There are a number of products used in the oil, gas or construction industries where coatings are applied to the surface of the structures to protect them from corrosion, rust or other types of premature deterioration due to the environments they are used in.
Coatings are used on buried products such as pipelines, septic tanks, or other chemical storage containers to protect against the moisture in the soil. Tank interiors are coated to protect against the liquid chemicals stored inside them. Coatings are also used on rebar or other building materials that are in contact with soil or to protect them from harsh weather conditions.
These coatings need to be applied in a continuous layer for them to protect and insulate properly. Minor flaws in the finished coating, such as pinholes, cracks, voids, or contaminants can allow the moisture to contact the structure’s surface and cause failures. Most of these defects or discontinuities, also known as ‘holidays’, are not easily visible to the naked eye and their detection is important to prolong the life of the structure.
Testing for the presence of holidays is usually accomplished using an electrical, non-destructive test method that can detect even the smallest discontinuities in the coating. There are various types of equipment available for holiday detection and they use a wide range of probes and accessories to be able to test a variety of coating substances and different coating thicknesses.
The Pipeline Inspection Company, located in Houston, Texas is one of the leading suppliers of coating inspection equipment around the world. Home to the SPY® brand of products, they manufacture Holiday Detectors and JeepMeters to provide efficient and economical coating inspection and testing in the field.
SPY Holiday Detectors are portable instruments that are designed to locate the coating discontinuities. They work on the principle that most coating materials are of a very high resistance, so they are poor electrical conductors. Electrical continuity testing can be used to identify any areas that provide a pathway for current to flow through the coating. An electrical voltage is applied to the coating by sweeping the detector over the coating surface. If no current flow is found, the coating is free from defects in that area. If any type of arcing or current flow is detected between the detector and the base material, it indicates the presence of a holiday in the coating.
SPY Holiday Detectors typically contain a DC power source, an electrode probe, a ground wire and an indicator such as an audible sound or a light to indicate when current is flowing. The output voltage can either be a continuous DC voltage or a pulsed DC signal that can produce more overall energy than an equivalent continuous DC voltage system.
The output voltage that is used for holiday testing is determined by the coating thickness. Low voltages, up to approximately 5 kV, are used when the coating is thin. Higher voltages, up to 20kV or higher, are used when the coating is thicker, up to 1 inch. The voltages used should be high enough so that the voltage is sufficient to cross the gap between the probe and the material. Higher voltages can also detect flaws that are locked within the coating, such as surface depressions or bubbles.
Holiday testing using high voltages requires that the safety recommendations listed in the operation manual are followed to ensure that the operator is not injured or the coating is not damaged during the test.
The output voltage of the holiday detectors can be influenced by environmental conditions, such as high humidity or soil moisture content, moisture on the materials or grounding problems. To be confident in the accuracy and performance of the holiday detector, special SPY JeepMeters can be used to accurately measure the voltage output of any holiday detector in the field.
SPY JeepMeters are lightweight and convenient units and are used by pipeline workers, inspectors and foremen to verify the voltages during testing or to ensure that the holiday detector is operating properly.
The various SPY JeepMeter models feature either an analog or an easy-to-read digital display and can measure output voltages up to 20kVDC. SPY JeepMeters have the versatility to measure both pulse and continuous DC voltage outputs.
It is recommended that the SPY Holiday Detectors and JeepMeters are calibrated at least once per year. More frequently calibrations should be performed based on the equipment usage and operating conditions. Due to the high voltages required, special equipment and calibration processes are needed to properly perform the calibration on these units.
e2b calibration has the capability to quickly and accurately calibrate your SPY device to maintain the manufacturer’s specifications. For more information on our SPY calibration services, contact e2b calibration.
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