60 years of excellence

www.elcometer.com

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

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

Introduction

The Problem - Flaws & Defects

Standards for Porosity Detection

Continuous DC High Voltage Testing

Pulsed DC High Voltage Testing

Conclusions

Content

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

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

The Problem

Flaws in cured coatings reduce service life:

Pipeline – internal and external coatings

Tank linings

Immersion Service

The Problem

Some Examples of Coating Flaws

Runs & Sags

Pinholes

Cratering

Cissing

Incorrect Coating Thickness

The Problem

Runs & Sags

Caused by excessive local thickness prior to cure

The Problem

Pinholes

Caused by air or blast media inclusion 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 thin coatings

Cracking due to excess coating thickness

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

Where: V = test voltage

and T is the thickness in

mm

TV 900,7

TV 250,1Where: V = test voltage

and T is the thickness in

mil

Test Standards

NACE

SP0490:2007

“Holiday Detection of Fusion-Bonded Epoxy External Coatings of 250 to 760 µm (10 to 30 mil) ”

Voltage Formula or Table

Where: V = test voltage

and T is the thickness in

µm

Where: V = test voltage

and T is the thickness in

mil

TV 104

TV 525

Test Standards

ASTM

D5162:2008

“Practice for Discontinuity (Holiday) Testing of Nonconductive Protective Coating on Metallic Substrates ”

Voltage Formula or Table

Where: V = test voltage,

Tc is the thickness in

mm or mil and M is a

constant dependant on

the range of the

thickness

TcMV

Test Standards

ASTM

D4787:2008

“Continuity verification for liquid or sheet linings applied to concrete substrates ”

Voltage Formula or Table

Where: V = test voltage,

Tc is the thickness in

mm or mil and M is a

constant dependant on

the range of the

thickness

TcMV

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 (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

Test Set-up

Signal return connected to

substrate

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

Continuous DC Testing

Test Set-up

Capacitive Signal Return Cable

Pulsed DC Testing

Test Set-up

35 kV Test Voltage

Range

Menu operated standards

Voltage calculator

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

Pulsed DC Testing

Signal Return Conductive Mat

Pulsed DC Testing

.

CONCLUSIONS

THE USE OF PULSED DC HOLIDAY DETECTORS FOR

FIELD TESTING PIPELINE COATINGS

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

.

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 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

.

Conclusions

Continuous DC vs. Pulsed DC

Testing

Continuous DC recommended when

accurate voltage setting required –

low dielectric strength coatings

.

Conclusions

Care when referencing a standard

The different standards produce different test voltages for

the same thickness

.

Conclusions

THANK YOU

FOR YOUR ATTENTION

Any Questions?

.

THE USE OF PULSED DC HOLIDAY DETECTORS

FOR FIELD TESTING PIPELINE COATINGS