ASTM B78-90(2007)
(Test Method)Standard Test Method of Accelerated Life of Iron-Chromium-Aluminum Alloys for Electrical Heating
Standard Test Method of Accelerated Life of Iron-Chromium-Aluminum Alloys for Electrical Heating
SIGNIFICANCE AND USE
This test method is used by producers of electrical heating alloys to measure the cyclic oxidation resistance of these alloys.
Because of the effect of environment, design and use, the life values obtained from this test method may not correlate with that of an appliance or industrial heating unit.
SCOPE
1.1 This test method covers the determination of the resistance to oxidation of iron-chromium-aluminum electrical heating alloys at elevated temperatures under intermittent heating using a constant-temperature cycle test. This test is used for internal comparative purposes only.
1.2 The values stated in inch-pound units are to be regarded as the standard. The metric equivalents of inch-pound units may be approximate.
1.3 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 become familiar with all hazards including those identified in the appropriate Material Safety Data Sheet (MSDS) for this product/material as provided by the manufacturer, to establish appropriate safety and health practices, and determine the applicability of regulatory limitations prior to use.
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Designation: B78 − 90 (Reapproved2007)
Standard Test Method of
Accelerated Life of Iron-Chromium-Aluminum Alloys for
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Electrical Heating
This standard is issued under the fixed designation B78; the number immediately following the designation indicates the year of original
adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.Asuperscript
epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope length of life.Ascreen of 40 wire mesh, 0.010-in. (0.025 mm)
wire diameter, market grade, may be used as a cover over the
1.1 This test method covers the determination of the resis-
individual stations.
tance to oxidation of iron-chromium-aluminum electrical heat-
ing alloys at elevated temperatures under intermittent heating 3.2 Terminals—The two terminals shall be spaced 2 in.
(50.8mm)apart,centertocenterandshallbesopositionedthat
using a constant-temperature cycle test. This test is used for
internal comparative purposes only. the wire specimen when secured therein shall be in a U-shaped
pattern as described in Section 5. The specimen terminal
1.2 The values stated in inch-pound units are to be regarded
junctions shall be 3 in. (76.2 mm) lower than the plane of the
as the standard. The metric equivalents of inch-pound units
top of the enclosure.
may be approximate.
4. Apparatus
1.3 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
4.1 The apparatus shall be similar to the requirements
responsibility of the user of this standard to become familiar
specified in 4.2 to 4.8, inclusive, and shall be connected as
with all hazards including those identified in the appropriate
shown in Fig. 2.
Material Safety Data Sheet (MSDS) for this product/material
4.2 Power Supply—The transformer or motor generator set
as provided by the manufacturer, to establish appropriate
shall be capable of delivering a controlled voltage of from 10
safety and health practices, and determine the applicability of
to 35 V to the circuit. It shall have a continuous current
regulatory limitations prior to use.
capacity of at least 20 A/specimen.
4.3 Voltage Control—The automatic voltage control shall be
2. Significance and Use
capable of maintaining across the bus bars a constant voltage
2.1 This test method is used by producers of electrical
within 60.5 %.
heating alloys to measure the cyclic oxidation resistance of
NOTE 1—It has been found impossible to make accurate tests without
these alloys.
voltage control, as changes in line voltage are sufficient to cause
2.2 Because of the effect of environment, design and use, considerable variation in the results obtained (see Annex A1).
the life values obtained from this test method may not correlate
4.4 Variable Transformer—The variable transformer shall
with that of an appliance or industrial heating unit.
be capable of adjusting the voltage across the specimen to
within approximately 0.25 % of any desired value within the
3. Test Panel
working range and shall have a continuous current rating of
approximately 25 A.
3.1 Size and Location—The dimensions of the test panel
shall be similar to those shown in Fig. 1.The test panel shall be
NOTE 2—A variable transformer having a working range of adjustabil-
located in a position free from drafts of air.
ity from approximately 0 to 20 V, provides for testing wires within a
considerable range of size and resistivity.
3.1.1 The enclosure shall fit tightly on the panel and the
glass slide shall fit snugly to prevent leakage of air at this point
4.5 Ammeter and Voltmeter—The ammeter and voltmeter
during the operation of the test, as even a slight draft of air in shall have an accuracy of 1 % of normal test deflection
contact with the specimen will cause excessive variation in
(approximately 15 A and 15 V respectively). For alternating
current the range shall be such as to give a reading above the
lower fifth of the scale range. The ammeter has appreciable
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resistance. A compensating resistance shall be cut into the
This test method is under the jurisdiction of ASTM Committee B02 on
Nonferrous Metals and Alloys and is the direct responsibility of Subcommittee
circuit to replace the resistance of the ammeter so that the
B02.10 on Thermostat Metals and Electrical Resistance Heating Materials.
over-all resistance of the circuit is not changed. This resistance
Current edition approved May 1, 2007. Published May 2007. Originally
shall be inserted in series with the contact of the upper switch
approved in 1959. Last previous edition approved in 2001 as B78 – 90 (2001). DOI:
10.1520/B0078-90R07. shown in Fig. 2.
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