Technical Seminar for Cathodic Protection

to GOGC Design Unit Specialists

Dr. Nick Kioupis, Cathodic & Lightning Protection

Section Head, DESFA

Interference

• DC

–Constant (CP systems of third

parties)

–Fluctuating (e.g. railways, dc

sources, mines, welding machines

–Tellurics

2

Sources of dc stray current

Trolley-buses and dc traction

systems

HVDC transmission

systems

DC sources

Industrial equipment (e.g.

welding machines)

DC telephone network

Cathodic protection systems

Traffic light equipment - dc operated

3

Stray current corrosion from dc railways interference

Identification and measurement of dc stray currents

• Recording of potential

• Voltage gradients along the pipeline and perpendicular to it

• DC line current measurement/recordings

• Line current measurement by current clamp method

• Current to polarisation probe or corrosion coupon

• Interference between CP systems

• Stray Current Mapper

5

Criteria according to ΕΝ 50162

• Criteria for non cathodically protected pipelines

• Criterion for cathodically protected pipeline

– IR free potential to be within acceptable limits (e.g. -0,85V, cf. EN

12954)

– Criteria related to how long an anodic current exits from a

probe/coupon

– Cathodic interference >500mV on (IR included) or EiRfree<El

6

Practical example of a real case of potential dip due to

crossing with foreign pipeline

IFO method to detect coating defects

13

Typical pattern of voltage gradients around a coating defect

14

2 and 3 electrodes methods

15

Adding-up method

16

Mathematically expressed:

[1] UA1 - UA2 = 0

[2] UA1 = UA2

(considering remote

ground)

Thus:

[3] UB1 - UA1 = UB1 - UA2

[4] UB2 - UA2 = UB2 - UA1

Assumption:

[5] ΔU1 = UB1 - UA1

[6] ΔU2 = UB2 - UA1

resulting in equation (for UA1):

[7] ΔU1 - UB1 = ΔU2 - UB2

[8] 0 = ΔU1 + (UB2 - UB1) - ΔU2

Thus:

ΔU2 = UB2 - UB1 + ΔU1

Adding-up

17

Pipe locators and coating defects detection with A-

frame

18

Investigation with Stray Current Mapper

19

DCVG and Pearson Tecniques

20

• ΑC

–Short-term

during fault currents

–Long-term

during

normal operation

of the powerline

21

Interference

• ΑC

–Capacitive

–Conductive

– Inductive

22

Interference

AC corrosion from powerlines interference

• History

• End of 1980s: First cases of a.c. corrosion in several european countries

• 2001: Publishing of the CEOCOR a.c. corrosion booklet that summarized all

relevant European experiences

• 2006: Acceptance of CEN/XP TS 15280 based on activities within

CEOCOR

• 2013: Issue of EN 15280 Evaluation of a.c. corrosion likelihood of buried

pipelines applicable to cathodically protected pipelines

• Conclusion

• The current standard represents the European experience collected within

the last 25 years

• there is no fundamental additional information that was not already known

by 2004

• There is vast field experience for all of the used thresholds

AC corrosion

Practical examples from pipelines in Switzerland

Limit length Lgr or spacing of a pipeline when laid

parallel to a 50Hz three phase high voltage overhead line

Interference distance according to NPR 2760

46

Analysis of induced overvoltages on a distribution pipeline by

a nearby lightning strike

47

Electrical Interferences measurements

• Cathodic protection potentials recordings at least for 24h

• Current magnitude and direction measured on coupons,

• Line current recording,

• Comparison of patterns of recordings on the stray current

source and on the pipeline itself,

• Corrosion rate recording on ER probes.

– Other measurements referenced in ΕΝ 50443.

48

Interference distances (prΕΝ 50443:2011)

49