Umbilical

Abstract

An umbilical for use in the offshore production of hydrocarbons comprising an assembly of functional elements at least one of which is an electrical power cable, characterised in that at least one conductor of at least one electrical power cable comprises one or more 6000 series aluminium strands.

Claims

1. An umbilical for use in the offshore production of hydrocarbons comprising an assembly of functional elements at least one of which is an electrical power cable with a voltage rating of 6 kV or higher, wherein the electrical power cable comprises one or more strands of 6000 series aluminium, each strand having a cross-section selected to provide said strand with an operating current and linear conductivity that is the same as a copper strand with a cross-section, wherein said 6000 series aluminum comprises aluminum, silicon, and magnesium, wherein said 6000 series aluminium further comprises Mg.sub.2Si precipitates, wherein the cross-section of said strand is larger than the cross-section of said copper strand but said strand weighs less than said copper strand, wherein the strands of 6000 series aluminium have a yield strength higher than 200 MPa.

2. An umbilical as claimed in claim 1, wherein all the strands of at least one of the conductors are comprised of 6000 series aluminium.

3. An umbilical as claimed in claim 1, wherein one, some or all of the strands of 6000 series aluminium are formed from one or more of aluminium alloys comprising at least 0.3-0.7% silicon, 0.35-0.9% magnesium, 0.1-0.5% iron, and 0.05%-0.1% copper.

4. An umbilical as claimed in claim 1, wherein one, some or all of the strands of 6000 series aluminium are formed from one or more of aluminium alloys comprising 0.5-0.9% silicon, 0.6-0.9% magnesium, 0.04-0.1% copper.

5. An umbilical as claimed in claim 1, wherein the strands of 6000 series aluminium have an electrical resistivity smaller than 35 n?.m (nano-ohm meter).

6. An umbilical as claimed in claim 1, wherein all the strands of all the conductors of the electrical power cable are comprised of 6000 series aluminium.

7. An umbilical as claimed in claim 1, wherein at least one conductor comprises one or more strands of 6000 series aluminium and one or more strands of 1000 series aluminium alloy, which comprises at least 99%.

8. An umbilical as claimed in claim 7, wherein all the strands of all the conductors of the electrical power cable are a combination of strands of 6000 series aluminium and strands of 1000 series aluminium.

9. An umbilical as claimed in claim 1, wherein the electrical power cable is able to provide 1-phase or 3-phase power.

10. An umbilical as claimed in claim 1, wherein the power cable is rated for 6 kV or more and is capable of transmitting 1 MW of power or more.

11. An umbilical as claimed in claim 1, wherein each strand is coldworked and aged.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

(2) FIG. 1 is a sectional view through a prior art power cable as described hereinabove;

(3) FIG. 2 is a sectional view through a first subsea umbilical (10) according to the present invention containing power cables (14), fillers (16), with an outer polymeric sheath (12);

(4) FIG. 3 is a sectional view through a second subsea umbilical (20) according to the present invention containing power cables (22), signal cables, optical fibre cables and thermoplastic hoses (24), and protected with steel wire armours (26);

(5) FIG. 4 is a sectional view through a third subsea umbilical (30) according to the present invention containing power cables (32), signal cables and steel tubes (34) and protected with steel wire armours (36);

(6) FIG. 5 is a sectional view through a fourth subsea umbilical (40) according to the present invention containing power cables (42), optical fibre cables and steel tubes (44), with an overall polymeric sheath (46); and

(7) FIG. 6 is a sectional view through a fifth subsea umbilical (50) according to the present invention containing power cables (52), an optical fibre cable (54), fillers (56), and protected with steel wire armours.

DESCRIPTION OF PREFERRED EMBODIMENTS

(8) An umbilical in accordance with an embodiment of the present invention comprises an assembly of functional elements, such elements including steel pipes and/or thermoplastic hoses, optical fibre cables, reinforcing steel or carbon rods, electrical power cables, and electrical signal cables bundled together with filler material and over-sheathed by a polymeric external sheath.

(9) Examples of various assembly arrangements according to the present invention are shown in FIGS. 2-6. Each of these embodiments includes at least one electrical power cable, generally in a symmetrical arrangement, and at least one conductor of one of the electrical power cables comprises one or more 600 series aluminium conductor strands as herein described. The strand(s) may be formed as described hereinabove.

(10) The present invention applies to individual power conductors and to bundled power conductors (such as a trefoil bundle for a 3-phase power supply).

(11) The power umbilicals and power cables according to the present invention can also be used to transfer the electrical energy generated by offshore windmills from said windmills to an onshore terminal.

(12) The 6000 series aluminium strands can also be used in or as a signal cable conductor(s).

(13) Various modifications and variations to the described embodiments of the invention will be apparent to those skilled in the art without departing from the scope of the invention as defined herein or in the appended claims. Although the invention has been described in connection with specific embodiments, it should be understood that the invention as claimed should not be unduly limited to such specific embodiments.