December 16 - December 23, 2013
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What is the risk of damaging a paint film by inspecting a repaired area more than twice with a high-voltage holiday detector?
Selected Answers
From
Christian Favennec of Naval Group on
April 23, 2014:
High voltage holiday detector is used to evaluate ...read more
High voltage holiday detector is used to evaluate if there are porosities or misses in a coating. This test is generally performed only once on the full area of the coating and at the nominal voltage defined by the supplier or calculated with ASTM D5162 and corresponding to the nominal dry film thickness. The porosities or misses are then identified, localized and repaired. The holiday test can be redone once, but only limited to the touch-up areas. If the result is ok, there is no need for and it is not recommended to perform more testing.
From
Tom Swan of M-TEST on
December 19, 2013:
If the coating is the specified thickness and if t ...read more
If the coating is the specified thickness and if the proper voltage is used, the number of times that you do a high voltage test should not be significant in maintaining the structural integrity of the coating. If the voltage is set too high or the coating has thin spots, then you may have a problem. I have been in several situations where the testing has been done more than once and no problems occurred. Now, if the first person does the testing at 10Kv and the second person decides that maybe 15Kv or 16Kv is better, you may have a problem.
From
William Slama of International Paint/Ceilcote Products on
December 18, 2013:
The purpose of high voltage holiday detection (spa ...read more
The purpose of high voltage holiday detection (spark testing) is to detect holes through a lining or coating. The holes (holidays) can then be repaired so that a corrosive environment cannot find a free passage to the
substrate. This is done by imposing an electrical stress across the lining to a conductive substrate
(usually carbon steel) and using a voltage such that a spark will easily arc if a hole exists through the
lining.
In order to ensure that an arc will form, the most typical recommendation is to use approximately 100 volts per mil based on the nominal thickness of the lining. This insures that there will still be enough voltage to jump an air gap at the maximum lining thickness. Both alternating and direct current testers accomplish the same result. It should be noted, however, that in some cases AC will produce more corona and may give erroneous readings, particularly if there is surface contamination.
Because this process puts a relatively high electrical stress on the lining and since the lining has a finite
dielectric strength, areas where the lining is thin or where a void exists but does not go all the way
through will usually break down electrically, causing (burning) a hole all the way through to the steel, resulting in a visible strong spark. When you spark test, in addition to finding existing holes, you will actually make new holes where the dielectric strength of the lining is exceeded.
For this reason, spark testing should be done only once, after completion of the lining (or area) and
before immersion or contamination of the lining. Where equipment is lined prior to final erection, it is
advisable to spark test only after erection so that any lining damage due to handling will be discovered at
that time.
Continued lining cross-linking, temperature cycles, and mechanical stresses of the substrate can change the lining's dielectric strength without having any actual pinholes (holes through to the substrate).
Actual chemical or water exposure definitely has been shown to reduce the dielectric strength of a lining/coating. High voltage inspection has caused serviceable, functioning linings to be burned through repeatedly, simply burning new holes in an otherwise good lining.
Repeated spark testing can burn new holes in a monolithic lining.
References: NACE RP0188-90, Standard Recommended Practice for Discontinuity (Holiday) Testing of
Protective Coatings;
ASTM D4787-93, Standard Practice for Continuity Verification of Liquid or Sheet Linings Applied to
Concrete Substrates;
ASTM D5162-91, Standard Practice for Discontinuity (Holiday) Testing of Nonconductive Protective
Coating on Metallic Substrates.
From
Parviz Babayev of Caspian Pipe Coating on
December 17, 2013:
High voltage may destroy the integrity of paint fi ...read more
High voltage may destroy the integrity of paint film. As a result, the coating loses its isolation property.
There are two types of non-destructive pinhole/holiday detection solutions for locating pinholes in a protective coating system: Low voltage Pinhole Detectors such as the PosiTest LPD and High voltage Holiday Detectors such as the PosiTest HHD and PosiTest HHD C.
Protective coatings and linings are applied to metallic and concrete substrates to prevent corrosion. Areas of thin or missing coating, called pinholes or holidays, can drastically reduce the life of a protective coating system. These discontinuities can be caused by entrapped air bubbles or particulate contamination that leave small regions of the substrate with little or no coating coverage, and if not repaired can become foci for corrosion. Even in areas where the dry film thickness is sufficient, pinholes or holidays can form, and they can be invisible to the naked eye. Therefore, testing of a cured coating using an electrical porosity detection instrument to locate pinholes is crucial to preventing coating failure.
