inspection equipment
The use of High Voltage Holiday Detectors
for field testing of pipeline coatings
Presenter:
Craig Woolhouse
Sales Manager
Elcometer Limited
© Elcometer Limited 2011
60 years of excellence
www.elcometer.com
Contents
Introduction
What is Porosity detection?
The Problem - Flaws & Defects
Standards for Porosity Detection
Continuous DC High Voltage Testing
Pulsed DC High Voltage Testing
AC High Voltage Testing
Conclusions and Questions
Introduction
Holiday Detection is used on cured
coatings to detect the presence of flaws
Wet Sponge Pinhole Detection
Continuous DC High Voltage Detection
Pulsed DC High Voltage Detection
AC High Voltage Detection
Introduction
Low Voltage Wet-Sponge Detection finds
pinholes through the coating
High Voltage Holiday Detection identifies
defects
Testing can be applied on site to internal
and external coatings
The Problem
Flaws in cured coatings reduce service life in:
Internal and External Pipeline Coatings
Tank Linings
Immersed applications
etc.
The Problem
The High Voltage Test Principle:
Be aware of the dielectric strength of the coating
Be aware of the film thickness of the coating
Apply a controlled voltage to the surface of the
coating
The presence of a defect will result in current
flow through the coating enabling detection of
the flaw to be possible
The Problem
Some Examples of Coating Flaws
Runs & Sags
Pinholes
Cratering
Cissing
Incorrect Coating Thickness
The Problem
Runs & Sags
Caused by excessive film
local thickness prior to cure
The Problem
Pinholes
Caused by air or blast media
inclusions in the coating
The Problem
Cratering
Caused by air release
from the partially cured
coating
The Problem
Cissing
Caused by contamination
of substrate by oil or grease
also known as crawling
or fisheyes
The Problem
Incorrect Coating Thickness
Profile peaks through
coatings
Cracking due to excess
thickness
Reduced service life
thin
coating
Test Standards
NACE
SP0188:2006
“Discontinuity (Holiday) Testing
of New Protective Coatings on
Conductive Substrates”
Test Voltage Table
Test Standards
NACE
RP0274:2004
“High Voltage Electrical
Inspection of Pipeline Coatings”
Voltage Formula or Table
V  7,900 T
Where: V = test voltage
and T is the thickness in
mm
Test Standards
NACE
SP0490:2007
“Holiday Detection of FusionBonded Epoxy External Coatings
of 250 to 760 µm”
Voltage Formula or Table
V  104 T
Where: V = test voltage
and T is the thickness in
µm
Test Standards
ASTM
D5162:2008
“Practice for Discontinuity
(Holiday) Testing of
Nonconductive Protective Coating
on Metallic Substrates ”
Voltage Formula or Table
V  M Tc
Where: V = test voltage,
Tc is the thickness in
mm and M is a constant
dependant on the range
of the thickness
Test Standards
ASTM
D4787:2008
V  M Tc
“Continuity verification for liquid or
sheet linings applied to concrete
substrates ”
Where: V = test voltage,
Tc is the thickness in
mm and M is a constant
dependant on the range
of the thickness
Voltage Formula or Table
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
Test Standards
Test Voltage Comparisons
Standard
Test Voltage for 500 µm
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
Test Options
High Voltage Pinhole Detection
The ‘High Voltage Technique’ is a method of locating flaws in
insulating coatings on conductive substrates.
A Pulsed DC or Continuous DC high voltage is passed over
the coating with a probe. If the probe crosses a defect in the
coating a spark is generated triggering an audible and /or
visual alarm, identifying areas of the coating where defects are
present.
Test Options
Pulsed DC & Continuous DC Explained
Voltage
Applied
‘Pulsed DC (Voltage)’ is a time dependent voltage signal with
specific periods of applied fixed voltage (with associated direct
current (DC) flow), interspaced by periods of no applied
voltage.
