ASTM D2837-22

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.
Designation: D2837 − 22
Standard Test Method for
Obtaining Hydrostatic Design Basis for Thermoplastic Pipe
Materials or Pressure Design Basis for Thermoplastic Pipe
Products
This standard is issued under the fixed designation D2837; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope* stress-rupture data that exhibit an essentially straight-line
relationshipwhenplottedonlogstress(pound-forcepersquare
1.1 This test method describes two essentially equivalent
inch) or log pressure (pound-force per square in. gage) versus
procedures: one for obtaining a long-term hydrostatic strength
logtime-to-fail(hours)coordinates,andforwhichthisstraight-
category based on stress, referred to herein as the hydrostatic
line relationship is expected to continue uninterrupted through
design basis (HDB); and the other for obtaining a long-term
at least 100000 h.
hydrostatic strength category based on pressure, referred to
herein as the pressure design basis (PDB). The HDB is based 1.2 Unless the experimentally obtained data approximate a
on the material’s long-term hydrostatic strength (LTHS),and straight line, when calculated using log-log coordinates, it is
the PDB is based on the product’s long-term hydrostatic not possible to assign an HDB/PDB to the material. Data that
pressure-strength (LTHS ). The HDB is a material property exhibit high scatter or a “knee” (a downward shift, resulting in
P
and is obtained by evaluating stress rupture data derived from a subsequently steeper stress-rupture slope than indicated by
testing pipe made from the subject material. The PDB is a the earlier data) but which meet the requirements of this test
productspecificpropertythatreflectsnotonlythepropertiesof method tend to give a lower forecast of LTHS/LTHS.Inthe
P
the material(s) from which the product is made, but also the case of data that exhibit excessive scatter or a pronounced
influenceonproductstrengthbyproductdesign,geometry,and “knee,” the lower confidence limit requirements of this test
dimensions and by the specific method of manufacture. The methodarenotmetandthedataareclassifiedasunsuitablefor
PDB is obtained by evaluating pressure rupture data. The analysis.
LTHS is determined by analyzing stress versus time-to-rupture
1.3 Afundamental premise of this test method is that when
(that is, stress-rupture) test data that cover a testing period of
the experimental data define a straight-line relationship in
not less than 10000 h and that are derived from sustained
accordance with this test method’s requirements, this straight
pressure testing of pipe made from the subject material. The
line may be assumed to continue beyond the experimental
data are analyzed by linear regression to yield a best-fit
period, through at least 100000 h (the time intercept at which
log-stress versus log time-to-fail straight-line equation. Using
the material’s LTHS/LTHS is determined). In the case of
P
this equation, the material’s mean strength at the 100000-h
polyethylene piping materials, this test method includes a
intercept (LTHS) is determined by extrapolation. The resultant
supplemental requirement for the “validating” of this assump-
value of the LTHS determines the HDB strength category to
tion. No such validation requirements are included for other
which the material is assigned. The LTHS is similarly
P
materials (see Note 1). Therefore, in all these other cases, it is
determined except that the determination is based on pressure
uptotheuserofthistestmethodtodeterminebasedonoutside
versustimedatathatarederivedfromaparticularproduct.The
information whether this test method is satisfactory for the
categorized value of the LTHS is the PDB. An HDB/PDB is
P
forecasting of a material’s LTHS/LTHS for each particular
P
one of a series of preferred long-term strength values.This test
combination of internal/external environments and tempera-
method is applicable to all known types of thermoplastic pipe
ture.
materials and thermoplastic piping products. It is also appli-
NOTE 1—Extensive long-term data that have been obtained on com-
cable for any practical temperature and medium that yields
mercial pressure pipe grades of polyvinyl chloride (PVC), polybutylene
(PB), and cross linked polyethylene (PEX) materials have shown that this
assumption is appropriate for the establishing of HDB’s for these
1 materials for water and for ambient temperatures. Refer to Note 2 and
This test method is under the jurisdiction ofASTM Committee F17 on Plastic
Appendix X1 for additional information.
Piping Systems and is the direct responsibility of Subcommittee F17.40 on Test
Methods.
1.4 The experimental procedure to obtain individual data
Current edition approved March 15, 2022. Published April 2022. Originally
points shall be as described in Test Method D1598, which
approved in 1969. Last previous edition approved in 2021 as D2837–21. DOI:
10.1520/D2837-22. forms a part of this test method. When any part of this test
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D2837 − 22
method is not in agreement with Test Method D1598, the 1.8 This international standard was developed in accor-
provisions of this test method shall prevail. dance with internationally recognized principles on standard-
ization established in the Decision on Principles for the
1.5 General references are included at the end of this test
Development of International Standards, Guides and Recom-
method.
mendations issued by the World Trade Organization Technical
1.6 This standard does not purport to address all of the
Barriers to Trade (TBT) Committee.
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
2. Referenced Documents
priate safety, health, and environmental practices and deter-
2.1 ASTM Standards:
mine the applicability of regulatory limitations prior to use.
D1243Test Method for Dilute Solution Viscosity of Vinyl
1.7 The values stated in inch-pound units are to be regarded
Chloride Polymers
as the standard. The values given in parentheses are for
D1598Test Method for Time-to-Failure of Plastic Pipe
information only and are not considered the standard.