Pinhole/holiday detection can be performed on non-conductive coatings applied to both metallic and concrete substrates. Although concrete is significantly less conductive than metal, it is still slightly conductive due to moisture content, and can carry enough current to allow holiday detectors to function. Corrosion and pitting beneath protective coatings can result in substantial coating failure in industries such as storage tanks, pipelines, and general construction.
Before testing is performed, pinhole/holiday detection instruments are grounded to an area of the bare metal substrate. High voltage detectors featuring pulse technology, such as the PosiTest HHD, can also be grounded using a trailing ground wire, grounding collar, or grounding mat. On concrete substrates, the ground wire is attached to the rebar or another metallic ground permanently installed in the concrete. If metallic ground is not visible, the ground wire is placed directly against the uncoated concrete surface.
The instrument outputs a voltage, charging the electrode as it is moved over the coating. When a holiday is encountered, current flows from the electrode to the substrate below. The current returns to the detector through the ground wire, completing the circuit and triggering an alarm.
Whether to utilize a low voltage or high voltage porosity detection instrument depends on the thickness of the applied coating. For coating thickness up to 20 mils (500 μm), low voltage pinhole detectors (wet sponges) are typically used. High voltage holiday detectors (spark testers) are used on coatings with a total thickness of 8 mils (200 μm) or greater.
DeFelsko offers low and high voltage porosity detectors for locating pinholes in non-conductive coatings and linings applied to electrically conductive substrates. These instruments conform to ASTM, NACE, ISO, and other standards for holiday detection. A long form Certificate of Calibration is included with each instrument at no additional cost.
Goto AJR to know more.
Low Voltage Pinhole Detector
The PosiTest LPD Low voltage Pinhole Detector is suitable for coating systems with a total thickness of up to 20 mils (500 μm).
High Voltage Holiday Detector
The PosiTest HHD and PosiTest HHD C High voltage Holiday Detectors are suitable for detecting defects in coating systems with a total thickness of 8 mils (200 μm) or greater.
Note: The low range of the PosiTest HHD varies with standards
The PosiTest LPD Low voltage Pinhole Detector is designed to detect defects in coating systems that are up to 20 mils (500 μm) thick. In use, an operator moves the moistened sponge over the coated surface. When a pinhole is encountered, current flows from the sponge into the substrate below. The current returns to the detector through the attached ground wire, completing the circuit and triggering audible and visible alarms.
A voltage selection button allows the user to cycle through four test settings (9-90 V) that comply with most standards and specifications.
The GroundSense™ feature visibly reassures the instrument is properly grounded with an indicator light for each selected voltage that will change from blinking to steady when a connection to ground is detected.
A wide range of adaptable sponge hardware and extension accessories are available for the PosiTest LPD. Roller sponge hardware for testing large surfaces, an inside-diameter sponge attachment and an 8-inch square customizable sponge that can be cut into any shape are available to suit a variety of test configurations.
For complete instrument and accessory options visit: PosiTest LPD Low voltage Pinhole Detector.
The PosiTest HHD and PosiTest HHD C High voltage Holiday Detectors are used for detecting defects in coatings of 8 mils (200 μm) or greater in thickness and features a charged conductive brush or spring electrode. Pulsed DC technology is used to detect flaws, emitted at a pulse of 30 times per second, making it safer and easier to ground. The principle of operation for high voltage holiday detectors is similar to low voltage detectors. The charged electrode is passed over the coating, and when a holiday is encountered current flows into the substrate below. The current returns to the detector through the ground wire, completing the circuit and triggering audible and visible alarms. The instrument can be used in a stick configuration out-of-the-box or in a shoulder-carried configuration using the optional wand attachment.
A user adjustable voltage output is maintained over the range of 0.5 to 35 kV. The advanced circuitry is capable of maintaining a precise voltage output so the instrument voltage will not drop under load. Using the voltage calculator in the menu, the operator can enter the dry film coating thickness and the standard they are conforming to, and the correct voltage will automatically be calculated.
Rolling spring electrodes for pipes and flat wire brushes are both available in various sizes. Electrode connectors are manufactured from stainless steel and aluminum to be corrosion resistant, and no tools are required to attach them. Adaptors for connecting other manufacturer’s spring and brush electrodes are available.
For complete instrument details and kit options visit: PosiTest HHD High voltage Holiday Detector.
