Hoses, and detecting failures in reinforced hoses

1. A flexible hose comprising a generally cylindrical tubular structure comprising at least one layer of steel ligaments near the outer longitudinally-extending surface, the steel ligaments being enclosed within a tubular layer comprising polymeric material, wherein the flexible hose also incorporates a multiplicity of sensing coils embedded within the tubular layer, each such sensing coil being a flat coil lying in a plane substantially parallel to the adjacent layer of steel ligaments, so that an axis of the coil orthogonal to the plane of the flat coil extends in a radial direction relative to the tubular structure.

2. The flexible hose according to claim 1 wherein each sensing coil is connected electrically to a signal processing circuit for amplifying and digitizing signals from the coil, the signal processing circuit also being embedded within the tubular layer.

3. The flexible hose according to claim 2 wherein the signal processing circuit comprises a power-receiving circuit for obtaining power from a radio-frequency electromagnetic field, and a transmission circuit for transmitting data by radio-frequency signals to an external radio-frequency receiver.

4. The flexible hose according to claim 2 further comprising a multiplicity of circuit boards embedded within the tubular layer, wherein each sensing coil is mounted on a circuit board embedded within the tubular layer, the circuit board also carrying the signal processing circuit for amplifying and digitizing signals from the sensing coil.

5. The flexible hose according to claim 4 wherein each circuit board carries a single sensing coil.

6. The flexible hose according to claim 2 wherein each circuit board embedded within the tubular layer is a flexible circuit board.

7. A method of monitoring or detecting stress in steel ligaments within a flexible hose, wherein the flexible hose is the flexible hose according to claim 1 , the method comprising subjecting the steel ligaments in the vicinity of the sensing coils to an alternating magnetic field less than saturation by means of at least one drive coil and a current source, receiving data from the sensing coils, and analyzing the data to provide information about the stress in the steel ligaments.

8. The method according to claim 7 , wherein the data from the sensing coils is received by radio-frequency transmission.

9. The method according to claim 7 wherein the hose in the vicinity of the sensing coils is subjected to an alternating magnetic field by arranging at least one drive coil that encircles the hose in the vicinity of the sensing coils.

10. The method according to according to claim 9 , wherein the alternating magnetic field is generated by two drive coils spaced apart axially along the hose.

11. The method according to claim 7 wherein the hose in the vicinity of the sensing coils is subjected to an alternating magnetic field in a direction that is radial relative to the longitudinal axis of that portion of the hose, by using the at least one drive coil in combination with a ferromagnetic yoke with radially-extending pole pieces.

12. The method according to claim 11 wherein the radially-extending pole pieces used to generate the alternating magnetic field are diametrically opposite each other relative to the longitudinal axis of the hose.

13. The method according to claim 12 wherein the ferromagnetic yoke is circular, and is arranged to surround the hose, the yoke being provided with at least one pair of diametrically opposite radially-extending pole pieces.

14. The method according to claim 11 wherein the magnetic field is generated using drive coils and two ferromagnetic yokes spaced apart along the length of the hose, so that ligaments within the hose between the two yokes are subjected to a magnetic field that is at least partly parallel to the ligaments.

15. The method according to claim 7 wherein the current source is arranged to supply a plurality of different frequencies in succession to each drive coil.