SIST EN 751-3:2022

SLOVENSKI STANDARD
SIST EN 751-3:2022
01-november-2022
Nadomešča:
SIST EN 751-3:1997
SIST EN 751-3:1997/AC:1999
Tesnilni materiali za kovinske navojne zveze v stiku s plini 1., 2. in 3. družine ter
vročo vodo - 3. del: Nesintrani PTFE trakovi in vrvice
Sealing materials for metallic threaded joints in contact with 1st, 2nd and 3rd family
gases and hot water - Part 3: Unsintered PTFE tapes and PTFE strings
Dichtmittel für metallene Gewindeverbindungen in Kontakt mit Gasen der 1., 2. und 3.
Familie und Heißwasser - Teil 3: Ungesinterte PTFE-Bänder und -Fäden
Matériaux d'étanchéité pour raccords filetés en contact des gaz du 1ère, 2ème et 3ème
groupe et de l'eau chaude - Partie 3 : Bandes et cordons en PTFE non fritté
Ta slovenski standard je istoveten z: EN 751-3:2022
ICS:
23.040.80 Tesnila za cevne zveze Seals for pipe and hose
assemblies
83.140.50 Tesnila Seals
SIST EN 751-3:2022 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN 751-3:2022

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SIST EN 751-3:2022


EN 751-3
EUROPEAN STANDARD

NORME EUROPÉENNE

June 2022
EUROPÄISCHE NORM
ICS 23.040.80 Supersedes EN 751-3:1996
English Version

Sealing materials for metallic threaded joints in contact
with 1st, 2nd and 3rd family gases and hot water - Part 3:
Unsintered PTFE tapes and PTFE strings
Matériaux d'étanchéité pour raccords filetés en contact Dichtmittel für metallene Gewindeverbindungen in
des gaz de la 1ère, 2ème et 3ème famille et de l'eau Kontakt mit Gasen der 1., 2. und 3. Familie und
chaude - Partie 3 : Bandes et cordons en PTFE non Heißwasser - Teil 3: Ungesinterte PTFE-Bänder und -
fritté Fäden
This European Standard was approved by CEN on 27 April 2022.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.

This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and
United Kingdom.





EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2022 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 751-3:2022 E
worldwide for CEN national Members.

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SIST EN 751-3:2022
EN 751-3:2022 (E)
Contents Page
European foreword . 3
Introduction . 5
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 7
4 Differentiation and classification of PTFE tapes and PTFE strings . 7
4.1 Differentiation . 7
4.2 Classification . 7
5 Requirements . 8
5.1 Requirements to be met by the PTFE tape and PTFE strings as received . 8
5.1.1 General . 8
5.1.2 Tape and string dimensions . 8
5.1.3 Mass . 8
5.1.4 Residual lubricant content . 9
5.1.5 PTFE structure and material . 9
5.1.6 Wrapping properties . 9
5.2 Requirements to be met by the PTFE tape and PTFE string after assembly . 9
5.2.1 Sealing properties . 9
5.2.2 Dismantling . 9
6 Test samples and documentation . 10
6.1 Test samples . 10
6.2 Test documentation . 10
7 Test methods . 10
7.1 General . 10
7.2 Test methods for PTFE tapes or PTFE strings as received . 10
7.2.1 Test of general requirements . 10
7.2.2 Measurement of dimensions . 10
7.2.3 Measurement of mass . 11
7.2.4 Determination of residual lubricant content . 11
7.2.5 Test of PTFE structure . 12
7.2.6 Test of wrapping properties . 12
7.3 Test of PTFE tapes or PTFE strings after assembly . 15
7.3.1 Test of sealing properties . 15
7.3.2 Test of dismantling . 19
8 Marking and instructions . 19
8.1 Marking on packages . 19
8.2 Instructions . 19
Annex ZA (informative) Relationship between this European Standard and the essential
requirements of Regulation (EU) 2016/426 aimed to be covered . 20
Bibliography . 21

