ASTM C743-87(2009)
(Test Method)Standard Test Method for Continuity of Porcelain Enamel Coatings
Standard Test Method for Continuity of Porcelain Enamel Coatings
ABSTRACT
This test method provides for easy detection of discontinuities and areas of light coverage that are not readily seen by visual inspection on corrosion protective porcelain enamel coatings. These two issues limit the protection to the metal substrate. Apparatus includes a nondestructive coating thickness gage, either an ac or a dc high-voltage discharge test instrument with a continuously variable output voltage, and a mesh wire gauze test probe. This test uses porcelain enameled glass coating specimens of any size which should be removed from an edge or the back of a specimen and then properly conditioned as specified. If the probe is wider than the specimen, the specimen edges should be masked using electrical insulating tape.
SCOPE
1.1 Porcelain enamel coatings are applied to metals to provide protection from corrosion as well as to enhance their appearance. This test method permits the easy detection of discontinuities and areas of light coverage, not readily seen by visual inspection, which limit the protection to the substrate. Somewhat similar tests applicable to the thicker glass coatings used for chemical reaction vessels are found in Test Methods C 536 and C 537.
1.2 Values stated in SI units are to be regarded as the standard. Inch-pound units are provided for information only.
1.3 This standard does not purport to address all of the safety problems, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Standards Content (Sample)
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Designation: C743 − 87(Reapproved 2009)
Standard Test Method for
Continuity of Porcelain Enamel Coatings
This standard is issued under the fixed designation C743; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 3.4 peak voltage—for ac meters, the voltage that will
discharge across the air gap or across a defect. The peak
1.1 Porcelain enamel coatings are applied to metals to
voltage is the RMS voltage multiplied by 1.414.
provide protection from corrosion as well as to enhance their
appearance. This test method permits the easy detection of
4. Apparatus
discontinuities and areas of light coverage, not readily seen by
4.1 Anondestructive coating thickness gage with a range of
visual inspection, which limit the protection to the substrate.
at least 0 to 0.5 mm in 0.03-mm increments (0 to 20 mils in
Somewhat similar tests applicable to the thicker glass coatings
1.0-mil increments).
used for chemical reaction vessels are found in Test Methods
C536 and C537.
4.2 Either an ac or a dc high-voltage discharge test instru-
ment with a continuously variable output voltage over the
1.2 Values stated in SI units are to be regarded as the
range of at least 0 to 4 kV as indicated on a built-in voltmeter.
standard. Inch-pound units are provided for information only.
Theinstrumentshallbecapableofbeingsetto0.1kVandshall
1.3 This standard does not purport to address all of the
have an insulated cable and probe and a means for indicating
safety problems, if any, associated with its use. It is the
(light, meter, or bell) a voltage discharge. Before use in this
responsibility of the user of this standard to establish appro-
test, the high-voltage discharge test instrument shall be cali-
priate safety and health practices and determine the applica-
brated in accordance with the procedure set forth in AnnexA1.
bility of regulatory limitations prior to use.
4.3 A test probe constructed of 100 mesh wire gauze as
2. Referenced Documents
illustrated in Fig. 1.
2.1 ASTM Standards:
5. Test Specimens
C536 Test Method for Continuity of Coatings in Glassed
5.1 Porcelain enameled specimens of any size may be used
Steel Equipment by Electrical Testing
in this test. The enamel shall be removed from an edge or the
C537 Test Method for Reliability of Glass Coatings on
backofthespecimentoprovideanelectricalgroundforthetest
Glassed Steel Reaction Equipment by High Voltage
instrument. If the probe is wider than the specimen, the edges
3. Terminology
of the specimen shall be masked with electrical insulating tape
to prevent discharges from occurring at the edges where
3.1 air-gap voltage—voltage needed to arc through a defect
porcelain coverage may be light.
that is open to both the surface of the porcelain enamel and the
metal substrate. The length of the air gap is estimated by
6. Conditioning
measuring the enamel thickness.
6.1 Before testing, wash the specimens with a 1 weight %,
3.2 overvoltage—difference between an applied test voltage
solution of trisodium phosphate on a soft cellulose sponge,
and the air-gap voltage for the porcelain enamel being tested.
rinse with tap water, and then rinse with distilled water. Then
3.3 RMS voltage—root mean square voltage, or “average”
dry the specimens thoroughly in air.
voltage, shown on ac test meters.
7. Procedure
7.1 Measuring the Enamel Thickness— Measure the enamel
This test method is under the jurisdiction ofASTM Committee B08 on Metallic
thickness at a minimum of three locations on the specimen.
and Inorganic Coatingsand is the direct responsibility of Subcommittee B08.12 on
Materials for Porcelain Enamel and Ceramic-Metal Systems.
Make these measurements to the nearest 0.03 mm (1.0 mil) in
Current edition approved April 15, 2009. Published June 2009. Originally
accordance with the operating instructions for the thickness
ε1
approved in 1973. Last previous edition approved in 2004 as C743 – 87 (2004) .
gage. Use the maximum value obtained as the enamel thick-
DOI: 10.1520/C0743-87R09.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or ness.
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
7.2 Selecting the Test Voltage—The test voltage to be used
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. depends upon the purpose for conducting the test. The test can
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C743 − 87 (2009)
FIG. 1 Test Probe
be used to determine (1) the presence of defects open to both 7.2.3.1 DC Test Instruments—Determine the test voltage in
theenamelsurfaceandthebasemetal,( 2)thelocationofareas accordance with 7.2.2, substituting the specified overvoltage
of light coverage in addition to defects open to both the enamel for the selected overvoltage as in 7.2.2.2 and 7.2.2.3.
surface and the base metal, or ( 3) compliance with a 7.2.3.2 AC Test Instruments—Divide the specified overvolt-
specification. According to the user’s purpose for conducting age by 1.414, then determine the test voltage as in 7.2.2,
the test, the following three instructions correspond respec- substituting the specified overvoltage divided by 1.414 for the
tively to (1), (2), or ( 3) above: selected overvoltage as in 7.2.2.2 and 7.2.2.3.
7.2.1 Test Method A—For Open Defects: 7.2.3.3 Probe the specimen as shown in 7.3.
7.2.1.1 Determine the air-gap voltage that corresponds to
7.3 Probing the Specimens:
the enamel thickness from the calibration curve described in
7.3.1 Connect the ground wire of test instrument to the base
the annex. This value is the test voltage.
metal of the specimen.
7.2.1.2 Probe the specimen in accordance with 7.3.
7.3.2 Turn on the test instrument.
7.2.2 Test Method B—For Light Coverage and Open De-
7.3.3 Set the output voltage (as indicated on the built-in
fects:
voltmeter) to the value selected in 7.2.
7.2.2.1 Determine the air-gap voltage that corresponds to
7.3.4 Let the voltage stabilize for 15 s.
the enamel thickness from the calibration curve described in
7.3.5 Hold the probe with a light pressure at approximately
the annex.
30° to the surface of the specimen.
7.2.2.2 Arbitr
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