Under Constant Internal Pressure
NOTE 2—Over 3000 sets of data, obtained with thermoplastic pipe and
E29Practice for Using Significant Digits in Test Data to
pipingassembliestestedwithwater,naturalgas,andcompressedair,have
Determine Conformance with Specifications
been analyzed by the Plastic Pipe Institute’s (PPI) Hydrostatic Stress
2.2 ISO Standard:
Board . None of the currently commercially offered compounds included
ISO 9080Plastic Piping and Ducting Systems, Determina-
in PPI TR-4, “PPI Listing of Hydrostatic Design Basis (HDB), Hydro-
static Design Stress (HDS), Strength Design Basis (SDB), Pressure tionofLong-TermHydrostaticStrengthofThermoplastics
Design Basis (PDB) and Minimum Required Strength (MRS) Ratings for
Materials in Pipe Form by Extrapolation
Thermoplastic Piping Materials or Pipe” exhibit knee-type plots at the
2.3 Plastics Pipe Institute:
listed temperature, that is, deviate from a straight line in such a manner
PPI TR-3Policies and Procedures for Developing Hydro-
that a marked drop occurs in stress at some time when plotted on
static Design Basis (HDB), Hydrostatic Design Stresses
equiscalar log-log coordinates. Ambient temperature stress-rupture data
thathavebeenobtainedonanumberofthelistedmaterialsandthatextend
(HDS), Pressure Design Basis (PDB), Strength Design
for test periods over 120 000 h give no indication of “knees.” However,
Basis (SDB), and Minimum Required Strength (MRS)
stress-rupture data which have been obtained on some thermoplastic
Ratings for Thermoplastic Piping Materials or Pipe
compounds that are not suitable or recommended for piping compounds
PPI TR-4PPI Listing of Hydrostatic Design Basis (HDB),
havebeenfoundtoexhibitadownwardtrendat23°C(73°F)inwhichthe
Hydrostatic Design Stress (HDS), Strength Design Basis
departure from linearity appears prior to this test method’s minimum
testing period of 10000 h. In these cases, very low results are obtained or
(SDB), Pressure Design Basis (PDB) and Minimum Re-
the data are found unsuitable for extrapolation when they are analyzed by
quired Strength (MRS) Ratings for Thermoplastic Piping
this test method.
Materials or Pipe
Extensive evaluation of stress-rupture data by PPI and others has also
indicated that in the case of some materials and under certain test
3. Terminology
conditions, generally at higher test temperatures, a departure from
linearity, or “down-turn”, may occur beyond this test method’s minimum
3.1 Definitions:
required data collection period of 10000 h.APPI study has shown that in
3.1.1 failure, n—bursting, cracking, splitting, or weeping
the case of polyethylene piping materials that are projected to exhibit a
(seepage of liquid) of the pipe during test.
“down-turn” prior to 100000 h at 73°F, the long-term field performance
of these materials is prone to more problems than in the case of materials
3.1.2 hoop stress, n—thetensilestressinthewallofthepipe
which have a projected “down-turn” that lies beyond the 100000-h
in the circumferential orientation due to internal hydrostatic
intercept. In response to these observations, a supplemental “validation”
pressure.
requirement for PE materials has been added to this test method in 1988.
This requirement is designed to reject the use of this test method for the
3.1.3 hydrostatic design basis (HDB), n—one of a series of
estimating of the long-term strength of any PE material for which
established stress values for a compound. It is obtained by
supplemental elevated temperature testing fails to validate this test
categorizing the LTHS in accordance with Table 1.
method’s inherent assumption of continuing straight-line stress-rupture
behavior through at least 100000 h at 23°C (73°F).
3.1.4 hydrostatic design stress (HDS), n—the estimated
When applying this test method to other materials, appropriate consid-
maximum tensile stress the material is capable of withstanding
eration should be given to the possibility that for the particular grade of
continuously with a high degree of certainty that failure of the
material under evaluation and for the specific conditions of testing,
pipewillnotoccur.Thisstressiscircumferentialwheninternal
particularly, when higher test temperatures and aggressive environments
are involved, there may occur a substantial “down-turn” at some point hydrostatic water pressure is applied.
beyond the data collection period. The ignoring of this possibility may
3.1.5 long-term hydrostatic strength (LTHS), n—the esti-
lead to an overstatement by this test method of a material’s actual
mated tensile stress in the wall of the pipe in the circumferen-
LTHS/LTHS . To obtain sufficient assurance that this test method’s
P
inherent assumption of continuing linearity through at least 100000 h is tial orientation that when applied continuously will cause
appropriate, the user should consult and consider information outside this
failure of the pipe at 100000 h. This is the intercept of the
testmethod,includingverylong-termtestingorextensivefieldexperience
stress regression line with the 100000-h coordinate.
withsimilarmaterials.Incasesforwhichthereisinsufficientassuranceof
the continuance of the straight-line behavior that is defined by the
experimental data, the use of other test methods for the forecasting of
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
long-term strength should be considered (see Appendix X1).
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.
2 4
Available from Plastics Pipe Institute (PPI), 105 Decker Court, Suite 825, Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
Irving, TX 75062, http://www.plasticpipe.org. 4th Floor, New York, NY 10036, http://www.ansi.org.
D2837 − 22
TABLE 1 Hydrostatic Design Basis Categories TABLE 2 Pressure Design Basis Categories
NOTE 1—The calculated LTHS shall be rounded to the nearest 10 psi in NOTE 1—The calculated LTHSP shall be rounded to the nearest 10 psi
accordance with the Rounding Method of Practice E29. in accordance with the Rounding Method of Practice E29.
