The detection of electrical currents passing from one pipeline system to another in such a way as to accellerate the corrosion processes.
This procedure requires the co-operation of the owners of all buried structures and pipelines in the vicinity of the pipeline under investigation.
- Recording voltmeter or data-logger.
- High resistance voltmeter.
- Two current interupters, or transformer/rectifier timers.
- Four standard copper/copper-sulphate electrodes.
- 100 M reel of connecting cable.
- Reel of armature wire on long line trailing holder.
- Report forms
14.1 Identify all relevant pipelines plant and buried structures along the subject pipeline route.
14.1.1. Examine all available drawings and compile a master drawing with all relevant information.
14.1.2. Write to all public authorities and pipeline operators in the subject area, requesting details of their buried pipelines, plant and equipment that might cause electrical discharge to the ground, or draw current from it. Details of all cathodic protection sysstems and protected structures, whether impressed or sacrificial, should be requested.
14.1.3. Walk the whole subject, pipeline route, where possible and view inaccessible areas from as close as possible, noting all man-made structures.
14.1.4. Form a committee of interested parties and include a member from electrical engineering and telecommunications sectionsof the subject pipeline operating company.
14.2.1. Conduct Procedure 6, over the pipeline 'immediate off potential' survey along the whole pipeline route.
14.2.2. Identify the locations where the ground potentials deviate from the average, in both the 'on' and 'off' modes.
14.2.3. Visit the sites where these deviations match the locations of possible 'foriegn' electrical influence.
14.2.4. Conduct a grid survey, using two electrodes in the same way as procedures 8 and 9. Eliminate the sites where the deviations can be identified as caused by coating faults or the influence of the subject pipelines own groundbed.
CO-OPERATIVE FIELD TESTING.
14.3.1. Arrange a site meeting with all interested parties.
14.3.2. Set the cathodic protection system switching on for 12 seconds and off for 3 seconds.
14.3.3. Establish 'remote earth from the subject pipeline and identify a test facility on the 'foreign' pipeline or structure.
14.3.4. Carry out Procedure 5 to establish the amount of influence that the subject pipeline has on the potential of the foreign service.
14.3.5. Identify the location where the foreign service is physically closest to the subject pipeline.
14.3.6. Carry out a grid survey, as 14.2.4., for the whole of this location.
14.3.7. Mark the peaks and depressions during the 12 seconds and 3 seconds intervals of the cathodic protection system switching.
14.3.8. Switch the CP system to its constant 'on' mode and arrange for the foreign service to be switched in a recognisable cycle.
14.3.9. Carry out a second grid survey, as at 14.3.6.and mark the locations of the peaks and epressions as before.
14.4.1. Arrange to excavate to examine the pipelines where any peak and depression from each survey, coincide.
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