ISO 3126:2005

INTERNATIONAL ISO
STANDARD 3126
Second edition
2005-03-01

Plastics piping systems — Plastics
components — Determination of
dimensions
Systèmes de canalisations en plastiques — Composants en
plastiques — Détermination des dimensions




Reference number
ISO 3126:2005(E)
©
ISO 2005

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ISO 3126:2005(E)
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ISO 3126:2005(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 3126 was prepared by the European Committee for Standardization (CEN) in collaboration with 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, in accordance with the Agreement on technical cooperation between ISO and CEN
(Vienna Agreement).
Throughout the text of this document, read “.this European Standard.” to mean “.this International
Standard.”.
This second edition cancels and replaces the first edition (ISO 3126:1974), which has been technically
revised.
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ISO 3126:2005(E)

C ontents           page
Foreword.v
1 Scope.1
2 Normative references .1
3 Terms, definitions and symbols .1
3.1 Terms and definitions.1
3.2 Symbols .1
4 Measuring devices .2
4.1 General requirements .2
4.2 Instruments .2
5 Determination of dimensions.3
5.1 General .3
5.2 Wall thicknesses .4
5.3 Diameters.5
5.4 Out-of-roundness .6
5.5 Pipe lengths .6
5.6 End squareness of pipes and fittings.7
6 Determination of other geometrical characteristics related to fittings .8
6.1 General .8
6.2 Bends .9
6.3 Branches .12
6.4 Reducers.14
7 Flanges, loose flanges and collar .15
7.1 General .15
7.2 Outside diameter of the flange, loose flange and collar.17
7.3 Bore diameter of the flange or collar.17
7.4 Bolt hole diameter .17
7.5 Bolt hole distribution.17
7.6 Concentricity of bolt circle diameter.17
7.7 Pitch circle diameter.17
7.8 Shoulder diameter of flange and collar .18
7.9 Flange and collar thickness .18
7.10 Length of the flange and collar.18
8 Other measurements .18
Bibliography .19



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ISO 3126:2005(E)

Foreword


This document (EN ISO 3126:2005) has been prepared by Technical Committee CEN /TC 155, "Plastics piping

systems and ducting systems", the secretariat of which is held by NEN in collaboration with Technical Committee
ISO/TC 138 "Plastics pipes, fittings and valves for the transport of fluids".
This European Standard shall be given the status of a national standard, either by publication of an identical text or
by endorsement, at the latest by September 2005, and conflicting national standards shall be withdrawn at the
latest by September 2005.
This document is one of a series of standards on test methods, which support system standards for plastics piping
systems and ducting systems.
According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following
countries are bound to implement this European Standard: Austria, Belgium, Cyprus, Czech Republic, Denmark,
Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,
Netherlands, Norway, Poland, Portugal, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.

