ASTM D2837-98a
(Test Method)Standard Test Method for Obtaining Hydrostatic Design Basis for Thermoplastic Pipe Materials
Standard Test Method for Obtaining Hydrostatic Design Basis for Thermoplastic Pipe Materials
SCOPE
1.1 This test method describes a procedure for obtaining a long-term hydrostatic strength category, referred to herein as the hydrostatic design basis (HDB), for thermoplastic pipe materials based on the material's long-term hydrostatic strength (LTHS). The LTHS is determined by analyzing stress versus time-to-rupture (that is, stress-rupture) test data that cover a testing period of not less than 10 000 h and that are derived from sustained pressure testing of pipe made from the subject material. The data are analyzed by linear regression to yield a best-fit log-stress versus log time-to-fail straight-line equation. Using this equation, the material's mean strength at the 100 000-h intercept (LTHS) is determined by extrapolation. The resultant value of the LTHS determines the HDB strength category to which the material is assigned. An HDB is one of a series of preferred long-term strength values. This test method is applicable to all known types of thermoplastic pipe materials, and for any practical temperature and medium that yields stress-rupture data that exhibit an essentially straight-line relationship when plotted on log stress (pound-force per square inch) versus log time-to-fail (hours) coordinates, and for which this straight-line relationship is expected to continue uninterrupted through at least 100 000 h.
1.2 Unless the experimentally obtained data approximate a straight line, when calculated using log-log coordinates, it is not possible to assign an HDB to the material. Data that exhibit high scatter or a "knee" (a downward shift, resulting in a subsequently steeper stress-rupture slope than indicated by the earlier data) but which meet the requirements of this test method tend to give a lower forecast of LTHS. In the case of data which exhibit excessive scatter or a pronounced "knee," the lower confidence limit requirements of this test method are not met and the data are classified as unsuitable for analysis.
1.3 A fundamental premise of this test method is that when the experimental data define a straight-line relationship in accordance with this test method's requirements, this straight line may be assumed to continue beyond the experimental period, through at least 100 000 h (the time intercept at which the material's LTHS is determined). In the case of polyethylene piping materials this test method includes a supplemental requirement for the "validating" of this assumption. No such validation requirements are included for other materials (see Note 1). Therefore, in all these other cases, it is up to the user of this test method to determine based on outside information whether this test method is satisfactory for the forecasting of a material's LTHS for each particular combination of internal/external environments and temperature.Note 1—Extensive long-term data that have been obtained on commercial pressure pipe grades of polyvinyl chloride (PVC), polybutlene (PB), and cross linked polyethlene (PEX) materials have shown that this assumption is appropriate for the establishing of HDB's for these materials for water and for ambient temperatures. Refer to Note 2 and Appendix X1 for additional information.
1.4 The experimental procedure to obtain individual data points shall be as described in Test Method D 1598, which forms a part of this test method. When any part of this test method is not in agreement with Test Method D 1598, the provisions of this test method shall prevail.
1.5 General references are included at the end of this test method.
1.6 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.
1.7 The values stated in inch-pound units are to be regarded as the standard. The values given in parentheses are for information only and are not considered the sta...
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Designation: D 2837 – 98a An American National Standard
Standard Test Method for
Obtaining Hydrostatic Design Basis for Thermoplastic Pipe
1
Materials
This standard is issued under the fixed designation D 2837; 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.
1. Scope priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use.
1.1 This test method describes a procedure for obtaining a
hydrostatic design basis for thermoplastic pipe materials, by
2. Referenced Documents
evaluating stress rupture test data derived from testing pipe
2.1 ASTM Standards:
made from the subject material. The method is applicable to all
D 1598 Test Method for Time-to-Failure of Plastic Pipe
known types of thermoplastic pipe and for any practical
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Under Constant Internal Pressure
temperature and medium.
E 29 Practice for Using Significant Digits in Test Data to
1.2 Unless the data approximate a straight line, when
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Determine Conformance with Specifications
calculated using log-log coordinates, it is not possible to assign
a hydrostatic design basis to the material. Data that exhibit high
3. Terminology
scatter or a “knee” give low (that is, conservative) extrapolated
3.1 Definitions:
values when evaluated. In addition, the lower confidence level
3.1.1 pressure—the force per unit area exerted by the
limits are not met and the data are classed as unsuitable.
medium in the pipe.
1.3 The values stated in inch-pound units are to be regarded
3.1.2 hoop stress—the tensile stress in the wall of the pipe
as the standard.
in the circumferential orientation due to internal hydrostatic
NOTE 1—Over 1200 sets of data, obtained with thermoplastic pipe and
pressure.
piping assemblies tested with water, natural gas, and compressed air, have
3.1.3 The following equations shall be used for the relation
been analyzed. None of the compounds in the lists of Recommended
between stress and pressure:
Hydrostatic Strengths and Design Stresses for Thermoplastic Pipe and
Fittings Compounds in PPI Technical Report TR4, issued at intervals for S 5 P D — t /2t for outside diameter controlled pipe (1)
~ !
over 12 years by the Plastics Pipe Institute, exhibit knee-type plots, that is,
deviate from a straight line in such a manner that a marked drop occurs in
or
stress at some time when plotted on equiscalar log-log coordinates. Data
S 5 P~d 1 t!/2t for inside diameter controlled pipe (2)
have been obtained for test periods over 120 000 h. It might be noted that
some thermoplastic compounds that are not suitable or recommended for
where:
piping components do exhibit knee-type plots at 23°C (73°F); in these
S = stress,
cases, very low results are obtained when the data are analyzed by this test
P = pressure,
method. Futher information on piping compounds may be found in the
D = average outside diameter,
references at the end of this test method.
d = average inside diameter, and
1.4 The experimental procedure to obtain individual data
t = minimum wall thickness.
points shall be as described in Test Method D 1598, which
3.1.4 failure— bursting, cracking, splitting, or weeping
forms a part of this test method. When any part of this test
(seepage of liquid) of the pipe during test.
method is not in agreement with Test Method D 1598, the
3.1.5 long-term hydrostatic strength (LTHS)— the esti-
provisions of this test method shall control.
mated tensile stress in the wall of the pipe in the circumferen-
1.5 General references are included at the end of this test
tial orientation that when applied continuously will cause
method.
failure of the pipe at 100 000 h. This is the intercept of the
1.6 This standard does not purport to address all of the
stress regression line with the 100 000-h coordinate.
safety concerns, if any, associated with its use. It is the
3.1.6 hydrostatic design basis (HDB)—one of a series of
responsibility of the user of this standard to establish appro-
established stress values for a compound. It is obtained by
categorizing the LTHS in accordance with Table 1.
3.1.7 service (design) factor—a number less than 1.00
1
This test method is under the jurisdiction of ASTM Committee F-17 on Plastics
(which takes into consideration all the variables and degree of
Piping Systems and is the direct responsibility of Subcommittee F17.40 on Test
Methods.
2
Current edition approved December 10, 1998. Published March 1999. Originally Annual Book of ASTM Standards, Vol 08.04.
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published as D 2837 – 69. Last previous edition D 2837 – 98. Annual Book of ASTM Standards, Vol 14.02.
Copyright © ASTM, 100 Barr Harbo
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