WO2014174253A1

WO2014174253A1 - Method and apparatus for evaluating cathodic protection

Info

Publication number: WO2014174253A1
Application number: PCT/GB2014/051203
Authority: WO
Inventors: Angus Craig DONALD
Original assignee: Isis Technical Services Limited
Priority date: 2013-04-23
Filing date: 2014-04-16
Publication date: 2014-10-30
Also published as: GB201307299D0; GB2513560A

Abstract

The present invention relates to a method for evaluating cathodic protection of an electrically conductive object, the method comprising the steps of: providing an electrically conductive probe, comprising at least a pair of spaced apart contact electrodes; placing the contact electrodes in electric contact with the object to be inspected; measuring electric resistance between the contact electrodes when in contact with the object; and measuring electric potential difference between at least one of the contact electrodes and at least one other electrode. The invention also relates to an apparatus for evaluating cathodic protection of an electrically conductive object.

Description

METHOD AND APPARATUS FOR EVALUATING CATHODIC PROTECTION

Field of the Invention

The present invention provides improved method and apparatus for evaluating cathodic protection of an object.

Background of the Invention

In the oil and gas industry various metallic or other electrically conductive structures, such as, for example marine vessels (e.g. offshore rigs, production buoys, barges etc.), harbour structures (e.g. jetties), production pipes and many more operate in harsh environments, such as sea water. One of the ways to protect these structures from corrosion is to provide a structure with cathodic protection based on the electrochemical cell principle. In an electrochemical cell, potential difference exists between two different metals (or other electric conductors) when they are placed in electrolyte. One type of known cathodic protection device comprises a sacrificial electrode (the anode), installed on the structure to be protected. The anode typically comprises a piece of metal, e.g. aluminium or zinc, different from that of the structure to be protected, e.g. a steel pipe. The anode is electrically connected to the structure (the cathode), for example, by wire or by simply positioning the anode and the cathode in physical contact. The environment, in which the structure operates, acts as the electrolyte. Because of the difference in the electric potential between the two metals, current is induced between the anode and the cathode. The anode releases positively charged metal ions into the electrolyte setting up current in the electrolyte, and thus decays and acts as the sacrificial electrode, while the electrons move from the anode to the cathode through the materials of the anode and the cathode. The electrons at the cathode are utilised in a reduction reaction depending on the type of the electrolytic medium and the metal of the anode. Thus the metal of the cathode is kept inert and does not decay.

In order to check whether a structure has adequate cathodic protection, it is inspected with a cathodic protection potential measurement device. Figure 1 schematically illustrates a typical conventional (prior art) cathodic protection potential measurement device 1. The device 1 comprises a probe 2 having a metal tip 3 which is brought into contact with a surface of an anode 5 or with another metal surface of the structure to measure the potential difference between the surface and a reference electrode 7, such as, for example, that of an electrolytic silver/silver chloride half-cell 9. The potential difference is measured in Volts (V) or millivolts (mV) by a voltmeter 11 and the value of the measurement determines whether the potential of the anode 5 is adequate to protect the structure 15.

In order for such a measurement to be accurate it is necessary to make sure that there is a good conductive contact between the probe and the material being measured, otherwise discrepancies and errors in readings will occur. Such conventional prior art devices do not provide a means for ascertaining whether or not a good electrical contact has been made between the probe and the material under inspection. Accordingly, the object of the present invention is to provide method and apparatus which obviate the above mentioned problem and mitigate discrepancies and errors caused by improper probe contact during measurements.

Summary of the Invention

According to a first aspect of the invention there is provided a method for evaluating cathodic protection of an electrically conductive object, the method comprising the steps of:

providing an electrically conductive probe, comprising at least a pair of spaced apart contact electrodes

placing the contact electrodes in electric contact with the object to be inspected

measuring electric resistance between the contact electrodes when in contact with the object; and

measuring electric potential difference between at least one of the contact electrodes and at least one other electrode.

In a preferred embodiment, the method comprises the step of providing the other electrode in the form of a reference electrode as (the reference electrode not being one of the at least a pair of contact electrodes) and electrically connecting the probe to the reference electrode.

