ISO 24568:2021

INTERNATIONAL ISO
STANDARD 24568
First edition
2021-07
Aerospace — Metric series pipe
coupling 8°30' up to 28 000 kPa
dynamic beam seal — Technical
specification
Reference number
ISO 24568:2021(E)
©
ISO 2021

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ISO 24568:2021(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2021
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
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Published in Switzerland
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ISO 24568:2021(E)

Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
3.1 Coupling . 2
3.2 Surface defects . 2
3.3 Quality assurance. 3
4 Symbols . 4
5 Requirements, inspection and test methods . 4
5.1 Test conditions and preparation of specimens for qualification . 4
5.1.1 General. 4
5.1.2 Tests fluids. 4
5.1.3 Specimen preparation . 4
5.1.4 Pipe assembly . 4
6 Quality assurance .16
6.1 Product qualification .16
6.2 Quality control records .16
6.3 Acceptance conditions .16
6.4 Rejection .17
6.5 Purchaser’s (user’s) quality control .17
7 Preparation for delivery .17
7.1 Cleaning .17
7.2 Preservation and packaging .17
Annex A (normative) Production batch identification .21
Bibliography .23
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ISO 24568:2021(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 of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso .org/
iso/ foreword .html.
This document was prepared by the Aerospace and Defence Industries Association of Europe –
Standardization (ASD-STAN) as EN 3275:2019 and drafted in accordance with its editorial rules. It was
assigned to Technical Committee ISO/TC 20, Aircraft and space vehicles, Subcommittee SC 10, Aerospace
fluid systems and components, and adopted, without modification other than those given below, under
the "fast-track procedure".
The main changes compared to EN 3275:2019 are as follows:
— the title was changed to have no more than three elements;
— Clause 2, normative references, was updated to only list references cited normatively in the text;
— Clause 3, terms and definitions, was updated to follow the rules of ISO/IEC Directives, Part 2, 2018;
— the tables were renumbered to follow the rules of ISO/IEC Directives, Part 2, 2018;
— Example 3 in A.1.3 was changed to normal body text as it contains a requirement;
— Figure 4 and Figure 7 were changed to be language neutral.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
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INTERNATIONAL STANDARD ISO 24568:2021(E)
Aerospace — Metric series pipe coupling 8°30' up to 28
000 kPa dynamic beam seal — Technical specification
1 Scope
This document specifies the required characteristics, inspection and test methods, quality assurance
and procurement requirements for metric series 8°30’ dynamic beam seal pipe couplings, for
temperature ranges type II and III according to ISO 6771 and nominal pressure up to 28 000 kPa.
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.
EN 2813, Aerospace series — Aluminium alloy AL‑P‑6061‑ — T6 — Drawn tube for pressure applications —
0,6 mm ≤ a ≤ 12,5 mm
EN 3120, Aerospace series — Titanium alloy TI‑P64003 — Cold worked and stress relieved — Seamless
tube for pressure systems — 4 mm ≤ D ≤ 51 mm, 690 MPa ≤ R ≤ 1 030 MPa
m
EN 10204, Metallic products — Types of inspection documents
ISO 1302, Geometrical Product Specifications (GPS) — Indication of surface texture in technical product
documentation
ISO 2685, Aircraft — Environmental test procedure for airborne equipment — Resistance to fire in
designated fire zones
ISO 2859-1, Sampling procedures for inspection by attributes — Part 1: Sampling schemes indexed by
acceptance quality limit (AQL) for lot‑by‑lot inspection
ISO 5855 (all parts), Aerospace — MJ threads
ISO 6771, Aerospace — Fluid systems and components — Pressure and temperature classifications
ISO 6772, Aerospace — Fluid systems — Impulse testing of hydraulic hose, tubing and fitting assemblies
ISO 7137, Aircraft — Environmental conditions and test procedures for airborne equipment
ISO 7257, Aircraft — Hydraulic tubing joints and fittings — Rotary flexure test
ISO 8625-1, Aerospace — Fluid systems — Vocabulary — Part 1: General terms and definitions related to
pressure
ISO 9538, Aerospace series — Hydraulic tubing joints and fittings — Planar flexure test
1)
TR 2674, Design and construction of pipeline for fluids in liquid or gaseous condition — Rigid lines,
installation
1) Published as ASD-STAN Technical Report at the date of publication of this standard by AeroSpace and Defence
industries Association of Europe – Standardization (ASD-STAN) (www .asd -stan .org).
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ISO 24568:2021(E)