December 16 - December 23, 2013
What is the risk of damaging a paint film by inspecting a repaired area more than twice with a high-voltage holiday detector?
Selected Answers
From
Christian Favennec of Naval Group on
April 23, 2014:
High voltage holiday detector is used to evaluate ...read more
High voltage holiday detector is used to evaluate if there are porosities or misses in a coating. This test is generally performed only once on the full area of the coating and at the nominal voltage defined by the supplier or calculated with ASTM D5162 and corresponding to the nominal dry film thickness. The porosities or misses are then identified, localized and repaired. The holiday test can be redone once, but only limited to the touch-up areas. If the result is ok, there is no need for and it is not recommended to perform more testing.
From
Tom Swan of M-TEST on
December 19, 2013:
If the coating is the specified thickness and if t ...read more
If the coating is the specified thickness and if the proper voltage is used, the number of times that you do a high voltage test should not be significant in maintaining the structural integrity of the coating. If the voltage is set too high or the coating has thin spots, then you may have a problem. I have been in several situations where the testing has been done more than once and no problems occurred. Now, if the first person does the testing at 10Kv and the second person decides that maybe 15Kv or 16Kv is better, you may have a problem.
From
William Slama of International Paint/Ceilcote Products on
December 18, 2013:
The purpose of high voltage holiday detection (spa ...read more
The purpose of high voltage holiday detection (spark testing) is to detect holes through a lining or coating. The holes (holidays) can then be repaired so that a corrosive environment cannot find a free passage to the
substrate. This is done by imposing an electrical stress across the lining to a conductive substrate
(usually carbon steel) and using a voltage such that a spark will easily arc if a hole exists through the
lining.
In order to ensure that an arc will form, the most typical recommendation is to use approximately 100 volts per mil based on the nominal thickness of the lining. This insures that there will still be enough voltage to jump an air gap at the maximum lining thickness. Both alternating and direct current testers accomplish the same result. It should be noted, however, that in some cases AC will produce more corona and may give erroneous readings, particularly if there is surface contamination.
Because this process puts a relatively high electrical stress on the lining and since the lining has a finite
dielectric strength, areas where the lining is thin or where a void exists but does not go all the way
through will usually break down electrically, causing (burning) a hole all the way through to the steel, resulting in a visible strong spark. When you spark test, in addition to finding existing holes, you will actually make new holes where the dielectric strength of the lining is exceeded.
For this reason, spark testing should be done only once, after completion of the lining (or area) and
before immersion or contamination of the lining. Where equipment is lined prior to final erection, it is
advisable to spark test only after erection so that any lining damage due to handling will be discovered at
that time.
Continued lining cross-linking, temperature cycles, and mechanical stresses of the substrate can change the lining's dielectric strength without having any actual pinholes (holes through to the substrate).
Actual chemical or water exposure definitely has been shown to reduce the dielectric strength of a lining/coating. High voltage inspection has caused serviceable, functioning linings to be burned through repeatedly, simply burning new holes in an otherwise good lining.
Repeated spark testing can burn new holes in a monolithic lining.
References: NACE RP0188-90, Standard Recommended Practice for Discontinuity (Holiday) Testing of
Protective Coatings;
ASTM D4787-93, Standard Practice for Continuity Verification of Liquid or Sheet Linings Applied to
Concrete Substrates;
ASTM D5162-91, Standard Practice for Discontinuity (Holiday) Testing of Nonconductive Protective
Coating on Metallic Substrates.
From
Parviz Babayev of Caspian Pipe Coating on
December 17, 2013:
High voltage may destroy the integrity of paint fi ...read more
High voltage may destroy the integrity of paint film. As a result, the coating loses its isolation property.
There are two types of non-destructive pinhole/holiday detection solutions for locating pinholes in a protective coating system: Low voltage Pinhole Detectors such as the PosiTest LPD and High voltage Holiday DetectorHoliday Detectors such as the PosiTest HHD and PosiTest HHD C.
Protective coatings and linings are applied to metallic and concrete substrates to prevent corrosion. Areas of thin or missing coating, called pinholes or holidays, can drastically reduce the life of a protective coating system. These discontinuities can be caused by entrapped air bubbles or particulate contamination that leave small regions of the substrate with little or no coating coverage, and if not repaired can become foci for corrosion. Even in areas where the dry film thickness is sufficient, pinholes or holidays can form, and they can be invisible to the naked eye. Therefore, testing of a cured coating using an electrical porosity detection instrument to locate pinholes is crucial to preventing coating failure.
