Cabling system corrugated centertube umbilical

Abstract

An umbilical (2) has a center tube (4) that is a steel tube, and that the cross section of the center tube (4) at the extremity of the umbilical (2) is made corrugated on a length that extends substantially from the extremity to a distance from the extremity so that fatigue strain on non corrugated parts of the steel tube is avoided when the extremity of the umbilical (2) is inserted into a bend stiffener (1).

Claims

1. A platform comprising: a topside hang-off; a bend stiffener is fixed to the topside hang-off and extends vertically below said topside hang-off, said bend stiffener is conically tapered with a wide end on the upside near the topside hang-off and a thin end on the other side; and an umbilical having a center steel tube the upper end of which is also fixed to the topside hang-off, said umbilical extending downward through said bend stiffener, wherein the cross section of the center steel tube of said umbilical is corrugated in an upper part beginning at the upper end where said umbilical is fixed to the topside hang-off, and where said umbilical extends through said bend stiffener, and remaining corrugated for a length which is less than a total length of said bend stiffener at which point said cross section of the center steel tube is no longer corrugated, so that said center tube gets less stiff inside the bend stiffener.

2. The platform as in claim 1, wherein said center tube is made of Super Duplex steel.

3. The platform as in claim 1, wherein said center tube is sheathed with a polyethylene sheath.

4. The platform as in claim 3, wherein a volume between the corrugated part of the center tube and the polyethylene sheath is filled with elastomer or soft polymer.

5. The platform according to claim 1, wherein the cross section of the umbilical center steel tube is corrugated for a length that is 70% of the total length of said bend stiffener.

6. The platform as claimed in claim 1, wherein the center tube is produced by welding together tube parts of 20 to 30 meters.

Description

DESCRIPTION OF THE DIAGRAMS

(1) The present invention will now be described, by way of example, with reference to the following diagrams wherein:

(2) FIG. 1 is a schematic illustration of an embodiment of a platform with an installed umbilical;

(3) FIG. 2 is a schematic illustration of a cross section of an umbilical with one large diameter Super Duplex center tube;

(4) FIG. 3 is a schematic illustration of a cross section of an umbilical with seven smaller diameter Super Duplex center tubes; and

(5) FIG. 4 is a longitudinal section view of a partly corrugated large diameter Super Duplex center tube.

DETAILED DESCRIPTION OF THE INVENTION

(6) Referring to FIG. 1, a schematic platform 3 installation according to the present installation is shown. The actual invention is to be found inside a part of an umbilical 2 starting from the platform 3 through an umbilical bend stiffener 1 and further down some limited distance. An umbilical 2 may be quite long, typically ranging from a few kilometers to 40 kilometers or more. It is expensive, not only due to its length, but also because of its complex construction. Referring to FIG. 2, an umbilical 2a is designed to convey different matter like produced oil and gas, usually in a center tube 4 surrounded by a polyethylene sheath 7, electric power in electrical cables 9, hydraulic power and other liquids in diverse supplementary tubes 6, optical signals (not shown), electrical signals (not shown), etc., possibly in different directions, all integrated in the umbilical 2.

(7) One important component when terminating an umbilical 2 to a platform 3 is a bend stiffener 1. A bend stiffener 1 is typically designed comprising a plurality of parts not to be covered here. It surrounds the upper end of an umbilical 2 and is fixed to the platform 3 while in the other end it is designed to be flexible to some degree. The purpose of the bend stiffener 1 is to spread the dynamic movement of the umbilical 2 on its inside so that it gets evenly distributed along the length of the bend stiffener 1.

(8) The stiffer an umbilical 2 gets, the longer and bigger the bend stiffener 1 has to be. The same relates to dynamic movement, more dynamic movement also requires longer bend stiffeners 1. If it is desirable to use a large Super Duplex center tube 4 of say 50 mm in an umbilical 2a, there are also two available options in the art; referring to FIG. 3 umbilical 2b may comprise seven smaller tubes 5 of 25 mm, each being surrounded by a polyethylene sheath 7, said smaller tubes 5 replacing the larger center tube 4. Another option is to use an extremely long bend stiffener 1. Both these alternatives make the umbilical 2 significantly more expensive.

(9) Referring to FIG. 4 a preferred embodiment of the present invention solves this problem by modifying the upper part of the center tube 4 so that it gets less stiff. This is done by corrugating the upper part I of the center tube 4. The corrugated upper part is still surrounded by a cylindrical polyethylene sheath 7, and the annular spaces between said corrugated part and said polyethylene sheath 7 are filled with soft polymer or elastomer materials 8. This way, important advantages are obtained:

(10) In the art it is known to corrugate stiff steel tubes to make them less bending rigidity and prone to material fatigue. This makes a steel tube more expensive and the friction on the inside increases.

(11) A corrugated center tube 4 in an umbilical 2, limited to the upper part I, results in considerable reduced cost compared to a completely corrugated center tube 4.

(12) A corrugated center tube 4 in an umbilical 2 limited to the upper part will result in reduced friction and therefore increased transmission capacity compared to using a completely corrugated center tube 4.

(13) The center tube 4 in an umbilical 2 is produced by welding together tube parts of for instance 20 to 30 meters. It is therefore no problem to combine one, or some limited number, of corrugated tube parts while the rest remains smooth.

(14) The corrugated part of the center 4 tube can be seen as an extension of the bend stiffener 1. When the umbilical 2 together with its bend stiffener 1 is exposed to dynamic motion, acceptable strain on the center tube 4 can be accomplished without the added cost of reverting to multiple center tubes 5 or a bend stiffener 1 having an excessive size.