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SIST EN 751-3:2022
EN 751-3:2022 (E)
European foreword
This document (EN 751-3:2022) has been prepared by Technical Committee CEN/TC 208 “Elastomeric
seals for joints in pipework and pipelines”, the secretariat of which is held by BSI.
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 December 2022, and conflicting national standards shall
be withdrawn at the latest by December 2022.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN 751-3:1996.
This document has been prepared under a Standardization Request given to CEN by the European
Commission and the European Free Trade Association, and supports essential requirements of EU
Directive(s) / Regulation(s).
For relationship with EU Directive(s) / Regulation(s), see informative Annex ZA, which is an integral part
of this document.
The following main technical changes have been made compared to EN 751-3:1996:
a) normative references have been updated;
b) definitions have been added;
c) requirements and tests for strings have been added;
d) differentiation between PTFE tapes and PTFE strings has been added;
e) restriction of use of APFO and PFOA has been added;
f) requirements and testing of mass per area and mass per length have been specified and added;
g) requirements and testing for the PTFE structure and material have been added;
h) wrapping properties have been specified;
i) possibility of adjustment has been deleted;
j) for the determination of residual lubricant content, a thermogravimetric method has been added;
k) for the determination of residual lubricant content, the quantities and associated vessel volumes
were reduced in the analytical method;
l) for the determination of structure and material, DSC method has been added;
m) testing of wrapping properties has been added and specified;
n) requirements for the test samples and their assembly have been added and specified;
o) evaluation of failed samples after assembly has been added;
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EN 751-3:2022 (E)
p) temperature cycling test has been revised and specified;
q) vibration test has been deleted;
r) marking has been clarified;
s) Annex ZA has been added.
The EN 751 series comprises the listed parts:
— Part 1: Anaerobic jointing compounds;
— Part 2: Non-hardening jointing compounds;
— Part 3: Unsintered PTFE tapes and strings.
Any feedback and questions on this document should be directed to the users’ national standards body.
A complete listing of these bodies can be found on the CEN website.
According to the CEN-CENELEC Internal Regulations, the national standards organisations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Croatia,
Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland,
Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of North
Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United
Kingdom.
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SIST EN 751-3:2022
EN 751-3:2022 (E)
Introduction
This document specifies requirements and test methods for tapes and strings produced from virgin
unsintered polytetrafluorethylene (PTFE) for use with metallic threaded joints. It specifies two classes of
PTFE tapes and PTFE strings – mainly differing in thickness and mass per area – for fine (F) and coarse
(G) threads.
A universally applicable PTFE tape or PTFE string may be used for all gas, potable water and hot water
installation.
In respect of potential adverse effects of the jointing compounds covered by this document on the quality
of water intended for human consumption this document provides no information as to whether the
jointing compounds may be used without restriction in any of the Member States of the EU or EFTA. The
use and characteristics of the jointing compounds should comply with current regulations, where they
exist, depending the acceptance of verifiable European criteria.
Compared to previous standard EN 751-3:1996, this document does not include an assessment of the
turning back properties. It has been determined in practice and during periodic tests that these
properties can only be reproduced to a limited extent. Turning back during installation should be avoided.
Should a connection made with PTFE tapes or threads nevertheless (have to) be turned back during
installation, this is the responsibility of the user. It is common sense that installations are checked for
tightness after completion.
Although PTFE natural colour is white and most common for PTFE tapes and PTFE strings, other colours
may be used as well.
Test practice since the standard was published has shown that the vibration test has not provided any
additional information about the tightness of the threaded connections. Therefore, the test was removed
from the test schedule of the standard.
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EN 751-3:2022 (E)
1 Scope
This document specifies requirements and test methods for unsintered polytetrafluorethylene (PTFE)
tapes and polytetrafluorethylene (PTFE) strings (PTFE tapes or PTFE strings, for short) which are
suitable for sealing threaded metallic joints as specified in EN 10226-1:2004.
This document covers two classes of PTFE tapes and PTFE strings suitable for fine (F) and coarse (G)
threads.
The PTFE tapes and PTFE strings are used as sealing materials for metallic threaded joints in contact with
st nd rd
1 family gases (town gas), 2 family gases (natural gas) and 3 family gases (liquefied petroleum gases
(LPG)) up to 500 kPa, up to 700 kPa for hot water of heating systems, and up to 20 kPa in gas appliances
and their auxiliary equipment. The maximum working pressure covered in this document is 2000 kPa
which is relevant to LPG storage. The temperature range is limited to −20 °C to 125 °C.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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.
1
EN 10242:1994, Threaded pipe fittings in malleable cast iron
EN 10255:2004+A1:2007, Non-alloy steel tubes suitable for welding and threading — Technical delivery
conditions
EN 12164:2016, Copper and copper alloys — Rod for free machining purposes
EN 10226-1:2004, Pipe threads where pressure tight joints are made on the threads — Part 1: Taper
external threads and parallel internal threads — Dimensions, tolerances and designation
EN 10226-3:2005, Pipes threads where pressure tight joints are made on the threads — Part 3: Verification
by means of limit gauges
EN ISO 11357-3:2018, Plastics — Differential scanning calorimetry (DSC) — Part 3: Determination of
temperature and enthalpy of melting and crystallization (ISO 11357-3:2018)
EN ISO 11358-1:2014, Plastics — Thermogravimetry (TG) of polymers — Part 1: General principles
(ISO 11358-1:2014)

