pinhole and porosity by elcometer

pinhole & porosity - uv pinhole detection, pin hole & high voltage detectors

Premature corrosion of a substrate is usually due to the failure of the coating. A major cause is the presence of flaws in the finished coating. Collectively referred to as a coating's porosity, the main types of flaw are describes below:

Runs and sags	The wet coating moves under gravity leaving a thin dry film.
Cissing	Occurs when a coating does not re-flow to cover the voids generated by air bubbles being released from the surface of a coating.
Cratering	Occurs when the substrate is wet or if the coating has poor flow characteristics, thus creating voids in the coating.
Pinholes	Caused either by air entrapment which is then released from the surface, or by the entrapment of particulates (dust, sand, etc.) which do not stay in place.
Over coating	If too much coating is applied to a substrate, as the coating cures it can crack from internal stresses of the coating.
Under coating	Areas are not coated or the coating flows away from particular edges, corners of a substrate and welds. Furthermore, over a rough surface profile, insufficient coating may leave the profile’s peaks exposed.

The consequent cost of repairs and subsequent loss of production can be considerable. Early inspection for coating flaws will prevent the expense and inconvenience of a coating failure. Instruments used to detect coating flaws are referred to by many different names, these include spark or jeep testers, porosity or holiday detectors and pinhole testers. There are three methods of testing, UV pinhole detection, wet sponge technique and high voltage technique. Elcometer has a range of products that meet your particular requirement.

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		Elcometer 270 Pinhole Detectors The Elcometer 270 pinhole detector range utilises the wet sponge method and has been designed to set a new standard for wet sponge testers - namely, a high quality, low voltage detector with similar accessories to a high voltage spark tester. This simple unit can be used as either a separate wand with the unit attached to your belt, or as an integrated wand with sponge attached.
		Elcometer 270 Pinhole Accessories The Elcometer 270 pin hole tester has a wide range of accessories to allow you to test your particular product effectively and more easily than ever before. From different sponge types and sizes to telescopic handles for floor and wall detection, we have a product to make your life easier.
		Elcometer 266 DC Holiday Detector The Elcometer 266 has been specifically designed to revolutionise high voltage DC testing of coatings by making it safer, easier and more reliable than previously possible.
		Elcometer 236 DC Holiday Detectors The Elcometer 236 holiday detector is perhaps one of the most advanced holiday detectors on the market today. Supplied in a convenient transit case for moving around the jobsite, the Elcometer 236's soft carry case allows the probe handle and wide range of accessories to be attached making the Elcometer 236 ideal for field, site or laboratory inspection.
		Elcometer 236 DC Holiday Detector Accessories The key feature of the Elcometer 236 is in the range of inspection accessories that are available. From carbon infused rubber used for inspections on delicate coatings, to rolling springs for external pipeline inspection, Elcometer has an accessory for your requirement.

Test Methods for Porosity

There are three methods of testing:

UV Pinhole Detection

UV light can be used as a low cost, quick method of detecting pinholes in coatings. A base coat containing a UV fluorescing additive is applied. When the UV flashlight shines on the coating, areas where the base coat is not covered fluoresce, clearly showing the location of the pinhole.

Wet Sponge Technique

Suitable for measuring insulating coatings on metal less than 500µm (20mils) on conductive substrates. The wet sponge technique is ideal for powder coatings and any thin coating where the User does not wish damage to occur to the coating.

A low voltage is applied to a sponge, moistened with a wetting agent. When the sponge moves over a coating flaw, liquid penetrates to the substrate and completes an electrical circuit, setting off the alarm.

This technique will identify coating flaws where the substrate is uncovered, i.e. cissing, cratering, pinholes and some forms of over and under coating flaws.

High Voltage Technique

Locates all flaws in insulating coatings on conductive substrates, the high voltage technique can be used to test coatings up to more than 7mm (275mils) thick. This method is ideal for inspecting pipelines and other protective coatings. Coatings on concrete can also be tested using this method.

A power supply generates a high DC voltage which is connected to a suitable probe with an earth return connected to the substrate. As the probe is passed over the coated substrate, a flaw is indicated by a spark at the contact point which sets off the alarm.

This technique is suitable for identifying all of the flaws described above, however care is required on thin coatings.

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