In one arrangement, the at least one other electrode may comprise another electrode of the at least two contact electrodes.

Preferably, the method is adapted to be carried out subsea, preferably in seawater.

Preferably, method involves placing the contact electrodes in electric contact with an outer surface of the object to be inspected, such as, for example, an outer wall of a pipe or a vessel.

Preferably, the method further comprises the step of, based on the measurements of the value of resistance between the electrodes when in contact with the object being inspected, ascertaining whether or not adequate electric contact has been established between the probe and the object so as to ensure that the potential difference measurement has not been influenced by the quality of the electric contact between the contact electrodes and the object under inspection and thereby to ensure that accurate evaluation of the cathodic protection of the object is being made. Higher resistance readings would indicate poor electric contact of the contact electrodes with the object whereas lower resistance readings would indicate adequate electric contact. Thus, the method preferably comprises the step of comparing the measured resistance with a predetermined threshold resistance value, wherein if the measured resistance is lower than a predetermined threshold resistance value, the contact electrodes are deemed to be in adequate electric contact with the object.

Preferably, the method comprises the step of arranging the contact electrodes electrically separate from each other, such that the contact electrodes represent terminals of an electric circuit rather than form a single terminal.

In one embodiment, the method comprises the step of providing the probe with a housing and accommodating the at least two contact electrodes within the housing, wherein the housing may be of elongate configuration. The method preferably comprises the step of mutually arranging the at least two electrodes, despite being spaced apart, to form a single tip. The method preferably comprises the step of spot stabbing the object being inspected with the probe. In order to place the electrodes in contact with the object, the object is "stabbed" with the tip of the probe, i.e. the tip is brought in contact with the object with force and substantially normal to the outer surface of the object.

The object under inspection may be, for example, a hull of a vessel, a pipe (e.g. a hydrocarbon production pipe), a jetty and many more objects which have cathodic protection arrangements applied thereto, and either an anodic or a cathodic part of the object can be inspected.

In one embodiment, the method includes the step of accommodating the reference electrode within the probe housing. In another embodiment, the method includes the step of arranging the reference electrode externally with respect to the probe housing.

The method further preferably comprises the step of providing the reference electrode preferably as part of an electrochemical half-cell, such as, for example, but not limited thereto, an Ag/AgCl half-cell, wherein potential difference exists between at least one contact electrode and the reference electrode, and measuring the potential difference by the instrument for measuring electric potential. The method may include the step of accommodating the half-cell within the probe housing or locating the half-cell externally with respect to the probe housing.

The method further preferably comprises the step of connecting the instrument for measuring electric potential which may comprise, for example, a voltmeter, connected in series between the reference electrode and one or more of the contact electrodes.

The method further preferably comprises the step of connecting the instrument for measuring electric resistance, which may comprise, for example, an ohmmeter, in parallel between the contact electrodes. Preferably, the method comprises the step of providing a switch arrangement and using the switch to connect/disconnect the instrument for measuring electric resistance and/or the instrument for measuring electric potential such that the resistance and the potential difference measurements are taken separately and without interfering with each other. For example, the switch arrangement may comprise a changeover switch arrangement and the method may comprise the step of simultaneously connecting one of the instrument for measuring electric resistance and/or the instrument for measuring electric potential and interrupting the other one of the two instruments.

In one arrangement, the method comprises the step of connecting only one contact electrode to the instrument for measuring electric potential. In another arrangement, the method includes connecting the instrument for measuring electric potential to two or more, in case the probe comprises more than two contact electrodes, contact electrodes of the probe, preferably including connecting the contact electrodes in parallel with respect to each other.

In an advantageous embodiment, the method comprises the step of using the probe in conjunction with a Remotely Operated Vehicle (ROV) or an Autonomous Inspection Vehicle (AIV) for remote measurements. Alternatively, the probe may be incorporated in a hand held unit and manually delivered to the object under inspection, for example, by a diver.

Preferably, the method includes providing the probe with a user interface to display the measurements, preferably, including providing a display, preferably an electronic display. Preferably, the method includes converting the measurements into electronic data and, preferably, transmitting the data to the display for presentation to the user. Preferably, the method comprises providing a storage means for storing the electronic data.

