Designation: F 38 – 00

Standard Test Methods for

Creep Relaxation of a Gasket Material1
This standard is issued under the fixed designation F 38; 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.

This standard has been approved for use by agencies of the Department of Defense.

1. Scope Relaxometer, Method B (F 38)7

1.1 These test methods provide a means of measuring the 3. Summary of Test Methods
amount of creep relaxation of a gasket material at a predeter-
mined time after a compressive stress has been applied. 3.1 In both test methods the specimen is subjected to a
1.1.1 Test Method A— Creep relaxation measured by means compressive stress between two platens, with the stress applied
of a calibrated strain gage on a bolt. by a nut and bolt.
1.1.2 Test Method B— Creep relaxation measured by means 3.2 In Test Method A, normally run at room temperature, the
of a calibrated bolt with dial indicator. stress is measured by a calibrated strain gage on the bolt. In
1.2 The values stated in SI units are to be regarded as the running the test, strain indicator readings are taken at intervals
standard. of time, beginning at the loading time, to the end of the test.
1.3 This standard does not purport to address all of the The strain indicator readings are converted to percentages of
safety concerns, if any, associated with its use. It is the the initial stress which are then plotted against the log of time
responsibility of the user of this standard to establish appro- in hours. The percentage of initial stress loss or relaxation can
priate safety and health practices and determine the applica- be read off the curve at any given time, within the limits of the
bility of regulatory limitations prior to use. total test time.
3.3 In Test Method B, run at room or elevated temperatures,
2. Referenced Documents the stress is determined by measuring the change in length of
2.1 ASTM Standards: the calibrated bolt with a dial indicator. The bolt length is
A 193 Specification for Alloy Steel and Stainless Steel measured at the beginning of the test and at the end of the test;
Bolting Materials for High-Temperature Service2 from this the percentage of relaxation is calculated.
B 637 Specification for Precipitation-Hardening Nickel Al-
4. Significance and Use
loy Bars, Forgings, and Forging Stock for High Tempera-
ture Services3 4.1 These test methods are designed to compare related
D 3040 Practice for Preparing Precision Statements for materials under controlled conditions and their ability to
Standards Related to Rubber and Rubber Testing4 maintain a given compressive stress as a function of time. A
F 104 Classification System for Nonmetallic Gasket Mate- portion of the torque loss on the bolted flange is a result of
rials5 creep relaxation. Torque loss can also be caused by elongation
2.2 ASTM Adjuncts: of the bolts, distortion of the flanges, and vibration; therefore,
Relaxometer, Method A (F 38)6 the results obtained should be correlated with field results.
These test methods may be used as a routine test when agreed
upon between the consumer and the producer.
NOTE 1—Test Method B was developed using asbestos gasket materials
and at issuance substantiating data were not available for other gasket
1
These test methods are under the jurisdiction of ASTM Committee F03 on materials.
Gaskets and are the direct responsibility of Subcommittee F03.20 on Methods of
Test. 5. Apparatus
Current edition approved Apr. 10, 2000. Published May 2000. Originally issued
1962 as D 2139. Redesignated in 1963. Last previous edition F 38 – 95. 5.1 Test Method A:
2
3
Annual Book of ASTM Standards, Vol 01.01. 5.1.1 Strain Indicator.8
Annual Book of ASTM Standards, Vol 02.04.
4
Discontinued—see 1986 Annual Book of ASTM Standards, Vols 09.01 and
5.1.2 Timer.
09.02.
5
Annual Book of ASTM Standards, Vol 09.02.
6 7
A print of this apparatus is available at a nominal cost from ASTM, 100 Barr Detailed working drawings of this apparatus are available from ASTM. Order
Harbor Drive, Conshohocken, PA 19428. Request Adjunct No. ADJF003801. Adjunct No. ADJF003802.

Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.