Range of Calculated LTHS Values Hydrostatic Design Basis Range of Calculated LTHS Values Pressure Design Values
P
psi (MPa) psi (MPA)
psi (MPa) psi (MPa)
96 to <120 (0.66 to <0.82) 100 (0.68)
190 to < 240 ( 1.31 to < 1.65) 200 ( 1.38)
120 to <153 (0.82 to <1.05) 125 (0.86)
240 to < 300 ( 1.65 to < 2.07) 250 ( 1.72)
153 to <190 (1.05 to <1.32) 160 (1.10)
300 to < 380 ( 2.07 to < 2.62) 315 ( 2.17)
190 to <240 (1.31 to <1.65) 200 (1.38)
380 to < 480 ( 2.62 to < 3.31) 400 ( 2.76)
240 to <300 (1.65 to <2.07) 250 (1.72)
480 to < 600 ( 3.31 to < 4.14) 500 ( 3.45)
300 to <380 (2.07 to <2.62) 315 (2.17)
600 to < 760 ( 4.14 to < 5.24) 630 ( 4.34)
380 to <480 (2.62 to <3.31) 400 (2.76)
760 to < 960 ( 5.24 to < 6.62) 800 ( 5.52)
480 to <600 (3.31 to <4.14) 500 (3.45)
960 to <1200 ( 6.62 to < 8.27) 1000 ( 6.89)
600 to <760 (4.14 to <5.24) 630 (4.34)
1200 to <1530 ( 8.27 to <10.55) 1250 ( 8.62)
760 to <960 (5.24 to <6.62) 800 (5.52)
1530 to <1730 (10.55 to <11.93) 1600 (11.03)
960 to <1200 (6.62 to <8.27) 1000 (6.89)
1730 to <1920 (11.93 to <13.24) 1800 (12.41)
1200 to <1530 (8.27 to <10.55) 1250 (8.62)
1920 to <2160 (13.24 to <14.89) 2000 (13.79)
1530 to <1730 (10.55 to <11.93) 1600 (11.03)
2160 to <2400 (14.89 to <16.55) 2250 (15.51)
1730 to <1920 (11.93 to <13.24) 1800 (12.41)
2400 to <2690 (16.55 to <18.55) 2500 (17.24)
1920 to <2160 (13.24 to <14.89) 2000 (13.79)
2690 to <3020 (18.55 to <20.82) 2800 (19.30)
2160 to <2400 (14.89 to <16.55) 2250 (15.51)
3020 to <3410 (20.82 to <23.51) 3150 (21.72)
2400 to <2690 (16.55 to <18.55) 2500 (17.24)
3410 to <3830 (23.51 to <26.41) 3550 (24.47)
2690 to <3020 (18.55 to <20.82) 2800 (19.30)
3830 to <4320 (26.41 to <29.78) 4000 (27.58)
3020 to <3410 (20.82 to <23.51) 3150 (21.72)
4320 to <4800 (29.78 to <33.09) 4500 (31.02)
3410 to <3830 (23.51 to <26.41) 3550 (24.47)
4800 to <5380 (33.09 to <37.09) 5000 (34.47)
3830 to <4320 (26.41 to <29.78) 4000 (27.58)
5380 to <6040 (37.09 to <41.62) 5600 (38.61)
4320 to <4800 (29.78 to <33.09) 4500 (31.02)
6040 to <6810 (41.62 to <46.92) 6300 (43.41)
4800 to <5380 (33.09 to <37.09) 5000 (34.47)
6810 to <7920 (46.92 to <54.62) 7100 (48.92)
5380 to <6040 (37.09 to <41.62) 5600 (38.61)
6040 to <6810 (41.62 to <46.92) 6300 (43.41)
6810 to <7920 (46.92 to <54.62) 7100 (48.92)
3.1.6 long-term hydrostatic pressure-strength (LTHS ),
P
n—the estimated internal pressure that when applied continu-
3.1.11 Thefollowingequationsshallbeusedfortherelation
ously will cause failure of the pipe at 100 000 h. This is the
between stress and pressure:
intercept of the pressure regression line with the 100 000-h
S 5 P~D 2 t!/2t for outsidediameter controlled pipe (3)
intercept.
or
3.1.7 pressure, n—the force per unit area exerted by the
S 5 P d1t /2t for inside diametercontrolled pipe (4)
~ !
medium in the pipe.
where:
3.1.8 pressure rating (PR), n—the estimated maximum wa-
S = stress,
ter pressure the pipe is capable of withstanding continuously
P = pressure,
with a high degree of certainty that failure of the pipe will not
D = average outside diameter,
occur.
d = average inside diameter, and
3.1.8.1 The PR and HDS/HDB are related by the following
t = minimum wall thickness.
equation.
PR 5 2 ~HDB!~DF!/~SDR 2 1! 5 2 ~HDS!/~SDR 2 1! (1) 4. Significance and Use
4.1 The procedure for estimating long-term hydrostatic
3.1.8.2 The PR and PDB are related by the following
strength or pressure-strength is essentially an extrapolation
equation:
withrespecttotimeofastress-timeorpressure-timeregression
PR 5 PDB DF (2)
~ !~ !
line based on data obtained in accordance with Test Method
3.1.9 pressure design basis (PDB), n—one of a series of
D1598. Stress or pressure-failure time plots are obtained for
established pressure values for plastic piping components
the selected temperature and environment: the extrapolation is
(multilayer pipe, fitting, valve, etc.) obtained by categorizing
made in such a manner that the long-term hydrostatic strength
the LTHS in accordance with Table 2.
or pressure strengthis estimated for these conditions.