Additionally, the method may include using the probe to inspect electrical continuity in electrical connections, such as for example, in cathodic protection cable and earth bonding connections. Furthermore, the method may comprise using the readings of the instrument for measuring electric potential as a calibration reference reading for undertaking a continuous cathodic potential survey. According to a second aspect of the invention there is provided a method for evaluating cathodic protection of an electrically conductive object, the method comprising the steps of:

electrically connecting the probe to a reference electrode (the reference electrode not being one of the at least a pair of contact electrodes)

measuring electric potential difference between at least one of the contact electrodes and the reference electrode.

According to a third aspect of the invention there is provided a method for evaluating cathodic protection of an electrically conductive object in subsea environment, the method comprising the steps of:

According to a fourth aspect of the invention there is provided an apparatus for evaluating cathodic protection of an electrically conductive object, the apparatus comprising: an electrically conductive probe, comprising at least a pair of spaced apart contact electrodes for electrically contacting the object to be inspected

an instrument for measuring electric potential difference between at least one of the contact electrodes and at least one other electrode; and

an instrument for measuring electric resistance between the contact electrodes when in contact with the object.

In a preferred embodiment, the other electrode comprises a reference electrode (the reference electrode not being one of the at least a pair of contact electrodes) and the probe is electrically connected to the reference electrode.

In one embodiment, the apparatus is configured for use in subsea environment, preferably, in seawater.

Preferably, the apparatus is adapted for placing the contact electrodes in electric contact with an outer surface of the object to be inspected, such as, for example, an outer wall of a pipe or a vessel.

Preferably, the apparatus is adapted to enable placement of the contact electrodes in electric contact with an outer surface of the object to be inspected.

By measuring the value of resistance between the electrodes when in contact with the object being inspected, it is possible to ascertain whether or not adequate electric contact has been established between the probe and the object to ensure that the potential difference measurement has not been influenced by the quality of the electric contact between the contact electrodes and the object under inspection and thereby to ensure that accurate evaluation of the cathodic protection of the object is being made. Higher resistance readings would indicate poor electric contact of the contact electrodes with the object whereas lower resistance readings would indicate adequate electric contact. Thus, if the measured resistance is lower than a predetermined threshold resistance value, the contact electrodes are deemed to be in adequate electric contact with the object.

Preferably, the contact electrodes are electrically separate, i.e. the contact electrodes represent terminals of an electric circuit rather than form a single terminal.

In one embodiment the probe comprises a housing and the at least two contact electrodes are accommodated within the housing. The housing may be of elongate configuration. Preferably, the at least two electrodes, although spaced apart, are mutually arranged to form a single tip. The probe is preferably configured to spot stab the object being inspected. In order to place the electrodes in contact with the object, the object is "stabbed" with the tip of the probe, i.e. the tip is brought in contact with the object with force and substantially normal to the outer surface of the object.

In one embodiment, the reference electrode is accommodated within the probe housing. In another embodiment, the reference electrode is located externally with respect to the probe housing. The reference electrode preferably forms part of an electrochemical half-cell, such as, for example, but not limited thereto, an Ag/AgCl half-cell, wherein potential difference exists between at least one contact electrode and the reference electrode, the potential difference being measured by the instrument for measuring electric potential. The half-cell is preferably accommodated within the probe housing but may be located externally with respect to the probe housing.

The instrument for measuring electric potential is preferably connected in series between the reference electrode and one or more of the contact electrodes and may comprise, for example, a voltmeter. The instrument for measuring electric resistance between the electrodes is preferably connected in parallel between the contact electrodes and may comprise, for example, an ohmmeter.

Preferably, a switch arrangement is provided for connecting/disconnecting the instrument for measuring electric resistance and/or the instrument for measuring electric potential such that the resistance and the potential difference measurements can be taken separately and without interfering with each other. For example, the switch arrangement may comprise a changeover switch arrangement for simultaneously connecting one of the instrument for measuring electric resistance and/or the instrument for measuring electric potential and interrupting the other one of the two instruments. In one arrangement, only one contact electrode is connected to the instrument for measuring electric potential. In another arrangement, the instrument for measuring electric potential may be connected to two or more, in case the probe comprises more than two contact electrodes, contact electrodes of the probe, i.e. the contact electrodes may be arranged in parallel with respect to each other.

