1. CORROSION MITIGATION OF A PIPELINE
PIPELINE CORROSION
MANAGEMENT SEMINAR
29TH JUNE 2017
CORROSION MITIGATION OF A PIPELINE
IN A METROPOLITAN AREA
Presented by: Jim Galanos

2. What is Corrosion?
Using steel as an example, the corrosion reaction that occurs (in simple terms) is:
Fe  Fe e- (anodic)
½ O2 + H2O + 2e-  20H- (cathodic)
In order for corrosion to occur, the following 4 items are required:
Active site or metal (metal which corrodes )
Passive site or metal (metal which is protected)
Electrical connection (bond) between anode and cathode
Electrolyte (water, soil, concrete)
In order for corrosion not to be present the following is needed:
Isolation from environment
Change the environment to a passive environment

3. Corrosion Mitigation Via Coatings
Coatings are typically used as the main corrosion protection means for ferrous metal structures. Coatings provide protection by isolating the metal from the surrounding environment.
A perfect coating which provides 100% protection, can neither be applied or maintained as coating breakdown occurs with day to day operation and with age, hence corrosion is initiated at coating defect locations.
Disbonded coatings can shield cathodic protection current flow to the structure being protected.

4. Corrosion Mitigation via Cathodic Protection
Buried and immersed metallic structures can be protected against corrosion via the application of cathodic protection (CP) using sacrificial anode or Impressed Current (ICCP) type
CP is an electrochemical process and involves a direct current being forced to flow from an external source (anode) to the structure being protected (cathode).
CP is widely used to complement coating systems, with the coating system being the main corrosion barrier.
As the coating breaks down with time and day-to-day operations, the cathodic protection system provides protection at coating defect locations.

5. Buried & Immersed Structures as per AS2832 Parts 1-4
Protection Criteria
Buried & Immersed Structures as per AS2832 Parts 1-4
Note:
Where MIC/SRB/ALWC is present a minimum potential of 100mV more negative than the minimum criteria should be maintained
*1. Above potentials are free of significant voltage gradient error.

6. Coating Disbondment
Under certain conditions, cathodic protection can cause coating disbondment
Occurs when a CP system “overprotects” a coated structure. Overly high current is applied, resulting in excessive hydrogen at the structure causing coating disbondment.
CP (Inst off) potentials of –1.2 to –1.4 volts vs Cu / CuSO4 can cause coating disbondment.
Stray currents are generally not an issue at disbonded coatings however they can cause accelerated corrosion at coating defects

7. Pipeline case study - background
Pipeline is 300mm NB and approximately 19km long.
Constructed over 55 years ago.
Route is through large metropolitan city with electrified DC rail network.
Originally coal tar enamel external coating, with numerous repairs throughout its life using petrolatum tape, heat shrink sleeves and epoxy.

8. Pipeline case study – CP system
Approx. 50-off test points installed along route.
Original CP system consisted of buried sacrificial (magnesium) anodes at some but not all test points.
ICCP system was retro-fitted in the 1970’s as the sacrificial anode CP system could no longer provide full protection.
ICCP consisted of:
2-off ICCP systems
1-off Railway Drainage Bond, upgraded to a TRAD (Transformer Rectifier Assisted Drainage) system, in the 1980’s

9. Pipeline case study – CP system review
CP current demand has increased over past 4-5 years.
CP unit outputs limited due to interference effects.
In some cases, potentials were shifting more positive (towards unprotected) despite the above.
Potentials were non-uniform, ranging from marginally protected to over-protected.
Some evidence of cathodic shielding which limits the effectiveness of CP.
The following CP system upgrades are either complete or in progress.

10. Pipeline case study – CP system upgrades (1)
An additional ICCP system was installed.
Purpose was to provide additional CP current, allow a better balancing between all ICCP/TRAD systems and provide more uniform potentials along the pipeline to limit under/ overprotected areas.
More uniform potentials allow the CP system operators greater confidence in monitoring potentials closer to the most negative potential limit and minimise low potentials between test points

11. Pipeline case study – CP system upgrades (1)
Existing ICCP system operated until 2015.
Prior to the October 2014 survey some output adjustments were made.
An additional ICCP system was required (near TP47) to provide additional CP current due to positive potential shifts.
Chart 1: Pipeline CP (On) Potential Summary 2014

12. Pipeline case study – CP system upgrades (2)
The results show a significant improvement in pipeline protection levels following new ICCP system commissioning.
Chart 2: Pipeline CP(On) Potential Summary 2016

13. Pipeline case study – CP system upgrades (2)
1-off existing CP unit could only operate at a limited output due to foreign structure CP interference effects.
This had been the case for many years.
The CP unit (TR unit) was operating in constant current mode rather than a more preferred Auto (constant potential) mode
Further interference testing showed that the installation of sacrificial anodes to the foreign structure would mitigate interference effects and allow the TR to:
(a) operate at a higher output
(b) operate in Auto control mode

14. Pipeline case study – CP Potential Chart

15. Pipeline case study – TR Current

16. Pipeline case study – CP Potential Chart

17. Pipeline case study – CP Potential Chart

18. Pipeline case study – CP system upgrades (3)
Recent potential testing shows a positive shift (towards unprotected) at the Terminal end (near TP1). A new ICCP system at TR2 is proposed, with similar aims to the previously installed ICCP system.
Chart 3: Pipeline CP(On) Potential Summary 2017

19. Examples - Corrosion Under Disbonded Pipe Coating
At this location, the CP potentials varied significantly from under protected to marginally protected.
CP had no effect under disbonded coating.

20. Examples - Calcareous Deposits at Coating Defects (Some Corrosion Where Coating is Shielding CP)
At this location, some evidence of calcareous deposits can be seen below disbonded coating providing some corrosion protection.
Potentials at this location varied between protected and slightly over protected.

21. EXAMPLES - Corrosion Under Disbonded Pipe Coating

22. EXAMPLES - Corrosion Under Disbonded Pipe Coating

23. Presented by: Jim Galanos Corrosion Control Engineering
THANK YOU
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Presented by: Jim Galanos
Corrosion Control Engineering
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