GB/T 20671.5-2020 English PDF (GBT20671.5-2020)

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GB/T 20671.5-2020: Classification system and test methods for nonmetallic gasket materials -- Part 5: Standard test method for creep relaxation of gasket materials
GB/T 20671.5-2020
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 23.100.60
Q 69
Replacing GB/T 20671.5-2006
Classification system and test methods for
nonmetallic gasket materials - Part 5: Standard test
method for creep relaxation of gasket materials
ISSUED ON: JUNE 02, 2020
IMPLEMENTED ON: APRIL 01, 2021
Issued by: State Administration for Market Regulation;
Standardization Administration of the People’s Republic of
China.
Table of Contents
Foreword ... 3 
1 Scope ... 6 
2 Normative references ... 6 
3 Principle ... 6 
4 Instruments and apparatuses ... 7 
5 Sample ... 8 
6 Test procedure ... 9 
7 Precision ... 12 
8 Test report ... 13 
Appendix A (Normative) Test method B - Creep relaxation tester bolt calibrating
procedure ... 14 
Appendix B (Informative) Examples of material technical indicator for relaxation
rate tester of test method B ... 17 
References ... 19 
Foreword
GB/T 20671, Classification system and test methods for nonmetallic gasket
materials, is divided into 11 parts:
-- Part 1: Standard classification system for nonmetallic gasket materials;
-- Part 2: Standard test method for compressibility and recovery of gasket
materials;
-- Part 3: Standard test method for fluid resistance of gasket materials;
-- Part 4: Standard test method for sealability of gasket materials;
-- Part 5: Standard test method for creep relaxation of gasket materials;
-- Part 6: Standard test method for adhesion of gasket materials to metal
surfaces;
-- Part 7: Standard test methods for tension testing of nonmetallic gasket
materials;
-- Part 8: Standard test method for flexibility of non-metallic gasket materials;
-- Part 9: Standard test method for binder durability of cork composition
gasket materials;
-- Part 10: Standard practice for evaluating thermal conductivity of gasket
materials;
-- Part 11: Standard practice for determining resistance of synthetic
polymeric materials to fungi.
This Part is Part 5 of GB/T 20671.
This Part was drafted in accordance with the rules given in GB/T 1.1-2009.
This Standard replaces GB/T 20671.5-2006, Classification system and test
methods for nonmetallic gasket materials - Part 5: Standard test method for
creep relaxation of gasket materials. Compared with GB/T 20671.5-2006, the
main technical changes, except editorial changes, are as follows:
-- Add the scope of application of this Part (see Chapter 1);
-- In the scope, delete “Use the value that is expressed in International
System of Units (SI) as the standard” and “This Part does not involve
safety issues that are related to its use. Users of this Part are responsible
Classification system and test methods for
nonmetallic gasket materials - Part 5: Standard test
method for creep relaxation of gasket materials
1 Scope
This Part of GB/T 20671 specifies the principle, instruments and apparatuses,
sample, test procedure, precision and test report for the test of creep relaxation
of nonmetallic gasket materials.
This Part applies to the determination of the creep relaxation of Model 1, Model
5 and Model 7 materials which are specified in GB/T 20671.1. It can also be
used for other models of materials as a reference.
2 Normative references
The following documents are indispensable for the application of this document.
For dated references, only the dated version applies to this document. For
undated references, the latest edition (including all amendments) applies to this
document.
GB/T 20671.1, Classification system and test methods for nonmetallic gasket
materials - Part 1: Standard classification system for nonmetallic gasket
materials
3 Principle
3.1 Test method A
It is generally carried out at room temperature. Use a strain gauge that is
calibrated on the bolt to measure the strain; place the sample between two flat
circular plates to be compressed. The pressure is provided by the bolts and
nuts that fasten the circular plates. In the test, from the beginning of the load to
the end of the test, read the reading on the strain display at regular intervals.
Convert the reading on the strain display into a percentage of the initial stress;
then, draw a relation curve of the logarithm of the percentage and time (in
hours). Within the range of the entire test time, the percentage of initial stress
loss or relaxation at any given time can be found from the curve.
3.2 Test method B
3 -- upper flat circular plate;
4 -- test sample;
5 -- lower flat circular plate;
6 -- bolt;
7 -- fixed station;
8 -- connect the strain indicator;
9 -- wire.
Figure 1 -- Relaxation rate tester for test method A
4.2 Test method B
4.2.1 Relaxation rate tester: The relaxation rate tester shall meet the
requirements of the test temperature calibrating procedure (see Appendix A).
The relaxation rate tester consists of two flat circular plates with special holes,
calibrated bolts, washers and nuts. The material is chromium-molybdenum
ferritic steel or nickel-based high-temperature alloy steel or other alloys (see
Appendix B), as shown in Figure 2.
4.2.2 Dial indicator assembly: It is composed of connecting sleeve, thimble,
fastening screw and dial indicator, as shown in Figure 2. The precision of the
dial indicator is not more than 0.0025 mm.
4.2.3 Socket wrench: 14.3 mm (9/16 in).
5 Sample
5.1 Test method A
The sample shall be a ring whose inner diameter is 33.02 mm ± 0.05 mm and
outer diameter is 52.32 mm ± 0.05 mm.
5.2 Test method B
5.2.1 Rectangular sample: width of 10.16 mm ± 0.38 mm, length of 31.75 mm
± 0.38 mm. Four such samples are required for each test.
5.2.2 Annular sample: the area is 1 290 mm2; it is recommended to use the
sample whose inner diameter is 15.62 mm and outer diameter is 43.56 mm.
5.2.3 For Model 4 Class 2 materials, the sample should be a long strip of 152.40
mm.
6.1.1 Clean the surface of the flat circular plate and the sample, to make it be
free of wax, release agent and oil (use isooctane or other suitable solvent to
wipe). Lubricate the threads of the bolts.
6.1.2 Use an initial stress of 13.8 MPa ± 0.3 MPa, unless otherwise specified.
6.1.3 Perform the test at 21 °C ~ 30 °C, unless otherwise specified.
6.1.4 Take apart the relaxation rate tester and put the sample between two flat
circular plates. The inner diameter of the sample and the inner diameter of the
flat circular plate shall be as concentric as possible. Put the bolt head into the
fixed station; screw on the thrust bearing and nut; tighten it lightly by hand or
apply a force just enough to fix the sample.
6.1.5 Connect and balance the strain display. Record the reading. Then, adjust
the reading of the strain display to the specified initial stress.
6.1.6 Apply pressure to the gasket by using a wrench to tighten the nut, until
the strain display reaches equilibrium. For a pressure of 17.8 kN, a torque of
about 30 N·m is required. The pressure shall be applied at a uniform rate and
reach the specified pressure within 10 s ± 2 s. This pressure is the “initial stress”.
6.1.7 Start timing when reaching the specified “initial stress”. Read the readings
on the strain display for 10 s, 1 min, 6 min, 30 min, 1 h, 5 h, 24 h, until the end
of the test (check the zero point of the strain display after the test).
6.1.8 Convert the reading of the strain display that is obtained in 6.1.7 into a
percentage of “initial stress”. On...