ASTM B78-90(2001)
(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
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 establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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NOTICE: This standard has either been superseded and replaced by a new version or withdrawn. Contact ASTM
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Designation:B78–90(Reapproved2001)
Standard Test Method of
Accelerated Life of Iron-Chromium-Aluminum Alloys for
Electrical Heating
ThisstandardisissuedunderthefixeddesignationB 78;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginal
adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.Asuperscript
epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope the wire specimen when secured therein shall be in a U-shaped
pattern as described in Section 5. The specimen terminal
1.1 This test method covers the determination of the resis-
junctions shall be 3 in. (76.2 mm) lower than the plane of the
tance to oxidation of iron-chromium-aluminum electrical heat-
top of the enclosure.
ing alloys at elevated temperatures under intermittent heating
using a constant-temperature cycle test. This test is used for
4. Apparatus
internal comparative purposes only.
4.1 The apparatus shall be similar to the requirements
1.2 The values stated in inch-pound units are to be regarded
specified in 4.2 to 4.8, inclusive, and shall be connected as
as the standard. The metric equivalents of inch-pound units
shown in Fig. 2.
may be approximate.
4.2 Power Supply—The transformer or motor generator set
1.3 This standard does not purport to address all of the
shall be capable of delivering a controlled voltage of from 10
safety concerns, if any, associated with its use. It is the
to 35 V to the circuit. It shall have a continuous current
responsibility of the user of this standard to establish appro-
capacity of at least 20 A/specimen.
priate safety and health practices and determine the applica-
4.3 VoltageControl—Theautomaticvoltagecontrolshallbe
bility of regulatory limitations prior to use.
capable of maintaining across the bus bars a constant voltage
2. Significance and Use within 60.5 %.
2.1 This test method is used by producers of electrical
NOTE 1—It has been found impossible to make accurate tests without
heating alloys to measure the cyclic oxidation resistance of voltage control, as changes in line voltage are sufficient to cause
considerable variation in the results obtained (see Annex A1).
these alloys.
2.2 Because of the effect of environment, design and use,
4.4 Variable Transformer—The variable transformer shall
the life values obtained from this test method may not correlate
be capable of adjusting the voltage across the specimen to
with that of an appliance or industrial heating unit.
within approximately 0.25 % of any desired value within the
working range and shall have a continuous current rating of
3. Test Panel
approximately 25 A.
3.1 Size and Location—The dimensions of the test panel
NOTE 2—A variable transformer having a working range of adjustabil-
shall be similar to those shown in Fig. 1.The test panel shall be
ity from approximately 0 to 20 V, provides for testing wires within a
located in a position free from drafts of air.
considerable range of size and resistivity.
3.1.1 The enclosure shall fit tightly on the panel and the
4.5 Ammeter and Voltmeter—The ammeter and voltmeter
glass slide shall fit snugly to prevent leakage of air at this point
shall have an accuracy of 1 % of normal test deflection
during the operation of the test, as even a slight draft of air in
(approximately 15 A and 15 V respectively). For alternating
contact with the specimen will cause excessive variation in
current the range shall be such as to give a reading above the
length of life.Ascreen of 40 wire mesh, 0.010-in. (0.025 mm)
lower fifth of the scale range. The ammeter has appreciable
wire diameter, market grade, may be used as a cover over the
resistance. A compensating resistance shall be cut into the
individual stations.
circuit to replace the resistance of the ammeter so that the
3.2 Terminals—The two terminals shall be spaced 2 in.
over-all resistance of the circuit is not changed. This resistance
(50.8mm)apart,centertocenterandshallbesopositionedthat
shall be inserted in series with the contact of the upper switch
shown in Fig. 2.
This test method is under the jurisdiction of ASTM Committee B02 on 4.6 Optical Pyrometer or Infrared Thermometer—The op-
Nonferrous Metals and Alloys and is the direct responsibility of Subcommittee
tical system shall be such as to provide a magnification of at
B02.10 on Thermostat Metals.
least four diameters. This may be accomplished by means of a
Current edition approved June 29, 1990. Published August 1990. Originally
special lens or combination of two standard lenses in the
published as B 78 – 59 T. Last previous edition B 78 – 81.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
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.
B78–90 (2001)
Metric Equivalents
in. mm
⁄2 12.7
5 ⁄32 131.0
7 ⁄4 184.2
21 ⁄2 546
22 559
52 1321
64 1626
FIG. 1 Test Panel
objective to provide a short focal length and the desired 5. Test Specimen
magnification (seeAnnexA1).These instruments must have an
5.1 The test specimen shall be 0.0254 in. (0.645 mm) in
accuracy of 610°F (5.5°C) and UBS traceability.
diameter. The length of the wire selected for test shall be such
NOTE 3—It is highly important that the temperatures of the test
as to give a test length of approximately 10 in. (254 mm).
specimen be adjusted as accurately as possible, as small variations in
5.2 The test specimen shall be representative with regard to
temperature result in considerable variation in length of life. Optical
thesurfaceoftheaverageofthecoilorspoolofwirewhichhas
pyrometer or infrared pycnometer makes it possible to determine the
been selected for test. Particular care shall be taken to see that
temperature at any particular point on the wire, and with the arrangement
the specimen selected is free from kinks. This precaution is
described, the temperature of a comparatively small wire may be taken
quite readily.
necessary, since a kink, even though later removed may cause
burnout at that point.
4.7 Interrupter—Some form of apparatus shall be used as
an interrupter to open and close the circuit.
NOTE 4—It is also very desirable to select and keep as a reference
4.8 Apparatus for Recording Time of Burnout—If no appa-
standard for comparison, a spool or coil of wire that is uniform in cross
ratus is available for recording the time of burnout, arrange-
section from one end to the other. Tests may then be made at any time on
ments shall be made for hourly observations for burnouts. the reference standard, and if conditions have changed they will be noted
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.
B78–90 (2001)
9.5 Adjust the temperature of the specimen to 2000°F
(1093°C).
9.6 Allow the specimen to operate under this condition until
2 h have elapsed, in order to bring the emissivity nearer to a
black body condition.
9.7 Set the temperature of the specimen to 2200°F
(1204°C). Maintain this balance until 1 min has elapsed.
9.8 After another 13 min, readjust the temperature of the
specimen to 2250°F (1232°C). Final adjustment shall be
completed within the next minute or a total of 15 min. The end
of this 15-min period is the start of the test. It is important to
maintain this time schedule.
9.9 Measure the voltage and the current and record the
values together with the starting temperature and time of
starting the test.
9.10 Start the interrupter, the timing device of which shall
have been previously regulated so that the “on” period and the
“off” period shall be equal and shall each have a duration of 2
FIG. 2 Electrical Circuit Diagram for Accelerated Life Test
min.
NOTE 7—Various cycles have been tried varying from 10 min on and 5
by the length of life of the standard. Comparisons between tests made at
min off to 30 s on and 30 s off, whence it was found that the 2-min-on and
different times on the standards and other wires may be correlated in this
2-min-off
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