APPARATUS AND METHOD FOR CORROSION PROTECTION MONITORING

1 . An apparatus for connection to a transformer rectifier unit which is operable to output an impressed cathodic protection current for cathodic protection of a metallic structure located below ground, the apparatus comprising:

a modulator unit in electrical connection with the transformer rectifier unit and arranged for permanent electrical connection with a metallic structure, wherein when the apparatus is in use the modulator unit is operable to receive the impressed cathodic protection current from the transformer rectifier unit and to modulate the impressed cathodic protection current to produce a current mapping signal which is applied to the metallic structure, such that the current mapping signal flowing in the metallic structure can be detected and measured wirelessly from above ground, and wherein the current mapping signal is directly derived from, and corresponds to, the impressed cathodic protection current, and wherein the modulator unit is operable to be controlled remotely.

2 . The apparatus for use in measuring the cathodic protection of a metallic structure located below ground, the apparatus comprising:

a transformer rectifier unit which is operable to output an impressed cathodic protection current for cathodic protection of a metallic structure located below ground; and

an apparatus as claimed in claim 1 for connection to the transformer rectifier unit and operable to output an impressed cathodic protection current for protection of a metallic structure located below ground.

3 . The apparatus as claimed in claim 1 , wherein the transformer rectifier unit is operable to be controlled remotely.

4 . The apparatus as claimed in claim 1 , further comprising a remote monitor unit for monitoring the transformer rectifier unit and/or the modulator unit.

5 . The apparatus as claimed in claim 1 , wherein the current mapping signal has a modulation frequency of between 1 Hz and 12 Hz

6 . The apparatus as claimed in claim 5 , wherein the current mapping signal has a modulation frequency of between 3 Hz and 8 Hz.

7 . The apparatus as claimed in claim 2 , wherein the modulator unit is integral with the transformer rectifier unit.

8 . The apparatus as claimed in claim 1 , wherein the current mapping signal is detectable above ground using a current mapping device.

9 . The apparatus as claimed in claim 8 , wherein the current mapping device is operable to transmit current mapping signal data wirelessly or via wired means to a control centre or monitoring station.

10 . The apparatus as claimed in claim 1 , wherein the modulator unit is further operable to generate a locatable AC output from the transformer rectifier unit.

11 . A method of surveying the impressed cathodic protection current in an underground metallic structure, the method comprising the steps of:

(i) connecting a transformer rectifier unit and an apparatus as claimed in claim 1 to an underground buried metallic structure:

(ii) operating the transformer rectified unit to supply a impressed cathodic protection current to provide cathodic protection for the structure:

(iii) operating the modulator unit of the apparatus to modulate the impressed cathodic protection current being supplied to the metallic structure to provide a current mapping signal to the metallic structure; and

(iv) wirelessly detecting and measuring the current mapping signal above ground.

12 . The method of surveying the impressed cathodic protection current in an underground metallic structure, the method comprising the steps of:

(i) connecting an apparatus as claimed in claim 2 to an underground buried metallic structure:

(ii) operating the transformer rectified unit to supply a impressed cathodic protection current to provide cathodic protection for the structure:

(iii) operating the modulator unit of the apparatus to modulate the impressed cathodic protection current being supplied to the metallic structure to provide a current mapping signal to the metallic structure; and

(iv) wirelessly detecting and measuring the current mapping signal above ground.

13 . The method of claim 11 , wherein the current mapping signal is wirelessly detected and measured above ground using a current mapping device to generate current map data.

14 . The method of claim 13 , wherein the current mapping device is operable to save the current mapping data and/or transmit the current mapping data wirelessly or via wired means to a control centre or monitoring station.

15 . The method of claim 13 further comprising the step of analysing the current mapping signal data to assess the cathodic protection applied across the metallic structure.

16 . The method of claim 11 , further comprising an intermediate step between step (i) and step (ii) of operating the modulator unit of the apparatus to generate a locatable higher frequency AC output from the transformer rectifier unit for detection by a receiving device above ground to locate the position of the underground metallic structure.

17 . The method of claim 16 , wherein the locatable higher frequency AC output is above 90 Hz.

18 . The method of claim 16 , wherein the locatable higher frequency AC output is generated by modulation of a DC current output from the transformer rectified unit.

19 . The method of claim 16 , wherein a portable locator transmitter is in electrical connection with the metallic structure and the locatable higher frequency AC output is generated by the portable locator transmitter either instead of or in addition to the modulator unit.

20 . The apparatus of claim 1 , wherein the metallic structure comprises a pipeline.

21 . The method of claim 11 , wherein the metallic structure comprises a pipeline.