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5.1.3 Relaxometer,6 composed of two platens, upper and 6.2.3 For Type 4 Class 2 materials, specimen size shall be
lower; a bolt, with mounted strain gage; and a thrust bearing as one continuous length of 152.4 mm (6.0 in.).
shown in Fig. 1. 6.3 A minimum of three tests shall be conducted.
5.1.4 Strain Gages,9 120 V resistance with a gage factor of 6.4 Nominal thickness of specimen shall be 0.8 mm (0.03
2.0 6 0.10 %. The gages shall be mounted to indicate tensile in.) unless otherwise agreed upon between the consumer and
strain and positioned to compensate for torque, temperature, the producer. For Type 4 materials the nominal thickness of the
and bending. The gages shall be mounted on the small diameter specimen shall be no greater than 1.78 mm (0.07 in.).
of the bolt about 50.8 mm (2 in.) from the head. The bolt with
mounted strain gages must be calibrated. 7. Conditioning
5.2 Test Method B: 7.1 Condition cut specimens in accordance with their clas-
5.2.1 Relaxometer,7,10 composed of two platens, special sification as required in Classification F 104.
drilled and calibrated bolt, washer and nut composed of
Specification A 193 Grade B7 or ASTM B 637 Grade UNS 8. Procedure
N07718 or other alloys of construction that would satisfy the 8.1 Test Method A:
calibration procedure (see Annex) for the test temperature 8.1.1 Clean all surfaces, platens, and specimen free of wax,
specified, and a dial indicator assembly as shown in Fig. 2. mold release, and oils. (Remove with isooctane or other
5.2.2 Box End Wrench. suitable solvent.) Lubricate bolt threads.
8.1.2 Use an initial stress of 13.8 6 0.3 MPa (2000 6 50
6. Test Specimen psi) unless otherwise specified.
6.1 Test Method A— The sample size shall be 33.02 6 0.05 8.1.3 Conduct the test at 20 to 30°C (70 to 85°F) unless
mm (1.300 6 0.002 in.) in inside diameter and 52.32 6 0.05 otherwise specified.
mm (2.0606 0.002 in.) in outside diameter. 8.1.4 Disassemble the relaxometer and place the specimen
6.2 Test Method B: between platens. The inside diameter of the specimen should
6.2.1 Specimen size shall be 10.16 6 0.381 mm (0.400 6 be nearly concentric with the inside diameter of the platens.
0.015 in.) wide by 31.75 6 0.381 mm (1.250 6 0.015 in.) long. Screw on the nut and thrust bearing and tighten very slightly,
Four specimens are required per test. by hand, or just enough to hold the specimen in place during
6.2.2 An annular specimen with 1290-mm2 (2.0-in. 2 ) subsequent handling. Mount the head of the bolt in a clamp.
surface area may also be used. A size of 15.62-mm (0.615-in.) 8.1.5 Hook up and balance the strain indicator. Record the
inside diameter by 43.56-mm (1.715-in.) outside diameter is reading. Then set the reading on the strain indicator for the
recommended. specified initial stress. (The microinches that are added to the
above reading will vary the stress and the strain gage bolt
8 calibration.)
A strain recorder such as the Leeds & Northrup Type G is preferred for this
purpose; however, SR-4 strain indicator Models L, K, and N from Baldwin-Lima- 8.1.6 Apply stress to the gasket by tightening the nut with a
Hamilton; HW-1 portable strain indicator from the Budd Co.; and Bridge Amplifier solid wrench until the strain indicator reaches a balance. A
and Meter BAM-1 from Ellis Associates have been found satisfactory. torque of approximately 30 N·m (22 lbf·ft) is required for a
9
Baldwin-Lima-Hamilton Type AB-7 strain gages have been found satisfactory.
10
Dario P. Bernasconi, 40 Farrington St., Stoughton, MA 02072 and Donald G.
compressive force of 17.8 kN (4000 lbf). The stress should be
Johnson, Metal Samples, Route 1, Box 152, Munford, AL 36268 are suppliers of the applied at uniform rate such that at the end of 10 6 2 s the
relaxometer. specified stress is reached. This is called the “initial stress.”

