Standard Practice
Discontinuity (Holiday)
Testing of New Protective
Coatings on Conductive
Substrates
REV 2006
Section 1: General
1.1 This
standard provides procedures for low-voltage wet sponge testing and
high-voltage spark testing of new coatings on conductive substrates.
1.2 Electrical
testing to determine the presence and number of discontinuities in a coating is
performed on a nonconductive coating applied to a conductive substrate. The
allowable number of discontinuities should be determined prior to conducting
this test, because the acceptable number of discontinuities varies depending on
coating thickness, design, and service conditions.
1.3 This
standard is not intended to provide data on service life, adhesion, or film
thickness of an applied coating system. Electrical testing does not detect
areas where the coating is thin (even as thin as 25 μm [1.0 mil]).
1.4 This
standard is intended for use only with new coatings applied to conductive
substrates. Inspecting acoating previously exposed to an immersion condition
could result in damage to the coating or cold produce an erroneous detection of
discontinuities due to permeation or moisture absorption of the coating.
Deposits may also be present on the surface, causing telegraphing. The use of a
high-voltage spark tester on previously exposed coatings can result in a spark
that damages an otherwise sound coating. A low-voltage wet sponge tester may be
used without damaging the coating but can produce erroneous readings.
1.5 To prevent
damage to a coating if a high-voltage spark tester is being used, the total
film thickness and dielectric strength of the coating system shall be
considered in selecting the appropriate voltage for detection of discontinuities.
1.6 The coating
manufacturer shall be consulted to obtain the following information, which can
affect the accuracy of the tests described in this standard to determine discontinuities:
(a) The length
of time required to adequately dry or cure the applied coating prior to
testing. Solvents retained in an uncured coating may form an electrically
conductive path through the film to the substrate.
(b) Whether the
coating contains electrically conductive fillers or pigments that may affect
the normal dielectric properties.
Section 3: Low-Voltage Wet Sponge Testing
3.1 Equipment
3.1.1 A low-voltage wet
sponge tester is an electronic device powered by a self-contained battery with voltages
ranging from 5 to 90 V direct current (DC), depending on the manufacturer’s circuit
design. It is used to locate discontinuities in a nonconductive coating applied
to a conductive substrate. Operation includes the use of an open-cell sponge
electrode saturated with a solution for exploring the coating surface, a ground
connection, and an audible or visual indicator for signaling a point of coating
discontinuity.
3.1.2 The operating
voltage of a low-voltage wet sponge tester is a function of the particular
electronic circuit design and does not affect the sensitivity of the device.
3.1.3 A number of
industry accepted, low-voltage wet sponge testers are commercially available.
Thefollow ing electronic principles describe two types of devices generally
used; others may be available but are not described in this standard.
3.1.3.1 One type of
low-voltage wet sponge tester is a lightweight, self-contained, portable device
based on the electrical principle of an electromagnetic sensitive relay or
solid-state electronic relay circuit that energizes an audible or visual
indicator when a coating discontinuity is detected. Generally, this type of
tester can be recalibrated in the field by the user.
3.1.3.2 Another type of
low-voltage wet sponge tester is a lightweight, self-contained, portable device
based on the principle of an electronic relaxation oscillator circuit that
reacts significantly to the abrupt drop in electrical resistance between the
high dielectric value of the coating and the conductive substrate at the point
of coating discontinuity. This results in a rise in oscillator frequency as
well as in the audible signal from the device. Generally, this type of tester
cannot be recalibrated in the field by the user.
3.2 Procedures for Use
3.2.1 Sufficient drying
or curing of the coating shall be allowed prior to conducting a test. The
length of time required for drying or curing shall be obtained from the coating
manufacturer. Solvents retained in the coating could produce erroneous indications.
3.2.2 The film thickness of the coating shall be measured with a on destructive dry film thickness gauge. If
the coating exceeds 500 μm (20 mil), the procedures for high-voltage spark
testing described in
Section 4 shall be
used. A low-voltage wet sponge tester shall not be used for determining the
existence of discontinuities in coatings having a total thickness greater than
500 μm (20 mil), due to the relative inaccuracy and lack of sensitivity of
low-voltage wet sponge testers.
3.2.3 The tester shall
be tested for sensitivity in accordance with Paragraph 3.3.
3.2.4 The ground wire
from the tester ground output terminal shall be attached to the conductive
substrate, and positive electrical contact shall be ensured.
3.2.5 The exploring
sponge lead shall be attached tothe output terminal.
3.2.6 The sponge shall
be saturated with tap water. The sensitivity of the test may be increased by
adding a low-sudsing wetting agent (such as that used in photographic film
development), combined at a ratio of 30 mL (1 fl oz) wetting agent to 3.8 L (1
gal) water. The sponge shall be wetted sufficiently to barely avoid dripping
while it is moved over the coating.
