Post Thumb

With today’s electronic instrumentation, it is possible to combine close interval potential surveys (CIPS) with direct current voltage gradient surveys (DCVG) of buried and underwater pipelines for improved accuracy in assessing the level of cathodic protec tion combined with locating coating defects without spatial errors. Modern electronic survey instruments are capable of stamping each reading with the time, date and submetre GPS coordinates. This provides information for accurate mapping of the pipe line location, current state of the cathodic protection system, and further allows personnel to accurately locate areas requiring excavation for coating repair. This paper will show by example how combined CIPS and DCVG surveys undertaken to NACE standards are of benefit to pipeline operators in ensuring cost and time-effective integrity management of their pipeline systems.

 

Sophisticated survey (DCVG) and local data logger instrument equipped with a GPS engine that can accurately measure the rectifier ON and OFF potential at each reading stamped with GPS coordinates, distance UTC time. Beside its logging features it is powerful and an accurate equipment for detecting and tracking the escaping currents of pipelines by using its barcode display option in DCVG mode.

Applications :

1. Accurate location of coating faults to within centimetres.

2. Approximate severity of coating faults which is closely related to size of coating damage.

3. Determine the degree of protection of steel exposed at coating faults.

4. Determine the approximate shape of coating fault particularly ruffling in tapes and crown cracking in coal tar.

5. Identify faults taking abnormal amounts of Cathodic Protection (CP) current.

6. Identify coating faults close to CP power sources that are taking abnormal amounts of CP current.

7. Recognise and locate interference from foreign structures.

8. Recognise and locate interference from foreign CP systems.

9. Identify coating faults picking up or discharging DC Traction Interference.

10. Identify Optimum location of where to site DC Traction Drainage Bonds.

11. Test the functional ability of Insulating Flanges and Joints (expressed as % efficiency of insulation).

12. Test the functional ability of pipeline support insulators.

13. Recognise without excavation the failure of field joints because of the regular spacing of coating faults.

14. Identify the quality of field bends on buried pipelines.

15. Assess the quality of protective coatings on valves and other pipeline components.

16. Assess the quality of the coating repair at CP cable attachments to pipelines.

17. Identify cable shorts inside metal test posts.

18. Identify which cable is attached to which pipe in a multi-pipeline CP test post.

19. Identify the extent of effectiveness of CP system along a pipeline, i.e. the throw of CP system.

20. Identify where a coating fault gets its CP from and as a result what happens to the

degree of protection of a coating fault if a CP transformer rectifiers become inoperative.

21. Pipelines in complex pipeline networks such as under city streets, within process plant tank farms (fire water mains, etc.)

22. Pipelines under concrete or under asphalt roads can be surveyed.

23. Ground beds can be located.

24. Lazy or defective anodes can be located within a shallow horizontal or vertical anode groundbed.

25. Field effect from anode bed can be assessed.

26. From the rate of decay of the pulsed DCVG signal amplitude, areas of greater coating

failure can be more readily recognized for closer study.

27. By studying the direction of current flow to faults the applied CP can be adjusted to ensure all faults are receiving adequate Cathodic Protection.

28. DCVG technology can be used on pipelines that cross rivers or estuaries, also on sea outfall pipes.

29. Lazy sacrificial anodes can be identified. Sacrificial anodes can also be located by DCVG technology.

30. DCVG technology can be applied to pipelines carrying all types of fluids, also to armoured electricity and telephone cables to identify damage to the outer protective coating on the armour sheathing.

31. Identify direct shorts inside steel casing pipes. Identify if casing has water shorting out carrier pipe.