FIG. 1 Relaxometer, Test Method A

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between the platens, being certain that the two ends overlap by
a minimum of 6.35 mm (0.25 in.).
8.2.3 Place the washer in position and screw on the nut,
finger tight.
8.2.4 Screw on the dial indicator assembly, finger tight, and
set the dial indicator at the zero reading.
8.2.5 Apply stress to the specimens by tightening the nut
with a wrench until the desired dial indicator reading is
reached. Record the reading (D0). Apply the stress in one
continuous motion with a maximum loading time of 3 s. A bolt
elongation of 0.1222 to 0.1270 mm (0.00481 to 0.00500 in.) is
typical for a compressive force of 26.7 kN (6000 lbf). Remove
the dial indicator assembly. (The calibration procedure is
outlined in Annex A1.)
NOTE 2—When testing materials thicker than 0.8 mm (0.03 in.), the
time to tighten the nut may be extended to 5 s maximum to allow for the
longer arc required to apply the test load.
8.2.6 Place the specimen unit in a hot air-circulating oven
for 22 h at 100 6 2°C (212 6 3.6°F), unless otherwise
specified. The maximum test temperature for Specification
A 193 Grade B7 shall not exceed 204.4°C (400°F) and the
maximum test temperature for ASTM B 637 Grade UNS
N07718 shall not exceed 482.2°C (900°F).11
8.2.7 Remove from the oven and cool to room temperature.
8.2.8 Replace the dial indicator assembly, finger tight, and
set the dial indicator at the zero reading. Loosen the nut,
without disturbing the dial indicator assembly, and record the
dial reading ( Df).
8.2.9 Calculate the percentage relaxation as follows:
Relaxation, % 5 @~D0 2 Df!/ D 0# 3 100 (1)

9. Report
9.1 Report the following information:
9.1.1 Identification and designation number of the material
tested,
9.1.2 Test temperature,
9.1.3 Length of the test, in hours,
9.1.4 “Initial stress” used, and the specimen thickness,
9.1.5 Percentage stress loss for each specimen, and
FIG. 2 Relaxometer and Dial Indicator Assembly, Test Method B 9.1.6 Average of all the results recorded in 9.1.5.

8.1.7 Beginning at the time of “initial stress,” take strain 10. Precision and Bias 12
indicator readings at intervals of 10 s, 1 min, 6 min, 30 min, 1 10.1 These precision and bias statements have been pre-
h, 5 h, 24 h, etc., or until the end of the test. (Check the zero pared in accordance with Practice D 3040. Please refer to this
of the strain indicator after the test.) practice for terminology and other testing and statistical
8.1.8 Convert the strain indicator readings of 8.1.7 to a concept explanations.
percentage of “initial stress.” Then plot this percentage on 10.2 Seven laboratories tested the following five gasket
semilog paper against the log of time in hours. materials (Classification F 104 material designations) for creep
8.2 Test Method B: relaxation: Type 1, Class 1; Type 1, Class 2; Type 5, Class 1;
8.2.1 Clean all surfaces and lightly lubricate the washer and Type 7, Class 1; Type 7, Class 2. Test Method B, Type 1
bolt threads; graphite and molybdenum disulfide have been conditioning was used by all laboratories. Rectangular test
found to be acceptable lubricants. specimens were prepared from gasket sheets by cutting them
8.2.2 Place rectangular specimens between the platens in
accordance with Fig. 2 and making sure they are no closer than
11
2 mm (0.078 inches) to the other pieces and the edge of the Some laboratories have found Alloy A-286 meets the calibration standard at
temperatures up to 482.2°C (900°F). The user may specify any alloy of construction
platens. If an annular specimen is used, center the specimen as long as the alloy meets the calibration standard for the desired test temperature.
around the bolt hole between the platens. If a Type 4 Class 2 12
Supporting data are available from ASTM Headquarters. Request RR: F-3-
specimen is used, center the specimen around the bolt hole 1009.