3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 8625-1 and the following
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 http:// www .electropedia .org/
3.1 Coupling
3.1.1
coupling assembly
assembled and torque-tightened nut, ferrule and pipe mating with e.g. unions, tees or elbows
Note 1 to entry: See Figure 1.
Key
1 dynamic beam seal
2 ferrule
3 nut
4 union end
Figure 1 — Example of coupling assembly
3.1.2
shaped part
forged part
coupling machined out of individual forging blank
Note 1 to entry: For crosses, tees and elbows machined out of bar or plate stock the term “shaped” may be used.
3.2 Surface defects
3.2.1
surface irregularity
nonconformity with general surface appearance, possible defect
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ISO 24568:2021(E)

3.2.2
crack
clean (crystalline) fracture passing through or across the grain boundaries that possibly follows
inclusions of foreign elements
Note 1 to entry: Cracks are normally caused by overstressing the metal during forging or other forming
operations, or during heat treatment. Where parts are subject to significant reheating, cracks are usually
discoloured by scale.
3.2.3
fold
doubling over of metal, which can occur during the forging operation
Note 1 to entry: Folds can occur at or near the intersection of diameter changes and are especially prevalent with
non-circular necks, shoulders and heads.
3.2.4
lap
fold (3.2.3) -like machining defect
3.2.5
seam
surface opening or crack (3.2.2) or extraneous material resulting from a defect obtained during e.g.
casting or forging
3.2.6
pit
void or hole in the surface as caused, for example, by corrosion
3.3 Quality assurance
3.3.1
production batch
definite quantity of some commodity or service produced at one time under conditions that are
presumed uniform
3.3.2
delivery batch
batch consisting of couplings with the same identity block which may come from different production
batches (3.3.1)
3.3.3
acceptable quality level
AQL
quality level which for the purposes of sampling inspection is the limit of a satisfactory process average,
when a continuing series of lots is considered
3.3.4
qualification
testing required to demonstrate successful performance of the coupling assembly (3.1.1) in simulated
service (overload, destructive and fatigue tests)
3.3.5
major defect
defect other than critical, that is likely to result in a failure or to reduce materially the usability of the
considered product for its intended purpose
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ISO 24568:2021(E)

3.3.6
minor defect
defect that is not likely to reduce materially the usability of the considered product for its intended
purpose, or that is a departure from established specification having little bearing on the effective use
or operation of this product
4 Symbols
A Elongation, in percent [%]
D Actual outside diameter of pipe, in millimetres [mm]
0
D Actual inside diameter of pipe, in millimetres [mm]
1
DN Nominal outside diameter of pipe
P Working pressure, in megapascals [MPa]
R Tensile strength, in megapascals [MPa]
m
R 0,2 % proof stress, in megapascals [MPa]
p0,2
σ Axial stress due to pressure, in megapascals [MPa]
x
5 Requirements, inspection and test methods
5.1 Test conditions and preparation of specimens for qualification
5.1.1 General
For requirements, inspection and test methods see Table 1.
5.1.2 Tests fluids
Unless otherwise specified, tests shall be carried out using e.g. a petroleum base hydraulic fluid
according to MIL-H-5606 for coupling assemblies of type II temperature range and a silicate ester base
hydraulic fluid according to MIL-H-8446 for those of type III temperature range. Water may be used,
whenever practical, for proof, burst, stress corrosion and re-use capability testing. For other than
hydraulic system applications, it is preferable to use system fluid for leakage (gaseous pressure) and
proof testing. When specified in the test method, the test fluid is used as a lubricant.
5.1.3 Specimen preparation
Shaped parts shall be machined with the grain flow of the bar or plate in the direction of the fluid.
Specimens shall be assembled as illustrated in Table 3. Installations on the pipe end shall be in
accordance with TR 2674. Prior to testing, all couplings shall be assembled using the maximum
specified torque. Except, when specified in Table 3, the coupling shall be assembled using the minimum
installation torque for at least half of the specimens, and maximum torques for the remainder.
5.1.4 Pipe assembly
The method of joining the pipe to the coupling end (brazing, welding, mechanical attachment, etc.) shall
not be detrimental to the properties, strength or geometry of the pipe and the coupling end. The joint
shall be in accordance with the design instructions and shall be inspected by direct measurement, X-ray
or other non-destructive methods.
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ISO 24568:2021(E)