3.2.7 If a wetting
agent is used, it must be completely removed by rinsing the holiday area prior
to repair. Additives can leave contaminants on the surface that can interfere
with adhesion of topcoats or repair coats and may contaminate stored product.
3.2.8 If a test is
conducted between coats of a multicoat system, a wetting agent shall not be
used.
3.2.9 Sodium chloride
(salt) shall not be added to the water because it can cause erroneous
indications of discontinuities. The salt, after drying on the coated surface,
can form a continuous path of conductivity. It also interferes with intercoat
adhesion of additional coats.
3.2.10 A bare spot on
the conductive substrate shall be contacted with the wetted sponge to verify
that the tester is properly grounded. This procedure shall be repeated
periodically during the test.
3.2.11 The sponge shall
be moved over the surface of the coating at a moderate rate of approximately
0.3 m/s (1 ft/s), using a double pass over each area. Sufficient pressure shall
be applied to maintain a wet surface. If a discontinuity is detected, the
sponge should be turned on end to determine the exact location of the discontinuity.
3.2.12 Discontinuities
that require repair shall be identified with a marker that is compatible with
the repair coating or one that is easily removable.
3.2.13 To prevent
telegraphing, care should be taken to ensure that the solution (tap water) is
wiped dry from a previously detected discontinuity before continuing the test.
3.3 Verifying Sensitivity of Equipment
3.3.1 The tester shall
be tested for sensitivity prior to initial use on each project and periodically
thereafter during the project, in accordance with the manufacturer’s
instructions.
3.3.2 The battery shall
be tested for proper voltage output according to the manufacturer’s
instructions.
3.3.3 The ground cable
shall be connected to the tester ground output terminal.
3.3.4 The tester shall
be switched to the “on” position, if neccessary.
3.3.5 The sponge shall
be saturated with a wetting solution consisting of tap water and a wetting
agent (see Paragraph 3.2.6).
3.3.6 The ground-cable
alligator clip shall be touched to the wetted sponge. The tester signal should
actuate in accordance with the manufacturer’s instructions.
3.3.7 If the tester
fails to signal, it shall be considered inoperative.
3.4 Verifying Tester
Calibration or Sensitivity
3.4.1 The following
procedures shall be used to verify calibration of testers having an
electromagnetic sensitive relay or solid-state electronic relay:
3.4.1.1 Test the
battery for proper voltage output. Refer
to the manufacturer’s instructions.
3.4.1.2 Switch the
tester to “on” or “calibrate,” if necessary.
3.4.1.3 Connect an
80,000-ohm resistor with an accuracy tolerance of ±5% across the output terminals.
The alarm should actuate.
3.4.1.4 Connect a
100,000-ohm resistor with an accuracy tolerance of ±5% across the output terminals.
The alarm should not actuate if properly calibrated.
3.4.1.5 If the tester
fails to perform as outlined in Paragraphs 3.4.1.3 and 3.4.1.4, adjust the
alarm circuit or return the tester to the manufacturer.
3.4.2 The following
procedures shall be used to verify sensitivity of testers having an electronic
relaxation oscillator circuit:
3.4.2.1 Test the
battery for proper voltage output. Refer to the manufacturer’s instructions.
3.4.2.2 Switch the
tester to “on.”
3.4.2.3 At different
intervals, a 10-megohm, 1-megohm, 100,000-ohm, and 10,000-ohm resistor should
be connected across the output terminals.
3.4.2.4 A discernible
increase in frequency should be detected as the resistance is decreased.
3.4.2.5 If the tester
fails to indicate a frequency change, it shall be considered inoperative.
Section 4: High-Voltage Spark Testing
4.1 High-voltage
spark testers are suitable for determining the existence of discontinuities in
coatings of all thicknesses. The coating manufacturer should be consulted for
proper test equipment and inspection voltage. Suggested starting voltages are
provided in Table 1.
CAUTION: Coatings that
are applied at thicknesses of less than 500 μm (20 mil) may be susceptible to
damage if tested with a high-voltage spark tester.
4.2 A
high-voltage spark tester may be used to determine discontinuities in coatings
on conductive concrete substrates. The conductivity of concrete varies
depending on moisture content, type, density, and location of rebars. Conductivity
shall be tested by attaching a ground wire to the rebar or another metallic
ground permanently installed in the concrete and touching the electrode to the
bare concrete. If the metallic ground is not visible, the ground wire shall be
placed directly against the bare concrete surface and weighted with a damp
cloth or wet-sand-filled paper bag. If the test indicates that the concrete is
not conductive, determining discontinuities with a high-voltage spark tester
will be ineffective.
4.3
Equipment
4.3.1 A
high-voltage (in excess of 800 V) spark tester is an electronic device used to
locate discontinuities in a nonconductive protective coating. It consists of an
electrical energy source, an exploring electrode, and a ground connection from
the indicator signaling current flow through a coating discontinuity to the
substrate.
