What is the purpose of the holiday test?

Premature corrosion of a substrate is usually due to a coating failure. A major cause is the presence of flaws in the finished coating, collectively referred to as porosity. Holiday test is used to detect holes, known as holidays or discontinuities, in a coating. Holiday testing allows the detection of even smallest coating flaws invisible to the naked eye. There are various techniques and equipment available for holiday detection.

Elcometer offers a range of holiday detectors that make holiday detection safer, faster and more reliable than ever before. Elcometer's range of holiday detection testers uses variety of techniques including high voltage holiday detection and DC pulsed holiday detection. All holiday detectors are available with a wide range of accessories that will allow holiday testing on all types of substrates and applications.

Holiday tests explained

High voltage holiday detection

High voltage holiday test is normally used to determine the existences of discontinuities in coating films. The high voltage, or porosity technique, can be used to test coatings up to 25mm (1") thick and is ideal for inspecting pipelines and other protective coatings. Coatings on concrete can also be tested using this method. There are two types of high voltage holiday detectors- Continuous DC and Pulsed DC.

Holiday Test by Wet Sponge Detector

Now, this test uses two 2 different voltage settings. The first is the 9V setting for thicknesses of 300µm or less and the second one is 90V for greater thicknesses up to 500µm.

Now let’s talk more about this instrument. The wet sponge detector consists of:

• An Open-cell sponge

• A set comprising of a connector and a shaft

• Audible discontinuity indicator

• A ground cable

• A wet sponge device

Phew! Finally done with our little “wet sponge”.

Holiday Test by High Voltage Detector

Now that our little “wet sponge” is out of the way, let’s move on to high voltage spark testing.

This test is reserved especially for thicknesses greater than 500µm.

Beware though, if you conduct this test on thicknesses that are any smaller, you run the risk of damaging your precious coating. We don’t want that, now do we?

The detector for this test is further divided into two distinct sub-types;

• Direct current

• Pulse type

You can’t test if you don’t know how to setup the detector, can you? The setup consists of:

• Electrodes,

• a ground cable,

• and an electrical device

In this case though, there is no specific voltage, so you have to look at the manufacturer’s specs for details. For example, when dealing with thicknesses of 1000µm ranging up to 1500µm, the specific voltage is around 5000V.

Applicable Standard

Now remember that regardless of whichever method you use, make sure that the coating is thoroughly dried out and fully cured as per manufacturer specifications.

Oh and also, don’t forget that the standard applicable here is ASTM D5162.

And, it is recommended that the Quality Control Coating Inspector must always refer to this specification religiously to get the right information so that they can perform the test effectively.

Now you know how to conduct a holiday test.

Happy testing!