1
This document is currently impacted by the stand-alone amendments EN 10242:1994/A1:1999 and
EN 10242:1994/A2:2003.
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3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https://www.iso.org/obp
— IEC Electropedia: available at https://www.electropedia.org/
3.1
PTFE tape
thread sealing tape manufactured from virgin unsintered polytetraflourethylene (PTFE) without fillers
or additives
3.2
PTFE string
thread sealing string manufactured from virgin unsintered polytetraflourethylene (PTFE) without fillers
or additives
Note 1 to entry: PTFE strings are also known as “PTFE cords”.
3.3
gas family
group of gaseous fuels with similar burning behaviour linked together by a range of Wobbe indices
Note 1 to entry: For further information on types of gases see EN 437:2021.
3.4
batch
any quantity of PTFE-tapes or PTFE strings manufactured in a single mix at one time
4 Differentiation and classification of PTFE tapes and PTFE strings
4.1 Differentiation
Tapes and strings differ in their geometry, weight per unit area and application. Both have a rectangular
geometry, whereby the tapes are thin and wide, while the strings are thick and narrow. Therefore, tapes
have to be wrapped overlapping, while strings are wrapped crosswise with a larger number of windings.
In addition, the strings have a greater weight per unit area.
NOTE 1 Typical tape dimensions; 12 mm × 0,10 mm.
NOTE 2 String dimensions; e.g. 2 mm × 0,5 mm, other cross sections are possible.
4.2 Classification
There are two classes of PTFE tapes and PTFE strings suitable only for fine (F) and for fine and coarse (G)
threads in accordance with Table 1.
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Table 1 — Classification of PTFE tapes and PTFE strings
Class Thread Nominal size
a
F EN 10226-1:2004 taper/parallel DN ≤ 10
G EN 10226-1:2004 taper/parallel DN ≤ 50
a
Class F tapes and strings may also be used for other dimensions when the number of turns of the thread is
-1
≥ 7,5 cm .
5 Requirements
5.1 Requirements to be met by the PTFE tape and PTFE strings as received
5.1.1 General
PTFE shall be produced without using APFO (ammonium perfluorooctanoate) and PFOA
(perfluorooctanoic acid).
The PTFE tape and PTFE string shall be free from inclusions or imperfections visible to the naked eye and
shall be free from any surface or edge defects, when tested in accordance with 7.2.1.
5.1.2 Tape and string dimensions
5.1.2.1 Length
The actual length of the PTFE tape and PTFE string, when tested in accordance with 7.2.2.1, shall not be
less than that marked on the spool/ dispenser.
5.1.2.2 Width
The actual width of the PTFE tape, when tested in accordance with 7.2.2.2, shall not differ from that
marked on the spool by more than ±0,5 mm.
The actual width of the PTFE string, when tested in accordance with 7.2.2.2, shall not differ from that
marked on the dispenser by more than ±10 %.
5.1.2.3 Thickness
The thickness of the PTFE tape and PTFE string, when tested in accordance with 7.2.2.3, shall not differ
from the stated value by more than ±10 %.
5.1.3 Mass
5.1.3.1 Mass per area for PTFE tapes
The mass per area of the PTFE tape, when tested in accordance with 7.2.3.1, shall be greater than 90 %
of the value declared by the manufacturer, but not less than:
2
— 60 g/m for class F;
2
— 100 g/m for class G.
5.1.3.2 Mass per length for PTFE strings
The mass per length of the PTFE string, when tested in accordance with 7.2.3.2, shall be greater than 90 %
of the value declared by the manufacturer, but not less than 0,3 g/m for both classes.
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5.1.4 Residual lubricant content
The residual lubricant content of the PTFE tape and PTFE string, when tested in accordance with 7.2.4.1
or 7.2.4.2, shall not exceed 0,1 % by mass.
5.1.5 PTFE structure and material
Using DSC (differential scanning calorimetry) method. The conditions during manufacture shall be such
that the tape or string remains in the unsintered state, during the test in accordance with 7.2.5 a shift or