In an advantageous embodiment, the apparatus is incorporated into a Remotely Operated Vehicle (ROV) or an Autonomous Inspection Vehicle (AIV) for remote measurements. Alternatively, the apparatus may be a hand held unit, such as, for example, one usable by a diver.

Preferably, a user interface is provided in the apparatus to display the measurements. Preferably, the user interface includes a display, preferably, an electronic display. Preferably, the measurements are converted into electronic data. Preferably, the data is transmitted to the display for presentation to the user. Preferably, a storage means is provided for storing the electronic data.

Additionally, the apparatus can be used to inspect electrical continuity in electrical connections, such as for example, in cathodic protection cable and earth bonding connections. Furthermore, the apparatus can be used in a continuous cathodic potential survey by utilising the readings of the instrument for measuring electric potential as a calibration reference reading.

According to a fifth aspect of the invention there is provided an apparatus for evaluating cathodic protection of an electrically conductive object, the apparatus comprising:

an electrically conductive probe, comprising at least a pair of spaced apart contact electrodes for electrically contacting the object to be inspected

an instrument for measuring electric potential difference between at least one of the contact electrodes and a reference electrode (the reference electrode not being one of the at least a pair of contact electrodes); the probe being electrically connected to the reference electrode; and

According to a sixth aspect of the invention there is provided an apparatus for evaluating cathodic protection of an electrically conductive object in subsea environment, the apparatus comprising:

Due to the method and apparatus of the present invention, accurate evaluation of cathodic protection of an object is made possible in subsea environment and/or without the need to use bulky and awkward equipment as the probe can be made having convenient compact configuration. All essential, preferred or optional features of one of the first to sixth aspects of the present invention can be provided in conjunction with the other one of the first to sixth aspects of the present invention and vice versa where appropriate. Detailed Description of the Invention

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

Figure 1 is a schematic illustration of a prior art cathodic protection measurement device; and

Figure 2 is a schematic illustration of a cathodic protection measurement apparatus in accordance with the present invention.

Referring to Figure 2, the method and apparatus for evaluating cathodic protection of an object in accordance with the present invention will now be jointly discussed below. It will be appreciated that although, the most advantageous application of the method and apparatus is in subsea environment, such as seawater, it will be appreciated that the use of the method and apparatus of the invention in other environments is envisaged. In Figure 2, the apparatus for evaluating cathodic protection of an electrically conductive object of the present invention is indicated generally by reference numeral 20.

The apparatus 20 comprises an electrically conductive probe 22. The probe 22 has an elongate housing 24. The housing 24 accommodates a pair of spaced apart contact electrodes 26, 28. The contact electrodes 26, 28 are electrically separate from each other, such that the contact electrodes 26, 28 represent terminals of an electric circuit rather than form a single terminal. The two electrodes 26, 28, despite being spaced apart, are mutually arranged to form a single tip 30 for spot stabbing an outer surface 31 of an object 32. The object 32 may be, for example, a hull of a vessel, a pipe (e.g. a hydrocarbon production pipe), a jetty and many more objects which have cathodic protection arrangements applied thereto, and either an anodic or a cathodic part of the object can 32 be inspected. The contact electrodes 26, 28 of the probe 22 are electrically connected to a reference electrode 34 arranged within the housing 24 of the probe 22. The reference electrode 34 forms part of an electrochemical half-cell 36 such as, for example, an Ag/AgCl half-cell, which is also accommodated within the housing 24. The half-cell 36 is selected such that potential difference exists between at least one contact electrode 26, 28 and the reference electrode 34.

