High Voltage Holiday Test
- 4 May 2018
- Posted by: Stm Coatech
- Category: Educational Articles
The Holiday test is a non-destructive testing method applied to protective coatings to detect unacceptable discontinuities such as small holes and voids. The test involves controlling an electric circuit to complete the current circuit and to see if there is current. This test is used to find film discontinuities that are not easily visible.
Project specifications for coating the interior surfaces of storage tanks, ships and rails and interior coating of liquid pipelines generally require continuous, non-porous and non-punctured paint / coating or lining systems. Extensive holiday detectors are used to rely on visual inspection to determine the number and location of skips, leaks, and pinholes so that the tank, ship, railway vehicle or pipeline can be repaired before being put into service. If this test is not carried out and there are any unidentified leaks in the paint / coating or lining system, the contents of the tank, ship, railway vehicle or pipeline may attack the exposed surface and cause deformation of the pit, loss of cross section, surface deformation. In addition, if the deterioration occurs, the interior may become contaminated with corrosion products and paint / coating lining. The Holiday test is administered by two industry tests. These are ASTM D5162 and NACE SP0188.
Pore / Holiday detection is usually carried out after topcoat application, but before complete curing, when paint / coating filminin needs to be repaired. Some project specifications require a holiday test to be carried out before the final coat is applied. If this is the case in your progeny, you will need to confirm the interlayer cleanliness of the surface before applying the next layer.
Choosing Holiday Detector
There are two types of holiday detectors. These types depend on the total thickness of your choice of paint / coating / lining system. Low voltage or wet sponge pore detectors are used on paints / coatings / linings with a thickness of less than 20 mils. High voltage pore detectors or spark testers are used in thicker paint / coating / lining than 20 mils. If you do not know the thickness of the paint / coating system, you have to measure the thickness before performing the holiday test. Both of these detectors will only work on non-destructive paint / coatings applied to the conductive surface.
In this article, the High Voltage Holiday Dedector will be examined.
There are two types of high voltage holiday detectors. These are a vibrating direct current detector and a continuous direct current detector. Vibrating direct current holiday detector is the most widely used type.
Continuous direct current detector is generally cheaper and works well in dry coatings. However, since this tester generates a constant current as it passes through the surface of the coating, it may give a flow back to the coating and cause a false pore to be detected. There is a sensitivity knob on these meters to set the milliamp setting to make the beep sound “beep”. For most coatings, the default setting usually works; but if you get a “beep” from the meter without a spark, you may need to change the setting.
Continuous direct current holiday detector discharges high voltage continuously and is suitable for nonconductive coatings in pipeline tests, storage tanks and pore tests on valves.
The vibrating direct current detector is versatile in terms of its ability to be used in damp environments, even when condensation is present in the coatings. Electrical pulses are produced between 20 and 60 cps. Each pulse is “open” for a period of 20 to 200 microseconds. Sensitivity does not require a knob and has the advantage of working in damp conditions.
High Voltage (Spark) Holiday Detector Usage
1.Get the detector.
This holiday detector consists of 7 basic components.
-24 “insulated rod
– black insulated cable
-electrode (neoprene rubber, brass brush or coil spring)
-clipsy uninsulated grounding
a detector unit with an adjustable voltage regulator operated by a rechargeable battery
– backup battery and battery charging unit
-transport box
The detector unit contains two pole heads. Loosen the jagged pole heads and tighten the pole heads again (only by hand tightening) by inserting one ground wire and the other electrode wire. The rod is then connected to the electrode lead.
2.Select the voltage setting.
When the high voltage holiday detector is used, choosing the voltage setting is the most important steps. If the selected voltage is too low, it will not be able to detect the pores even if the detector is present. If the voltage is set too high, you may damage the paint / coating. You can learn the correct voltage setting from the manufacturer of the project specification or paint / coating system.
In the light of this information, ASTM D5162 contains the formula for calculating voltage settings for “Conductivity Paint / Coatings Non-Conductive Paint / Coating Test on Metallic Surfaces”.
- The table on the right provides a list of voltages calculated for the paint / coating thickness range of 20 to 95 miles using the equation.Remove the protective cover from the ‘Voltage setting’ port and use a screwdriver to turn the switch to the desired voltage (looking at the table) and replace the protective cover.
3. Attach the splicing wire to the structure and to the ground.
Connect the earthing wire to the structure you inspected. It is very important that the wire is in contact with bare steel. This means that you may need to remove a small part of the paint / coating to properly ground the detector.4. Turn on the detector and verify its continuity.
Set On / Off switch to “On / On” position. You will hear a buzzing sound if you do not hear it, the battery may need to be charged or replaced.To confirm continuity, you must touch the uncoated area of the electrode, or create a deliberate pore. Grounding is sufficient if the electrode gives a signal after being driven here. If it does not give a signal, touch the electric earthing wire. If you hear a signal, the detector works properly, but grounding is not enough. In this case, you should correct the contact with the surface or the ground of the wire. If it still does not signal, the detector is not working properly and should not be used.
5. Inspect the coated / coated surfaces.
After confirming that the detector is in working condition and that the grounding contact is sufficient, inspect the electrode by painted / coated surfaces at a linear foot speed of approximately 7 seconds using the systematic overlay method. The detector has an audible alarm that will signal if it detects a pore. There will also be a spark that visually indicates the location of the fugitive. Circle the defective area with another oil-free pen that can be cleaned after the pore is repaired.
STM Coatech, Paint Test Equipment (UK) and PWCI (Australia) which is the Turkey distributor.
STM Coatech, SSPC PCI (International Coating Enspektörlüg), and Corroder (MPA Group England), Turkey, Romania, Ukraine, Georgia, Russia, Azerbaijan, Turkmenistan, Kazakhstan, Iraq, Qatar, Kuwait, Oman, the Sudan and Algeria official licensors.
It is also authorized examination center of the country we have already mentioned above, especially Turkey. Corrodere Training Courses are listed below.
1.Icorr Level 1
2.Icorr Level 2
3.Icorr Level 3
4.IMO PSPC
5.Corrodere Hot Galvanizing
6.Corrodere Insulation Inspector
7.Practical Workshop Icorr 1,2,3
8.Corrodere Marine & Offshore Inspector
9.Transition to Icorr
REFERENCES:
1.Paint Square, Fundamentals of Holiday Detection, date of access: 2 May 2018, http://www.paintsquare.com/library/articles/applicator_training_bulletin__fundamentals_of_holiday_detection.pdf
2.Caltrans, Method for Holiday Detection in Epoxy-Coated Reinforcing Steel, date of access: 2 May 2018, http://www.dot.ca.gov/hq/esc/ctms/pdf/CT_685dec02.pdf
3.Raven Lining Systems, Holiday Inspection Technical Bulletin, date of access: 2 May 2018, http://www.ravenlining.com/wp-content/uploads/2014/09/Holiday-Inspection-Testing-Coatings.pdf
4. Corrosion Pedia, Tools & Tips: Holiday Detection on Coated Steel & Concrete Substrates, date of access: 2 May 2018, https://www.corrosionpedia.com/2/4173/corrosion-prevention/application-methods/tools-tips-holiday-detection-on-coated-steel-concrete-substrates