ASTM C743-87(1998)
(Test Method)Standard Test Method for Continuity of Porcelain Enamel Coatings
Standard Test Method for Continuity of Porcelain Enamel Coatings
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 C536 and C537.
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 may involve hazardous materials, operations, and equipment. This standard does not purport to address all of the safety problems 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.
General Information
Relations
Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: C 743 – 87 (Reapproved 1998)
Standard Test Method for
Continuity of Porcelain Enamel Coatings
This standard is issued under the fixed designation C 743; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope 4. Apparatus
1.1 Porcelain enamel coatings are applied to metals to 4.1 A nondestructive coating thickness gage with a range of
provide protection from corrosion as well as to enhance their at least 0 to 0.5 mm in 0.03-mm increments (0 to 20 mils in
appearance. This test method permits the easy detection of 1.0-mil increments).
discontinuities and areas of light coverage, not readily seen by 4.2 Either an ac or a dc high-voltage discharge test instru-
visual inspection, which limit the protection to the substrate. ment with a continuously variable output voltage over the
Somewhat similar tests applicable to the thicker glass coatings range of at least 0 to 4 kV as indicated on a built-in voltmeter.
used for chemical reaction vessels are found in Test Methods The instrument shall be capable of being set to 0.1 kV and shall
C 536 and C 537. have an insulated cable and probe and a means for indicating
1.2 Values stated in SI units are to be regarded as the (light, meter, or bell) a voltage discharge. Before use in this
standard. Inch-pound units are provided for information only. test, the high-voltage discharge test instrument shall be cali-
1.3 This standard does not purport to address all of the brated in accordance with the procedure set forth in Annex A1.
safety problems, if any, associated with its use. It is the 4.3 A test probe constructed of 100 mesh wire gauze as
responsibility of the user of this standard to establish appro- illustrated in Fig. 1.
priate safety and health practices and determine the applica-
5. Test Specimens
bility of regulatory limitations prior to use.
5.1 Porcelain enameled specimens of any size may be used
2. Referenced Documents
in this test. The enamel shall be removed from an edge or the
2.1 ASTM Standards: back of the specimen to provide an electrical ground for the test
C 536 Test Method for Continuity of Coatings in Glassed instrument. If the probe is wider than the specimen, the edges
Steel Equipment by Electrical Testing of the specimen shall be masked with electrical insulating tape
C 537 Test Method for Reliability of Glass Coatings on to prevent discharges from occurring at the edges where
Glassed Steel Reaction Equipment by High Voltage porcelain coverage may be light.
3. Terminology 6. Conditioning
3.1 air-gap voltage—the voltage needed to arc through a 6.1 Before testing, wash the specimens with a 1 weight %,
defect that is open to both the surface of the porcelain enamel solution of trisodium phosphate on a soft cellulose sponge,
and the metal substrate. The length of the air gap is estimated rinse with tap water, and then rinse with distilled water. Then
by measuring the enamel thickness. dry the specimens thoroughly in air.
3.2 overvoltage—the difference between an applied test
7. Procedure
voltage and the air-gap voltage for the porcelain enamel being
7.1 Measuring the Enamel Thickness— Measure the enamel
tested.
3.3 RMS voltage—the root mean square voltage, or “aver- thickness at a minimum of three locations on the specimen.
Make these measurements to the nearest 0.03 mm (1.0 mil) in
age” voltage, shown on ac test meters.
3.4 peak voltage—for ac meters, the voltage that will accordance with the operating instructions for the thickness
gage. Use the maximum value obtained as the enamel thick-
discharge across the air gap or across a defect. The peak
voltage is the RMS voltage multiplied by 1.414. ness.
1 3
This test method is under the jurisdiction of ASTM Committee B-8 on Metallic Suitable test equipment is available from Associated Research, Inc., 8221 North
and Inorganic Coatings and is the direct responsibility of Subcommittee B08.12 on Kimble Ave., Skokie, IL 60076 and The Pfaudler Co., Div. of Sohio, 1000 West
Materials for Porcelain Enamel and Ceramic-Metal Systems. Ave., Rochester, NY 14603.
Current edition approved Aug. 28, 1987. Published October 1987. Originally Suitable probes are available from Associated Research, Inc., 8221 North
published as C 743 – 73. Last previous edition C 743 – 79. Kimble Ave., Skokie, IL 60076 and The Pfaudler Co., Div. of Sohio, 1000 West
Annual Book of ASTM Standards, Vol 02.05. Ave., Rochester, NY 14603.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
C 743
FIG. 1 Test Probe
7.2 Selecting the Test Voltage—The test voltage to be used 7.2.3.1 DC Test Instruments—Determine the test voltage in
depends upon the purpose for conducting the test. The test can accordance with 7.2.2, substituting the specified overvoltage
be used to determine (1) the presence of defects open to both
for the selected overvoltage as in 7.2.2.2 and 7.2.2.3.
the enamel surface and the base metal, ( 2) the location of areas
7.2.3.2 AC Test Instruments—Divide the specified overvolt-
of light coverage in addition to defects open to both the enamel
age by 1.414, then determine the test voltage as in 7.2.2,
surface and the base metal, or (3) compliance with a specifi-
substituting the specified overvoltage divided by 1.414 for the
cation. According to the user’s purpose for conducting the test,
selected overvoltage as in 7.2.2.2 and 7.2.2.3.
the following three instructions correspond respectively to (1),
7.2.3.3 Probe the specimen as shown in 7.3.
(2), or ( 3) above:
7.3 Probing the Specimens:
7.2.1 Test Method A—For Open Defects:
7.2.1.1 Determine the air-gap voltage that corresponds to 7.3.1 Connect the ground wire of test instrument to the base
the enamel thickness from the calibration curve described in metal of the specimen.
the annex. This value is the test voltage.
7.3.2 Turn on the test instrument.
7.2.1.2 Probe the specimen in accordance with 7.3.
7.3.3 Set the output voltage (as indicated on the built-in
7.2.2 Test Method B—For Light Coverage and Open De-
voltmeter) to the value selected in 7.2.
fects:
7.3.4 Let the voltage stabilize for 15 s.
7.2.2.1 Determine the air-gap voltage that co
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.