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ISO 3126:2005(E)
1 Scope
This document specifies methods for measurement and/or determination of the dimensions of plastics pipes and
fittings and the accuracy of the measurement.
It specifies procedures for measuring angles, diameters, lengths, squareness and wall thicknesses for the
purposes of checking conformity to geometric limits.
NOTE This document is using metric units. However the procedures and tolerances are applicable to other units by using
appropriate conversion factors.
2 Normative references
The following referenced documents are 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/R 463, Dial gauges reading in 0,01 mm, 0,001 in and 0,0001 in.
ISO 3599, Vernier callipers reading to 0,1 and 0,05 mm.
ISO 3611, Micrometer callipers for external measurement.
ISO 6507-1, Metallic materials — Vickers hardness test — Part 1: Test method.
3 Terms, definitions and symbols
3.1 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1.1
accuracy
closeness of agreement between a test result and the accepted reference value
NOTE  The term "accuracy", when applied to a set of test results, involves a combination of random components and a
common systematic error or bias component (ISO 3534-1).
3.1.2
calibration
set of operations that establish, under specified conditions, the relationship between values of quantities indicated
by a measuring instrument or measuring system, or values represented by a material measure or a reference
material, and the corresponding values realised by standards
3.1.3
reference standard
internationally accepted definition of a given unit of measurement
3.2 Symbols
b : distance between the edge of a flange bolt hole and its bore
1
b : distance between the edge of a flange bolt hole and its outside diameter
2
b : distance between the centre of a flange bolt hole and its bore
3
b : distance between the centre of a flange bolt hole and its outside diameter
4
c : distance between the edges of two adjacent flange bolt holes
1
c : distance between the centres of two adjacent flange bolt holes
2
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ISO 3126:2005(E)
d : outside diameter of a (part of a) component
e
d : mean inside diameter of the main of a branch
i,m
d : outside diameter of a socket end
1
d : outside diameter of a spigot end
2
d : bore of a flange
3
d : diameter of a flange bolt hole
4
D : outside diameter of a flange
e : wall thickness of a component
k : pitch circle diameter of a flange
L : effective length of a branch
e,b
L : effective length of the main of a branch
e,m
L : effective length of a reducer
e,r
L : effective length of the socket end of a fitting
e,so
L : effective length of the spigot end of a fitting
e,sp
L : length of the straight part of a socket or a spigot end of a fitting
str
L : length of the tapered part of a reducer
t
L : maximum out-of-squareness distance from theoretical
1
L : measured distance from the root of the angle between a straight ruler and a reference surface to the
2
component along the surface
L : measured distance from the root of the angle between a straight ruler and a reference surface to the
3
component along the ruler
L : vertical distance from a reference surface to the nearest point of the upper end
4
L : socket insertion depth
5
L : overall length of a branch main
6
L : distance, measured in the centre-line plane of a branch, between the end of the branch spigot or socket to
7
the bottom of the main
L : overall length of a reducer
8
L : distance between the edges of two selected bolt holes of a flange
9
L : overall length of a flange in axial direction
10
γ : calculated angle of out-of-squareness
θ : angle of bend or branch
4 Measuring devices
4.1 General requirements
4.1.1 Accuracy of measuring devices
The measuring device shall be selected so that together with the associated procedures used the required
accuracy of the measured dimension is obtained.
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ISO 3126:2005(E)
4.1.2 Calibration
Device used for measuring shall be calibrated at regular intervals of time in accordance with the quality plan of the
user of this document. The calibration shall be traceable to an accredited reference standard (see 3.1.3).
4.2 Instruments
4.2.1 Contact instruments
4.2.1.1 In use the instruments shall not apply a force to the surface of the test piece that will cause local
deformation.
4.2.1.2 Measuring devices that require contact between the test piece and one or more surfaces, e.g. a tube
micrometer, shall conform to the following:
a) the surface in contact with the internal surface of a component shall have a radius less than that of the test
piece surface with which it is in contact;
b) the surface in contact with the external surface of a component shall be either flat or radiused;
c) the contact surfaces of the instrument shall have a hardness not less than 500 HV when tested in accordance
with ISO 6507-1.
4.2.1.3 Micrometer callipers shall conform to ISO 3611 if applicable. Vernier callipers shall conform to ISO 3599 if
applicable.
4.2.1.4 If the measuring instrument incorporates a dial gauge, it shall conform to ISO/R 463.
4.2.1.5 If the device comprises a circumference tape (π tape), it shall be graduated in diameters expressed in
millimetres. When a force of 2,5 N is applied in the longitudinal direction to the extremities of the tape, the
elongation of the tape shall not exceed 0,05 mm/m.
4.2.1.6 Measuring instruments may be used in conjunction with a setting standard of calibrated thickness or
length, and then used as a comparator, i.e. to measure small differences between the setting piece and the
measured dimension on the test piece.
NOTE This is particularly recommended when measuring large diameter or thick walled components.
4.2.1.7 Go/no-go gauges may be used for checking conformity to specific limits.
4.2.1.8 Contact instruments other than those mentioned in 4.2.1.3, 4.2.1.4, 4.2.1.5 and 4.2.1.7 may also be used.
Ultrasonic measuring devices shall be regarded as non-contact instruments (see 4.2.2).
4.2.2 Non-contact instruments
If non-contact instruments or devices based on e.g. optical or ultrasonic scanning devices are used, the accuracy
of measurement shall conform to accuracy levels specified in the relevant subclause of Clause 5 or their use shall
be restricted to finding relevant positions for measurements to be made by other means, e.g. points comprising
maximum or minimum dimensions.
5 Determination of dimensions
5.1 General
5.1.1 Ensure that measurement of dimensions is carried out by personnel trained in the applicable equipment
and procedures.
5.1.2 Unless otherwise specified in the referring standard, ensure that either:
a) the temperature of the measuring device, the test piece and the ambient air temperature are at (23 ± 2) °C; or
b) results are correlated by calculation or experience to their value at 23 °C.
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ISO 3126:2005(E)
5.1.3 Examine the test piece surface for any features that could affect dimensional measurements, e.g. marking,
parting lines, blisters or inclusions. If found, record their nature and effects on the measurement.
5.1.4 For selection of the cross-section(s) in which to make measurements, one or more of the following shall
apply, as applicable:
a) select cross-section(s) as specified by the referring standard;
b) identify a cross-section not less than 25 mm from the end or in accordance with the component manufacturer's
specification;
c) for measurements of a dimension associated with another dimension, e.g. to enable calculation of a further
dimension, the cross-section shall be appropriate to the dimension to be calculated.
5.1.5 Results of measurements are rounded as specified in 5.2.3, 5.3.3 and 5.3.4. When determining mean
values the rounding shall be done after the arithmetic mean value has been calculated.
5.2 Wall thicknesses
5.2.1 General
Select instrument(s) or device(s) and associated procedures for measuring wall thickness so that the accuracy of
the result is within the limits given in Table 1, unless otherwise specified in the referring standard.
Table 1 — Measurement of wall thickness
Dimensions in millimetres
Required accuracy of Round arithmetic mean
Wall thickness
a
individual result value to the nearest:
≤ 10 0,03 0,05
> 10 and ≤ 30 0,05 0,1
> 30 0,1 0,1
a
 Exactly intermediate values shall be rounded up.

