CP Design�Land Pipelines-Aluminium Alloy Anodes Used for Submarine Pipelines

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1. Haward Technology Middle East 1Section 19
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Section 19
DC Isolation & Over-Voltage
Protection on CP Systems

2. Haward Technology Middle East 2Section 19
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Typical Problems
AC grounding without affecting CP
Decoupling in code-required bonds
AC voltage mitigation
Over-voltage protection
Hazardous locations

3. Haward Technology Middle East 3Section 19
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Conflicting Requirements
Structures must be cathodically protected (CP)
CP systems require DC decoupling from ground
All electrical equipment must be AC grounded
The conflict: DC Decoupling + AC Grounding

4. Haward Technology Middle East 4Section 19
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Reasons to DC Decouple From
Electrical System Ground
If not decoupled, then:
•CP system attempts to protect grounding system
•CP coverage area reduced
•CP current requirements increased
•CP voltage may not be adequate

5. Haward Technology Middle East 5Section 19
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Isolation problems
Insulation strength/breakdown
FBE coating: 5kV
Asphalt coating: 2-3kV
Flange insulators: 5-10kV?
Monolithic insulators: 20-25kV

6. Haward Technology Middle East 6Section 19
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Over-Voltage Protection
From:
•Lightning (primary concern)
•Induced AC voltage
•AC power system faults

7. Haward Technology Middle East 7Section 19
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Over-Voltage Protection Goal
Minimize voltage difference between points of
concern:
•At worker contact points
•Across insulated joints
•From exposed pipelines to ground
•Across electrical equipment

8. Haward Technology Middle East 8Section 19
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Step Potential

9. Haward Technology Middle East 9Section 19
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Touch Potential

10. Haward Technology Middle East 10Section 19
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Over-voltage Protection: Products and Leads
Both the protection product and the leads have voltage
across them
Lead length can be far more significant than the
product conduction level

11. Haward Technology Middle East 11Section 19
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Effect of Lead Length
Leads develop extremely high inductive voltage during
lighting surges
Inductive voltage is proportional to lead length
Leads must be kept as short as possible
Not a significant effect seen with AC

12. Haward Technology Middle East 12Section 19
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Key Parameters of Lightning Waveform
Lightning has very high di/dt (rate of change of
current)

13. Haward Technology Middle East 13Section 19
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
AC and Lightning Compared

14. Haward Technology Middle East 14Section 19
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Over-Voltage Protection: Best Practices
Desired characteristics:
Lowest clamping voltage feasible
Designed for installation with minimal lead length
Fail-safe (fail “shorted” not “open”)
Provide over-voltage protection for both lightning and
AC fault current

15. Haward Technology Middle East 15Section 19
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Example: Insulated Joint

16. Haward Technology Middle East 16Section 19
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Example: Insulated Joint

17. Haward Technology Middle East 17Section 19
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Example: Insulated Joint

18. Haward Technology Middle East 18Section 19
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Insulated Joint Protection Summary
Rate for:
AC fault current expected
Lightning surge current
Block CP current to DC voltage across joint
AC induction (low AC impedance to collapse AC
voltage) – rate for available current
Hazardous location classification

19. Haward Technology Middle East 19Section 19
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Grounding System Review
Secondary (user) grounding system
Primary (power co) grounding system
These systems are normally bonded

20. Haward Technology Middle East 20Section 19
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Grounding System Schematic
Primary
Arrester
Fuse Distribution
Transformer
Primary
Neutral
Primary
Ground
Secondary
Ground
Service
Entrance
Ground
Service Entrance
Grounding
Conductor
Electrical
Equipment
On Cathodically
Protected System

21. Haward Technology Middle East 21Section 19
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Situation: Pipeline with Electrical Equipment
Grounded electrical equipment affects CP system
Code requires grounding conductor
Pipeline in service (service disruption undesirable)

22. Haward Technology Middle East 22Section 19
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Decoupler characteristics
High impedance to DC current
Low impedance to AC current
Passes induced AC current
Rated for lightning and AC fault current
Fail-safe construction
Third-party listed to meet electrical codes

23. Haward Technology Middle East 23Section 19
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Grounding System After Decoupling
Primary
Arrester
Fuse
Distribution
Transformer
Primary
Neutral
Primary
Ground
Secondary
Ground
Service
Entrance
Ground
Service Entrance
Grounding
Conductor
Electrical
Equipment
On Cathodically
Protected System
PCR

24. Haward Technology Middle East 24Section 19
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Issues Regarding Decoupling
NEC grounding codes apply: 250.2,
250.4(A)(5), 250.6(E)
Decoupler must be certified (UL, CSA, etc.)
No bypass around decoupler

25. Haward Technology Middle East 25Section 19
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Rating for Equipment Decoupling
Rate for:
AC fault current/time in that circuit
Can rate by coordinating with ground wire size
Decoupler must be certified (UL, etc)
Steady-state AC current if induction present
DC voltage difference across device
Hazardous area classification

26. Haward Technology Middle East 26Section 19
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Example: MOV

27. Haward Technology Middle East 27Section 19
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Decoupling Single Structures:
When is it Impractical?
Too many bonds in a station from CP system to ground
 Bonds can’t be reasonably located
Solution: Decouple the entire facility

