Transcript Corrosion-Conference-Porosity-2011-Presentation

inspection equipment
The use of High Voltage Holiday Detectors
for field testing of pipeline coatings
Presenter:
Craig Woolhouse
Regional Sales Manager
Elcometer Limited
© Elcometer Limited 2011
60 years of excellence
www.elcometer.com
Contents
Introduction
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
High Voltage Holiday Detection is used on
cured coatings to ensure there are no flaws
Continuous DC
Pulsed DC
AC
The Problem
Flaws in cured coatings reduce service life in:
Internal and External pipeline coatings
Tank linings
Immersed applications
The Problem
The 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
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
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
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
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