Table 1 — Requirements, inspection and test methods
Sub- Requirement Inspection and test method Q A
Characteristic
clause
a
5.2 Materials Conformity with the product Chemical analysis or certificate of compli- X X
standards ance according to EN 10204 issued by the
100 % 100 %
semi-finished product manufacturer.
a
5.3 Dimensions Conformity with the product Suitable measuring instruments X X
standards
100 % 50 %
Fluid passages Conformity with the product A ball with a diameter 0,5 mm less than the X X
standards minimum diameter specified for the pas-
100 % 20 %
sage shall pass through the coupling.
a
5.4 Product Marking shall be according to Visual examination X X
product standards and defini-
identification 100 % 100 %
tion documents including batch
identification of Annex A. It shall
be legible and shall not adversely
affect the material or the func-
tioning of the products.
a
5.5 Surface Conformity with the product Suitable measuring instruments or X X
roughness standards visual-tactile samples
100 % 100 %
Interpreted in accordance with
ISO 1302
a
5.6 Surface Conformity with the product Visual examination X X
treatment standards
The thread shall be tested using a gauge 100 % 100 %
with a tolerance class of 4h6h.
Key
Q qualification
A acceptance
a
Applicable to parts prior to assembly.
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ISO 24568:2021(E)

Table 1 (continued)
Sub- Requirement Inspection and test method Q A
Characteristic
clause
a
5.7 Surface defects Parts shall be free from surface Visual inspection using suitable methods X X
defects indicated in 3.3 liable to
100 % 100 %
have an adverse effect on their
characteristics and endurance. Visual examination X X
100 % 100 %
Threads Threads may be cut, rolled or Thread flanks in rolled threads shall be X X
ground, except titanium alloys examined by micro-examination. Speci-
10 % 5 %
which shall be cut or rolled. The mens shall be taken from the finished part
external threads of couplings by sectioning on a longitudinal plane across
should be rolled and, if ma- the threaded area. The specimens shall be
chined, shall have an arithmeti- polished and etched to reveal the surface
cal mean deviation, Ra, of the defects.
profile of 3,2 μm or smoother in
accordance with ISO 1302.
The grain flow in rolled threads
shall be continuous and follow
the general thread contour with
the maximum density at the
thread root.
Laps, cracks, surface irregu-
larities and seams (see 3.2)
are not acceptable on any part
of the pressure thread flank,
in the thread root or on the
non-pressure thread flank. Laps
and seams, depths of which are
within the limits of Table 2, are
acceptable on the crest and the
non-pressure thread flank above
the pitch diameter.
5.8 Proof pressure The coupling assembly shall The coupling assembly shall be connected X
withstand a pressure equal to to a pressure source with one end free to
twice the nominal pressure of move. Rate of pressure increase shall be
the fluid system for 5 min at (150 000 ± 37 500) kPa/min.
ambient temperature without
leakage and shall not show any
evidence of permanent defor-
mation or other malfunction
when using the specified torque
values.
5.9 Gaseous The coupling assembly shall The coupling assembly shall be solvent X
pressure withstand a gaseous pressure cleaned and air dried prior to testing. It
equal to the nominal pressure shall be assembled and tightened to the
for 5 min, at ambient tempera- minimum torques specified in Table 4. It
ture. There shall be no visible shall then be pressurized with nitrogen to
formation of bubbles after 1 min the nominal pressure. This pressure shall
at pressure or other malfunc- be maintained for 5 min while the speci-
tion that would affect assembly mens are immersed in water or suitable oil
or disassembly when using the (see Figure 2).
torque values specified.
5.10 Hydraulic The coupling assembly shall The coupling assembly shall be impulse X
impulse resist- withstand 200 000 impulse pres- tested at the temperatures and in the se-
ance sure cycles without leakage. quence specified in ISO 6772.
Key
Q qualification
A acceptance
a
Applicable to parts prior to assembly.
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ISO 24568:2021(E)

