ASTM C743-87(2014)e1

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
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Designation: C743 − 87 (Reapproved 2009) C743 − 87 (Reapproved 2014)
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.
ε NOTE—Introduction was added and minor units abbreviations corrected editorially in June 2014.
INTRODUCTION
This test provides a means to evaluate a porcelain enamel coating for pinholes, discontinuities, and
insufficient application to better assess the ability of the coating to protect the substrate.
1. 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 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.
2. Referenced Documents
2.1 ASTM Standards:
C536 Test Method for Continuity of Coatings in Glassed Steel Equipment by Electrical Testing
C537 Test Method for Reliability of Glass Coatings on Glassed Steel Reaction Equipment by High Voltage
3. Terminology
3.1 air-gap voltage—voltage needed to arc through a defect that is open to both the surface of the porcelain enamel and the
metal substrate. The length of the air gap is estimated by measuring the enamel thickness.
3.2 overvoltage—difference between an applied test voltage and the air-gap voltage for the porcelain enamel being tested.
3.3 RMS voltage—root mean square voltage, or “average” voltage, shown on ac test meters.
3.4 peak voltage—for ac meters, the voltage that will discharge across the air gap or across a defect. The peak voltage is the
RMS voltage multiplied by 1.414.
4. Apparatus
4.1 A nondestructive coating thickness gage with a range of at least 0 to 0.5 mm in 0.03-mm 0.03 mm increments (0 to 20 mils
in 1.0-mil 1.0 mil increments).
4.2 Either an ac or a dc high-voltage discharge test instrument with a continuously variable output voltage over the range of
at least 0 to 4 kV as indicated on a built-in voltmeter. The instrument shall be capable of being set to 0.1 kV and shall have an
insulated cable and probe and a means for indicating (light, meter, or bell) a voltage discharge. Before use in this test, the
high-voltage discharge test instrument shall be calibrated in accordance with the procedure set forth in Annex A1.
This test method is under the jurisdiction of ASTM Committee B08 on Metallic and Inorganic Coatingsand is the direct responsibility of Subcommittee B08.12 on
Materials for Porcelain Enamel and Ceramic-Metal Systems.
Current edition approved April 15, 2009May 1, 2014. Published June 2009 June 2014. Originally approved in 1973. Last previous edition approved in 20042009 as
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C743 – 87 (2004)(2009). . DOI: 10.1520/C0743-87R09.10.1520/C0743-87R14E1.
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volume information, refer to the standard’s Document Summary page on the ASTM website.
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C743 − 87 (2014)
4.3 A test probe constructed of 100 mesh wire gauze as illustrated in Fig. 1.
5. Test Specimens
5.1 Porcelain enameled specimens of any size may be used in this test. The enamel shall be removed from an edge or the back
of the specimen to provide an electrical ground for the test instrument. If the probe is wider than the specimen, the edges of the
specimen shall be masked with electrical insulating tape to prevent discharges from occurring at the edges where porcelain
coverage may be light.
6. Conditioning
6.1 Before testing, wash the specimens with a 1 weight %, solution of trisodium phosphate on a soft cellulose sponge, rinse with
tap water, and then rinse with distilled water. Then dry the specimens thoroughly in air.
7. Procedure
7.1 Measuring the Enamel Thickness—Measure the enamel thickness at a minimum of three locations on the specimen. Make
these measurements to the nearest 0.03 mm (1.0 mil) in accordance with the operating instructions for the thickness gage. Use the
maximum value obtained as the enamel thickness.
7.2 Selecting the Test Voltage—The test voltage to be used depends upon the purpose for conducting the test. The test.The test
can be used to determine (1) the presence of defects open to both the enamel surface and the base metal, (2) the location of areas
of light coverage in addition to defects open to both the enamel surface and the base metal, or (3) compliance with a specification.
According to the user’s purpose for conducting the test, the following three instructions correspond respectively to (1), (2), or (3)
above:
7.2.1 Test Method A—For Open Defects:
7.2.1.1 Determine the air-gap voltage that corresponds to the enamel thickness from the calibration curve described in the
annex. This value is the test voltage.
7.2.1.2 Probe the specimen in accordance with 7.3.
7.2.2 Test Method B—For Light Coverage and Open Defects:
7.2.2.1 Determine the air-gap voltage that corresponds to the enamel thickness from the calibration curve described in the
annex.
7.2.2.2 Arbitrarily select the overvoltage to be used. (Increasingly smaller defects are located with this test as the overvoltage
is increased. Therefore, confidence that ware passing this test will have a long, corrosion-free service life is increased as the
overvoltage is increased.)
FIG. 1 Test Probe
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C743 − 87 (2014)
7.2.2.3 Add the selected overvoltage to the air-gap voltage. This value is the test voltage.
7.2.2.4 Probe the specimen in accordance with 7.3.
7.2.3 Test Method C—For Compliance with a
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