Frequently Asked Questions
FUNCTION – All Holiday (Porosity)
Detectors
OPERATING PRINCIPLES - High Voltage Units
-PRINCIPLES
-USAGE
-COMPLIANCE
-MAINTENANCE AND SAFETY
OPERATING PRINCIPLES - Low Voltage Units
USAGE - Low Voltage Units
PCWI Compact High Voltage Crest Meters
FUNCTION – All Holiday (Porosity) Detectors
Q1. What is the function of PCWI Holiday Detectors?
A1. They are test instruments that detect and indicate the location
of pinholes and bare spots (Holidays) on non-conductive coatings,
linings or films that have been applied for corrosion protection
on metal and concrete surfaces.
Q2. What types of non-conductive coatings are applied in corrosion
prevention?
A2. Thin epoxies, vinyl, paints, polyethylene, rubber, porcelain,
enamels, etc., hot applied coal tar, asphalt and heavy mastic
materials. Most anti-corrosive coatings are of a dielectric material
and in order to detect defects through these surfaces a suitable
test voltage is applied.
Q3. What is corrosion and how is it caused?
A3. Corrosion is the gradual wearing away to destruction of material.
It can be caused by atmospheric exposure or by chemical reaction
with corrosive agents - hence the necessity to apply complete
sealing coatings to eliminate moisture permeable defects.
Q4. When would a PCWI Porosity Detector be used?
A4. They would be used in both pre and post installation by the
contractor (manufacturer), to confirm the efficiency of his original
sealing coat, and by the maintenance engineers in periodic examinations.
Q5. In what industries is corrosion of major concern?
A5. Because corrosion is of serious concern over almost all aspects
of industry, both operationally and cost-wise, a short list of
major industries would include: Mining; Fabrication; Engineering
and Construction; Paint Companies; Oils and Petrochemicals; Municipal
and Government Authorities such as City Councils, Electricity,
Water and Sewage, Defense; and others.
Q6. How is the testing of coatings by PCWI Holiday Detectors
cost effective?
A6. For newly constructed tanks, pipelines and other installations
where corrosion prevention coatings have had to be applied, specifications
will normally call for a specific coating to a specific thickness.
With the use of a PCWI Detector in verification of the competency
of the sealing coating, the contractor can be assured that his
coatings responsibility has been met: In terms of cost effectiveness,
with the low capital and operating costs of PCWI Detectors, the
contractor will have an element of freedom from claims at a very
low price.
OPERATING PRINCIPLES - High Voltage Units
PRINCIPLES
Q1. On what principle do PCWI Porosity Detectors operate?
A1. The unit is a low frequency high voltage detector that delivers
a stabilized pre-set pure DC output via a probe to an inspection
electrode. As the electrode moves over the coating surface, if
it encounters a pin hole or bare spot, a small current flows
actuating a visible (non-hazardous) spark at the point of contact
and a visible and audible alarm in the unit. A neon alarm in
the probe handle provides 360° visibility to the user.
Q2. How is the applied voltage pre-set?
A2. The voltage required is pre-set manually on the unit to a
minimum level determined by the thickness of film of the coating
product and its generic type i.e.: Rubber, Vinyl, Epoxy etc.
Detailed instructions are set out in the unit Operator Handbook.
It is important to follow these instructions in setting voltages
as some surfaces have a much higher dielectric strength than
others - consequently offering a high resistance to the conduction
of electricity. Applied test voltages should only be sufficient
to detect faults, otherwise overstressing of the dielectric strength
may occur with possible surface rupturing.
Q3. What are the minimum and maximum film thicknesses that
can be tested with PCWI Detectors?
A3. This depends on the type of coating applied. Australian
Standard AS3894.1-1991 states a minimum of 150µm - see Operator
Handbook for coatings/voltages relationship. Refer to Operating
Instructions.
Q4. It has been said that AC Porosity Detectors offering output
ranges from 5 to 30kV at 1.5mA are preferable to direct DC
units at high voltages, because direct DC Detectors may experience
excessive voltage drop due to special conditions of testing,
location, weather, testing object, or coating thickness etc.
It is further stated that unlike high voltage direct DC types,
with AC there is no danger of residual voltage discharges. How
does this relate to PCWI Detectors?
A4. They have a voltage sensor that holds the voltage to the
desired level.
Q5. Do the PCWI Detectors provide the same voltage automatically
on various pipe diameters without resetting and what is the tolerance?
A5. Yes - the feedback circuit automatically adjusts for
this.