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 F 38
with the long dimension in the machine direction. Tests were 10.3 The precision results for the A193 Grade B7 Fixture
conducted in accordance with Test Methods F 38 Test Method are given in Table 1.
B, with an initial stress of 20.68 MPa (3000 psi) applied on a 10.4 Additional F-38 Round Robin test data regarding the
1290-mm2 (2-in.2) sample area, total of 26.7-kN (6000-lb) evaluation of ASTM B 637 UNS N07718 is provided in
compressive force. The tests were conducted for 22 h at 100°C Appendix X1.
(212°F). The tests were conducted in triplicate on each material 11. Keywords
using the A193 Grade B7 Fixture. 11.1 creep relaxation; deflection; gasket material; platens;
relaxometer; strain; stress; temperature; torque bolt; torque loss

TABLE 1 Precision of Creep Relaxation Test of Gasket Materials, Using Coefficient of Variation Method of Presenting Results

NOTE 1—S 5 standard deviation.

CV 5 % coefficient of variation 5 (S 3 100)/(average).
LSD 5 % least significant difference between two individual test results based on a 95 % confidence level, 5 2 =2 (CV).
NOTE 2—An annular specimen can be used in place of rectangular specimens for Type 1, Class 2; Type 5, Class 1; Type 7, Class 1; and Type 7, Class
2. An annular specimen cannot be used in place of rectangular specimens for Type 1, Class 1 because of the statistically significant difference in results.
Material Type and Relaxation Values, % Repeatability Reproducibility
Class, Classification
F 104 Range Average S CV, % LSD, % S CV, % LSD, %
Type 1, Class 1 11.5–15.4 13.3 1.22 9.4 26.5 1.58 11.9 33.7
Type 1, Class 2 27.2–33.7 30.9 1.87 6.2 17.6 2.52 8.2 23.1
Type 5, Class 1 4.0–8.9 6.3 1.27 18.1 51.2 2.01 31.9 90.1
Type 7, Class 1 14.2–24.5 18.1 1.33 8.0 22.7 3.93 21.8 61.5
Type 7, Class 2 20.7–28.5 26.0 0.97 4.2 11.8 3.10 11.9 33.7

ANNEX

(Mandatory Information)

A1. TEST METHOD B CREEP RELAXATON APPARATUS: BOLT CALIBRATION PROCEDURE

A1.1 Purpose relaxometer without gaskets. Load the bolt to obtain a deflec-
A1.1.1 To precondition (strain relieve) the bolts at elevated tion of 0.13 6 0.0013 mm (0.00500 6 0.00005 in.) and record
temperature prior to calibration. this value as the original deflection. Place the fixture in a
A1.1.2 To calibrate the bolts after preconditioning, and on a circulating air oven preheated to 50°F above the intended
periodic basis after use. Bolts used at temperatures greater than maximum test temperature. After 22 h, remove the fixture from
205°C (401°F) should be recalibrated more often than bolts the oven, cool to room temperature, and remove the load from
used at lower test temperatures. the bolt, measuring the deflection to the nearest 0.0013 mm
A1.1.3 To ensure that the bolt is functioning properly. (0.00005 in.). Record this deflection as the final deflection.
Should the calibration of a bolt result in an elongation of less Repeat this cycle until the original and final deflection differ by
than 0.114 mm (0.00450 in.) or more than 0.140 mm (0.00550 a value that does not show a trend to decrease further from one
in.) at 26.7 kN (6000 lbf), the bolt should be discarded. cycle to the next. Typically, the bolts will stabilize at 3 % or
less difference between the original and final deflection.
A1.2 Apparatus
NOTE A1.1—Normally, seven cycles or less are sufficient to precondi-
A1.2.1 Relaxometer, in accordance with 5.2.1 of Test Meth- tion bolts.
ods F 38, modified so that each platen can accept a pair of steel
dowel pins. A1.3.2 with the steel washer in place of the gasket, and
A1.2.2 Spacer, washer-shaped, 0.80 6 0.13 mm (0.031 6 tighten the nut only finger tight. Mount the fixture in the
0.005 in.) thick. calibration apparatus as shown in Fig. A1.1. Adjust the span so
A1.2.3 Tensile Testing Machine, capable of obtaining and that no tensile load is applied to the relaxometer bolt and set the
recording a load of 26.7 kN (6000 lbf). The maximum dial indicator at zero. Apply the tensile force until a load of
allowable system error equals 0.5 % of the applied load. 4.45 kN (1000 lbf) is attained. Maintain this load and record
A1.2.4 Calibration Apparatus, to connect the relaxometer the bolt elongation by estimating to the nearest 0.0013 mm
to the tensile machine. See Fig. A1.1. (0.00005 in.) on the dial indicator. Continue loading the bolt,
recording the elongation at 4.45-kN increments up to 26.7 kN
A1.3 Procedure (6000 lbf).
A1.3.1 If the bolts to be calibrated are new, they must be A1.3.3 Remove the tensile load from the relaxometer bolt.
preconditioned using the following procedure. Assemble the If the dial indicator does not read zero (within 0.0025 mm

