ASTM C537-87(2004)e1
(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
SIGNIFICANCE AND USE
The widespread use of glassed-steel equipment in highly corrosive chemical processes has made it necessary to detect weak spots in the coating and repair them before catastrophic failure occurs in service. This test is intended to detect discontinuities and thin areas in a glass coating on metal to ensure that the coating is defect free and has sufficient thickness to withstand the prescribed service conditions. A test voltage may be selected at any desired value up to 20 000 V, thus making the test applicable to a wide range of thickness requirements. When, because of bubbles or defects, the thickness of glass at any spot is less than enough to withstand the applied voltage, a puncture results with an accompanying indication of a defect. Remedial action is then required to repair the defect before the equipment can be used for corrosive service. (When such defects are found before the equipment leaves the manufacturer’plant another application of glass can usually be applied and fired to become an integral part of the coating.)
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.
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 .
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Designation:C537–87(Reapproved2004)
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.
e NOTE—Keywords were added editorially in September 2004.
1. Scope conducting inclusion, etc.) so that the dielectric strength of the
remaining glass is less than some preset desired amount, the
1.1 This test method covers the determination of the reli-
dielectricstrengthofair-plus-remaining-glassbreaksdownand
ability of glass coating on metal and is intended for use by
a discharge occurs. Built-in current-limiting devices ensure
manufacturers of equipment that is designed to withstand
electrical safety to the operator. A variable voltage control
highly corrosive conditions where a failure of the coating in
allows selection of a voltage which assures a predetermined
service would cause extreme damage to the exposed metal. Its
minimum thickness of glass.
use outside the manufacturer’s plant is discouraged because
improper or indiscriminate testing can cause punctures that are
4. Significance and Use
difficult to repair without returning the equipment to the
4.1 Thewidespreaduseofglassed-steelequipmentinhighly
manufacturer’s plant. This test method detects not only exist-
corrosive chemical processes has made it necessary to detect
ingdiscontinuitiesintheglasscoating,butalsoareaswherethe
weak spots in the coating and repair them before catastrophic
glass may be thin enough to be likely to result in premature
failure occurs in service. This test is intended to detect
failure in service.
discontinuities and thin areas in a glass coating on metal to
1.2 This standard does not purport to address all of the
ensure that the coating is defect free and has sufficient
safety concerns, if any, associated with its use. It is the
thickness to withstand the prescribed service conditions.Atest
responsibility of the user of this standard to establish appro-
voltage may be selected at any desired value up to 20 000 V,
priate safety and health practices and determine the applica-
thus making the test applicable to a wide range of thickness
bility of regulatory limitations prior to use. For specific
requirements. When, because of bubbles or defects, the thick-
precautionary statements, see Section 7.
ness of glass at any spot is less than enough to withstand the
2. Terminology applied voltage, a puncture results with an accompanying
indication of a defect. Remedial action is then required to
2.1 Definition:
repair the defect before the equipment can be used for
2.1.1 glassed steel, glass-lined steel, or glass-coated steel—
corrosive service. (When such defects are found before the
designations generally applied to a class of porcelain enamels
equipment leaves the manufacturer’s plant another application
that have high resistance to chemical attack at elevated
of glass can usually be applied and fired to become an integral
temperatures and pressures.
part of the coating.)
3. Summary of Test Method
5. Interferences
3.1 This test method consists essentially of grounding the
5.1 Sincethetestmethodiselectrical,itisnecessarytohave
metal structure of the equipment to the ground side of a
a good ground connection between the instrument and the
direct-current high-voltage generator and sweeping the glass
metal substrate of the equipment being tested. It is also
surface with a high-potential probe on the end of an insulated
necessary that the surface of the glass be reasonably clean and
handle and cable. Wherever a discontinuity exists or the
dry. A wet surface will conduct enough of the high voltage to
coating is thin enough (by reason of a concealed bubble or
any exposed metal, including the edges of the glass coating, so
that an indication of a “contact” may be obtained over a large
This test method is under the jurisdiction ofASTM CommitteeB08 on Metallic
area instead of at localized spots that can be marked and
and Inorganic Coatings and is the direct responsibility of SubcommitteeB08.12 on
identified for repair.
Materials for Porcelain Enamel and Ceramic-Metal Systems.
Current edition approved Aug. 1, 2004. Published September 2004. Originally
approved in 1964. Last previous edition approved in 1998 as C 537 – 87 (1998).
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
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C537–87 (2004)
FIG. 1 Circuit Diagram, 20000-V D-C Tester
6. Apparatus 7.4 Unless the surface to be tested is clean and dry, there
may be sufficient conduction along the surface to cause a
6.1 Thetesteriscomposedofasourceofhigh-voltagedirect
capacitance discharge even if there is no direct path to ground.
current with a suitable device to limit the current. A constant-
Such a capacitance discharge is recognizable from a true
voltage transformer is used to supply a more uniform voltage
failure because the discharge spark is not confined to certain
source than the usual 115-V, 60-Hz line to which it is
spotsbutisageneraldischargetoalargeareaofthemoistglass
connected.The power supply unit consists of a suitable step-up
surface. Continuous application of the probe to such areas
transformer along with a voltage-control device, a current-
serves only to build up a capacitance charge on the surface of
limiting rheostat, a rectifier, and appropriate safety and remote
the vessel eventually resulting in a discharge through the
control r
...
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