Time
Test Options
Pulsed DC & Continuous DC Explained
‘Continuous DC (Voltage)’ is a voltage level of unvarying, time
independent nature caused by direct current (DC) flow.
Voltage
Applied
The word Continuous is used to reinforce the unchanging
character and so differentiate against Pulsed DC.
Time
Test Options
‘Pulsed
DC (Voltage)’ :
Voltage Applied
Pulsed DC & Continuous DC Explained
Time
The Elcometer 280 operates using this
principle
The Elcometer 236 and 266 operate
using this principle
Voltage Applied
‘Continuous DC (Voltage)’ :
Time
Continuous DC Testing
Test Set-up
Signal return cable connected to
uncoated substrate
Menu Operated Standards
Voltage Calculator
Integrated Jeep Tester
DC Voltage from 0.5 to 30 kV
Conductive Electrodes
Safety – voltage generated in handle
Continuous DC Testing
Test Electrodes
Insulated Handle
Rolling Spring
Internal Pipe Brush
Metal or Conductive Rubber Brush Electrodes
Extension rods
Pulsed DC Testing
Test Set-up
Capacitive (Trailing) Signal
Return Cable
Menu Operated Standards
Voltage Calculator
Integrated Jeep Tester
35 kV Test Voltage Range
Conductive Electrodes
Safety handle
Pulsed DC Testing
The Voltage Calculator
The voltage calculator function within the
Elcometer 280 is designed to automatically
calculate the test voltage.
•Select the required standard from the list
•Adjust the dry film thickness to the required
value
•Press OK to set the instrument voltage to the
calculated value
Pulsed DC Testing
The Voltage Calculator
Alternatively, the voltage can be adjusted
manually
•Switch the gauge on
• Adjust the voltage to the required level
• Press OK to set the instrument voltage
Pulsed DC Testing
The 2 Key Advantages of the Pulsed DC System
1) Direct metal-to-metal ground contact is not required
As a pulsed DC system does not need the direct
metal-to-metal ground contact that a continuous DC
system requires, it can be used with a trailing lead.
This means that you do not always need to connect
the earth to the component – ideal in many test
situations such as testing on large surface areas or
on pipelines.
Pulsed DC Testing
The 2 Key Advantages of the Pulsed DC System
2) Pulsed DC systems can be used on damp or dirty surfaces
Using Pulsed DC technology, the Elcometer 280 is
designed to ensure that the energy is contained
within very short pulses. Each pulse having more
energy than an equivalent Continuous DC System.
This means that the Elcometer 280 can be used to
test for holidays over slightly conductive coatings, or
dirty or damp surfaces
Pulsed DC Testing
Electrodes options
Stainless Steel Rolling Springs
Phosphor-Bronze Rolling Springs
Band Brushes
Wire Brushes up to 1 m wide
Internal Pipe Brushes
Conductive Rubber Strip up to 1m wide
Electrode Adaptors
AC Testing
AC High Voltage Testers are also available
Typically mains operated (inconvenient for site work)
Surface contamination & moisture can cause AC sparks
High AC voltage is more hazardous than DC
inspection equipment
The use of High Voltage Holiday Detectors
for field testing of pipeline coatings
Conclusions
© Elcometer Limited 2011
60 years of excellence
www.elcometer.com
Conclusions
The key to successful high voltage holiday
detection is the selection of the correct test
voltage for the dielectric strength of the coating:
Too low a voltage and
flaws will be missed
Too high a voltage and
the coating will be burnt
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
Conclusions
Continuous DC or 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
Continuous DC recommended when
accurate voltage setting required
especially with lower dielectric strength
coatings
Conclusions
Care when referencing a standard
The different standards produce different
test voltages for the same thickness
inspection equipment
The use of High Voltage Holiday Detectors
for field testing of pipeline coatings
Thank you for your attention
Questions?
© Elcometer Limited 2011
60 years of excellence
www.elcometer.com