4.3.2 The
exploring electrode shall be of the type capable of maintaining continuous
contact with the surface being inspected, including bolts, raised areas, etc.
It shall be kept clean and free of coating material.
4.3.3 A
high-voltage spark tester can be identified as either a pulse type tester or a
direct current tester. A pulse type tester discharges a cycling, high-voltage pulse.
A direct current tester discharges continuous voltage.
4.4
Procedures for Use
4.4.1 Sufficient
drying or curing of the coating shall be allowed prior to conducting a holiday
test. The length of time required for drying or curing shall be obtained from
the coating manufacturer. Solvents retained in the coating could produce
erroneous results, as well as an explosive environment.
4.4.2 The
thickness of the coating shall be measured with a nondestructive dry film
thickness gauge. If the coating is less than 500 μm (20 mil), procedures for low-voltage
testing should be considered (see Section3). Although the high-voltage spark
tester is suitable for determining discontinuities in coatings less than 500 μm
(20 mil), the coating manufacturer should be consulted before using this test.
Certain coatings can be damaged if tested with this equipment.
4.4.3 The
high-voltage spark tester shall be calibrated in accordance with Paragraph 4.6.
4.4.4 The
high-voltage spark tester shall be adjusted to the proper voltage for the
coating thickness being tested. In selecting the inspection voltage, sufficient
voltage shall be provided to break the air gap that exists at the holiday. This
air gap varies depending on the total applied film thickness. Excessive voltage
may produce a holiday in the coating. The maximum voltage for the applied
coating shall be obtained from the coating manufacturer. Table 1 contains
suggested
voltages that
may be used as guides.
4.4.5 The ground
wire from the high-voltage spark tester ground output terminal shall be
attached to the conductive substrate, and positive electrical contact shall be
ensured. When testing concrete surfaces, the ground wire shall be attached to
the rebars. If the
rebars are not
visible, the ground wire shall be placed directly against the bare concrete
surface and weighted with a damp cloth or wet-sand-filled paper bag.
4.4.6 Contact
shall be made with the exploring electrode on the conductive substrate to
verify that the tester is properly grounded. This test shall be conducted
periodically during the testing of the coating.
4.4.7 The
exploring electrode shall be moved over the surface of the dry coating at a
rate of approximately 0.3 m/s (1 ft/s) using a single pass. Moisture on the coating
surface can cause erroneous indications. If moisture exists, it shall be
removed or allowed to dry
before the test
is conducted.
4.4.8
Discontinuities that require repair shall be identified with a marker that is
compatible with the repair coating or one that is easily removable.
4.5 Verifying
Operation of Equipment
4.5.1 The
following procedures shall be used to verify operation of high-voltage spark
testers:
4.5.1.1 Test the
energy source (battery) for proper voltage output according to the manufacturer’s
instructions.
4.5.1.2 Connect
the exploring electrode and grounding cable to the terminals of the tester.
4.5.1.3 Switch
the tester to the “on” position.
4.5.1.4 Touch
the exploring electrode to the ground cable alligator clip. The tester signal should
actuate in accordance with the manufacturer’s operating instructions.
4.5.1.5 If the
tester fails to signal, it shall be considered inoperative.
4.6
Calibration
4.6.1 Before the
initial tests, the tester shall be calibrated to the specified voltage to be
used for holiday detection. The tester shall be recalibrated periodically
thereafter. The following procedure shall be used:
4.6.1.1 Connect
a high-voltage voltmeter between the probe and the ground lead.
4.6.1.2 Switch
the tester to the “on” position.
4.6.1.3 Compare
the voltage of the voltmeter with the output voltage of the tester. Depending
on the type of tester, adjust to the specified voltage (±5%) using either the
variable regulator or predetermined selector switch.
4.6.1.4 Switch
the tester to the “off” position.
4.6.1.5
Disconnect the voltmeter.
Section 5: Testing of Repaired Area
5.1 Sufficient
drying or curing of the repair coating shall be allowed prior to retesting. The
length of time required for drying or curing shall be obtained from the coating
manufacturer.
5.2 The test
shall be conducted following the procedures previously outlined in this
standard for the type of tester selected.
5.3 Only those
areas that have been repaired shall be retested, unless otherwise specified.
Section 6: Safety
6.1 Precautions
shall be taken to prevent electrical shock.This is particularly important if
the tester is powered by line voltage. The manufacturer’s safety instructions
shall be followed to prevent electrical shock.
6.2 Prior to
conducting high-voltage tests in an enclosure, an inspection shall be conducted
to indicate whether the enclosure is safe for entry, including testing for
flammable or explosive gas. Solvents retained in the coating can produce an
explosive environment.
6.3 If testing
is being conducted with a high-voltage spark tester, complete, proper
electrical grounding (to earth) of the substrate shall be ensured.
