WO2009116966A1

WO2009116966A1 - Shear pin sensor

Info

Publication number: WO2009116966A1
Application number: PCT/US2008/003564
Authority: WO
Inventors: Aidan Nolan; Daniel Mcstay; Gordon Shiach
Original assignee: Fmc Technologies, Inc.
Priority date: 2008-03-19
Filing date: 2008-03-19
Publication date: 2009-09-24

Abstract

A shear pin sensor includes a shear pin, an optical fiber which is associated with the shear pin, a light emitter which transmits a light through the optical fiber, a photo detector which detects the light transmitted through the optical fiber, and a signal processing unit which is connected to the photo detector. In operation, a break in the shear pin causes a change in the light detected by the photo detector, and this change is detected by the signal processing unit.

Description

SHEAR PIN SENSOR BACKGROUND OF THE INVENTION

The present invention is related to a sensor for detecting the breakage of a shear pin. More particularly, the invention is directed to a shear pin sensor which comprises an optical fiber that is associated with the shear pin, such as by being positioned axially within the shear pin, and a photo detector for detecting a change in the light transmitted through the optical fiber in response to breakage of the shear pin.

Shear pins are typically used to link certain components of a mechanical system together until the application of a predetermined force on one of the components causes the shear pin to break. In some applications, a shear pin may be used to connect two components together temporarily. In these applications, the shear pin is designed to fail and thus disconnect the components upon the application of a predetermined force to one of the components. In other applications, a shear pin may be used as a sort of mechanical fuse between two components. In such applications, the shear pin links the two components together but is designed to break if one of the components is subjected to a force approaching that which may cause the component to break. In the field of subsea completion systems, for example, shear pins are used to prevent damage to certain ROV-actuated components during ROV installation, adjustment and maintenance operations. The shear pins are designed such that the application of an excessive force to the ROV-actuated component will result in breakage of the shear pin. Knowing that the shear pin has broken enables the ROV operator to stop the operation and prevent the ROV-actuated component from being damaged. However, in subsea systems involving ROV operations, breakage of the shear pins cannot easily be determined.

Therefore, a need exists for a shear pin sensor which automatically detects when a shear pin has broken. SUMMARY OF THE INVENTION

In accordance with the present invention, a shear pin sensor is provided which comprises a shear pin, an optical fiber which is associated with the shear pin, a light emitter which transmits a light through the optical fiber, a photo detector which detects the light transmitted through the optical fiber, and a signal processing unit which is connected to the photo detector. In operation, a break in the shear pin causes a change in the light detected by the photo detector, and this change is detected by the signal processing unit. In one embodiment of the invention, the optical fiber extends axially through the shear pin, the light emitter is positioned at a first end of the optical fiber and the photo detector is positioned at a second end of the optical fiber. Thus, a break in the shear pin will disrupt the light transmitted through the optical fiber and result in a change in the light detected by the photo detector. In another embodiment of the invention, the optical fiber extends axially through the shear pin, both the light emitter and the photo detector are positioned at a first end of the optical fiber, and the shear pin sensor further comprises a reflective element which is positioned at a second end of the optical fiber. In this embodiment, a portion of the light generated by the light emitter is reflected back through the optical fiber by the reflective element. Consequently, a break in the shear pin will disrupt the light transmitted through the optical fiber and result in a change in the light detected by the photo detector. The reflective element may be a broadband device or a wavelength specific device, such as a Bragg grating or a interference filter. In yet another embodiment of the invention, the shear pin sensor includes an optical pressure sensor which is mounted in operational engagement with the shear pin. In this embodiment, both the light emitter and the photo detector are positioned at a first end of the optical fiber and the optical pressure sensor is positioned at a second end of the optical fiber. A portion of the light generated by the light emitter is reflected back through the optical fiber by the optical pressure sensor, with for example the intensity or wavelength of this reflected light being related to the pressure exerted on the optical pressure sensor. Thus, a break in the shear pin will cause a change in the pressure exerted on the optical pressure sensor, and this will result in a change in the light detected by the photo detector. In a further embodiment of the invention, multiple shear pin sensors are combined into an integrated system capable of monitoring a plurality of shear pins. The shear pin sensor system of this embodiment therefore includes a plurality of shear pins, a number of optical fibers, each of which is associated with a corresponding shear pin, means for transmitting a light through each optical fiber, means for detecting the light transmitted through each optical fiber, and a signal processing unit which is connected to the light detecting means. In operation, a break in each shear pin causes a change in the light detected by the light detecting means, and the signal processing unit detects the change and generates a unique signal indicative of the break in each shear pin.

