An Introduction to Pinholes and Holidays - Porosity Detection

Corrosion is caused by a steel substrate and oxygen, while contaminants such as water can accelerate the process.
The coating is there to protect the steel from oxygen and contaminants. A flaw in the coating can leave the substrate poorly protected, or in some cases completely exposed.
These flaws are referred to as Holidays, Discontinuities, or Pinholes within the coatings industry; and are often very small or invisible to the naked eye - which is where flaw detectors come in.
CONTENTS
0:31 - What causes corrosion?
0:50 - Types of coating flaws
2:26 - Low Voltage Pinhole or Wet Sponge Technique
3:38 - High Voltage or Holiday Detection Method
5:03 - Continuous DC and Pulsed DC
7:14 - UV Pinhole Technique
There are, essentially, three flaw detection methods…
1. The Low Voltage Pinhole, or Wet Sponge Technique such as the Elcometer 270, is for testing insulating coatings less than 500μm (20mils) thick on conductive substrates, and is ideal for powder coatings and other applications where you do not wish to damage the coating.
The wet sponge method for detecting pinholes - which is a little bit of a misnomer, as the sponge should be damp, and not wet - also works through capillary action.
When you pass a damp sponge steadily over the coated surface, the water is drawn through the holes by capillary action, and when it touches the bare substrate it completes a low voltage circuit, as the test unit is grounded to an uncoated section of the substrate being examined.
When the circuit is complete, the unit alarms, letting you know where you have a pinhole.
2. The High Voltage or Holiday Detection method is where a high voltage current is applied to a probe, which is passed over the coated surface.
The voltage should be high enough so that in areas
where the coating is electrically weaker due to a flaw, there is sufficient voltage to break down the gap between the probe and the substrate.
When this break down occurs, the current flows through the substrate, and back into the unit via a grounding cable, setting off an alarm to signal a flaw has been detected.
This allows you to detect flaws that don’t go all the way down to the substrate, as well as voids within the coating.
The high voltage method comes in 2 versions - Continuous DC and Pulsed DC.
Continuous DC is where the current to the probe is constant, and is used to test insulation coatings on conductive substrates up to 7.5mm (300mils) thick.
Elcometer has two continuous DC detectors: the Elcometer 236, where the power supply is generated within the instrument and sent to the probe handle via a high voltage cable; and the Elcometer 266, where the power supply is generated within the handle, and connected back to the instrument via a low voltage cable.
Pulsed DC, on the other hand, is where the energy is contained in very short pulses, with each pulse having more energy than an equivalent Continuous DC instrument.
The break in energy stops the probe from building up a charge on the surface, allowing you to safely test for flaws on damp, dirty, or slightly conductive coatings.
Using state of the art electronics, the Elcometer 280 Pulsed DC Holiday Detector can test coatings up to 25mm (1”).
3. The UV Pinhole technique - such as the Elcometer 260, which makes use of a fluorescent coating, which is applied to the surface as a base coat. Once the second coat is applied, any pinholes fluoresce when you shine a UV light on them, revealing their location.
Each test method is explored in much more detail in the Elcometer Pinhole and High Voltage Detector series. Visit www.elcometer.c... to find out more.
For more information on Elcometer's range of Pinhole and Holiday Detectors, please contact Elcometer at [e-mail] or visit our website: www.elcometer.c...
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Click here to download the video script in English:
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STANDARDS:
Elcometer 270
AS 3894.2, ASTM D 5162-A, ASTM G6, ASTM G62-A, BS 7793-2, ISO 8289-A, ISO 14654, JIS K 6766, NACE RP 0188, NACE SP 0188, NACE TM0384
Elcometer 236
ANSI/AWWA C213, AS 3894.1, ASTM C 536, ASTM C 537, ASTM D 4787, ASTM G 6, ASTM D 5162-B, ASTM G 62-B, BS1344-11, DIN 55670, EN 14430, ISO 2746, JIS K 6766, NACE RP0188, NACE RP0274, NACE RP0490, NACE SP0188, NACE SP0490
Elcometer 266
ANSI/AWWA C213, AS 3894.1, ASTM C 536, ASTM C 537, ASTM D 4787, ASTM D 5162-B, ASTM G 62-B, BS1344-11, DIN 55670, EN 14430, ISO 2746, ISO 29601, JIS K 6766, NACE RP0274, NACE RP0188, NACE RP0190, NACE RP0490, NACE SP0188, NACE SP0490
Elcometer 280
AS 3894.1, ANSI/AWWA C203, ANSI/AWWA C214, ASTM D4787, ASTM D5162, ISO 2746, ISO 29601, JIS G 3491, JIS G 3492, NACE RP0274, NACE SP0188, NACE SP0490, NACE TM0186, NACE TM0384
Elcometer 260
ASTM E 2501

[@courchar]

I'm studying for my NACE cip 3, and have found your videos invaluable. Keep up the good work

[@rahulrdubey]

helpful for understanding very basic of holiday test

[@yuvarajv4134]

Coating flaws part is really amazing.

[@thatsallfolks3115]

Yuvaraj V we inspect after every job completed.

[@azharazirmd5640]

Yes yuvi

[@fransvos5665]

Interesting explanation with just one little remark though: Oxygen is not strictly needed to have corrosion; in oxygen depleted acidic environments corrosion is possible as well and can be severe. Key here is that at the cathodic side of the corrosion cell the oxygen-requiring reactions can be taken over by the hydrogen-reaction if oxygen is depleted/absent.

[@flaviogonzalez2482]

Excelente explicación, seria de mucha ayuda si la doblan al español

[@ElcometerOfficialChannel]

Gracias por su comentario. Algunos de nuestros videos tienen subtítulos en varios idiomas, y todos nuestros subtítulos son proporcionados por nuestras oficinas locales y distribuidores, para asegurar una traducción precisa. Si desea subtítulos en español en vídeos específicos, puede contactar con su distribuidor local de Elcometer para solicitar que traduzcan un vídeo. Para encontrar su distribuidor local de Elcometer, por favor visite www.elcometer.com/en/contact-us.html Gracias una vez más.

[@yasirmughal4271]

I have a question for holiday test coating must need to be fully cured or not

[@ElcometerOfficialChannel]

Thank you for your comment. The coating should be fully cured before you perform a holiday test. If you have any further questions, please contact [e-mail] or visit www.elcometer.com/contact-us to find your local Elcometer distributor.

[@n.h.simanullang1250]

is it possible to test porosity concrete with an iron substrate with a thickness of 75 mm

[@ElcometerOfficialChannel]

Thank you for your comment. We need some more information about your application to be able to provide assistance. Please contact our technical support department by emailing [e-mail] or visit www.elcometer.com/contact-us to find your local Elcometer distributor.