P
3.1.9.1 Discussion—An assessment should be conducted of
NOTE 3—Test temperatures should preferably be selected from the
theapplicabilityofthistestmethodforthedeterminationofthe
following: 68°F (20°C), 73°F (23°C), 140°F (60°C), 176°F (80°C),
pressure design basis for products made using composite
180°F (82°C), and 200°F (93°C). It is strongly recommended that data
construction. be generated at 73°F (23°C) for comparative purposes.
3.1.10 service (design) factor (DF), n—a number less than 4.2 The hydrostatic or pressure design basis is determined
1.00 (which takes into consideration all the variables and by considering the following items and evaluating them in
degree of safety involved in a thermoplastic pressure piping accordance with 5.4.
installation) which is multiplied by the HDB to give the HDS, 4.2.1 Long-term hydrostatic strength or hydrostatic
or multiplied by the PDB to give the pressure rating. pressure-strength at 100000 h,
D2837 − 22
4.2.2 Long-term hydrostatic strength or hydrostatic islessthanthehoursthespecimenhasbeenundertest,thenuse
pressure-strength at 50 years, and the point. Determine the final line for extrapolation by the
4.2.3 Stress that will give 5% expansion at 100000 h. method of least squares using the failure points along with
4.2.4 The intent is to make allowance for the basic stress- those non-failure points selected by the method described
strain characteristics of the material, as they relate to time. above. Unless it can be demonstrated that they are part of the
same regression line, do not use failure points for stresses or
4.3 Results obtained at one temperature cannot, with any
pressures that have failure times less than 10 h. Include failure
certainty, be used to estimate values for other temperatures.
points excluded from the calculation by this operation in the
Therefore, it is essential that hydrostatic or pressure design
report, and identify them as being in this category. Refer also
bases be determined for each specific kind and type of plastic
to Appendix 9.
compound and each temperature. Estimates of long-term
strengths of materials can be made for a specific temperature
NOTE5—Itshouldbenotedthatcontrarytothecustominmathematics,
it has been the practice of those testing plastics pipe to plot the
provided that calculated values, based on experimental data,
independent variable (stress) on the vertical (y) axis and the dependent
are available for temperatures both above and below the
variable (time-to-failure) on the horizontal (x) axis. The procedure in
temperature of interest.
Appendix X2 treats stress as an independent variable.
4.4 Hydrostatic design stresses are obtained by multiplying
5.2.3 Determine the suitability of the data for use in
thehydrostaticdesignbasisvaluesbyaservice(design)factor.
determining the long-term hydrostatic strength or hydrostatic
4.5 Pressure ratings for pipe may be calculated from the
pressure-strength and hydrostatic or pressure design basis of
hydrostatic design stress (HDS) value for the specific material
plastic pipe as follows:
used to make the pipe, and its dimensions using the equations
5.2.3.1 Extrapolate the data by the method given in Appen-
in 3.1.11.
dix X2, to 100000 h and 50 years, and record the extrapolated
4.5.1 Pressure ratings for multilayer pipe may be calculated
stress or pressure values (4.2.1 and 4.2.2), and
by multiplying the pressure design basis (PDB) by the appro-
5.2.3.2 Calculate, by the method given in Appendix X3, the
priate design factor (DF).
lower confidence value of stress at 100 000 h.
5.2.3.3 If the lower confidence value at 100 000 h differs
5. Procedure
from the extrapolated LTHS/LTHS value by more than 15%
P
5.1 General—Generated data in accordance with Test
of the latter, or M in Appendix X3 is zero or negative, or b in
Method D1598.
theequation h= a+ bfinAppendixX2ispositive,considerthe
data unsuitable.
5.2 Stress Rupture—Obtain the data required for 4.2.1 and
4.2.2 as follows:
5.3 Circumferential Expansion—Obtain the data required
5.2.1 Obtain a minimum of 18 failure stress/pressure-time
for 4.2.3 as follows:
points for each environment. Distribute these data points as
5.3.1 Initially test at least three specimens at a stress of
follows:
50% of the long-term hydrostatic strength determined in
Hours Failure Points
5.2.3.1 until the circumferential expansion exceeds 5% or for
<1000 At least 6
2000 h, whichever occurs first. Measure the expansion of the
10 to 1000 At least 3
1000 to 6000 At least 3 circumferenceinthecenterofthatsectionofthepipespecimen
After 6000 At least 3
thatisundertesttothenearest0.02mm(0.001in.)periodically
After 10 000 At least 1
(Note 6) during the test, unless the expansion at some other
NOTE 4—When the long-term stress regression line of a compound is
point is greater, in which case measure the section with the
known, this method may be used, using fewer points and shorter times, to
maximum expansion. Calculate the changes in circumference
confirm material characteristics, or to evaluate minor process or formu-
for each specimen as a percentage of the initial outside
lation changes. See also PPI TR-3, “Policies and Procedures for Devel-
oping HDB, SDB, PDB, and MRS Ratings for Thermoplastic Piping circumference. Calculate the expansion at 100 000 h for each
Materials or Pipe.”
specimen by the method given in Appendix X4 or by the
plotting technique described in 5.3.3. If the calculated expan-
5.2.2 Analyze the test results by using, for each specimen,
sionforoneormoreofthespecimenstestedexceeds5%,then
the logarithm of the stress in psi or pressure in psig and the
use the hydrostatic stress as determined from circumferential
logarithm of the time-to-failure in hours as described in
expansion measurements as the stress value to be categorized
Appendix X2 (Note 5). Calculate the strength at 100 000 h.
to establish the hydrostatic design basis.