5.2.2 Maximum and minimum wall thicknesses
Move the measuring device until the positions of the maximum and/or minimum wall thicknesses as appropriate in
the selected cross-sections are found and record the observed value(s).
5.2.3 Mean wall thickness
In each selected cross-section, take at least six measurements of the wall thickness at regular intervals around the
circumference.
From the values obtained, calculate the arithmetic mean value, round in accordance with Table 1 and record the
answer as the mean wall thickness, e .
m
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ISO 3126:2005(E)
5.3 Diameters
5.3.1 General
5.3.1.1 Select the instrument(s) or device(s) and associated procedures for measuring diameters (outside or
inside) of the test piece at the selected cross-section(s), so that the accuracy of the result is in accordance with
Table 2, unless otherwise specified in the referring standard.
Table 2 — Measurement of diameter
Dimensions in millimetres
Nominal diameter Required accuracy of Round arithmetic mean
a
DN individual result
value to the nearest:
≤ 600 0,1 0,1
600 < DN ≤ 1600 0,2 0,2
> 1600 1 1
a
 Exactly intermediate values shall be rounded up.

5.3.1.2 For measuring the diameter(s) of components, select the relevant cross-section(s) in accordance
with 5.1.4.
5.3.2 Measurement of maximum and minimum diameter
Move the measuring device in each selected cross-section until the appropriate extreme value(s) of the diameter
are found and record the observed value(s).
5.3.3 Mean outside diameter
The mean outside diameter, d , may be determined from either:
e,m
a) direct measurement using a π-tape; or
b) a calculated value derived from a series of individual measurements conforming to Table 3, taken at regular
intervals around each of the selected cross-sections.
In case of item b), calculate the arithmetic mean of the individual measurements, round in accordance with Table 2
and record the answer as the mean outside diameter, d .
e,m
Table 3 — Number of individual diameter measurements
for a given nominal size
Nominal size of pipe Number of individual diameter measurements
or fitting required in a given cross section
≤ 40 4
> 40 and ≤ 600 6
> 600 and ≤ 1600 8
> 1600 12

5.3.4 Mean inside diameter
Using a device conforming to 5.3.1.1, determine either:
a) a series of individual measurements conforming to Table 3 at regular intervals; or
b) direct measurement using an inside π-tape.
Calculate the arithmetic mean of the individual measurements obtained in a), round in accordance with Table 2 and
record it as the applicable mean inside diameter, d .
i,m
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ISO 3126:2005(E)
5.3.5 Neutral diameter
Using the values determined in accordance with 5.2 and/or 5.3 without rounding, calculate the mean diameter, d ,
m
using one of the following equations as applicable:
d = d − e ;
m e,m m
d = d + e ;
m i,m m
d = 0,5(d + d ).
m e,m i,m
where:
d is the mean outside diameter at the appropriate cross-section;
e,m
e is the mean wall thickness at the appropriate cross-section;
m
d is the mean inside diameter at the appropriate cross-section.
i,m
Record the calculated mean diameter after rounding in accordance with Table 2.
NOTE This procedure is not applicable to thermoplastics structured-wall pipes and fittings.
5.4 Out-of-roundness
Determine the extreme values of the specified diameter in the chosen cross-section in accordance with 5.3.2 with
the accuracy as specified in Table 4 and calculate the out-of-roundness as defined in the relevant product
standard.
Table 4 — Accuracy for out-of-roundness measurement
Nominal diameter DN Required accuracy of
individual result
≤ 315 0,1
315< DN ≤ 600 0,5
> 600 1

5.5 Pipe lengths
5.5.1 Select measuring instrument(s) or device(s) and associated procedures so that the accuracy of the result is
in accordance with Table 5 unless otherwise specified in the referring standard.
Table 5 — Measurement of lengths
Length Required accuracy of Round arithmetic mean
a
mm individual result value to the nearest:
≤ 1000 1 mm 1 mm
> 1000 0,1 % 1 mm
a
 Exactly intermediate values shall be rounded up.

