Angular displacement of flexible pipe

1. Apparatus for determining a bending radius of a flexible pipe for transporting production fluids from one location to another, comprising:

at least one bend sensor element comprising an elongate flexible substrate and at least one bend sensitive element on the substrate that has at least one electrical characteristic that is responsive to angular displacement of the substrate; and

a flexible crush resistant elongate housing that supports and surrounds the bend sensor element to allow a relative motion between the housing and the bend sensor element, wherein a cavity is provided in the housing and the substrate is at least partially slideable in the cavity.

2. The apparatus as claimed in claim 1 , further comprising:

the housing comprises an elongate cavity that extends along a longitudinal axis associated with the housing and in which the substrate of each sensor element is located.

3. The apparatus as claimed in claim 1 , further comprising:

at least a first end of the substrate of each sensor element in the housing is a free end that is slideable with respect to the surrounding housing.

4. The apparatus as claimed in claim 3 wherein a remaining end of each substrate is also a free end.

5. The apparatus as claimed in claim 1 , further comprising:

at least one locating element in the housing that locates a respective substrate in the housing and urges the substrate into a bent configuration when the housing bends but which allows sliding motion of the substrate with respect to the housing.

6. The apparatus as claimed in claim 5 , further comprising:

the at least one locating element comprises a plurality of biasing pins provided between an upper and/or lower surface of the substrate and the housing.

7. The apparatus as claimed in claim 6 wherein each biasing pin is a foam plug.

8. The apparatus as claimed in claim 5 , further comprising:

the at least one locating element comprises at least one U-shaped element provided between a respective edge of the substrate and the housing.

9. The apparatus as claimed in claim 8 wherein the at least one U-shaped element comprises two elongate U-shaped foam strips each providing a guide channel in which a respective edge of a substrate is locatable.

10. The apparatus as claimed in claim 1 , further comprising:

the substrate is at least partially slidable in a cavity in the housing.

11. The apparatus as claimed in claim 1 wherein:

the bend sensitive element comprises a track of a conductive ink on a first surface of the substrate; and

a first and further electrical connector are disposed on the substrate, each connected to a respective end of the track.

12. The apparatus as claimed in claim 11 , further comprising:

a further conductive material deposited over at least one portion of the conductive ink track.

13. The apparatus as claimed in claim 12 wherein said at least one portion comprises a plurality of spaced apart regions of the conductive ink track.

14. The apparatus as claimed in claim 11 wherein the conductive track comprises a region of a binder material and conductive particles printed or deposited on the substrate.

15. The apparatus as claimed in claim 11 wherein the conductive ink comprises a mixture of a first ink type and at least one further ink type.

16. The apparatus as claimed in claim 1 , further comprising:

each housing and respective supported sensor element is located in a flexible pipe or in a bend stiffener.

17. A method for monitoring bending of a flexible pipe for transporting production fluids from one location to another, comprising the steps of:

as a flexible pipe bends, bending at least one flexible crush resistant housing that supports and surrounds an elongate flexible substrate of at least one bend sensor element and allowing a relative motion between the housing and the bend sensor element that includes at least partial sliding of the substrate in a cavity provided in the housing;

varying an electrical characteristic provided by a bend sensitive element on the substrate as the substrate bends with the housing; and

determining a bend radius associated with a region of the flexible pipe where the housing is located responsive to the electrical characteristic.

18. The method as claimed in claim 17 , further comprising:

determining the bend radius in real time as the flexible pipe bends.