ISO 23228:2011

INTERNATIONAL ISO
STANDARD 23228
First edition
2011-10-01
Thermoplastics pipes for the
conveyance of fluids — Determination
of the stress-rupture resistance of
moulding materials using plain strain
grooved tensile (PSGT) specimens
Tubes en matières thermoplastiques pour le transport des fluides —
Détermination de la résistance à la rupture sous contrainte des
matériaux de moulage, au moyen d’éprouvettes de traction rainurées à
déformation plane
Reference number
ISO 23228:2011(E)
©
ISO 2011

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ISO 23228:2011(E)
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ISO 23228:2011(E)
Contents Page
Foreword . iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
5 Apparatus . 2
5.1 Loading system . 2
5.2 Constant temperature system . 3
5.3 Timing device . 3
5.4 Failure detection device . 3
5.5 Sample grips . 3
5.6 Calibration and accuracy of the apparatus . 3
6 Test specimen . 4
6.1 Dimensions . 4
6.2 Measurements . 5
6.3 Specimen preparation . 5
7 Conditioning . 6
8 Procedure . 6
9 Calculation . 6
10 Test report . 7
Annex A (informative) Determination of specimen dimensions for the plane strain condition . 8
Bibliography . 9
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ISO 23228:2011(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International
Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 23228 was prepared by Technical Committee ISO/TC 138, Plastics pipes, fittings and valves for the
transport of fluids, Subcommittee SC 5, General properties of pipes, fittings and valves of plastic materials and
their accessories — Test methods and basic specifications.
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ISO 23228:2011(E)
Introduction
ISO/TC 138 provides test methods for determining the resistance to internal pressure which are essential for
assessing the properties and durability of thermoplastics piping system parts. These test methods constitute a
basis for the determination of short-term and long-term strength characteristics. However, with regard to moulding
materials for pipes and fittings, until the publication of this International Standard, no satisfactory test method has
existed in which the material can be exposed to stress conditions that mimic internally pressurized pipes.
The method specified here has been demonstrated to replicate the stress conditions of internally pressurized
end-capped pipes by the use of plaque specimen having a reduced section in the form of a groove positioned
perpendicular to the uniaxial loading direction. This method is useful for evaluating the stress-rupture resistance
of moulding materials and experimental resins being developed for pipes and fittings as well as for those pipes
that are difficult to test, such as larger diameter pipes.
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INTERNATIONAL STANDARD ISO 23228:2011(E)
Thermoplastics pipes for the conveyance of fluids —
Determination of the stress-rupture resistance of moulding
materials using plain strain grooved tensile (PSGT) specimens
1 Scope
This International Standard specifies a method for the determination of the time-to-failure of thermoplastics
resins and compounds for piping and fitting applications by the use of a plane strain grooved tensile specimen
in a stress-rupture test.
The grooved tensile specimen produces a biaxial state of stress on uni-axial loading, which is taken to be
indicative of the stress conditions found in pressurized solid-wall plastics pipes. The ratio of the stress in
the axial direction to the transverse direction approximates that for a pressurized end-capped solid-wall pipe
[4]–[7]
specimen .
It is intended that the data generated on these specimens be utilized to determine the stress-rupture (time to
failure) resistance of moulding materials for pipes and fittings as well as experimental piping resins.
This method is also applicable to stress-rupture evaluations of pipes which are difficult to test, e.g. larger
diameter pipes, including their batch release tests.
[2]
This International Standard is not intended to replace the stress-rupture test of ISO 1167 , which uses internally
pressurized end-capped pipes.
2 Normative references
The following referenced document is indispensable for the application of this document. For dated references,
only the edition cited applies. For undated references, the latest edition of the referenced document (including
any amendments) applies.
ISO 3126, Plastics piping systems — Plastics components — Determination of dimensions
3 Terms and definitions
For the purposes of this International Standard, the following terms and definitions apply.
3.1
stress-rupture test
test at which a constant nominal stress is applied and maintained until specimen rupture (failure)
3.2
failure time
t
f
time at which a specimen fails by gross yielding or by through thickness slow crack propagation on stress-
rupture loading
NOTE The failure time is expressed in hours.
3.3
applied nominal stress
σ
n
applied stress calculated using the undeformed minimum groove cross-sectional area
NOTE The applied nominal stress is expressed in megapascals.
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ISO 23228:2011(E)
3.4
plane strain condition in the groove
zero strain condition in the groove axis where there exists no change in displacement along the groove on load
application perpendicular to the groove axis
NOTE In PSGT specimens, the stress biaxiality is developed in the groove as a result of the plane strain condition in
the groove. Plane strain condition also occurs in the end-capped pipe when internally pressurized.
3.5
long-term hydrostatic strength
σ
LTHS
quantity with the dimensions of stress, which represents the predicted mean hydrostatic hoop strength at a
temperature, T, and failure time, t
f
NOTE The long-term hydrostatic strength is expressed in megapascals.
3.6
long-term strength
σ
LTS
quantity with the dimension of stress, which represents the predicted mean strength at a temperature, T, and
failure time, t
f
NOTE 1 The long-term strength is expressed in megapascals.
NOTE 2 Long-term strength σ is similar to long-term hydrostatic strength σ ; however, they differ in the mode of
LTS LTHS
loading, tensile versus hydrostatic.
4 Principle
A plane strain grooved tensile (PSGT) specimen is made from a moulded flat plaque of finite width and length
dimensions having reduced area (see Figures 1 and 2). The concave grooves are made along the width of the
specimen and perpendicular to the axis of the direction of uni-axial loading. The plane strain condition in the
groove is induced by the deformation constraint in the groove. This is the result of the difference between the
reduced thickness, e , of the groove and unreduced thickness, e, of the test specimen, as illustrated in Figure 2.
g
With the appropriate dimensions applied (see Table 1 and Figure 2) a plane strain condition, and hence biaxial
stress state, is generated in the groove on uniaxial loading. After conditioning in the test medium, the specimen
is subjected to a specified constant load for sustained time duration until the test specimen fails, at which point
the stress and corresponding rupture time are recorded. In this manner, it can be tested in various controlled
environments, and at specified constant temperatures, in order to obtain the long-term strength capacity of
moulding materials for pipes and fittings. Such a controlled environment can be accomplished by, but is not
limited to, immersing the specimens in a controlled-temperature water bath or circulating-air oven.
The PSGT stress-rupture data obtained from moulding materials, experimental piping resins and samples
obtained from pipes and fittings can be extrapolated in accordance with a method such as that specified
[3]
in ISO 9080 for providing estimations on their long-term strength properties. For estimating the effect of
extrusion processing on pipes, the results from PSGT specimen can be compared with the results generated
[2]
with pipes according to ISO 1167 .
5 Apparatus
5.1 Loading system
Any device that is capable of continuously applying constant load on the specimen may be used. The device
shall be capable of reaching the test load without exceeding it and holding it to within ±1 % of the applied
load throughout duration of the test. A loading system that utilizes an electro-pneumati
...