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FIG. A1.1 Schematic of Bolt Calibration Apparatus

(0.0001 in.)), reject the data. Reset the dial indicator to zero average bolt elongation against the bolt loads on linear graph
and reload the bolt in accordance with A1.3.2, recording the paper. The curve must be a straight line.
elongations. Apply the loads to the relaxometer bolt three
consecutive times, recording the elongation at the 4.45-kN
(1000-lbf) increments.
A1.3.4 Prepare a bolt calibration curve by plotting the

APPENDIX

(Nonmandatory Information)

X1. EVALUATION OF ASTM B 637 UNS N07718

X1.1 The attached F-38 Round Robin test data regarding for informational purposes only in Tables X1.1 and X1.2 and
the evaluation of ASTM B 637 UNS N07718 was completed Figs. X1.1-X1.4.
by the Creep Relaxation task group, F3.20.01, and is provided

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TABLE X1.1 F-38 Round Robin Test Data—ASTM B 637 UNS N07718
TESTER Test Lab 1 Test Lab 2A Test Lab 3
TEMPERATURE DEG. F 212 350 500 650 212 500 700 900 700 900
SAMPLE 1 25.6 % 32.3 % 42.5 % 44.2 % 26.7 % 50.9 % 49.9 % 80.4 % 43.5 % 68.0 %
SAMPLE 2 24.3 % 31.6 % 45.8 % 41.6 % 27.6 % 51.3 % 50.3 % 82.4 % 45.1 % 78.5 %
Type 7, Class 1 SAMPLE 3 22.3 % 29.6 % 46.7 % 41.8 % 27.2 % 52.3 % 49.8 % 83.4 % 47.4 % 74.4 %
AVERAGE 24.1 % 31.2 % 45.0 % 42.5 % 27.2 % 51.5 % 50.0 % 82.1 % 45.3 % 73.6 %

SAMPLE 1 13.4 % 21.5 % 32.5 % 34.2 % 17.6 % 33.3 % 41.4 % 41.3 % 42.6 % 42.4 %
SAMPLE 2 11.9 % 19.4 % 32.4 % 35.6 % 16.7 % 34.0 % 41.7 % 41.5 % 40.0 % 42.6 %
Type 7, Class 2 SAMPLE 3 12.2 % 17.7 % 31.3 % 36.0 % 17.6 % 33.8 % 42.2 % 41.3 % 41.9 % 42.4 %
AVERAGE 12.5 % 19.5 % 32.1 % 35.3 % 17.3 % 33.7 % 41.8 % 41.4 % 41.5 % 42.5 %