28. Haward Technology Middle East 28Section 19
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Decoupling from Power Utility
Primary
Arrester
Fuse Distribution
Transformer
Primary
Neutral
Primary
Ground
Secondary
Ground
Service
Entrance
Ground
Service Entrance
Grounding
Conductor
Electrical
Equipment
On Cathodically
Protected System
PCR

29. Haward Technology Middle East 29Section 19
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Decoupling From the Power Utility
Separates user site/station from extensive utility
grounding system
Installed by the power utility
Decoupler then ties the two systems together

30. Haward Technology Middle East 30Section 19
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Decoupling from Power Utility

31. Haward Technology Middle East 31Section 19
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Decoupling from utility

32. Haward Technology Middle East 32Section 19
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Decoupling from utility

33. Haward Technology Middle East 33Section 19
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Decoupling from utility

34. Haward Technology Middle East 34Section 19
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Decoupling from utility
Primary and secondary have AC continuity but DC
isolation
CP system must protect the entire secondary grounding
system

35. Haward Technology Middle East 35Section 19
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Rating for Utility Decoupling
Rate for:
Primary (utility) phase-to-ground fault current/time
Ask utility for this value
Select decoupler that exceeds this value

36. Haward Technology Middle East 36Section 19
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Case study – station decoupling

37. Haward Technology Middle East 37Section 19
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Induced AC Voltage
Pipelines near power lines develop “induced voltage”
Can vary from a few volts to several hundred volts
Voltages over 15V should be mitigated (NACE RP-0177)
Mitigation: reduction to an acceptable level

38. Haward Technology Middle East 38Section 19
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Induced AC Mitigation Concept
Create a low impedance AC path to ground
Have no detrimental effect on the CP system
Provide safety during abnormal conditions

39. Haward Technology Middle East 39Section 19
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Example: Mitigating Induced AC
Problem:
•Open-circuit induced AC on pipeline = 30 V
•Short-circuit current = 10 A
•Then, source impedance: R(source) = 30/10 = 3 ohms
Solution:
•Connect pipeline to ground through decoupler

40. Haward Technology Middle East 40Section 19
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Example: Mitigating Induced AC
Typical device impedance:
X = 0.01 ohms
0.01 ohms << 3 ohm source
10A shorted = 10A with device
V(pipeline-to-ground) = I . X = 0.1 volts
Result: Induced AC on pipeline reduced from 30 V to 0.1 V

41. Haward Technology Middle East 41Section 19
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Mitigation of Induced AC
Rate for:
Induced max AC current
DC voltage to be blocked
AC fault current estimated to affect pipeline

42. Haward Technology Middle East 42Section 19
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Mitigation of Induced AC
Two general approaches:
•Spot mitigation
•Continuous mitigation

43. Haward Technology Middle East 43Section 19
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Spot Mitigation
Reduces pipeline potentials at a specific point (typ.
accessible locations
Commonly uses existing grounding systems
Needs decoupling

44. Haward Technology Middle East 44Section 19
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Mitigation example sites

45. Haward Technology Middle East 45Section 19
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Mitigation
example sites

46. Haward Technology Middle East 46Section 19
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Mitigation example
sites

47. Haward Technology Middle East 47Section 19
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Continuous Mitigation
Reduces pipeline potentials at all locations
Provides fairly uniform over-voltage protection
Typically requires design by specialists

48. Haward Technology Middle East 48Section 19
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Continuous Mitigation
Gradient control wire choices:
•Zinc ribbon
•Copper wire
•Not tower foundations!

49. Haward Technology Middle East 49Section 19
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Hazardous Locations
Many applications described are in Hazardous Locations
as defined by NEC Articles 500-505
Most products presently used in these applications are:
•Not certified
•Not rated for hazardous locations use

50. Haward Technology Middle East 50Section 19
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Hazardous Location Definitions
Class I = explosive gases and vapors
Division 1: present under normal conditions (always
present)
Division 2: present only under abnormal conditions

51. Haward Technology Middle East 51Section 19
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Hazardous Locations

52. Haward Technology Middle East 52Section 19
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
CFR 192.467
e.“An insulating device may not be installed where
combustible atmosphere is anticipated unless
precautions are taken to prevent arcing.”

53. Haward Technology Middle East 53Section 19
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
CFR 192.467
f.“Where a pipeline is located in close proximity to
electric transmission tower footings . . . it must be
provided with protection against damage due to fault
current or lightning, and protective measures must be
taken at insulating devices.”

54. Haward Technology Middle East 54Section 19
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
CFR 192 link to NEC
CFR 192 incorporates the National Electrical Code
(NEC) “by reference”
This classifies hazardous locations
Defines product requirements and installation methods

55. Haward Technology Middle East 55Section 19
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Guidance Documents (Haz Loc)
AGA XF0277 – gas facilities
API RP-500 – petroleum facilities
CFR 192.467 – gas pipeline regs
NEC section 500-505 - haz loc definitions,
requirements
CSA C22.2 No. 213 – product requirements
UL 1604 – product requirements

56. Haward Technology Middle East 56Section 19
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
End of this
Section