INTERNATIONAL ISO
STANDARD 9969
Third edition
2016-01-15
Thermoplastics pipes —
Determination of ring stiffness
Tubes en matières thermoplastiques — Détermination de la
rigidité annulaire
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ISO 9969:2016
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Reference number
ISO 9969:2016(E)
© ISO 2016
ISO 9969:2016(E)
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ISO 9969:2016
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ISO 9969:2016(E)
Contents Page
Foreword......................................................................................................................................................................................................................................... iv
1 Scope.................................................................................................................................................................................................................................. 1
2 Normative references....................................................................................................................................................................................... 1
3 Symbols........................................................................................................................................................................................................................... 1
4 Principle......................................................................................................................................................................................................................... 1
5 Apparatus...................................................................................................................................................................................................................... 2
6 Test pieces.................................................................................................................................................................................................................... 3
6.1 Marking and number of test pieces........................................................................................................................................ 3
6.2 Length of test pieces............................................................................................................................................................................ 3
6.3 Inside diameter of test piece(s)................................................................................................................................................. 4
6.4 Age of test pieces.................................................................................................................................................................................... 4
7 Conditioning............................................................................................................................................................................................................... 5
8 Procedure..................................................................................................................................................................................................................... 5
9 Calculation of ring stiffness........................................................................................................................................................................ 7
10 Test report.................................................................................................................................................................................................................... 8
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ISO 9969:2016(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.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
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. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the meaning of ISO specific terms and expressions related to conformity
assessment, as well as information about ISO’s adherence to the WTO principles in the Technical
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Barriers to Trade (TBT) see the following URL: Foreword - Supplementary information
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The committee responsible for this document is 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.
ISO 9969:2016
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This third edition cancels and replaces10e263b55dd6/iso-9969-2016
the second edition (ISO 9969:2007), which has been
technically revised.
iv © ISO 2016 – All rights reserved
INTERNATIONAL STANDARD ISO 9969:2016(E)
Thermoplastics pipes — Determination of ring stiffness
1 Scope
This International Standard specifies a test method for determining the ring stiffness of thermoplastics
pipes having a circular cross section.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. 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 Symbols
For the purposes of this document, the following symbols apply.
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dn nominal diameter of(standards.iteh.ai)
pipe mm
di inside diameter of the test piece of pipe mm
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ec construction height
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F loading force kN
F0 pre-load force N
L length of test piece mm
p pitch of ribs or windings mm
S ring stiffness kN/m2
y vertical deflection mm
4 Principle
The ring stiffness is determined by measuring the force and the deflection while deflecting the pipe at
a constant deflection speed.
A cut length of pipe supported horizontally is compressed vertically between two parallel flat plates
moved at a constant speed that is dependent upon the diameter of the pipe.
A plot of force versus deflection is generated. The ring stiffness is calculated as a function of the force
necessary to produce a 3 % diametric deflection of the pipe.
NOTE It is assumed that the test temperature is set by the referring standard, if appropriate (see 8.1).
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ISO 9969:2016(E)
5 Apparatus
5.1 Compressive testing machine, capable of a constant rate of crosshead movement, via a pair of
parallel plates (5.2), as appropriate to the nominal diameter of the pipe in conformance with Table 1,
with sufficient force and travel to produce the specified diametric deflection (see Clause 8).
Table 1 — Deflection speeds
Inside diameter, di, of the test Deflection speed
piece of pipe mm/min
mm
di ≤ 100 2 ± 0,1
100 < di ≤ 200 5 ± 0,25
200 < di ≤ 400 10 ± 0,5
400 < di ≤ 710 20 ± 1
di > 710 0,03 × di ± 5 %
di shall be determined in accordance with 6.3.
5.2 A pair of hard and rigid plates, through which the testing machine can apply the necessary force,
F, to the test piece.
The plates shall have flat, smooth and clean surfaces for contact with the test piece.
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The stiffness and hardness of each plate shall be sufficient to prevent bending or deformation to an
extent that would affect the results. (standards.iteh.ai)
The length of each plate shall be at least equal toISO the length of the test piece. The width of each plate
9969:2016
shall not be less than the width of the contact surface with the test piece while under load plus 25 mm.
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5.3 Dimensional measuring devices, capable of determining
— individual values for the length of a test piece (see 6.2.2 and 6.2.3) to with an accuracy of ± 1 mm,
— the inside diameter of a test piece to with an accuracy of ± 0,5 %, and
— the change of inside diameter of a test piece in the direction of loading with an accuracy of 0,1 mm
or 1 % of the deflection, whichever is the greater.
An example of a device for measuring the inside diameter of corrugated pipe is shown in Figure 1.
Figure 1 — Example of device for measuring inside diameter of corrugated pipe
5.4 Force measuring device, capable of determining with an accuracy of ± 2 % the force necessary to
produce a deflection of up to 4 % of the test piece.
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ISO 9969:2016(E)
6 Test pieces
6.1 Marking and number of test pieces
The pipe of which the ring stiffness is to be determined shall be marked on its outside with a line along
one generatrix over its entire length. Three test pieces, a, b and c, respectively, shall be taken from this
marked pipe such that the ends of the test pieces are perpendicular to the pipe axis and their lengths
conform to 6.2.
