1. inspection equipment
THE USE OF PULSED DC HOLIDAY DETECTORS
FOR FIELD TESTING PIPELINE COATINGS
Author:
John Fletcher
FICORR
Technical Support Manager
Elcometer Limited
© Elcometer Limited 2011 60 years of excellence
www.elcometer.com

2. inspection equipment
THE USE OF PULSED DC HOLIDAY DETECTORS
FOR FIELD TESTING PIPELINE COATINGS
Presented by Craig Woolhouse
Regional Sales Manager
Elcometer Limited
© Elcometer Limited 2011 60 years of excellence
www.elcometer.com

3. Content
Introduction
The Problem - Flaws & Defects
Standards for Porosity Detection
Continuous DC High Voltage Testing
Pulsed DC High Voltage Testing
Conclusions

4. Introduction
High Voltage Holiday Detection is used on
cured coatings to ensure there are no flaws
Two main high voltage equipment types
Continuous DC
Pulsed DC

5. Introduction
Continuous AC High Voltage Testers are also
available but these are often mains operated,
which is inconvenient for site work
Surface contamination & moisture cause AC sparks
High AC voltage is more hazardous than DC

6. The Problem
Flaws in cured coatings reduce service
life:
Pipeline – internal and external coatings
Tank linings
Immersion Service

7. The Problem
Some Examples of Coating Flaws
Runs & Sags
Pinholes
Cratering
Cissing
Incorrect Coating Thickness

8. The Problem
Runs & Sags
Caused by excessive
local thickness prior
to cure

9. The Problem
Pinholes
Caused by air or blast
media inclusion in the
coating

10. The Problem
Cratering
Caused by air release
from the partially cured
coating

11. The Problem
Cissing
Caused by contamination
of substrate by oil or
grease
(also known as crawling
or fisheyes)

12. The Problem
Incorrect Coating Thickness
Profile peaks through
thin coatings
Cracking due to excess
coating thickness

13. Test Standards
NACE
SP0188:2006
“Discontinuity (Holiday)
Testing of New Protective
Coatings on Conductive
Substrates”
Test Voltage Table

14. Test Standards
NACE
RP0274:2004 V  7,900 T
Where: V = test voltage
“High Voltage Electrical and T is the thickness in
Inspection of Pipeline mm
Coatings”
Voltage Formula or Table V  1,250 T
Where: V = test voltage
and T is the thickness in
mil

15. Test Standards
NACE
SP0490:2007 V  104 T
“Holiday Detection of Fusion- Where: V = test voltage
and T is the thickness in
Bonded Epoxy External µm
Coatings of 250 to 760 µm
(10 to 30 mil) ” V  525 T
Voltage Formula or Table Where: V = test voltage
and T is the thickness in
mil

16. Test Standards
ASTM
D5162:2008 V  M Tc
“Practice for Discontinuity Where: V = test voltage,
Tc is the thickness in
(Holiday) Testing of mm or mil and M is a
Nonconductive Protective constant dependant on
the range of the
Coating on Metallic thickness
Substrates ”
Voltage Formula or Table

17. Test Standards
ASTM
D4787:2008 V  M Tc
“Continuity verification for Where: V = test voltage,
Tc is the thickness in
liquid or sheet linings applied mm or mil and M is a
to concrete substrates ” constant dependant on
the range of the
thickness
Voltage Formula or Table

18. Test Standards
ISO
BS EN ISO29601:2011
“Paints and varnishes –
Corrosion protection by
protective paint systems –
Assessment of porosity in a
dry film”
Test Voltage Table

19. Test Standards
Test Voltage Comparisons
Standard Test Voltage for 500 µm (20
mil) Coating
NACE SP0188 2.5 kV
NACE RP0274 6.0 kV
NACE SP0490 2.3 kV
ASTM D4787 (Formula) 2.3 kV
ASTM D4787 (Table) 2.7 kV
BS EN ISO 29601 2.9 kV

20. Continuous DC Testing
Test Set-up
Signal return connected to
substrate
DC Voltage from 0.5 to 30 kV
Conductive Electrodes

21. Continuous DC Testing
Test Electrodes
Insulated Handle
Rolling Spring
Internal Pipe Brush
Metal or Conductive Rubber
Brush Electrodes
Extension rods

22. Pulsed DC Testing
Test Set-up
Capacitive Signal Return Cable

23. Pulsed DC Testing
Test Set-up
35 kV Test Voltage
Range
Menu operated standards
Voltage calculator

24. Pulsed DC Testing
Full Set of Electrodes
Band brushes
Wire brushes up to 1 m wide
Internal pipe brushes
Conductive Rubber Strip
Electrode adaptors
Steel rolling springs
Phosphor-Bronze Rolling Springs

25. Pulsed DC Testing
Signal Return Conductive Mat

26. THE USE OF PULSED DC HOLIDAY DETECTORS FOR
FIELD TESTING PIPELINE COATINGS
CONCLUSIONS
.

27. Conclusions
The key to successful high voltage holiday detection
is the selection of the correct test voltage:
Too low a voltage and
flaws will be missed
Too high a voltage and
the coating will be burnt
.

28. Conclusions
Care must be taken with low
dielectric strength coating:
Thin sections may not resist the
high voltage if the dielectric strength
is low
Breakdown voltage of air is:
4 kV/mm
Some coatings have a dielectric
strength of 6 kV/mm
.

29. Conclusions
Continuous DC vs. Pulsed DC
Testing
Determined by practical issues
Pulsed DC when direct connection
to substrate is not possible
Pulsed DC when coating is damp or
dirty
.

30. Conclusions
Continuous DC vs. Pulsed DC
Testing
Continuous DC recommended when
accurate voltage setting required –
low dielectric strength coatings
.

31. Conclusions
Care when referencing a standard
The different standards produce different test voltages for
the same thickness
.

32. THE USE OF PULSED DC HOLIDAY DETECTORS
FOR FIELD TESTING PIPELINE COATINGS
THANK YOU
FOR YOUR ATTENTION
Any Questions?
.