ASTM C356-22

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Designation: C356 − 17 C356 − 22
Standard Test Method for
Linear Shrinkage of Preformed High-Temperature Thermal
Insulation Subjected to Soaking Heat
This standard is issued under the fixed designation C356; 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.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope
1.1 This test method covers the determination of the amount of linear shrinkage and other changes that occur when a preformed
thermal insulating material is exposed to soaking heat. This test method is limited to preformed high-temperature insulation that
is applicable to hot-side temperatures in excess of 150°F (66°C), with the exception of insulating fire brick which is covered by
Test Method C210.
1.2 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical
conversions to SI units that are provided for information only and are not considered standard.
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 safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.4 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
C168 Terminology Relating to Thermal Insulation
C210 Test Method for Reheat Change of Insulating Firebrick
C411 Test Method for Hot-Surface Performance of High-Temperature Thermal Insulation
3. Terminology
3.1 Definitions—Terminology C168 shall apply to the terms used in this test method.
4. Significance and Use
4.1 Linear shrinkage, as used in this test method, refers to the change in linear dimensions that has occurred in test specimens after
they have been subjected to soaking heat for a period of 24 h and then cooled to room temperature.
This test method is under the jurisdiction of ASTM Committee C16 on Thermal Insulation and is the direct responsibility of Subcommittee C16.31 on Chemical and
Physical Properties.
Current edition approved May 1, 2017May 1, 2022. Published June 2017May 2022. Originally approved in 1960. Last previous edition approved in 20102017 as
C356 – 10.C356 – 17. DOI: 10.1520/C0356-17.10.1520/C0356-22.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
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C356 − 22
4.2 Most insulating materials will begin to shrink at some definite temperature. Usually the amount of shrinkage increases as the
temperature of exposure becomes higher. Eventually a temperature will be reached at which the shrinkage becomes excessive. With
excessive shrinkage, the insulating material has definitely exceeded its useful temperature limit. When an insulating material is
applied to a hot surface, the shrinkage will be greatest on the hot face. The differential shrinkage which results between the hotter
and the cooler surfaces often introduces strains and may cause the insulation to warp. High shrinkage may cause excessive warpage
and thereby may induce cracking, both of which are undesirable. High shrinkage may also open gaps at the insulation joints to
an excessive extent rendering the application less efficient and more hazardous. In order to predict the limit of permissible
shrinkage in service, the degree of linear shrinkage to be tolerated by specimens of an insulating material when subjected to
soaking heat must be determined from experience.
4.3 It is recognized that a fixed relation between linear shrinkage under soaking heat and actual shrinkage in service cannot be
established for different types of insulating materials. Generally the amount of shrinkage increases with time of exposure. The
amount and rate of increase varies from one material to another. In addition, the various types of materials may have different
amounts of maximum permissible shrinkage. Therefore, each product must define its own specific limits of linear shrinkage under
soaking heat.
5. Apparatus
5.1 Furnace—A gas-fired or electrically heated muffle furnace, having a size sufficient to accommodate at least four test specimens
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and two dummyguard specimens, 6 by 2 ⁄2 by 1 ⁄2 in. (152.4 by 63.5 by 38.1 mm) (Note 1), spaced so as to allow a clearance of
at least ⁄2 in. (12.7 mm) on all surfaces of every test specimen. The guard specimens shall be placed in such a manner to protect
the test specimen from open flames or exposed heating elements of the furnace. The temperature of the furnace shall be controlled
throughout the volume occupied by the specimens to within 6 1 % of the desired temperature. A furnace-temperature indicator
or recorder is required.
NOTE 1—If the structure is not homogeneous throughout its thickness, or if thinner materials are under test, then test the specimen at the original thickness.
For smaller ovens, unable to accommodate the required number of specimens, it will be necessary to make several test batches in order to secure the
minimum number of specimens required.
5.2 Oven—A controlled-temperature conditioning oven with range up to at least 250°F (121°C).
5.3 Specimen-Measuring Apparatus—An instrument suitable for measuring a gauge length up to 6 in. (152.4 mm), and having an
accuracy of measurement of 0.002 in. (0.05 mm) or better. Care must be taken, by the use of proper measuring techniques, to
ensure reproduction of any measurement to within 0.01 in. (0.2 mm). It is particularly important to avoid crushing the ends of the
specimens during measurement, especially in the case of soft materials.
NOTE 2—Reference points, such as pins, inserted near the ends of the specimen, serve to improve reproducibility without specimen damage; or it is
acceptable to insert metal strips may be inserted between the specimen ends and the jaws of the caliper. Suggested instruments are dilatometers, vernier
caliper, or comparators. One suitable type of comparator is equipped with a fine adjustment. It has a long-range, continuous dial indicator. The dial is
attached to a wide-face ( ⁄2-in. (12.7-mm) diameter flat) button point which is held against the specimen by internal spring pressure. When the point is
lifted ⁄2 in. (12.7 mm), the pressure is about 50 g, corresponding to a bearing force of 0.6 psi (4.8 kPa), and suitable for very soft materials. For harder
materials, an additional weight of 0.25 lb (0.114 kg) may be applied, making the load of the specimen, at ⁄2 in. (12.7 mm) compression of the spring,
about 1.9 psi (13.1 kPa). Directly beneath the button point is another wide-face button point tapped to the base of the comparator. The comparator is
adjustable and requires a set of steel shaftings, ⁄2 in. (12.7 mm) in diameter, having lengths at 1-in. (25.4-mm) intervals from 1 to 6 in. (25.4 to 152.4
mm), to zero the comparator accurately.
5.4 Balance—A balance, having an accuracy of 0.01 g, for weighing the specimen before and after heating.
6. Sampling and Preparation of Test Specimens
6.1 All samples that will be required to complete the tests shall be selected at one time and in such a manner as to be representative
of the average of the material.
6.2 Specimens for any one test condition shall be selected from the original sample lot so as to be as representative as possible.
The specimens shall be cut or sawed from full-size pieces in such a manner that they will be fully representative of the entire,
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full-size piece as well as of the material generally. These specimens shall be cut to size 6 by 2 ⁄2 by 1 ⁄2 in. (152.4 by 63.5 by 38.1
mm), in such a manner that the length and width are cut parallel to the length and width, respectively, of the original, full-size piece.
C356 − 22
If it is impossible to faithfully represent the material by cutting to a 1 ⁄2-in. (38.1-mm) thick specimen, or for thinner pieces, then
the original thickness of the material shall be tested. Rectangular specimens cut
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