Q6. Can a PCWI Detector be supplied with a mains power pack
suitable for varying AC Voltages e.g.: 100, 110, 200/240v etc.?
A6. Yes - although any 1 amp 12 volt lead-acid battery charger
will be adequate.
Q7. Do damp coatings or moist and humid conditions affect
the operation of the PCWI Detector?
A7. As wet surfaces are generally conductive, this could
affect the unit operationally. Atmospheric moisture is unlikely
to do so. Some user preference exists for DC pulse units over
direct DC units under wet operating conditions. This choice could
be misleading, however, because the loss depends on the size
of the electrode and the possible conductivity of the moisture.
These circumstances could cause the test voltage to drop to such
an extent that there is insufficient test voltage to locate faults.
Q8. In relation to the PCWI DC Detector, what is the function
and limitations of an AC Detector?
A8. These are generally used for the testing of rubber coatings
in excess of 1.5 mm thickness. Because they have a high dielectric
constant, they tend to overheat with prolonged use and should
only be considered, useful for intermittent use. They are considered
a crude method with erratic output voltage.
Q9. What checks are available on the functioning of the PCWI
Detectors?
A9. A range of tests can be undertaken by employing the appropriate
PCWI Detector Crest Meter. Details are available in Crest Meter
brochure and Crest Meter Operator handbook. (i.e.: Voltage output
and visual display; Continuity of leads etc.)
Q10. Is the PCWI Detector wired for earphones?
A10. Yes.
Q11. Can the PCWI Detector be operator belt mounted?
A11. No - the unit is supplied with an adjustable harness
for waist, chest or shoulder mounting. The waist mounting is
equivalent to a normal belt position.
USAGE
Q1. Can the PCWI Detector be kept in continuous service?
A1. Yes! The PCWI Detector has a slip out battery pack that
is interchangeable. The battery pack can be fully recharged in
10 hours via the charger and the unit can also operate off mains
power via the Charger.
Q2. Is the high voltage application destructive to any of
the generally used sealing coatings?
A2. No! The applied voltage to the coating is non-destructive,
provided the voltage applied is within the parameters set down
in the Operator Handbook for the type and thickness of coating.
Q3. It is noted that the PCWI Detector employs wire brush
inspection electrodes and not wet sponges. What are the advantages
of the wire brush electrodes and the limitations of the wet sponge
electrodes?
A3. Wire brush electrodes are faster to use, larger areas
can be covered and there is no contamination from the water.
Wet Sponge (cellulose) electrodes are used in low-voltage detectors,
having an output of less than 100 VDC. The wet sponge method
is not satisfactory for the detection of other than gross faults
in thin film coatings, and is unsuitable for use where thicker
coatings in excess of 150µm have been applied.
Q4. PCWI offers a maximum internal and external pipe-brushes
at 20" (500 mm). Can brushes of greater diameter be provided
to complement the Detector?
A4. Brushes larger than 20" (500 mm) are too large to
handle; hence we do not offer brush sizes in excess of 20".
Coils are substituted when larger pipes are tested. Note: All
coil sizes can be used in place of brushes.
Q5. Under what conditions are Carbon filled silicone-rubber
brush electrodes of advantage?
A5. These can provide longer life but require the application
of higher voltages.
Q6. Are PCWI wire brushes interchangeable or compatible with
competitive detectors and vice-versa?
A6. Yes, with suitable adapters, which PCWI can manufacture
to suit.
Q7. Will wire brush electrodes insure good inspection even
in corners and around irregular shapes where pinholes or bare
spots (holidays) are likely to occur?
A7. Yes! PCWI Detectors can accommodate a complete range
of brushes (see Brochure for illustrations).
Q8. It is stated that under practical conditions, it is impossible
to obtain an absolutely uniform thickness of an applied coating
to a metallic surface, due to unevenness, mill scale or other
surface blemishes. Using a "dry testing technique" by
applying a high test-voltage to locate faults over the thickest
section of the film, the thin areas of film could be ruptured
due to excessive test voltage, even though these thinner film
areas are perfectly homogeneous. Under these circumstances wet
sponge testing utilizing a low voltage can be effective - True
or false?
A8. This is False! Rupturing will only occur if far too high
a voltage is applied when testing. Passing the electrode over
a test panel with similar (thinner) coating thickness will quickly
determine whether the voltage is set to a level that will cause
rupturing in the thinner areas.
Q9. Can cable makers use the PCWI Detector for testing? Does
this require a cable tester electrode box?
A9. Yes - this box can be made on special order.