Includeasfailuresattheconclusionofthetestthosespecimens
which have not failed after being under test for more than
NOTE 6—It is suggested that these measurements be made once every
10000hiftheyincreasethevalueoftheextrapolatedstrength.
24 h during the first 5 days, once every 3 days during the next 6 days, and
Accomplish this by first obtaining the linear log-log regression once a week thereafter. The periods shall be selected on the basis of past
experiencewiththetypeofpipesothattheywillbereasonablydistributed
equation for only the specimens that failed, by the method of
to obtain a good plot.
least squares as described in Appendix X2.Then use the stress
inpsiorpressureinpsigforeachspecimenthathasbeenunder 5.3.2 The stresses and distribution of specimens used to
test for more than 10 000 h, and that has not failed, with this determine hydrostatic stress from circumferential expansion
regression equation to calculate the time in hours. If this time measurements shall be as follows:
D2837 − 22
the manufacturing and testing variables, specifically normal
Approximate Percent of Long-Term Minimum Number of
Hydrostatic Strength (see 5.2) Specimens
variations in the material, manufacture, dimensions, good
20 3
handling techniques, and in the evaluation procedures in this
30 3
test method and in Test Method D1598 (Note 8). The second
40 3
50 3
groupconsiderstheapplicationoruse,specificallyinstallation,
60 3
environment, temperature, hazard involved, life expectancy
Subject the specimens to test until the circumferential
desired, and the degree of reliability selected (Note 9). Select
expansion exceeds 5% or for 2000 h, whichever occurs first.
the service factor so that the hydrostatic design stress obtained
5.3.3 Theresultsmaybecalculatedbythemethodsgivenin
provides a service life for an indefinite period beyond the
Appendix X4 and Appendix X5 or plotted by the following
actual test period.
procedures. Plot the percent changes in circumference against
NOTE 8—Experience to date, based on data submitted to PPI, indicates
time in hours on log-log graph paper. Draw a straight line by
that variation due to this group of conditions are usually within 610%,
the method of least squares, with time as the independent
for any specific compound.
variable as described in Appendix X4. Calculate the expansion
NOTE 9—It is not the intent of this standard to give service (design)
ofthecircumferenceinpercentat100000hforeachspecimen
factors. The service (design) factor should be selected by the design
by the equation from Appendix X4: engineer after evaluating fully the service conditions and the engineering
properties of the specific plastics under consideration. Alternatively, it
c 5 a'15.00 b' (5)
may be specified by the authority having jurisdiction.
It is recommended that numbers selected from ANSI Standard Z17.1-
Do not use extrapolations of curves for specimens that
1973forPreferredNumbers,intheR10series(25%increments)beused,
expandmorethan5%inlessthan1000h.Plotthecorrespond-
namely, 0.80, 0.63, 0.50, 0.40, 0.32, 0.25, 0.20, 0.16, 0.12, or 0.10. If
ing expansion-stress points from the 100000 h intercept on
smallerstepsseemnecessaryitisrecommendedthattheR20series(12%
increments)beused,namely,0.90,0.80,0.71,0.63,0.56,0.50,0.45,0.40,
log-log graph paper and draw a line representative of these
0.36, 0.32, 0.28, 0.25, 0.22, 0.20, 0.18, 0.16, 0.14, 0.12, 0.112, or 0.10.
points by the method of least squares with stress as the
independent variable as described in Appendix X5.
5.6 Determination or Validation of the HDB for Polyethyl-
5.3.4 Calculatethestresscorrespondingtoacircumferential
ene Materials, or Both—Apply any of the following proce-
expansion of 5.00% in accordance with 5.3.3 and Appendix dures to PE material to validate its HDB at any temperature.
X5. The stress is the antilog of r in the equation c5a"1b" r in
When an elevated temperature HDB is validated, all lower
Appendix X5. Use the values for a" and b" as calculated in temperature HDB’s are considered validated for that material.
Appendix X5 and 0.6990 for c.This stress may be obtained by
If a brittle failure occurs before 10000 h when testing in
calculation or read from the circumferential expansion-stress accordance with 5.2, theAlternate Method (Procedure I) shall
plot obtained in 5.3.3. In cases of disagreement, use the
be used. Procedure I may also be used to determine the HDB
calculation procedure. at elevated temperatures for some PE materials.
5.6.1 Alternate Method Procedure I:
5.4 Hydrostatic Design Basis—The procedure for determin-
5.6.1.1 Develop stress rupture data in accordance with 5.2
ing the HDB shall be as follows (see also Appendix X8):
forthetemperatureatwhichanHDBisdesired.Usingonlythe
5.4.1 Calculate the hydrostatic strength at 100 000 h
ductile failures, determine the linear regression equation. The
(LTHS) in accordance with 5.2.
failure point data must be spread over at least two log decades.
5.4.2 Calculate the hydrostatic strength at 50 years in
The stress intercept at 100000-h using this equation is the
accordance with 5.2.3.1.
“ductile” LTHS.