The apparatus 20 includes a voltmeter 38, for measuring electric potential difference between at least one of the contact electrodes 26, 28 and the reference electrode 34 and an ohmmeter 40 for measuring electric resistance between the contact electrodes 26, 28 when the electrodes are in contact with the object 32. The voltmeter 38 is connected in series between the reference electrode 34 one of the contact electrodes 26, 28. The ohmmeter 40 is connected in parallel between the contact electrodes 26, 28. The apparatus 20 includes a switch arrangement 42 provided to connect/disconnect the ohmmeter 40 or the voltmeter 38 such that the resistance and the potential difference measurements can be taken separately and without interfering with each other. The switch arrangement 42 may be provided in the form of a changeover switch for simultaneous connection of one of the voltmeter 38 or the ohmmeter 40 and interruption of the other one of the two instruments. In order to measure potential difference with the reference electrode 34, it is sufficient to connect only one contact electrode to the voltmeter 38. In other arrangements, both (or more, in case the apparatus 20 comprises more than two contact electrodes) contact electrodes 26, 28 of the probe 22 can be connected to the voltmeter 38 in parallel to each other.

In order to evaluate cathodic protection of the object 32, the contact electrodes 26, 28 are placed in electric contact with the object 32, either a sacrificial anode thereof (not shown in Figure 2) or the cathodic part of the object 32 (i.e. the object itself in most cases, i.e. a pipe). In order to place the electrodes 26, 28 in contact with the object 32, the object 32 is "stabbed" with the tip 30 (formed by the electrodes 26, 28) of the probe 22, i.e. the tip 30 is brought in contact with the object 32 with force and substantially normal to the outer surface 31 of the object 32. Next, electric resistance between the contact electrodes 26, 28 while in contact with the object 32 is measured using the ohmmeter 40. Then, based on the measurements of the value of resistance between the electrodes 26, 28 when in contact with the object 32 it is ascertained whether or not adequate electric contact has been established between the probe 22 and the object 32. Higher resistance readings would indicate poor electric contact of the contact electrodes 26, 28 with the object 32 whereas lower resistance readings would indicate adequate electric contact. The measured resistance is then compared with a predetermined threshold resistance value, and if the measured resistance is lower than a predetermined threshold resistance value, the contact electrodes 26, 28 are deemed to be in adequate electric contact with the object 32. In this manner, it is ensured that the subsequent potential difference measurements will not be affected by the quality of the electric contact between the contact electrodes 26, 28 and the object 32 and thereby to ensure that accurate evaluation of the cathodic protection of the object 32 will be made. Once it has been established that good electric conductive contact between the contact electrodes 26, 28 and the object 32 has been made, electric potential difference between at least one of the contact electrodes 26, 28 and the reference electrode 34 is measured using the voltmeter 38, the value of the potential difference being indicative of the level of cathodic protection applied to the object 32.

Although not shown in Figure 2, the probe 22 may be delivered to the object 32 by a Remotely Operated Vehicle (ROV) or an Autonomous Inspection Vehicle (AIV) for remote measurements. Alternatively, the probe 22 may be incorporated in a hand held unit (not shown in Figure 2) and manually delivered to the object 32, for example, by a diver. Further, although not shown in Figure 2, the probe 22 may be provided with a user interface and an electronic display to display the measurements. The measurements are converted into electronic data and the data is transmitted to the display for presentation to the user. The apparatus 20 preferably includes a storage means for storing the electronic data.

Additionally, the probe 20 may be used to inspect electrical continuity in electrical connections, such as for example, in cathodic protection cable and earth bonding connections. Also, the readings of the voltmeter 38 can be used as calibration reference readings for undertaking a continuous cathodic potential survey.

Whilst specific embodiments of the present invention have been described above, it will be appreciated that modifications are possible within the scope of the present invention.

Claims

1. A method for evaluating cathodic protection of an electrically conductive object, the method comprising the steps of:

providing an electrically conductive probe, comprising at least a pair of spaced apart contact electrodes;

placing the contact electrodes in electric contact with the object to be inspected;

2. A method as claimed in claim 1, wherein the at least one other electrode comprises another electrode of the at least two contact electrodes

3. A method as claimed in claim 1, the method comprising the step of providing the at least one other electrode in the form of a reference electrode (the reference electrode not being one of the at least a pair of contact electrodes) and electrically connecting the probe to the reference electrode.

4. A method as claimed in any preceding claim, wherein the method is adapted to be carried out subsea.

5. A method as claimed in any preceding claim, wherein method involves placing the contact electrodes in electric contact with an outer surface of the object to be inspected.