Q10. Can the PCWI Detector be used in the testing of flaws
in Heavy-Duty glass?
A10. This depends on the thickness of the glass and the voltage
required.
Q11. Can the PCWI Detector be used in the testing of asbestos
cement substrates?
A11. No - most of the cementious products are conductive.
COMPLIANCE
Q1. What certifications of compliance do PCWI Detectors carry?
A1. Conforms to Australian Standard AS3894.1-2002, ASTM G62-87
(1998), NACE RP0274-98, NACE RP0490-2001, NACE RP0188-99, ASTM
D4787-93 (1999), JIS G-3491, JIS G-3492, ANSI/AWWA C214-89, ANSI/AWWA
C213-94, ISO 2746:1998 & AS3894.1-2002
MAINTENANCE AND SAFETY
Note: It is critical that the Operators Handbook is read
and fully understood before the unit is turned on.
Q1. What operator safety precautions are required?
A1. Safety precautions are shown in the Operator Handbook
in detail and should be followed. As with all high voltage test
equipment it should be operated by responsible, trained and authorized
Personnel.
Q2. The Operator Handbook recommends the wearing of rubber
gloves!
A2. These are recommended as a safety precaution.
Q3. Does the PCWI Detector carry a safety switch incorporated
in the test probe handle? This is not shown in the probe handle
diagram in the operator handbook.
A3. No - the momentary switch on the front panel serves the
same purpose.
Q4. Is the PCWI Detector completely sealed against dirt, water
and corrosion to ensure a high degree of reliability?
A4. The unit is completely sealed against dirt and dust but
it is not possible to make it completely waterproof.
Q5. What is the battery life expectancy?
A5. Dependent upon usage: The manufacturer rating is four
(4) years.
Q6. What warranty is provided with the unit?
A6. All equipment sold by PCWI is guaranteed for one (1)
year from date of purchase provided the instrument has not been
modified, misused or abused, excluding batteries, probes, brushes
and leads - which are subject to wear. Procedures for any guarantee
claim are set out in the Operators Handbook.
Q7. What information is given about "Troubleshooting" maintenance
on site?
A7. The Operator's handbook sets out Symptoms - Causes -
Solutions - for on-site maintenance.
Q8. If on-site maintenance is inadequate and repair becomes
necessary what prompt service is available for repair and recalibration?
A8. A full range of replacements is always available and
quick return to service is assured.
OPERATING PRINCIPLES - Low Voltage Units (Wet Sponge Method)
Q1. On what principle does the low voltage wet sponge unit
operate?
A1. The low voltage instrument employs a cellulose sponge
as an inspection electrode. When moistened with water, the electrode
is moved over the coated surface under inspection; when the electrode
passes a void or bare spot, moisture from the wet sponge (electrode)
penetrates the coating making contact with the conductive substrate,
resulting in a drop in electrical resistance. As a result, a
small current flow activates an audible alarm enabling identification
of the defect location.
Q2. Is the applied voltage user selectable?
A2. Yes, each unit has three settings: 9; 67.5; and 90 volts.
USAGE - Low Voltage Units
Q1. What is the most general usage for Wet Sponge Detectors?
A1. Wet Sponge Detectors are generally used extensively to
check the surface continuity of very thin applied coatings -
less than 150µm (i.e.: whitegoods) where potential for rupturing
of the coating could occur with high voltage units.
Q2. Can Wet Sponge units be used on thicker coatings?
A2. Yes! But the test process will be slower because of the greater
penetration time. Prewashing the coating surface may speed this
up.
Q3. Will Wet Sponge electrodes ensure good inspection in corners
and around irregular shapes?
A3. Yes. The flexibility of the sponge ensures good inspection.
PCWI Compact High Voltage Crest Meters
Q1. What is the function of the PCWI Compact Crest Meter?
A1. The Crest Meter has the following functions:
1. To test the output of the PCWI Compact Porosity (Holiday)
Detector and to verify the voltage on the visual display.
2. To test the continuity of the leads and to verify the voltage
on the visual display.
3. To test the PCWI Compact Detector under load with an applied
voltage - this test verifies all earth leads and connections,
and partially loads the system.
4. To test the PCWI Compact Detector under full load.
This test verifies all earth leads and connections, fully loads
the system, indicates pull down voltage and displays actual test
voltage. This test is as per Australian Standard 3894.1-1991
for setting test voltages.
Q2. What certification does the PCWI Compact Crest Meter carry?
A2. Certification is an option, however both the Crest Meter
and the DC Probe can be supplied as checked against a NATA certified
Crest Meter.