Thus, the shear pin sensor of the present invention provides a simple, effective means for automatically detecting when a shear pin has failed. In addition, several shear pin sensors may be incorporated into an integrated system capable of automatically detecting the breakage of any of a plurality of shear pins.

These and other objects and advantages of the present invention will be made apparent from the following detailed description, with reference to the accompanying drawings. In the drawings, the same reference numbers may be used to denote similar components in the various embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic representation of a first embodiment of the shear pin sensor of the present invention;

Figure 2 is a schematic representation of a second embodiment of the shear pin sensor of the present invention; Figure 3 is a schematic representation of a third embodiment of the shear pin sensor of the present invention;

Figure 4 is a schematic representation of one embodiment of an integrated system of multiple shear pin sensors of the present invention; and

Figure 5 is a schematic representation of another embodiment of an integrated system of multiple shear pin sensors of the present invention. DETAILED DESCRIPTION OF THE INVENTION

A first embodiment of the shear pin sensor of the present invention is shown in Figure 1. The shear pin sensor of this embodiment, which is indicated generally by reference number 10, includes a shear pin 12 which in use may be positioned, for example, in a corresponding bore in a component C. The shear pin sensor 10 comprises an optical fiber 14 which extends axially through the shear pin 12, a light emitter 16 which is positioned at one end of the optical fiber and a photo detector 18 which is positioned at the opposite end of the optical fiber. The light emitter 16 and the photo detector 18 may be incorporated into the shear pin 12 or into respective housings which are connected to the ends of the shear pin.

The photo detector 18 is connected to a signal processing unit 20, which is programmed to measure the change in amplitude of the light received by the photo detector. The signal processing unit 20 may in turn be connected to a central controller 22, which is ideally configured to provide an operator with an indication of the status of the shear pin 12 in response to the signals received from the signal processing unit.

In operation, the light emitter 16 generates a light which is transmitted through the optical fiber 14 and received by the photo detector 18. If the shear pin 12 should break, the transmission of light through the optical fiber 14, and thus the light received by the photo detector 18, will be disrupted. The signal processing unit 20 will accordingly determine that the amplitude of the light received by the photo detector 18 has changed. If this change in light level is sufficiently large to correspond to a break in the shear pin 12, the signal processing unit 20 will send an appropriate alarm or failure indication signal to the central controller 22 in order to notify the operator that the shear pin has broken. Referring to Figure 2, a second embodiment of the shear pin sensor of the present invention, which is indicated generally by reference number 10', is shown to comprise a shear pin 12 which in use may be positioned, for example, in corresponding aligned bores in adjacent first and second components Ci and C₂. The shear pin sensor 10' includes an optical fiber 14 which extends through the shear pin 12, a light emitter 16 which is positioned at a first end of the optical fiber, a photo detector 18 which is also positioned at the first end of the optical fiber, and a reflective element 24 which is positioned at the second end of the shear pin. The light emitter 16 and the photo detector 18 may be incorporated into the shear pin 12 or into a housing which is connected to the shear pin.

The reflective element 24 reflects a portion of the light generated by the light emitter 16 back through the optical fiber 14 to the photo detector 18. The reflective element 24 may be integrated into the optical fiber 14 or comprise a reflective coating or a distinct device which is fixed to the optical fiber. In addition, the reflective element 24 may be a broadband device or a wavelength specific device, such as an interference filter or a Bragg grating. If the latter, the photo detector 18 ideally comprises a spectral response which corresponds to the wavelength of the reflective element 24.

The operation of the shear pin sensor 10' is similar to the operation of the shear pin sensor 10. A break in the shear pin 12 will disrupt the optical path through the optical fiber 14 and hence decrease the light detected by the photo detector 18. The change in the level of light detected by the photo detector 18 is measured by the signal processing unit 20 and, if this change is sufficiently large to correspond to a break in the shear pin 12, the signal processing unit 20 will send an appropriate alarm or failure indication signal to the central controller 22. Another embodiment of the shear pin sensor of the present invention is illustrated in Figure 3. The shear pin sensor of this embodiment, which is indicated generally by reference number 10", comprises a shear pin 12 which in use may be positioned, for example, in a corresponding bore in a component C and which is connected to a mounting assembly 26 that in turn is connected to the component C. The mounting assembly 26 houses a conventional optical pressure sensor 28, and the shear pin 12 is secured to the mounting assembly such that, when the shear pin is intact it will exert a positive pressure on the optical pressure sensor, and when the shear pin is broken this pressure will be relieved.