change in the peak temperature of the initial melting peak shall be given. The enthalpy for the first heating
shall be significantly higher than for the second one. The following peak temperatures shall be met:
— (345 ± 5) °C during heating up from ambient temperature to (380 ± 5) °C;
— (312 ± 5) °C during cooling down from (380 ± 5) °C to (50 ± 5) °C;
— (327 ± 5) °C during heating up from (50 ± 5) °C to (380 ± 5) °C.
NOTE Experience shows that these requirements only can be met by use of virgin materials.
PTFE tapes or PTFE strings shall be manufactured from virgin consistent PTFE that does not contain any
filler (exception of colour) and is free of APFO and/or PFOA.
5.1.6 Wrapping properties
When wrapped around the specified thread in accordance with 7.2.6.1 or 7.2.6.2, the PTFE tape shall
conform to and hold the thread form. The finishing end of the PTFE tape shall remain in position with no
tendency to unwind. During wrapping the PTFE tape shall not break, tear, or split.
When wrapped around the specified thread in accordance with 7.2.6.3 or 7.2.6.4, the PTFE string shall
conform to and hold the thread form. The finishing end of the PTFE string shall remain in position with
no tendency to unwind. During wrapping the PTFE string shall not break, tear, or split.
5.2 Requirements to be met by the PTFE tape and PTFE string after assembly
5.2.1 Sealing properties
5.2.1.1 General
When tested in accordance with the methods described in 7.3.1 the PTFE tape and PTFE string shall not
permit any leakage, when each test assembly is tested in accordance with 7.3.1.2 and 7.3.1.3 in sequence.
5.2.1.2 Tightness
When pressurized, within 1 h after preparation all the joints in the test assemblies shall not leak, when
tested in accordance with 7.3.1.2.
5.2.1.3 Resistance to temperature cycling
The sealing properties of the PTFE tapes and PTFE strings shall not be impaired by the temperature
cycling test in accordance with 7.3.1.3.
5.2.2 Dismantling
When dismantling the screwed joints with commercial tools, after all tests in accordance with 7.3.2 have
been completed, there shall be no damage or corrosion of the threads.
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6 Test samples and documentation
6.1 Test samples
The manufacturer shall submit spools of the PTFE tape or dispensers of PTFE string in original packing
to the test laboratory as followed:
— PTFE tape class F: 10 spools;
— PTFE tape class G: 20 spools;
— PTFE string:  5 dispensers.
6.2 Test documentation
The following documents shall be submitted to the test laboratory:
a) technical data sheet with description of the PTFE tape or PTFE string including classification
according to Table 1, mass per area for PTFE tapes, mass per length for PTFE strings and dimensions
of the PTFE tape or string (nominal length, width and thickness);
b) installation procedure with application and wrapping instructions;
c) declaration from the manufacturer that the PTFE tapes or PTFE strings are manufactured from virgin
consistent PTFE, does not contain any filler (exception of colour) and are free of APFO and/or PFOA.
7 Test methods
7.1 General
All samples of PTFE tape or PTFE string used for the tests in 7.2 and 7.3 shall be taken from
spools/dispensers omitting the first 20 cm of the PTFE tape or PTFE string (except for testing according
to 7.2.2.1).
7.2 Test methods for PTFE tapes or PTFE strings as received
7.2.1 Test of general requirements
PTFE tapes or PTFE strings from three different spools/ dispensers are inspected for inclusions and
defects when measuring the dimensions.
7.2.2 Measurement of dimensions
7.2.2.1 Length
PTFE tapes or PTFE strings from three different spools/ dispensers are measured free of tension along
their length to an accuracy of 0,2 % of the total length.
7.2.2.2 Width
Measure the width of the three PTFE tapes with a micrometer gauge or an optical comparator to an
accuracy of 0,1 mm at two points approximately 50 mm from each end and at a minimum of three other