SAMPLE 1 13.6 % 20.1 % 21.6 % 25.6 % 15.5 % 30.8 % 32.3 % 56.9 % 34.8 % 54.3 %
SAMPLE 2 12.4 % 19.4 % 25.8 % 25.6 % 15.6 % 30.4 % 32.1 % 56.0 % 27.8 % 53.7 %
Type 7, Class 1 SAMPLE 3 9.6 % 17.9 % 25.0 % 23.9 % 16.2 % 32.5 % 36.1 % 56.3 % 29.8 % 59.8 %
AVERAGE 11.9 % 19.1 % 24.1 % 25.0 % 15.8 % 31.2 % 33.5 % 56.4 % 30.8 % 55.9 %

SAMPLE 1 5.2 % 1.9 % 4.0 % 5.7 % 4.7 % 7.7 % 10.7 % 22.2 % 10.7 % 29.5 %
SAMPLE 2 2.8 % 3.0 % 4.5 % 3.8 % 4.9 % 7.4 % 9.9 % 18.1 % 7.7 % 18.5 %
Type 5, Class 1 SAMPLE 3 2.4 % 1.5 % 3.6 % 2.4 % 5.5 % 5.9 % 10.8 % 20.2 % 6.9 % 35.2 %
AVERAGE 3.5 % 2.1 % 4.0 % 4.0 % 5.0 % 7.0 % 10.5 % 20.2 % 8.4 % 27.7 %
A
Test Lab 2 used calibrated F-38 fixtures made with Alloy A-286.

TABLE X1.2 F-38 Round Robin Test Data—ASTM B 637 UNS N07718
TESTER Test Lab 4 Test Lab 5
TEMPERATURE DEG. F 212 350 500 550 212 350 500 700
SAMPLE 1 27.0 % 35.5 % 46.4 % 45.3 % 18.5 % 30.4 % 46.0 % 47.8 %
SAMPLE 2 9.8 % 34.9 % 37.6 % 42.1 % 19.0 % 30.0 % 50.0 % 40.0 %
Type 7, Class 1 SAMPLE 3 42.8 % 38.1 % 46.4 % 46.4 %
AVERAGE 26.5 % 36.2 % 43.5 % 44.6 % 18.8 % 30.2 % 48.0 % 43.9 %

SAMPLE 1 14.7 % 21.1 % 32.0 % 30.4 % 10.9 % 18.5 % 34.8 % 37.0 %

SAMPLE 2 10.5 % 20.6 % 28.1 % 31.6 % 14.0 % 20.0 % 29.0 % 35.0 %
Type 7, Class 2 SAMPLE 3 13.0 % 19.0 % 29.9 % 28.7 %
AVERAGE 12.7 % 20.2 % 30.0 % 30.2 % 12.5 % 19.3 % 31.9 % 36.0 %

SAMPLE 1 11.3 % 20.0 % 22.4 % 24.9 % 6.5 % 17.4 % 32.6 % 26.1 %

SAMPLE 2 14.9 % 19.4 % 22.4 % 23.6 % 8.0 % 18.0 % 26.0 % 31.0 %
Type 7, Class 1 SAMPLE 3 13.5 % 16.4 % 24.9 % 23.8 %
AVERAGE 13.2 % 18.6 % 23.2 % 24.1 % 7.3 % 17.7 % 29.3 % 28.6 %

SAMPLE 1 1.2 % 5.2 % 4.7 % 6.3 % 3.3 % 2.2 % 5.4 % 6.5 %

SAMPLE 2 1.3 % 1.3 % 1.8 % 4.8 % 3.0 % 4.0 % 5.0 % 9.0 %
Type 5, Class 1 SAMPLE 3 2.0 % 4.5 % 3.2 % 4.9 %
AVERAGE 1.5 % 3.7 % 3.2 % 5.3 % 3.2 % 3.1 % 5.2 % 7.8 %

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FIG. X1.1 ASTM B 637 UNS N07718 Type 7, Class 1

FIG. X1.2 ASTM B 637 UNS N07718 Type 7, Class 2

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FIG. X1.3 ASTM B 637 UNS N07718 Type 7, Class 1

FIG. X1.4 ASTM B 637 UNS N07718 Type 5, Class 1

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