Pinhole/holiday detection can be performed on non-conductive coatings applied to both metallic and concrete substrates. Although concrete is significantly less conductive than metal, it is still slightly conductive due to moisture content, and can carry enough current to allow holiday detectors to function. Corrosion and pitting beneath protective coatings can result in substantial coating failure in industries such as storage tanks, pipelines, and general construction.
Before testing is performed, pinhole/holiday detection instruments are grounded to an area of the bare metal substrate. High voltage detectors featuring pulse technology, such as the PosiTest HHD, can also be grounded using a trailing ground wire, grounding collar, or grounding mat. On concrete substrates, the ground wire is attached to the rebar or another metallic ground permanently installed in the concrete. If metallic ground is not visible, the ground wire is placed directly against the uncoated concrete surface.
The instrument outputs a voltage, charging the electrode as it is moved over the coating. When a holiday is encountered, current flows from the electrode to the substrate below. The current returns to the detector through the ground wire, completing the circuit and triggering an alarm.
Whether to utilize a low voltage or high voltage porosity detection instrument depends on the thickness of the applied coating. For coating thickness up to 20 mils (500 μm), low voltage pinhole detectors (wet sponges) are typically used. High voltage holiday detectors (spark testers) are used on coatings with a total thickness of 8 mils (200 μm) or greater.
DeFelsko offers low and high voltage porosity detectors for locating pinholes in non-conductive coatings and linings applied to electrically conductive substrates. These instruments conform to ASTM, NACE, ISO, and other standards for holiday detection. A long form Certificate of Calibration is included with each instrument at no additional cost.
Low Voltage Pinhole Detector
The PosiTest LPD Low voltage Pinhole Detector is suitable for coating systems with a total thickness of up to 20 mils (500 μm).
High Voltage Holiday Detector
The PosiTest HHD and PosiTest HHD C High voltage Holiday Detectors are suitable for detecting defects in coating systems with a total thickness of 8 mils (200 μm) or greater.
Note: The low range of the PosiTest HHD varies with standards
The PosiTest LPD Low voltage Pinhole Detector is designed to detect defects in coating systems that are up to 20 mils (500 μm) thick. In use, an operator moves the moistened sponge over the coated surface. When a pinhole is encountered, current flows from the sponge into the substrate below. The current returns to the detector through the attached ground wire, completing the circuit and triggering audible and visible alarms.
A voltage selection button allows the user to cycle through four test settings (9-90 V) that comply with most standards and specifications.
The GroundSense™ feature visibly reassures the instrument is properly grounded with an indicator light for each selected voltage that will change from blinking to steady when a connection to ground is detected.
A wide range of adaptable sponge hardware and extension accessories are available for the PosiTest LPD. Roller sponge hardware for testing large surfaces, an inside-diameter sponge attachment and an 8-inch square customizable sponge that can be cut into any shape are available to suit a variety of test configurations.
For complete instrument and accessory options visit: PosiTest LPD Low voltage Pinhole Detector.
The PosiTest HHD and PosiTest HHD C High voltage Holiday Detectors are used for detecting defects in coatings of 8 mils (200 μm) or greater in thickness and features a charged conductive brush or spring electrode. Pulsed DC technology is used to detect flaws, emitted at a pulse of 30 times per second, making it safer and easier to ground. The principle of operation for high voltage holiday detectors is similar to low voltage detectors. The charged electrode is passed over the coating, and when a holiday is encountered current flows into the substrate below. The current returns to the detector through the ground wire, completing the circuit and triggering audible and visible alarms. The instrument can be used in a stick configuration out-of-the-box or in a shoulder-carried configuration using the optional wand attachment.
A user adjustable voltage output is maintained over the range of 0.5 to 35 kV. The advanced circuitry is capable of maintaining a precise voltage output so the instrument voltage will not drop under load. Using the voltage calculator in the menu, the operator can enter the dry film coating thickness and the standard they are conforming to, and the correct voltage will automatically be calculated.
Rolling spring electrodes for pipes and flat wire brushes are both available in various sizes. Electrode connectors are manufactured from stainless steel and aluminum to be corrosion resistant, and no tools are required to attach them. Adaptors for connecting other manufacturer’s spring and brush electrodes are available.
For complete instrument details and kit options visit: PosiTest HHD High voltage Holiday Detector.