points equally spaced between the first two readings.
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7.2.2.3 Thickness
Measure the thickness of the three PTFE tapes or PTFE strings with a thickness gauge, capable of reading
to an accuracy of not less than 0,002 5 mm and having an indenter of not less than 6,3 mm in diameter.
The thickness gauge shall apply a pressure at the indenter of (15 ± 5) kPa. The thickness is measured at
two points approximately 50 mm from each end of the tape and at a minimum of three other points
equally spaced between the first two readings.
7.2.3 Measurement of mass
7.2.3.1 Measurement of mass per area for PTFE tapes
After measuring the dimensions, cut three pieces of PTFE tape about 100 mm long from each of the three
spools; one from each of the two ends and one from the middle of the PTFE tape. Measure the length to
an accuracy of 1 mm and the width to an accuracy of 0,1 mm and the mass to an accuracy of 0,1 mg. Use
the length and the width of the single pieces to calculate their mass per area.
7.2.3.2 Measurement of mass per length for PTFE strings
After measuring the dimensions, cut three pieces of PTFE string about 1 000 mm long from each of the
three dispensers; one from each of the two ends and one from the middle of the PTFE string. Measure the
length to an accuracy of 10 mm and the mass to an accuracy of 0,1 mg. Use the length of the single pieces
to calculate their mass per length.
7.2.4 Determination of residual lubricant content
7.2.4.1 Analytical method
Clean and dry an extraction sleeve with glass frit with a maximum pore diameter within the range 100 μm
to 160 μm and weigh to the nearest 0,1 mg.
Cut three samples of PTFE tape to give a weight of approximately 7,5 g. Place a single sample into the
extraction thimble fitted with the sintered glass plate and weigh to an accuracy of 0,1 mg.
Insert the extraction sleeve with glass frit and PTFE tape or PTFE string into a Soxhlet extractor with a
nominal capacity of 100 ml. Fill 150 ml to 200 ml of petroleum ether (boiling range 40 °C to 60 °C) into a
250 ml boiling flask. Assemble the boiling flask, Soxhlet extractor, and condenser and subject the PTFE
tape or string to at least 60 extractions during a continuous period of not less than 4 h.
After the extraction is completed, remove the extraction sleeve from the apparatus and dry for about 1 h
at (20 ± 5) °C in a fume cupboard.
Clean, dry and weigh a metal crucible to an accuracy of 0,1 mg. Transfer the extracted PTFE tape or PTFE
string from the extraction sleeve to the metal crucible and place them in an air circulation oven at
0
(300 ± 5) °C for ( 6 ) h. At the end of this period remove the metal crucible from the oven, cool in a
-0,5
desiccator, and weigh the crucible with the PTFE tape or PTFE string to an accuracy of 0,1 mg.
The residual lubricant content shall be calculated as a percentage difference between the original mass
of the PTFE tape or PTFE string and the mass of the PTFE tape or PTFE string after the heating treatment.
Calculate the mean value of three measurements to an accuracy of 0,01 %.
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7.2.4.2 Thermogravimetric method
For the test (20 ± 2) mg of PTFE tape or PTFE string shall be used to perform TGA measurement.
The PTFE tape or PTFE string shall be tested by thermogravimetric analysis (TGA) in accordance with
EN ISO 11358-1:2014. The following procedure done continuously by the TGA apparatus shall be used:
— the sample shall be heated up from ambient temperature to 240 °C with a thermal gradient of
30 K/min;
— during heating the mass decreases continuously, at the temperature the lubricant evaporates a step
in the curve is visible;
— the loss of mass at this step has to be measured.
7.2.5 Test of PTFE structure
For the test (10 ± 0,3) mg of PTFE tape or PTFE string shall be used to perform DSC measurement.
The PTFE tape or PTFE string shall be tested by melting endotherm temperature test (DSC) in accordance
with EN ISO 11357-3:2018. The following procedure
...