Depending on the type of optical pressure sensor employed, it may be incorporated in, connected to or positioned in optical communication with one end of an optical fiber 14, and the shear pin sensor 10" further comprises a light emitter 16 and a photo detector 18 which are both positioned at the opposite end of the optical fiber. As in the previous embodiments, the photo detector 18 may be connected to a signal processing unit 20 which in turn may be connected to a central controller 22.

In operation, light from the light emitter 16 is transmitted through the optical fiber 14 toward the optical pressure sensor 28, which reflects a portion of this light back through the optical fiber to the photo detector 18. The intensity or wavelength of the light reflected by the optical pressure sensor 28 varies with the pressure exerted on the sensor. Accordingly, when the shear pin 12 is intact, the photo detector 18 will detect a certain intensity or wavelength of light, and when the shear pin is broken, the photo detector will detect a different intensity or wavelength of light. If the shear pin 12 should break, the resulting change in pressure on the optical pressure sensor 28 will produce a change in the light detected by the photo detector 18. This change will be measured by the signal processing unit 20, which in turn will send an appropriate alarm or failure indication signal to the central controller 22.

As an alternative to the optical pressure sensor 28, other devices which change their optical properties, such as polarization, color or fluorescence, when subjected to changes in stress or pressure may be used in the shear pin sensor 10". These opto-mechanical devices may be attached within the shear pin 12 or within a separate mounting assembly to which the shear pin is connected.

The shear pin sensors of any of the above-described embodiments may be combined into an integrated system of multiple shear pin sensors capable of monitoring a plurality of shear pins. Referring to Figure 4, for example, a representative shear pin sensor system, generally 100, is shown to comprise three shear pins sensors 10' which each comprise a corresponding shear pin 12. As was described above, each shear pin sensor 10' includes a dedicated optical fiber 14, light emitter 16, photo detector 18 and signal processing unit 20. In addition, each signal processing unit 20 is configured to generate a unique signal which identifies its corresponding shear pin sensor 10' to the central controller 22 so that, if a specific shear pin 12 should break, the central controller 22 can identify that shear pin. Although the shear pin sensor system 100 has been described to include shear pin sensors 10', it should be understood that a similar system could be constructed with shear pin sensors similar to the shear pin sensors 10 and 10" described above.

Another embodiment of a shear pin sensor system in accordance with the present invention is shown in Figure 5. The shear pin sensor system of this embodiment, which is indicated generally by reference number 200, includes a number of shear pin sensors 210 which each comprise a respective shear pin 12 that in use may be mounted in a corresponding component C. Each shear pin sensor 210 may be similar, for example, to the shear pin sensor 10" described above in that the shear pin 12 is connected to a mounting assembly 26 which is connected to the component C and within which an optical pressure sensor 28 is positioned. In contrast to the shear pin sensor 10", however, each shear pin sensor 210 does not comprise a dedicated light emitter 16 and photo detector 18. Instead, a single light emitter 16 and photo detector 18 are mounted at one end of a principal optical fiber 14' which is connected to the optical pressure sensor of each shear pin sensor 210 by a corresponding branch optical fiber 14".

In this embodiment, each optical pressure sensor 28 may be selected to reflect a unique wavelength of light in response to a change in pressure on its corresponding shear pin 12. The use of such wavelength selective optical pressure sensors allows the shear pin sensors 210 to be multiplexed over a single principal fiber 14'. In addition, the shear pin sensor system 200 may comprise a wavelength selective photo detector 18 to identify the light from each individual optical pressure sensor 28. Examples of suitable wavelength selective photo detectors may include CCD's, gratings, interference filters and interferometers. The shear pin sensor system 200 may also use specific multiplexing techniques, such as time of flight multiplexing, to identify the individual shear pins 12. Based on this shear pin-specific information, the signal processing unit 20 is capable of identifying each shear pin sensor 21 and transmitting a corresponding unique signal to the central controller 22 so that, if a specific shear pin 12 should break, the central controller 22 can identify that shear pin.

