention;

[0093] FIG. 4 is a cross-sectional view of the electric cable of FIG. 3;

[0094] FIG. 5 is an enlarged scale detail of an outer portion of an outer armor of the electric cables of FIGS. 1-4 showing an intermetallic layer interposed between a steel tape forming the armor and an aluminium coating layer of the sheet;

[0095] FIG. 6 is a graph of an energy dispersive spectroscopy (EDS) elemental analysis of an intermetallic compound at the interface between the steel tape and the aluminum coating layer.

DETAILED DESCRIPTION OF THE CURRENTLY PREFERRED EMBODIMENTS

[0096] In the following detailed description of preferred embodiments of the present disclosure, numerous specific details are set forth in order to provide a more thorough understanding of the claimed subject matter.

[0097] However, it will be apparent to one of ordinary skill in the art that the preferred embodiments disclosed herein may be practiced without these specific details. In other instances, well-known features have not been described in detail to avoid unnecessarily complicating the description.

[0098] The preferred embodiments disclosed herein relate to a cable 10 for use with a downhole pump. The downhole pump may be any pump known in the art, such as an electrical submersible pump.

[0099] As such, a cable 10 of the present disclosure may be capable of better withstanding long-term exposure to the severe environment encountered downhole, in particular the exposure to an aqueous medium comprising hydrogen sulfide and carbon dioxide dissolved therein.

[0100] Accordingly, as from FIGS. 1-4, a cable 10 is provided with an outer armor 19 comprising a interlocked carbon steel tape comprising an aluminium coating 22 (shown in FIG. 5) that is continuously bonded.

[0101] In FIGS. 1 and 2, a round electric cable 10 for use with a downhole pump 2 according to the present invention is shown.

[0102] The cable 10 extends along a longitudinal axis X-X.

[0103] The round cable 10 comprises three cores 11 each of which comprises one power transmissive element or conductor 12.

[0104] The present invention, however, could also deal with mono-polar or multi-polar cables, too.

[0105] The cable 10 can comprise additional cores with different transmissive elements too, such as optical transmissive elements or combined electro-optical transmissive elements (not shown).

[0106] Each cable core 11 comprises, in order from the centre outwards the conductor 12 and an insulating layer 14.

[0107] The material used for the conductor 12 for a cable 10 in accordance with the present disclosure may include any metallic electrically conducting material known in the art.

[0108] As such, a metallic conductor may include: solid copper or aluminium rod, stranded copper or aluminium wires, copper or aluminium clad steel wires, titanium clad copper wire, and/or any other conducting wire known in the art.

[0109] The insulating layer 14 comprises a polymeric base material known in the art and suitable for the purpose.

[0110] Preferably, the insulating coating layer 14 comprises polypropylene or ethylene propylene diene monomer (EPDM) synthetic rubber as a polymeric base material.

[0111] The cores 11 of the cable 10 are embedded within a filler 17 preferably made of a suitable polymeric material such as polyethylene.

[0112] The cable 10 preferably comprises at a radially outer position with respect to the filler 17 a protective sheath 18 made of any suitable material adapted to protect the cores 11 from mechanical damage.

[0113] Preferably, the protective sheath 18 can be made of a material selected from nitrile and EPDM rubber.

[0114] In the embodiment illustrated in the drawings, the outer armor 19 containing the cable cores 11 of the cable 10 is provided at a radially outer position with respect to the protective sheath 18.

[0115] Further protective layers (not illustrated) can be present in radial internal position with respect to the outer armor 19, according to specific application requirement. See, for example, http://petrowiki.org/ESP_power_cable.

[0116] As detailed in FIG. 5, the outer armor 19 can comprise a carbon steel tape 20 wound according to short-pitch helical interlocked windings and comprising an aluminum coating layer 22 applied on both the outer and the inner surfaces and, preferably, also on the edges thereof.

[0117] Preferably, the aluminum coating layer 22 comprises silicon.

[0118] An intermetallic layer 21 preferably made of an alloy which comprises a FeAlSi intermetallic compound is formed at an interface between the steel tape 20 and the aluminum coating layer 22.

[0119] The round cable 10 according to the present disclosure can be made by any known techniques for the deposition of layers of suitable materials.

[0120] With reference to FIGS. 3-4, a further embodiment of the cable 10 according to the invention will now be illustrated.

[0121] In the following description and in such figures, the elements of the cable 10 which are structurally and functionally equivalent to those described above with reference to the embodiment shown in FIGS. 1 and 2 will be indicated with the same reference numbers and will not be further described.

[0122] In the preferred embodiment illustrated in FIGS. 3-4, the cable 10 is a flat cable comprising three cores 11 disposed in a mutual planar configuration.

[0123] All the cores 11 lie substantially parallel in a common plane and adjacent one to the other. In a section of the cable 10 transversal with respect to the lengthwise direction thereof, the cores 11 lie substantially centred on a common transversal plane Y-Y.

[0124] In this embodiment of the cable 10, the outer armor 19 presents two substantially flat sides 19a parallel to the above cited common plane Y-Y and two opposite curved sides 19b surrounding a portion of two lateral cores 11.

[0125] Similarly to the preceding embodiment, the outer armor 19 preferably comprises a carbon steel tape 20 wound according to short-pitch helical interlocked windings and comprising an aluminum coating layer 22 applied on both surfaces and on the edges thereof.

[0126] Similarly to the preceding embodiment, the aluminum coating layer 22 preferably comprises silicon.

[0127] As illustrated in FIG. 5, an intermetallic layer 21 preferably made of an alloy which comprises a FeAlSi intermetallic compound is also in this case formed at an interface between the steel tape 20 and the aluminum coating layer 22.