5.4.3 Estimate the long-term hydrostatic strength using
5.6.1.2 To determine the brittle failure performance, solve
expansion test data and in accordance with 5.3.
forthethreecoefficientsoftherateprocessmethodequationas
NOTE 7—For all the presently used stress rated thermoplastic pipe
follows:
materials in North America, the 5% expansion strengths are not the
(1)Select an elevated temperature appropriate for the
limiting factor. Therefore, this measurement is not required for such
polyethylene material. The maximum temperature chosen
materials.
should not be greater than 95°C (203°F).
5.4.4 Determine the hydrostatic design basis (HDB) by
(2)Select a stress at this temperature at which all failures
categorizing, in accordance with Table 1, the applicable hy-
occurinthebrittlemode(acrackthroughthepipewallwithno
drostatic strength value as specified below:
5.4.4.1 UsetheLTHSvalue(5.4.1)ifitislessthan125%of
the 50-year value (5.4.2), and less than the expansion strength
value (5.4.3).
TABLE 3 Validation of 73 °F (23 °C) HDB
5.4.4.2 Use the 50-year value if it is less than 80% of the
HDB to be 193 °F (90 °C) Test Temperature / 176 °F (80 °C) Test
LTHS value, and less than the expansion strength value.
Validated (psi) Temperature
5.4.4.3 Usetheexpansionstrengthvalueifitislessthanthe
Stress (psi) Time (h) Stress (psi) Time (h)
1600 735 70 825 200
LTHS and 50-year values.
1250 575 70 645 200
5.5 Hydrostatic Design Stress—Obtain the hydrostatic de- 1000 460 70 515 200
800 365 70 415 200
sign stress by multiplying the hydrostatic design basis by a
630 290 70 325 200
service (design) factor selected for the application on the basis
500 230 70 260 200
of two general groups of conditions. The first group considers
D2837 − 22
TABLE 4 Validation of 100 °F (38 °C) HDB
T = absolute temperature, °K (K=C+273),
HDB to be 193 °F (90 °C) Test Temperature /
S = hoop stress, psi, and
Validated (psi) 176 °F (80 °C) Test Temperature
A, B, C = constants.
Stress (psi) Time (h) Stress (psi) Time (h)
(6) Usingthismodel,calculatethestressinterceptvalueat
1600 850 300 960 1000
1250 670 300 750 1000
100000 h for the temperature at which the HDB is desired.
1000 600 300 600 1000
This resulting stress intercept is the “brittle” LTHS.
800 535 300 480 1000
NOTE 10—The ISO 9080 four coefficient model may be used if it has
630 340 300 380 1000
a better statistical fit to the data.
500 265 300 300 1000
5.6.1.3 Use the lower value of the ductile failure LTHS (see
5.6.1.1) or the brittle failure LTHS (see 5.6.1.2) to determine
TABLE 5 Validation of 120 °F (49 °C) HDB
the HDB category per Table 1 for this PE material. The HDB
HDB to be 193 °F (90 °C) Test Temperature /
determined by this procedure is considered validated.
Validated (psi) 176 °F (80 °C) Test Temperature
5.6.2 Standard Method (Procedure II)—The HDB for a PE
Stress (psi) Time (h) Stress (psi) Time (h)
material at a desired temperature is validated when the follow-
1600 970 1100 1090 3400
1250 760 1100 850 3400
ing criterion is met:
1000 610 1100 685 3400
5.6.2.1 Develop stress rupture data in accordance with 5.2
800 490 1100 545 3400
630 385 1100 430 3400 for the temperature at which an HDB is desired. Analyze the
500 305 1100 345 3400
data to determine the linear regression equation. Extrapolate
this equation to 100000 h to determine the LTHS. Use Table 1
to determine the HDB category at this temperature.
TABLE 6 Validation of 140 °F (60 °C) HDB
5.6.2.2 Use Tables 3-7 to define the time and stress require-
HDB to be 193 °F (90 °C) Test Temperature /
ments needed to validate this HDB.Test at least six specimens
Validated (psi) 176 °F (80 °C) Test Temperature
at the stress level determined by the tables. These specimens
Stress (psi) Time (h) Stress (psi) Time (h)
1250 860 3800 970 11300
must have a minimum log average time exceeding the value
1000 690 3800 775 11300
shown in the table to validate the HDB. For example, to
800 550 3800 620 11300
validate an HDB of 1000 psi at 140°F (60°C), this required
630 435 3800 490 11300
500 345 3800 390 11300
time is 3800 h at 193°F (90°C)⁄690 psi or 11300 h at 176°F
400 275 3800 310 11300
(80°C)⁄775 psi.
5.6.2.3 If a temperature/stress condition in the tables results
in a premature ductile failure for a particular PE material, the
TABLE 7 Validation of 160 °F (71 °C) HDB
stress at that temperature may be lowered by 15%. The
HDB to be 193 °F (90 °C) Test Temperature /
corresponding required time for this lowered stress is then six
Validated (psi) 176 °F (80 °C) Test Temperature
times the value in the table. For example, when validating an
Stress (psi) Time (h) Stress (psi) Time (h)
1250 975 12600 1100 37500
HDB of 1600 psi at 73°F, if testing at 80°C⁄825 psi results in
1000 780 12600 885 37500
ductile failures, lower the stress to 700 psi and retest. The
800 625 12600 705 37500
630 495 12600 550 37500 required time to validate using this condition is now 1200 h. If
500 390 12600 440 37500
ductilefailuresstilloccur,thestressmaybeloweredto595psi
400 315 12600 350 37500
and the corresponding time is increased to 7200 h.