6.2 Length of test pieces
6.2.1 The length of each test piece shall be determined by calculating the arithmetic average of three
to six measurements of length equally spaced around the perimeter of the pipe, as given in Table 2. The
length of each test piece shall conform to 6.2.2, 6.2.3, 6.2.4 or 6.2.5, as applicable.
Each of the three to six length measurements shall be determined to within 1 mm.
For each individual test piece, the smallest of the three to six measurements shall not be less than
0,9 times the largest length measurement.
Table 2 — Number of length measurements
Nominal diameter, dn, of pipe
Number of length measurements
mm
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d ≤ 200
n 3
(standards.iteh.ai)
200 < d < 500
n 4
dn ≥ 500 6
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6.2.2 For pipes that have nominal 10e263b55dd6/iso-9969-2016
diameters equal to or less than 1 500 mm, the average length of the
test pieces shall be (300 ± 10) mm.
6.2.3 For pipes that have nominal diameters larger than 1 500 mm, the average length of the test pieces
in millimetres shall be at least 0,2 dn.
6.2.4 Structured wall pipes with perpendicular ribs, corrugations or other regular structures shall be
cut such that each test piece contains a whole number of ribs, corrugations or other structures. The cuts
shall be made at the mid point between the ribs, corrugations or other structures.
The length of the test pieces shall be the minimum whole number of ribs, corrugations or other structures
resulting in a length of 290 mm or greater or, for pipes greater than 1 500 mm, 0,2 dn or greater.
See Figure 2.
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ISO 9969:2016(E)
Key
L length of test piece
p pitch
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Figure 2 — Test piece cut out of perpendicularly ribbed pipe
(standards.iteh.ai)
6.2.5 Structured wall pipes with helical ribs, corrugations or other regular structures shall be cut such
that the length of the test pieces is equal to the inside diameter ± 20 mm but not less than 290 mm nor
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6.3 Inside diameter of test piece(s)
The inside diameters, dia, dib and dic, of the respective test pieces, a, b and c (see 6.1), shall be
determined either as
a) the arithmetic average of four or more measurements in accordance with ISO 3126 of one cross
section at mid-length, where each measurement shall be determined with an accuracy of ± 0,5 %, or
b) measured at mid-length cross-section by means of a π tape in accordance with ISO 3126.
The calculated or measured average inside diameter for each test piece, a, b and c, shall be recorded, as
dia, dib and dic, respectively.
The average value, di, of these three calculated values shall be calculated using Formula (1):
d ia + d ib + d ic
di = (1)
3
6.4 Age of test pieces
At the start of testing in accordance with Clause 8, the age of the test pieces shall be at least 24 h.
For type testing, and in case of dispute, the age of the test pieces shall be (21 ± 2) days.
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ISO 9969:2016(E)
7 Conditioning
The test pieces shall be conditioned in air at the test temperature (see 8.1) for at least 24 h immediately
prior to testing in accordance with Clause 8.
8 Procedure
8.1 Unless otherwise specified in the referring standard, carry out the following procedure at
(23 ± 2) °C or, in countries where 27 °C is used as standard laboratory temperature, at (27 ± 2) °C.
In case of dispute, (23 ± 2) °C shall be used.
NOTE It is probable that the test temperature has an influence on the ring stiffness.
8.2 If it can be determined in which position the test piece has the lowest ring stiffness, place the first
piece, a, in this position in the loading device.
Otherwise, place the first test piece in such a way that the marking line or split line is in contact with
the upper parallel plate.
In the loading device, rotate the two other test pieces, b and c, respectively 120° and 240° in relation to
the position of the first test piece when placing them in their loading devices.
8.3 For each test piece, attach the deflection gauge and check the angular position of the test piece in
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relation to the upper plate.
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Position the test piece with its longitudinal axis parallel to the plates and with its middle point vertically
under the centre-line of the load cell.
ISO 9969:2016
In order to obtain the correct reading from the load cell, it is necessary to position the test piece so the
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expected resulting force is approximately in line with the axis of the load cell.
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8.4 Lower the loading plate until it touches the upper part of the test piece.
Apply one of the following pre-load forces, F0, as applicable, rounded up to the nearest newton if
calculated from Formula (2), taking into account as applicable the mass of the loading plate:
a) for pipes with di less than or equal to 100 mm, F0 shall be 7,5 N;
b) for pipes with di larger than 100 mm, F0 shall be calculated using Formula (2) in newtons and the
result rounded up where necessary to the next higher newton:
F0 = 250 × 10−6di × L1 (2)
where
di is the mean actual inside diameter of the pipe test piece, in millimetres;
L1 is the calculated average length of the test piece, in millimetres.
The actually applied pre-load force shall be between 95 % and 105 % of the calculated force when
measured with the accuracy possible with the load cell used for the test.
Then adjust the deflection gauge and load cell to zero.
In case of dispute, the zero adjustment method shall be used, see 8.6.
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