A pinhole detector is a non‐destructive instrument for detecting discontinuities in a coating system including pinholes, cracks and thin spots. Other names include porosity detector, continuity tester, sponge tester and holiday detector.
There are two types of pinhole detectors, low voltage (wet sponge) and high voltage (spark tester). Low voltage detectors, like the PosiTest LPD, are typically used on coating systems less than 500 µm (20 mils) thick. High voltage spark testers operate at voltages up to 35,000V which can seriously harm the operator and damage the coating if the test is not correctly conducted. They tend to be more expensive and more complex than low‐voltage pinhole detectors.
A low‐voltage pinhole test is performed by moving a moistened, electrified sponge over a non‐conductive coating applied to a conductive substrate. The instrument is‘grounded’ or ‘earthed’ to the conductive substrate, typically by clamping onto an uncoated area. When the coating is continuous and no defects are present, electricity is unable to pass from the sponge to the substrate through the non‐conductive coating. But when the electrified sponge encounters a flaw in the coating, electricity is able to flow into the substrate and travel back to the instrument through the ground wire, completing the circuit and setting off the audible and visible alarms.
After a protective coating has been applied, it is important to ensure there are no defects or discontinuities present that expose the substrate beneath. Small areas of thin or missing coating, called ‘pinholes’ or ‘holidays’, can become foci for corrosion and drastically reduce the life of a protective coating system. They can be invisible to the naked eye. Porosity detectors are often used in applications where corrosion is difficult to monitor, or in aggressive service environments where performance of the protective coating is critical.
When measuring coating thickness, concrete is not considered a ‘conductive’ substrate, as it is much less conductive than metal. However, concrete is still slightly conductive, and can carry enough current to allow low‐voltage pinhole detectors to function. Therefore, for the purposes of low‐voltage pinhole detection, concrete is considered a ‘conductive’ substrate.
The challenge when conducting low‐voltage pinhole testing on concrete is to ensure the instrument is properly grounded. If there is exposed rebar or metal protruding from the concrete, this is the easiest solution. An alternative is to drive a metal rod (or piece of rebar) into the ground nearby the concrete to at least the depth of the slab, relying on the earth to conduct the electric current between the rod and the slab.
The PosiTest LPD has been designed as a fully customizable unit and offers a number of features not typically found in other competitive instruments.
Sometimes pinholes are so miniscule that water has difficulty reaching the conductive substrate underneath, especially on thicker coatings when the water must penetrate further into a pinhole to reach the substrate. In these instances, inspectors will use a surfactant (wetting agent) to lower the surface tension of the water, allowing the solution to better penetrate the pinhole.
No. The PosiTest LPD does not record any data.
Each PosiTest LPD is calibrated at all test voltages with a load of known electrical resistance and a voltmeter, each traceable to a National Metrology Lab. A Long Form Certificate of Calibration containing actual measured values is included with every instrument. No other device provides this level of Certification.
The cost to recertify is $95 and includes a Long Form Certificate of Calibration. Recertification usually takes one day.
No. Our instruments are designed for simple operation, feature easy-to-use menus, both full and quick instruction manuals, and helpful videos. In lieu of demonstration models, we provide unlimited technical support via telephone and/or email, and a limited 30-day money back guarantee.
The PosiTest LPD arrives fully calibrated and ready to measure. A Long-Form Certificate of Calibration traceable to NIST or PTB is included, which documents actual readings taken by your instrument at our calibration laboratory on standards traceable to a national metrology institute.
No other device provides this level of Certification. Beware of ‘Certificates’ or ‘Certificates of Conformance’ offered by competitors. These typically do not include actual instrument readings, and are often insufficient to meet common quality requirements.
The PosiTest LPD Low voltage Pinhole Detector has four specific pre-set voltages. These voltages were chosen because they are specified in various international standards and/or they match the operating voltages of other commercially available instruments. Most standards do not specify a specific voltage, and instead allow a range of voltages- for example, NACE SP0188 specifies a range of 5V-90V with no guidance on the proper voltage setting for a given application or coating thickness.
At the time of writing, we are aware of only two international standards specify a specific voltage and sensitivity:
In general, we have found that settings of 67.5V, 80 kΩ (for metal substrates) or 67.5V, 90 kΩ (for concrete substrates) are most commonly accepted and used for the vast majority of applications.