5.5.2 Use equipment conforming to 5.5.1 to determine the overall length and/or the effective length, as
applicable, of an individual pipe.
To determine the overall length of the pipe, take measurements along the internal or external surface, parallel to
the axis of the pipe, on at least three positions spaced at regular intervals around its circumference. Pipes cut by a
machine that ensures a square cut need only to be measured in one position.
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ISO 3126:2005(E)
When applicable calculate the arithmetic mean value from the measured values, round in accordance with Table 5
and record the result as the overall length of the pipe.
From the overall length of the pipe, subtract the socket insertion depth(s), if any, and record the result obtained as
the effective length of the pipe.
5.6 End squareness of pipes and fittings
5.6.1 General
Select instrument(s) or device(s) and associated procedure for measuring the end squareness of pipes and fittings
so that the estimated accuracy of measurement is 0,5 mm for DN ≤ 200 and 1 mm for DN > 200 unless otherwise
specified in the referring standard.
5.6.2 Principle
The following procedures assume that the outside surface of the pipe or fitting is parallel to its longitudinal axis. It is
also assumed that either a steel square or plumb bob is used as the reference plane though any equipment
capable of being set square to the components axis can be used. The steel square technique is suitable for small
and medium size components whereas the plumb bob is suitable for medium or large size components.
In accordance with Figure 1, a steel square or a plumb bob is positioned such that it touches the components. The
out-of-squareness, γ, is then calculated using the measured outside diameter and the measured distance, L , (see
1
Figure 1).
If the end of the pipe or fitting is square to its longitudinal axis there will not be any difference in the distance to a
reference plane that is known to be square to its longitudinal axis and from any two diametrical points at the end of
the component (see Figure 1).
Key
1 90° steel square
2 point of contact
3 plumb bob
4 flat surface plate

Figure 1 — Determination of end squareness
5.6.3 Procedure
5.6.3.1 Using a steel square
Determine the outside diameter of the component as described in 5.3.3.
Place the component on a horizontal flat surface plate. Use as necessary packing between the component and the
surface to overcome problems such as sockets or other protrusions that cause the component axis not to be
parallel to the surface.
Position the square as shown in Figure 1 so that it touches the component across its diameter.
Rotate the component until it is in the position where the gap between the square and the pipe end is maximised. If
the square only touches at one point, determine and record the maximum distance, L , (see Figure 1) at the point
1
diametrically opposite the point of contact.
Unless otherwise specified in the referring standard calculate the out-of-squareness using the following equation:
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ISO 3126:2005(E)
L
1
γ = arc tan
d
e
where:
γ is the out-of-squareness, in degrees;
L is the maximum difference between the upper and lower distances to the plane, in millimetres;
1
d is the outside diameter of the component, in millimetres.
e
5.6.3.2 Using a plumb bob
Determine the outside diameter of the component as described in 5.3.3.
Place the component on a horizontal flat surface plate. Use as necessary packing between the component and the
surface to overcome problems such as sockets or other protrusions that cause the component axis not to be
parallel to the surface.
Position the plumb bob at the top of the component as shown in Figure 1 and adjust its length so that the distance
between the bob and the surface corresponds to the wall thickness of the component.
Rotate the component until it is in the position where the gap between the plumb bob and the pipe end is
maximised.
If the plumb bob does not touch the component at the point in contact with the surface then determine and record
the maximum distance L (see Figure 1) at the point diametrically opposite the point of contact.
1
Unless otherwise specified in the referring standard calculate the out-of-squareness using the following equation:
L
1
γ = arc tan
d
e
where:
γ is the out-of-squareness, in degrees;
L is the maximum difference between the upper and lower distances to the plane, in millimetres;
1
d is the outside diameter of the component, in millimetres.
e
6 Determination of other geometrical characteristics related to fittings
6.1 General
Subclauses 6.2 to 6.4 give accuracy requirements and at least one procedure or method for measuring
characteristics of the following types of components:
— 6.2 Bends;
— 6.3 Branches;
— 6.4 Reducers.
Alternative equipment and/or procedures to those given in these clauses may be used providing the measurement
accuracy conforms to 6.2.1, 6.3.1, 6.4.1 and 7.1 as applicable.
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ISO 3126:2005(E)
Table 6 — Other measurements
Dimensions in millimetres unless otherwise stated
Required accuracy of Round arithmetic mean
Measurement of:
a
individual result value to the nearest:
Linear dimensions:
  ≤ 10 0,1 0,1
> 10 and ≤ 200 0,5 1
> 200 and ≤ 1000 1 1
> 1000 and ≤ 4000 0,1 % 1
Angular dimensions 1° 1°
a
 Exactly intermediate values shall be rounded up.

6.2 Bends
6.2.1 General
Select instrument(s) or device(s) and associated proced
...