Although the shear pin sensor system 200 has been described as including shear pin sensors 210 which are similar to the shear pin sensor 10", it should be readily apparent that a similar system could be constructed with shear pin sensors which are similar to the shear pin sensor 10' described above.

It should be recognized that, while the present invention has been described in relation to the preferred embodiments thereof, those skilled in the art may develop a wide variation of structural and operational details without departing from the principles of the invention. For example, the various elements shown in the different embodiments may be combined in a manner not illustrated above. Therefore, the appended claims are to be construed to cover all equivalents falling within the true scope and spirit of the invention.

Claims

We Claim:

1. A shear pin sensor which includes: a shear pin; an optical fiber which is associated with the shear pin; a light emitter which transmits a light through the optical fiber; a photo detector which detects the light transmitted through the optical fiber; and a signal processing unit which is connected to the photo detector; wherein a break in the shear pin causes a change in the light detected by the photo detector; and wherein the change is detected by the signal processing unit.

2. The shear pin sensor of claim 1 , wherein the optical fiber extends axially through the shear pin, the light emitter is positioned at a first end of the optical fiber and the photo detector is positioned at a second end of the optical fiber.

3. The shear pin sensor of claim 1 , wherein the optical fiber extends axially through the shear pin, both the light emitter and the photo detector are positioned at a first end of the optical fiber, and the shear pin sensor further comprises a reflective element which is positioned at a second end of the optical fiber.

4. The shear pin sensor of claim 3, wherein the reflective element comprises a wavelength specific device.

5. The shear pin sensor of claim 3, wherein the reflective element comprises a Bragg grating which is incorporated into the second end of the optical fiber.

6. The shear pin sensor of claim 3, wherein the reflective element comprises an interference filter which is connected to the second end of the optical fiber.

7. The shear pin sensor of claim 1 , further comprising: an optical pressure sensor which is mounted in operational engagement with the shear pin; wherein both the light emitter and the photo detector are positioned at a first end of the optical fiber and the optical pressure sensor is positioned at a second end of the optical fiber.

8. A shear pin sensor system which comprises: a plurality of shear pins; a number of optical fibers, each of which is associated with a corresponding shear pin; means for transmitting a light through each optical fiber; means for detecting the light transmitted through each optical fiber; and a signal processing unit which is connected to the light detecting means; wherein a break in each shear pin causes a change in the light detected by the light detecting means; and wherein the signal processing unit detects the change and generates a unique signal indicative of the break in each shear pin.

9. The shear pin sensor system of claim 8, wherein: each optical fiber extends axially through its corresponding shear pin; the light transmitting means comprises a plurality of light emitters, each of which is positioned at a first end of a corresponding optical fiber; and the light detecting means comprises a plurality of photo detectors, each of which is positioned at a second end of a corresponding optical fiber.

10. The shear pin sensor system of claim 8, wherein: each optical fiber extends axially through its corresponding shear pin; the light transmitting means comprises a plurality of light emitters, each of which is positioned at a first end of a corresponding optical fiber; the light detecting means comprises a plurality of photo detectors, each of which is positioned at the first end of a corresponding optical fiber; and the shear pin sensor system further comprises a plurality of reflective elements, each of which is positioned at a second end of a corresponding optical fiber.

11. The shear pin sensor system of claim 10, wherein each reflective element comprises a wavelength specific device.

12. The shear pin sensor system of claim 10, wherein each reflective element comprises a Bragg grating which is incorporated into the second end of its corresponding optical fiber.

13. The shear pin sensor system of claim 10, wherein the reflective element comprises an interference filter which is connected to the second end of its corresponding optical fiber.

14. The shear pin sensor of claim 8, further comprising: a plurality of optical pressure sensors, each of which is mounted in operational engagement with a corresponding shear pin and is positioned at a first end of a corresponding optical fiber; wherein the light transmitting means comprises a light emitter which is positioned in optical communication with a second end of each optical fiber; and wherein the light detecting means comprises a photo detector which is positioned in optical communication with the second end of each optical fiber.

15. The shear pin sensor of claim 14, further comprising a principal optical fiber which is positioned between the light emitter and the photo detector on the one hand and the second end of each optical fiber on the other hand.