[0128] FIGS. 1-5 show just two possible embodiments of a cable according to the present invention: it is obvious that modifications known in the art can be made to these embodiments, while still remaining within the scope of the present invention.

[0129] The present invention is further described in the following examples, which are merely for illustration and must not be regarded in any way as limiting the invention.

Example 1

[0130] In order to evaluate the hydrogen sulfide corrosion and cracking resistance of Al-coated carbon steel tapes to be used for building the outer armor of a cable according to the present invention, specimens of carbon steel tapes were subjected to a first ageing test act according to NACE Standard TM0177-96 sulfide stress corrosion cracking (SSCC) test specifications.

[0131] The Al-coated carbon steel tapes were obtained as described above by hot dip coating a carbon-manganese steel tape in a bath containing aluminum which comprises silicon (10% wt).

[0132] The thickness of the aluminum coating layer was of about 30 m, while the thickness of the intermetallic layer comprising a FeAlSi intermetallic compound was of about 5 m.

[0133] In the test carried out, the FeAlSi intermetallic compound in the intermetallic layer was determined to have the formula Al.sub.5.3SiFe.sub.1.5.

[0134] The tests were made under the following conditions: [0135] Preloading of the specimens by deflection method, with comparator [0136] Test solution: A of EFC 16 (European Federation of Corrosion) [0137] pH solution: 3.8-4.2 [0138] Volume/surface ratio: 30 cm.sup.3/cm.sup.2 [0139] Gas test: 10% wt H.sub.2S+90% wt CO.sub.2 or 100% wt H.sub.2S [0140] Stress level: 90% of AYS (average yield stress) [0141] Visual exam on every specimen, after corrosion test

[0142] The opposite ends of the aluminum coated carbon steel tapes were protected with epoxy paint.

[0143] The specimens were preloaded according to the NACE standard specifications and submerged in test solutions at saturation phase.

[0144] The parameters for the SSCC test are summarized in the following Table 1.

TABLE-US-00001 TABLE 1 Four point Maximum stress loading bending 90% Y.sub.0,2% Gas 10% wt H.sub.2S 90% wt CO.sub.2 100% wt H.sub.2S Duration 720, 1440, 2160, 3000, and 4320 hours

[0145] The tested specimens were: aluminum coated carbon steel tapes and comparative uncoated carbon steel tapes as specified in Table 2 below.

[0146] Specifically, the specimens were submerged in the test solution containing a gas formed by 10% wt H.sub.2S+90% wt CO.sub.2 in water at room temperature.

[0147] In Table 2 below the ageing test details for a NACE Standard TM0177-96 SSCC test with a gas formed by 10% wt H.sub.2S+90% wt CO.sub.2 and results are listed.

TABLE-US-00002 TABLE 2 No. of Size** Sample samples (mm) Hours Examination RESULT Aluminum coated strip 1 2 120 7 2 720 No failure - no PASS cracks 1 1 120 7 2 1440 No failure - no PASS cracks 1 1 120 7 2 3000 No failure - no PASS cracks 2 6 200 7 2 720 No failure - no PASS cracks 2 3 200 7 2 1440 No failure - no PASS cracks 2 3 200 7 2 2160 No failure - no PASS cracks 3 1 150 7 2 4320 No failure - no Pass Cracks Uncoated steel 1* 2 120 7 2 (720) Failure 480 NO hours PASS 2* 3 200 7 2 (720) hydrogen NO induced PASS cracking *= comparative **length width thickness

[0148] After just 480 hours of ageing, the comparative uncoated steel tapes were already wrecked.

[0149] At the end of the ageing test the solution was dirty, as a result of the corrosion of the comparative uncoated specimens.

[0150] Differently, at the end of the ageing test the aluminum coated specimens according to the invention were substantially unharmed and their solution was clear, a sign of the protective action exerted by the aluminum.

[0151] In Table 3 below the ageing test details for a NACE Standard TM0177-96 SSCC test with 100% wt H.sub.2S and results are listed for Al-coated carbon steel tapes according to the present invention.

TABLE-US-00003 TABLE 3 No. of Size** Sample samples (mm) Hours Examination RESULT Aluminum coated strip 1 2 120 7 2 720 No failure - no PASS cracks 2 2 200 7 2 1440 No failure - no PASS cracks **length width thickness

[0152] The coated samples remained substantially unharmed after prolonged contact with a 100% wt hydrogen sulfide gas solution.

Example 2

[0153] To verify the adhesion characteristics of the Al coating layer to the carbon steel tape a three point bending test was carried out. Aluminium coated steel tapes according to the invention (0.625 mm120 mm; aluminium coating thickness: 30 m) were bent to 70, 90 or 180 with corresponding plastic deformation up to 30% (external) and 68% (internal). None of the tested samples showed detachment of or cracking in the aluminium coating.

Example 3

[0154] A steel tape (0.625 mm120 mm) hot dip coated with aluminium containing 10 wt % of silicon according to the invention was observed by energy dispersive spectroscopy (EDS) for elemental analysis.

[0155] FIG. 6 shows the result of the analysis of a section at the interface between the steel tape (on the right side) and the aluminium coating (on the left side). In such a figure, the % of element concentration is reported in ordinate and the thickness in microns is reported in abscissae starting from the aluminium coating.

[0156] In a region of about 4.73 m on both sides of the median plane (shown with a thickened vertical line in FIG. 6) of an interface layer (having a total thickness of about 9.46 m), an intermetallic compound, containing aluminium (continuous line), silicon (dashed line) and iron (dotted line), is present in significant amounts.