Content Introduction The Problem - Flaws & Defects Standards for Porosity Detection Continuous DC High Voltage Testing Pulsed DC High Voltage Testing Conclusions
IntroductionHigh Voltage Holiday Detection is used oncured coatings to ensure there are no flaws Two main high voltage equipment types Continuous DC Pulsed DC
IntroductionContinuous AC High Voltage Testers are alsoavailable 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 ProblemFlaws in cured coatings reduce servicelife: 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 ProblemRuns & Sags Caused by excessive local thickness prior to cure
The ProblemPinholes Caused by air or blast media inclusion in the coating
The ProblemCratering Caused by air release from the partially cured coating
The ProblemCissing Caused by contamination of substrate by oil or grease (also known as crawling or fisheyes)
The ProblemIncorrect 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 StandardsNACE 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
Test StandardsNACE 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
Test StandardsASTM 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
Test StandardsASTM 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
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 kVASTM D4787 (Formula) 2.3 kV ASTM D4787 (Table) 2.7 kV BS EN ISO 29601 2.9 kV
Continuous DC TestingTest Set-up Signal return connected to substrate DC Voltage from 0.5 to 30 kV Conductive Electrodes
Continuous DC TestingTest Electrodes Insulated Handle Rolling Spring Internal Pipe Brush Metal or Conductive Rubber Brush Electrodes Extension rods
Pulsed DC Testing Test Set-up Capacitive Signal Return Cable
Pulsed DC TestingTest Set-up 35 kV Test Voltage Range Menu operated standards Voltage calculator
Pulsed DC TestingFull 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
THE USE OF PULSED DC HOLIDAY DETECTORS FOR FIELD TESTING PIPELINE COATINGS CONCLUSIONS .
ConclusionsThe key to successful high voltage holiday detectionis 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 .
ConclusionsCare must be taken with lowdielectric 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 .
ConclusionsContinuous DC vs. Pulsed DCTesting Determined by practical issues Pulsed DC when direct connection to substrate is not possible Pulsed DC when coating is damp or dirty .
ConclusionsContinuous DC vs. Pulsed DCTesting Continuous DC recommended when accurate voltage setting required – low dielectric strength coatings .
ConclusionsCare when referencing a standard The different standards produce different test voltages for the same thickness .
THE USE OF PULSED DC HOLIDAY DETECTORS FOR FIELD TESTING PIPELINE COATINGS THANK YOU FOR YOUR ATTENTION Any Questions? .