5.6.3 Rate Process Method (Procedure III)—If there are no
brittle failures before 10 000 h when developing the data
according to 5.2, this rate process method may be used to
visible evidence of material deformation).This set of tempera-
validate the HDB.
ture and stress is called Condition I. Test at least six pipe
5.6.3.1 Develop data for the brittle failure performance as
specimens at this Condition I until failure.
described in 5.6.1.2, except use the data from Condition I,
(3)At the same temperature, select another stress about 75
Condition II, and the LTHS value at 100 000 h determined
to 150 psi lower than for Condition I. Test at least six pipe
from the linear regression model to calculate the A, B, and C
specimens at this Condition II until failure.
coefficients for the rate process model.
(4)Select a temperature 10°C (18°F) to 20°C (36°F)
5.6.3.2 Using this model, calculate the mean estimated
lower than the one in Condition I and use the same stress as
failure time for the temperature and stress used in Condition
Condition I. This is Condition III. Test at least six pipe
III. When the average time (log basis) for the six specimens
specimens at this Condition III until failure.
tested at Condition III has reached this time, the extrapolation
(5)Using all these brittle failure data points from Condi-
to100000htoobtaintheLTHShasbeenvalidated.(Examples
tions I, II, and III, calculate theA, B, and C coefficients for the
are shown in Appendix X9.)
following three-coefficient rate process method equation:
5.6.4 ISO 9080 Based Method for Validation of 140 °F
B ClogS
(60 °C) HDB (Procedure IV)—With some PE compounds the
logt 5 A1 1 (6)
T T
where: For additional information contact the Plastics Pipe Institute Hydrostatic Stress
Board Chairman, 105 Decker Court, Suite 825, Irving, TX 75062, http://
t = time, h,
www.plasticpipe.org
D2837 − 22
NOTE 11—The Long-Term Hydrostatic Strength at 50 years (LTHS50)
rate process method may result in very long test times to
is not to be used for pressure rating calculations. The maximum stress is
generate brittle failures. This method may also be used to
stillcalculatedusingtheHDB(withtheappropriatedesignservicefactors)
validateaHDBat140°F(60°C).Itcannotbeusedifthereare
obtained from the LTHS at 100000 h. PE materials meeting this
brittle failures before 10 000 h when developing the data
additional substantiation of the 73°F (23°C) extrapolation shall be
according to 5.2 to establish the HDB at 140°F.
denoted by an asterisk (*) in PPI TR-4.
5.6.4.1 Develop a linear regression according to 5.2 based
5.8 Pressure Rating—Calculate the pressure rating for each
on ductile stress-rupture data at either 80°C or 90°C. Use
diameterandwallthicknessofpipefromthehydrostaticdesign
Table 8 to determine the appropriate data level for the
stress(hydrostaticdesignbasis×servicefactor)forthespecific
temperature to be validated. The regression data must satisfy
material in the pipe by means of the equations in 3.1.11.
the following requirements:
5.9 Pressure Design Basis—The procedure for determining
(1)The 97.5% LCL ratio for these data must be greater
the PDB shall be as follows:
than 90%.
5.9.1 Calculate the hydrostatic pressure-strength at 100 000
(2)Non-failed specimens at the longest running times may
h (LTHS ) in accordance with 5.2.
P
be included in the regression provided their inclusion does not
5.9.2 Calculate the hydrostatic pressure-strength at 50 years
decrease the LTHS (see 5.2.2).
in accordance with 5.2.3.1.
5.6.4.2 The log average of the five longest running times
5.9.3 Determine the pressure design basis (PDB) by
(used in the regression) must exceed the minimum time t
max
categorizing, in accordance with Table 2, the applicable hy-
indicated in Table 8 to validate the HDB at 140°F (60°C)
drostatic pressure-strength value as specified below:
(Example shown in Appendix X9).
5.9.4 Use the LTHS value (5.9.1) if it is less than 125 % of
P
5.7 Substantiation of the HDB for Polyethylene Materials—
the 50-year value (5.9.2).
When it is desired to show that a PE material has additional
5.9.4.1 Use the 50-year value if it is less than 80 % of the
ductile performance capacity than is required by validation of
LTHSP value.
the73°F(23°C)time/stresscurveto100000hours,oneofthe
following three procedures may be used to further substantiate
6. Report
thatthestressregressioncurveislineartothe50year(438000
6.1 The report shall include the following:
h) intercept.
6.1.1 Complete identification of the sample, including ma-
5.7.1 If the HDB at 140°F (60°C) or higher temperature
terialtype,source,manufacturer’snameandcodenumber,and
has been validated by 5.6.2 or 5.6.4, then linear extrapolation
previous significant history, if any,
of the 73°F (23°C) stress regression curve to 50 years
6.1.2 Pipe dimensions including nominal size, average and
(438000 h) is substantiated.
minimum wall thickness, and average outside diameter,
5.7.2 If the HDB at 73°F (23°C) has been validated by
6.1.3 Test temperature,
5.6.3,usethetwelvedatapointsfromConditionIandII,along
6.1.4 Test environment inside and outside of the pipe,
with the 50 year (438000 h) intercept value, to solve for the
6.1.5 Atable of the stresses in pounds-force per square inch
three-coefficient rate process extrapolation equation. Then
or pressures in pounds-force per square inch gage and the
usingthisnewmodel,calculatethemeanestimatedfailuretime
time-to-failureinhoursforallthespecimenstested.Specimens
forConditionIII.Whenthelogaveragetimeforsixspecimens
thataredesignatedasfailuresaftertheyhavebeenunderstress
tested at Condition III has reached this time, linear extrapola-
or pressure for more than 10000 h shall be indicated,
tion of the 73°F (23°C) stress regression curve to 50 years
6.1.6 The estimated long-term hydrostatic strength or
(438000 hours) is substantiated.
