ASTM C537-87(1998)
(Test Method)Standard Test Method for Reliability of Glass Coatings on Glassed Steel Reaction Equipment by High Voltage
Standard Test Method for Reliability of Glass Coatings on Glassed Steel Reaction Equipment by High Voltage
SCOPE
1.1 This test method covers the determination of the reliability of glass coating on metal and is intended for use by manufacturers of equipment that is designed to withstand highly corrosive conditions where a failure of the coating in service would cause extreme damage to the exposed metal. Its use outside the manufacturer's plant is discouraged because improper or indiscriminate testing can cause punctures that are difficult to repair without returning the equipment to the manufacturer's plant. This test method detects not only existing discontinuities in the glass coating, but also areas where the glass may be thin enough to be likely to result in premature failure in service.
1.2 This standard does not purport to address all of the safety concerns, 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. For specific precautionary statements, see Section 7.
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Designation: C 537 – 87 (Reapproved 1998)
Standard Test Method for
Reliability of Glass Coatings on Glassed Steel Reaction
Equipment by High Voltage
This standard is issued under the fixed designation C 537; 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 handle and cable. Wherever a discontinuity exists or the
coating is thin enough (by reason of a concealed bubble or
1.1 This test method covers the determination of the reli-
conducting inclusion, etc.) so that the dielectric strength of the
ability of glass coating on metal and is intended for use by
remaining glass is less than some preset desired amount, the
manufacturers of equipment that is designed to withstand
dielectric strength of air-plus-remaining-glass breaks down and
highly corrosive conditions where a failure of the coating in
a discharge occurs. Built-in current-limiting devices ensure
service would cause extreme damage to the exposed metal. Its
electrical safety to the operator. A variable voltage control
use outside the manufacturer’s plant is discouraged because
allows selection of a voltage which assures a predetermined
improper or indiscriminate testing can cause punctures that are
minimum thickness of glass.
difficult to repair without returning the equipment to the
manufacturer’s plant. This test method detects not only exist-
4. Significance and Use
ing discontinuities in the glass coating, but also areas where the
4.1 The widespread use of glassed-steel equipment in highly
glass may be thin enough to be likely to result in premature
corrosive chemical processes has made it necessary to detect
failure in service.
weak spots in the coating and repair them before catastrophic
1.2 This standard does not purport to address all of the
failure occurs in service. This test is intended to detect
safety concerns, if any, associated with its use. It is the
discontinuities and thin areas in a glass coating on metal to
responsibility of the user of this standard to establish appro-
ensure that the coating is defect free and has sufficient
priate safety and health practices and determine the applica-
thickness to withstand the prescribed service conditions. A test
bility of regulatory limitations prior to use. For specific
voltage may be selected at any desired value up to 20 000 V,
precautionary statements, see Section 7.
thus making the test applicable to a wide range of thickness
2. Terminology requirements. When, because of bubbles or defects, the thick-
ness of glass at any spot is less than enough to withstand the
2.1 Definition:
applied voltage, a puncture results with an accompanying
2.1.1 glassed steel, glass-lined steel, or glass-coated steel—
indication of a defect. Remedial action is then required to
designations generally applied to a class of porcelain enamels
repair the defect before the equipment can be used for
that have high resistance to chemical attack at elevated
corrosive service. (When such defects are found before the
temperatures and pressures.
equipment leaves the manufacturer’s plant another application
3. Summary of Test Method of glass can usually be applied and fired to become an integral
part of the coating.)
3.1 This test method consists essentially of grounding the
metal structure of the equipment to the ground side of a
5. Interferences
direct-current high-voltage generator and sweeping the glass
5.1 Since the test method is electrical, it is necessary to have
surface with a high-potential probe on the end of an insulated
a good ground connection between the instrument and the
metal substrate of the equipment being tested. It is also
This test method is under the jurisdiction of ASTM CommitteeB-8 on Metallic necessary that the surface of the glass be reasonably clean and
and Inorganic Coatings and is the direct responsibility of SubcommitteeB08.12 on
dry. A wet surface will conduct enough of the high voltage to
Materials for Porcelain Enamel and Ceramic-Metal Systems.
any exposed metal, including the edges of the glass coating, so
Current edition approved Aug. 28, 1987. Published October 1987. Originally
published as C 537 – 64 T. Last previous edition C 537 – 82.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
C 537 – 87 (1998)
FIG. 1 Circuit Diagram, 20 000-V D-C Tester
that an indication of a “contact” may be obtained over a large ducting surfaces may lead to personnel at some distance from
area instead of at localized spots that can be marked and the probe. Discharge the probe tip by grounding it after turning
identified for repair. off the instrument and before changing probe tips. Although the
current is low enough to be electrically safe, the involuntary
6. Apparatus
reaction from a surprise discharge might cause injury.
6.1 The tester is composed of a source of high-voltage direct 7.4 Unless the surface to be tested is clean and dry, there
may be sufficient conduction along the surface to cause a
current with a suitable device to limit the current. A constant-
voltage transformer is used to supply a more uniform voltage capacitance discharge even if there is no direct path to ground.
Such a capacitance discharge is recognizable from a true
source than the usual 115-V, 60-Hz line to which it is
connected. The power supply unit consists of a suitable step-up failure because the discharge spark is not confined to certain
spots but is a general discharge to a large area of the moist glass
transformer along with a voltage-control device, a current-
limiting rhe
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