Table 1 (continued)
Sub- Requirement Inspection and test method Q A
Characteristic
clause
5.11 Minimum burst The coupling assembly shall The coupling assembly shall be connected X
pressure withstand a pressure equal to to a pressure source with one end free to
four times the nominal pressure move.
of the fluid system for 5 min,
Rate of pressure increase shall be
when tested at ambient temper-
(150 000 ± 37 500) kPa/min.
ature.
There shall be no leakage or
burst.
Pipe expansion is permissible.
The coupling assemblies need
not meet any disassembly or
assemblies requirements after
this test.
5.12 Flexure fatigue Coupling assembly welded to Shall be in accordance with either ISO 7257 X
resistance pipes shall achieve a target min- or ISO 9538. The bending stress shall be
imum flexure fatigue stress of determined prior to the application of
7
130 MPa for 10 cycles. internal pressure.
For other methods of joining the In order to obtain the true bending stress,
coupling to the pipe the mini- it is always necessary to measure the strain
mum flexure fatigue levels for dynamically at the flexure test frequency.
each DN size shall be as shown in The tolerance for the specified bending
Table 5 or Table 6. stress shall be from 0 % to 10 %.
Specimens according to Figure 3 NOTE If it is desired to express the
shall pass this test without leak- stress in terms of combined pressure and
age from the coupling assembly bending stress, the axial pressure stress is
or the pipe/coupling interface. calculated by the formula:
2
Recorded S/N curves shall show
D
1
characteristics equal to or great- σ =⋅P
x
2 2
DD−
er than those of Figure 4.
0 1
Thrust wire coupling assemblies
shall achieve the flexure fatigue
7
stress of 130 MPa for 10 cycles,
measured at the pipe/
coupling joint.
5.13 Stress corro- The coupling assembly shall The coupling assembly shall be installed X
sion resistance withstand salt spray exposure in a test apparatus (see Figure 5) which
without any of the following imposes a bending stress level equal to
defects: (85 ± 5) % of R of the pipe material at
p0,2
the beam seal interface.
Key
Q qualification
A acceptance
a
Applicable to parts prior to assembly.
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ISO 24568:2021(E)

Table 1 (continued)
Sub- Requirement Inspection and test method Q A
Characteristic
clause
a) indications of cracking or Internal pressure equal to the nominal
pitting of the exposed sur- pressure of the hydraulic system shall be
faces when visually exam- applied without removing the bending
ined at 10 times magnifica- stress. The coupling assembly shall then be
tion; subjected to the salt spray test in accord-
ance with ISO 7137.
b) indications of inter- or
After exposure, the coupling assembly
transgranular corrosive at-
shall be subjected to the minimum burst
tack during metallurgical
pressure test. The coupling assembly shall
examination of longitudinal
then be cleaned and subjected to micro-ex-
and transverse sections of
amination by sectioning.
the coupling assembly.
5.14 Re-use capa- The coupling assembly shall The coupling assembly shall be tested X
bility withstand 25 repeated assem- according to Figure 6 with one end torqued
blies, without any of the follow- to the maximum and the other to the mini-
ing defects: mum value of the tightening torque with no
additional lubricant permitted for the first
a) leakage at any of the proof
tightening. Each coupling assembly shall
pressure tests;
then be disassembled, and the sealing face
rotated 60° to 90°; the coupling assembly
b) inability to tighten the cou-
shall then be lubricated with the test fluid
pling by hand;
on threads only and retorqued to the orig-
inal value to a minimum of 25 times. After
c) nut deformation;
each fifth and the final tightening opera-
tion, the coupling shall be subjected to the
d) excessive galling or dam-
gaseous pressure test according to 5.9.
age to any surfaces of the
coupling assembly which
prevents the specified tight-
ening torques from being
applied smoothly;
e) gaseous leakage after the fi-
nal tightening operation.
The torque to damage shall also Every sixth tightening, the union on the
be determined and the values test fixture shall be replaced.
recorded. For couplings in titani-
The test fixture shall be designed to ensure
um alloy it shall not be less than
that all assembly forces are induced into
two times the maximum torque,
the dynamic beam seal.
according to Table 4 up to DN 18
or 202 Nm starting from DN 20.
The torque to damage shall be determined
For other materials values to be
as follows:
specified.
Damage is defined as one or Using one specimen, the curve torque/
more of the following defects: angular rotation of the nut shall be estab-
lished using a calibrated torque wrench
a) distortion or cracking of the
and a means of measuring the angular
dynamic beam seal;
rotation of the nut. The nut and ferrule
thread and contact faces shall be lubricat-
b) plastic deformation of any
ed with the test fluid, but none is allowed
part of the nut or ferrule;
on the sealing face or dynamic beam seal.
The torque shall be increased until plastic
c) leakage.
deformation occurs (see Figure 7).
Key
Q qualification
A acceptance
a
Applicable to parts prior to assembly.
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ISO 24568:2021(E)

