1. Field Testing for Shorted Casings
AUCSC May 2019
System Diagnostics
J. Block

2. DOT Regulations for Natural Gas Transmission Line Title 49 CFR 192
DOT Regulations for Natural Gas Transmission Line Title 49 CFR External corrosion control: Electrical isolation
–(c) Except for unprotected copper inserted in ferrous pipe, each pipeline must be electrically isolated from metallic casings that are a part of the underground system. However, if isolation is not achieved because it is impractical, other measures must be taken to minimize corrosion of the pipeline inside the casing.
–(d) Inspection and electrical tests must be made to assure that electrical isolation is adequate.

3. DOT Regulations for Hazardous Liquid Lines
Title 49 CFR
(a) electrically isolate each buried or submerged pipeline from other metallic structures, unless you electrically interconnect and cathodically protect the pipeline and the other structures as a single unit.
(c) inspect and electrically test each electrical isolation to assure the isolation is adequate.

4. NACE Standard SP0169 Requirements
 effectiveness of isolating fittings, continuity bonds, and casing isolation should be evaluated during periodic surveys. This may be accomplished by electrical measurements.

5. NACE Standard SP0200 Requirements
6.2 Monitoring: One or more of the following basic electrical test methods should be used to monitor pipelines and casings on an annual basis.
–6.2.1 Potential Survey
–6.2.2 Internal Resistance
–6.2.3 Four-Wire IR Drop
–6.2.4 Cycling Rectifier
–6.2.5 Casing Depolarization
–6.2.6 Direct Resistance Measurement
–6.2.7 Pipe/Cable Locator

6. Casing Testing:
One LDC Approach

9. CIS
Pipe-to-Soil Survey

10. CIS Survey
- 0.90
- 0.68
- 0.65
- 0.71
- 0.73
- 0.69
- 0.70
- 0.78
- 0.95
- 0.96
- 0.72
- 0.93
- 0.83
NACE International (National Association of Corrosion Engineers) recommends connection to the structure under test (pipeline) in this convention.
Steel pipe

11. - 0.95
- 0.85
- 0.75

12. - 0.98
- 0.90
- 1.47
- 0.44
- 0.93
- 0.52
- 0.11
- 0.33
- 0.77
- 0.22
- 0.95
- 0.66
- 0.71
- 0.83
- 0.23
- 0.85
- 1.67
- 0.93
- 0.69
- 0.65
- 0.50
- 0.68
Steel pipe
Steel pipe

13. Coated Steel Pipe with coating defects
The effects of stray current from an electrified transit system can be extremely detrimental to buried metallic structures in the vicinity of the rail tracks. A well coated pipeline can reduce interference current from entering or exiting the pipe surface. Defects in the coating (coating holidays) can provide a path for stray current damage to the pipeline.
Coated Steel Pipe
Coated Steel Pipe with coating defects

16. Casing Test: C = clear E = electrolytic M = metallic
Structure-to-soil readings that have similar value may indicate an electrolytic condition or metallic short between the pipe and casing. Structure-to-soil readings that have the same value may indicate a metallic short
P/S C E M
DC Voltage Shift
DC current applied to one structure drives the other structure more negative, may indicate a metallic short. DC current applied to one structure drives the other structure less negative or none, indicates a cleared casing C E M
PΩ-earth & CΩ - earth
Calculated resistance to earth values that are similar may indicate an electrolytic condition. Calculated resistance to earth values that have the same value may indicate a metallic short C E M
Calculated resistance between pipe and casing that is ≤ to 1 Ω may indicate an electrolytic condition or possibly a metallic short. If resistance value is ≤ the sum of the pipe-to-earth and casing-to-earth, this may indicate an electrolytic condition or metallic short.
PΩ - CΩ C E M
Application of a signal locator between the casing and the pipeline that is greatly reduce or lost may indicate a metallic short. Application of a signal locator between the casing and the pipeline that is maintained along the pipeline indicates a cleared crossing.
Signal Locator C E M
Head-Set
Connecting a head-set between the casing and the pipeline will present an audible tone. Tone indicates a voltage potential which may indicate a cleared casing or an electrolytic condition. Lack of an audible tone may indicate a metallic short. C E M

17. Structure to Soil Potential
Structure-to-soil readings that have similar value may indicate an electrolytic condition or metallic short between the pipe and casing. Structure-to-soil readings that have the same value may indicate a metallic short

18. - .71
- .76

19. DC VOLTAGE SHIFT
DC current applied to one structure drives the other structure more negative, may indicate a metallic short. DC current applied to one structure drives the other structure less negative or none, indicates a cleared casing

20. - 0.87 - 0.73 - 0.76 - 0.76 External Current Source
Temporary Ground Bed

21. - 0.70
- 0.71
- 0.95
- 0.71

22. Pipe Ω-earth & Casing Ω-earth
Calculated structure resistance-to- earth values that are similar may indicate an electrolytic condition. Calculated structure resistance- to- earth values that have the same value may indicate a metallic short

23. AMPS I On Off ∆ V Ω I On Off ∆ V Ω 3.01 - 1.30 - .76 .54 .18 2.96
- 0.76
- 1.30
- 1.18
- 0.71
External Current Source
Temporary Ground Bed
AMPS I On
Off
∆ V Ω I On
Off
∆ V Ω
3.01
- 1.30
- .76
.54
.18
2.96
- 1.18
- .71
.47
.16

24. Pipe Ω vs. Casing Ω
Calculated resistance between pipe and casing that is ≤ to 1Ω may indicate an electrolytic condition or possibly a metallic short. If resistance value is ≤ the sum of the pipe-to-earth and casing-to-earth, this may indicate an electrolytic condition or metallic short.

25. Clear

26. Casing and Carrier Clear
-0.05
-1.59
1.12
Battery
Casing and Carrier Clear I On
Off
∆ V Ω
1.12
- 1.59
- .05
1.54
1.39

27. Electrolytic

28. Possible Electrolytic condition between Casing and Carrier
-0.05
-1.02
1.28
Battery
Possible Electrolytic condition between Casing and Carrier I On
Off
∆ V Ω
1.28
- 1.02
- .05
0.97
.75

29. Shorted

30. Suspect Metallic Short between Casing and Carrier
-0.76
-0.03
3.89
Battery
Suspect Metallic Short between Casing and Carrier I On
Off
∆ V Ω
3.89
- 0.76
- .03
0.73
.18

31. Soil Resistivity Meter
P 1
P 2
C 2
C 1

32. Signal Locator
Application of a signal locator between the casing and the pipeline. A signal that is greatly reduced or lost, may indicate a metallic short. Application of a signal locator between the casing and the pipeline that is maintained along the pipeline indicates a cleared crossing.

33. Brand X Pipe & Cable Locator

35. ACVG

39. 700 A
600 A
500 A
400 A

41. 700 A
600 A
500 A
400 A

42. Vent Line or Coating Holiday ?

43. Head-Set
Connecting a head-set between the casing and the pipeline will present an audible tone. Tone indicates a voltage potential which may indicate a cleared casing or an electrolytic condition. Lack of an audible tone may indicate a metallic short.

44. Battery

48. Gas Main 90 ° at top
Gas Main 90 ° at bottom
Steam Conduit 170 °
Ground Water 120 °

49. 54” Casing
12” Casing
8” Gas Main
Support Bracket
32” Steam Conduit
6” Condensate Line
12” Steam Pipe