6. A method as claimed in any preceding claim, further comprising the step of, based on the measurements of the value of resistance between the electrodes when in contact with the object being inspected, ascertaining whether or not adequate electric contact has been established between the probe and the object being inspected so as to ensure that the electric potential difference measurement has not been influenced by the quality of the electric contact between the contact electrodes and the object under inspection.

7. A method as claimed in claim 6, where the method comprises the step of comparing the measured resistance with a predetermined threshold resistance value, wherein if the measured resistance is lower than a predetermined threshold resistance value, the contact electrodes are deemed to be in adequate electric contact with the object.

8. A method as claimed in any preceding claim, further comprising the step of arranging the contact electrodes electrically separate from each other, such that the contact electrodes represent terminals of an electric circuit rather than form a single terminal.

9. A method as claimed in any preceding claim, further comprising the step of providing the probe with a housing and accommodating the at least two contact electrodes within the housing.

10. A method as claimed in claim 9, wherein the housing is of elongate configuration.

11. A method as claimed in any preceding claim, further comprising the step of mutually arranging the at least two contact electrodes, despite being spaced apart, to form a single tip.

12. A method as claimed in any preceding claim, further comprising the step of spot stabbing the object being inspected with the probe.

13. A method as claimed in any one of claims 9 to 12, further comprising the step of accommodating the reference electrode within the probe housing.

14. A method as claimed in any one of claims 9 to 12, further comprising the step of arranging the reference electrode externally with respect to the probe housing.

15. A method as claimed in any one of claims 3 to 14, further comprising the step of providing the reference electrode as part of an electrochemical half-cell, wherein potential difference exists between at least one contact electrode and the reference electrode, and measuring the potential difference by the instrument for measuring electric potential difference.

16. A method as claimed in any one of claims 3 to 15, further comprising the step of connecting the instrument for measuring the electric potential difference in series between the reference electrode and one or more of the contact electrodes.

17. A method as claimed in any one of claims 1 to 16, further comprising the step of connecting the instrument for measuring the electric resistance, in parallel between the contact electrodes.

18. A method as claimed in any one of claims 1 to 17, further comprising the step of providing a switch arrangement and using the switch to connect/disconnect the instrument for measuring electric resistance and/or the instrument for measuring electric potential difference such that the resistance and the potential difference measurements are taken separately and without interfering with each other.

19. A method as claimed in claim 18, wherein the switch arrangement comprises a changeover switch arrangement and the method comprises the step of simultaneously connecting one of the instrument for measuring electric resistance and/or the instrument for measuring electric potential difference and interrupting the other one of the two instruments.

20. A method as claimed in any preceding claim, further comprising the step of connecting only one contact electrode to the instrument for measuring electric potential difference.

21. A method as claimed in any one of claims 1 to 19, further comprising the step of connecting the instrument for measuring electric potential difference to two or more, in case the probe comprises more than two contact electrodes, contact electrodes of the probe, and connecting the contact electrodes in parallel with respect to each other.

22. A method as claimed in any preceding claim, further comprising the step of using the probe in conjunction with a Remotely Operated Vehicle (ROI) or an Autonomous Inspection Vehicle (AIV) for remote measurements.

23. A method as claimed in any one of claims 1 to 21, further comprising the step of incorporating the probe in a hand held unit and manually delivering to the object under inspection.

24. A method as claimed in any one of claims 1 to 23, further comprising the step of including providing the probe with a user interface to display the measurements.

25. A method as claimed in any one of claims 1 to 24, further comprising the step of converting the measurements into electronic data and transmitting the data to the display for presentation to the user.

26. An apparatus for evaluating cathodic protection of an electrically conductive object, the apparatus comprising:

an electrically conductive probe, comprising at least a pair of spaced apart contact electrodes for electrically contacting the object to be inspected;

27. An apparatus as claimed in claim 26, wherein, the at least one other electrode comprises another electrode of the at least two contact electrodes.

28. An apparatus as claimed in claim 26, wherein the at least one other electrode comprises a reference electrode (the reference electrode not being one of the at least a pair of contact electrodes) and the probe is electrically connected to the reference electrode.