pressure-strength,
5.7.3 If the HDB at 73°F (23°C) has been validated by
6.1.7 The estimated stress at 50 years,
5.6.2, linear extrapolation of the stress regression curve to 50
6.1.8 A table of the percent circumferential expansion
years (438000 hours) is substantiated when the log average
versus time data and the estimated stress at 5.00% expansion.
failure time of six test specimens at 176°F (80°C) surpasses
Thisitemneednotbereportedifprevioustestresultsshowthat
6000 h, or at 193°F (90°C) surpasses 2400 h at a stress of no
the stress calculated for 5% expansion is significantly greater
more than 100 psi below where all failures are ductile. A
than that reported in 6.1.6 or 6.1.7, or for PDB values.
ductile failure reference stress shall be established by 3
6.1.9 The hydrostatic design basis or pressure design basis,
specimens all failing in the ductile mode at the same tempera-
6.1.10 The nature of each of the failures observed shall be
ture.
included in the table of stresses or pressures and times-to-
failurementionedin6.1.5(referto3.1.1forfailuretypes,other
descriptors may also be used),
TABLE 8 Validation of HDB at 140 °F
6.1.11 Any unusual behavior observed in the tests, as well
193 °F (90 °C) 176 °F (80 °C)
as any data for specimens that were not included in the
Temperature to be Regression Regression
regression analysis in a separate table and the reason why they
validated °F Data Min Data Min.
A B A B
Level .t Level t
were excluded (for example: nonfailure/on-test, stopped
max max
140 °F E-6 5500 E-10+ 17 000
testing, equipment problems, less than 10 h or not part of
(60 °C)
regression),
A
Per data interval requirements in PPI TR-3.
B 6.1.12 If the material is polyethylene, the results of the
t = log average of 5 longest test times (included in regression)
max
validation in accordance with 5.6,
D2837 − 22
6.1.13 Dates of test, and design basis since the result merely states whether there is
6.1.14 Name of laboratory and supervisor of the tests. conformance to the criteria for success specified in the proce-
dure.
7. Precision and Bias
7.1 No statement is made about either the precision or the
bias of Test Method D2837 for measuring the hydrostatic
APPENDIXES
(Nonmandatory Information)
X1. METHODOLOGY FOR THE FORECASTING OF THE LONGER-TERM HYDROSTATIC STRENGTH OF THERMOPLAS-
TIC PIPING MATERIALS IN CONSIDERATION OF THE NATURE OF THEIR STRESS-RUPTURE BEHAVIOR
X1.1 Similartowhathasbeenobservedformetalsathigher is a gradual “downturn,” or a relatively sharp “knee”) in the
temperatures, the stress-rupture data obtained on thermoplas- slope of the initially defined stress-rupture line. In such cases,
tics piping materials generally yields a relatively straight line the stress-rupture data can best be characterized by means of
when plotted on log stress versus log time-to-fail coordinates. twostraightlines:aninitiallineoffairlyflatslope;followedby
By means of regression analysis, such straight-line behavior a second line of steeper slope. The change in slope from the
can readily be represented by a mathematical equation. Using firsttothesecondlinecanbeminimal,inwhichcasethestress
this equation, the long-term strength of a material for a time rupture behavior is generally sufficiently well-characterized by
under load much beyond the longest time over which the data a single average line; or, the change can be significant, in
were obtained can be determined by extrapolation. This which case, it is more accurately represented by two straight
straight-linebehaviorhasbeenobservedtoholdtruefornearly lines, each with a different slope (see Fig. X1.1). Should there
all plastic piping materials, provided failures always occur by occur a significant downward trend in slope, the extrapolation
the same mechanism. However, it has also been observed that of the trend solely defined by the earlier stage of stress-rupture
when the cause of failure transitions from one mechanism to behavior may result in an excessive overestimation of a
another, that is, from failure caused by excessive ductile material’sactualLTHS.Foramoreaccurateforecast,itshould
deformation to a failure resulting by the initiation and growth be made based on the trend exhibited by the second straight
of a crack, this may result in a significant downward shift (that line, a trend that may not always be evidenced by the data
FIG. X1.1 Schematic of the Stress-Rupture Characteristics of a Material Which Exhibits Two Stages in Stress-Rupture Properties, and of
the Shift in the Stress-Rupture Lines that Results by Increasing the Test Temperature.
D2837 − 22
collected during the minimum testing period of 10000 h, as thermoplastic piping materials that are chemically and physi-
required by this test method. cally similar to the material of interest. Another kind is very
extensive field experience with specific kinds and grades of
X1.2 Studies conducted on polyolefin pipes indicate that,
materials. For example, as previously mentioned, it is well-
exclusiveofpotentialeffectsofpolymerchemicaldegradation,
established both through testing and very extensive experience
or aging, that may occur in consequence of the effects of
that rigid PVC piping materials which have been formulated
environments that are aggressive to the polymer, stress-rupture
usingPVCresinsofcertainminimummolecularweightexhibit
failurescanoccurovertwostages.Inthefirststage,failuresare
no “downturn” at ambient temperatures through at least
ofaductilenature,but,inthesecond,theyaretheconsequence
100000 h when tested using water or air as the pressure
of the initiation an
...