Table 1 (continued)
Sub- Requirement Inspection and test method Q A
Characteristic
clause
The specimen shall then be subjected to the
gaseous pressure test according to 5.9.
If no leakage occurs, the specimen shall be
disassembled and the dynamic beam seal
examined for cracks or distortion. If the
dynamic beam seal is not damaged, the
torque to damage shall be determined in
accordance with Figure 7.
If leakage or cracking of the dynamic beam
seal is observed, a second specimen shall
be tested. This specimen shall be torqued
to the maximum value and subjected to a
gaseous pressure test according to 5.9 and
the dynamic beam seal examined for cracks
or distortion.
The coupling assembly shall then be pro-
gressively torqued in increments equal to
20 % of the difference between the defor-
mation torque of the first specimen and the
maximum torque of Table 4 for couplings in
titanium alloy. For other materials values
to be specified.
After each increment the specimen shall
be subjected to the gaseous pressure test
according to 5.9 and the dynamic beam
seal examined for cracks or distortion.
Any leakage, cracking or distortion shall
be noted. The torque value at which no
damage was found shall be considered as
the torque to damage.
5.15 Tensile The coupling assembly shall The coupling assembly shall be mounted X
strength withstand a tensile load that in a tensile test machine with no internal
is equal to or greater than the fluid or pressure. The tensile load shall
(coupling
product of the burst pres- be applied at a constant speed at a rate
assembly with
sure and the cross sectional area of (4 ± 2,5) mm/min until rupture of the
welded ferrule
of the pipe. associated pipe.
only)
It shall be demonstrated that the
coupling assembly is at least as
strong as the associated pipe.
5.16 Thermal shock The coupling assembly shall not The coupling assembly shall be mounted X
resistance leak during the test. in a low temperature test chamber and
connected to a pressure source of test fluid
which can be heated to maximum tempera-
ture ±5 °C.
The coupling assembly shall be cooled to
−55 °C ± 2 °C for a minimum of 2 h. At the
end of this period, test fluid at the maxi-
mum temperature shall be introduced at a
minimum pressure of 350 kPa.
Within 15 s of the fluid entering the cou-
pling assembly the pressure shall be raised
to proof pressure and held for 15 min.
Key
Q qualification
A acceptance
a
Applicable to parts prior to assembly.
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ISO 24568:2021(E)

Table 1 (continued)
Sub- Requirement Inspection and test method Q A
Characteristic
clause
5.17 Resistance to The coupling assembly shall be Shall be in accordance with ISO 2685. X
fire fireproof for 15 min without
leakage.
(if required)
Key
Q qualification
A acceptance
a
Applicable to parts prior to assembly.
Table 2 — Acceptable lim
...