29. An apparatus as claimed in any one of claims 26 to 28, wherein the apparatus is configured for use in subsea environment.

30. An apparatus as claimed in any one of claims 26 to 29, wherein the apparatus is adapted for placing the contact electrodes in electric contact with an outer surface of the object to be inspected.

31. An apparatus as claimed in any one of claims 26 to 30, wherein the contact electrodes are electrically separate such that the contact electrodes represent terminals of an electric circuit.

32. An apparatus as claimed in any one of claims 26 to 31, wherein the probe comprises a housing and the at least two contact electrodes are accommodated within the housing.

33. An apparatus as claimed in any one of claims 26 to 32, wherein the housing is of elongate configuration.

34. An apparatus as claimed in any one of claims 26 to 33, wherein the at least two contact electrodes, although spaced apart, are mutually arranged to form a single tip.

35. An apparatus as claimed in any one of claims 26 to 34, wherein the probe is configured to spot stab the object being inspected.

36. An apparatus as claimed in any one of claims 28 to 35, wherein the reference electrode is accommodated within the probe housing.

37. An apparatus as claimed in any one of claims 28 to 35, wherein the reference electrode is located externally with respect to the probe housing.

38. An apparatus as claimed in any one of claims 28 to 37, wherein the reference electrode forms part of an electrochemical half-cell, wherein potential difference exists between at least one contact electrode and the reference electrode, the potential difference being measurable by the instrument for measuring electric potential.

39. An apparatus as claimed in claim 38, wherein the half-cell is an Ag/AgCl half- cell.

40. An apparatus as claimed in claim 38 or claim 39, wherein the half-cell is accommodated within the probe housing.

41. An apparatus as claimed in claim 38 or claim 39, wherein the half-cell is located externally with respect to the probe housing.

42. An apparatus as claimed in any one of claims 28 to 41, wherein the instrument for measuring electric potential is connected in series between the reference electrode and one or more of the contact electrodes.

43. An apparatus as claimed in any one of claims 26 to 42, wherein the instrument for measuring electric resistance between the electrodes is connected in parallel between the contact electrodes.

44. An apparatus as claimed in any one of claims 26 to 43, wherein the apparatus further comprises a switch arrangement for connecting/disconnecting the instrument for measuring electric resistance and/or the instrument for measuring electric potential difference such that the resistance and the potential difference measurements can be taken separately and without interfering with each other.

45. An apparatus as claimed in claim 44, wherein the switch arrangement comprises a changeover switch arrangement for simultaneously connecting one of the instrument for measuring electric resistance and/or the instrument for measuring electric potential and interrupting the other one of the two instruments.

46. An apparatus as claimed in any one of claims 26 to 45, wherein only one contact electrode is connected to the instrument for measuring electric potential difference.

47. An apparatus as claimed in any one of claims 26 to 45, wherein the instrument for measuring electric potential difference is connected to two or more, in case the probe comprises more than two contact electrodes, contact electrodes of the probe.

48. An apparatus as claimed in any one of claims 26 to 47, wherein the apparatus is incorporated into a Remotely Operated Vehicle (ROI) or an

Autonomous Inspection Vehicle (AIV) for remote measurements.

49. An apparatus as claimed in any one of claims 26 to 47, wherein the apparatus is a hand held unit.

50. An apparatus as claimed in any one of claims 26 to 49, wherein the apparatus comprises a user interface to display the measurements.

51. An apparatus for evaluating cathodic protection of an electrically conductive object, the apparatus comprising:

an electrically conductive probe, comprising at least a pair of spaced apart contact electrodes for electrically contacting the object to be inspected; an instrument for measuring electric potential difference between at least one of the contact electrodes and a reference electrode, the reference electrode not being one of the at least pair of contact electrodes; and

52. An apparatus for evaluating cathodic protection of an electrically conductive object in subsea environment, the apparatus comprising:

53. A method for evaluating cathodic protection of an electrically conductive object substantially as herein described with reference to the accompanying drawings.

54. An apparatus for evaluating cathodic protection of an electrically conductive object substantially as herein described with reference to the accompanying drawings.