ISO 9938:2022

INTERNATIONAL ISO
STANDARD 9938
Third edition
2022-01
Aerospace — Polytetrafluoroethylene
(PTFE) hose assemblies, classification
204 °C/28 000 kPa — Procurement
specification
Aéronautique et espace — Tuyauteries flexibles en
polytétrafluoroéthylène (PTFE), classification 204 °C/28 000 kPa —
Spécification d'approvisionnement
Reference number
ISO 9938:2022(E)
© ISO 2022

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ISO 9938:2022(E)
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© ISO 2022
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Published in Switzerland
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ISO 9938:2022(E)
Contents  Page
Foreword .v
1 Scope . 1
2  Normative references . 1
3  Terms and definitions . 1
4  Requirements . 1
4.1 General . 1
4.2 Qualification . 2
4.3 Materials . 2
4.3.1 General . 2
4.3.2 Metals . 2
4.4 Construction . 2
4.4.1 General . 2
4.4.2 Inner tube . 3
4.4.3 Reinforcement . 3
4.4.4 Fittings . 3
4.5 Inner tube requirements . 3
4.5.1 Density and relative density . 3
4.5.2 Tensile strength . 3
4.5.3 Elongation . 3
4.5.4 Tube roll . 4
4.5.5 Tube proof-pressure . 4
4.5.6 Electrical conductivity . 4
4.6 Hose . 4
4.6.1 Dimensional requirements. 4
4.6.2 Physical requirements. 4
4.6.3 Bore check . 4
4.7 Screw threads . . 4
4.8 Part numbering of interchangeable parts . 4
4.9 Identification of products . 4
4.9.1 General . 4
4.9.2 Fittings . 5
4.9.3 Hose assembly . 6
4.10 Workmanship . 6
4.10.1 General . 6
4.10.2 Dimensions and tolerances . 6
4.10.3 Cleaning . 6
4.11 Hose assembly — Test and performance requirements . 6
4.11.1 Proof pressure . 6
4.11.2 Elongation and contraction . 6
4.11.3 Volumetric expansion . 6
4.11.4 Leakage . 7
4.11.5 Thermal shock . 7
4.11.6 Impulse. 7
4.11.7 Assembly flexibility . 7
4.11.8 Stress degradation . 7
4.11.9 Pneumatic surge . 7
4.11.10 Pneumatic effusion . 8
4.11.11 Repeated installation . 8
4.11.12Burst pressure at room temperature . 9
4.11.13 Electrical conductivity . 9
4.11.14 Fire resistance . 9
5  Quality assurance . 9
5.1 Responsibility for inspection. 9
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ISO 9938:2022(E)
5.2 Classification of inspections . 10
5.3 Qualification inspections . 10
5.3.1 Qualification test samples . 10
5.3.2 Test report, test samples and data for the purchaser. 10
5.3.3 Qualification testing .12
5.3.4 Criteria for requalification .12
5.4 Quality conformance inspections .12
5.4.1 General .12
5.4.2 Individual tests .12
5.4.3 Sampling tests .12
5.4.4 Periodic control tests .13
5.4.5 Rejection and re-test . .13
5.4.6 Changes in inspection procedures . 13
5.4.7 Destructive test sample .13
5.5 Test conditions . 14
5.5.1 Assembly, ends and hose . 14
5.5.2 End connections . 14
5.5.3 Test fluids . . 14
5.5.4 Temperature measurements . 14
5.5.5 Pressure measurements . 14
5.5.6 Preparation of test specimens . 14
5.6 Inspection methods. 15
5.6.1 Examination of product. 15
6  Preparation for delivery .15
6.1 Storage and packaging . .15
6.2 Marking . 15
7  Ordering data .15
Annex A (informative) Equivalent components .16
Bibliography .17
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ISO 9938:2022(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 Technical Committee ISO/TC 20, Aircraft and space vehicles,
Subcommittee SC 10, Aerospace fluid systems and components.
This third edition cancels and replaces the second edition (ISO 9938:1994), which has been technically
revised.
The main changes are as follows:
— Clause 2 was updated;
— references in the whole document were updated;
— column "Material No." was added to Table 1;
— NOTE in 4.4.4.1 was deleted;
— Annex A now only contains the equivalent components.
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 9938:2022(E)
Aerospace — Polytetrafluoroethylene (PTFE) hose
assemblies, classification 204 °C/28 000 kPa —
Procurement specification
1 Scope
This document specifies requirements for polytetrafluoroethylene (PTFE) hose assemblies for use in
aircraft hydraulic systems at temperatures between –55 °C and +204 °C and at a nominal pressure up
to 28 000 kPa (280 bar). The hose assemblies are also suitable for use within the same temperature and
pressure limitations in aircraft pneumatic systems where some gaseous diffusion through the wall of
the PTFE liner may be tolerated.
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.
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 5855-3, Aerospace — MJ threads — Part 3: Limit dimensions for fittings for fluid systems
ISO 7258, Polytetrafluoroethylene (PTFE) tubing for aerospace applications — Methods for the
determination of the density and relative density
ISO 8829-1:2009, Aerospace — Test methods for polytetrafluoroethylene (PTFE) inner-tube hose assemblies
— Part 1: Metallic (stainless steel) braid
3  Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminology 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/
4  Requirements
4.1  General
The use of these hose assemblies in high pressure pneumatic storage systems is not recommended.
ln addition, installations in which the limits specified in this document are exceeded, or in which the
application is not covered specifically by this document, for example for oxygen, shall be subject to the
approval of the purchaser.
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ISO 9938:2022(E)
4.2  Qualification
Hose assemblies supplied in accordance with this document shall be representative of products which
have been subjected to and which have successfully passed the requirements and tests specified in this
document.
4.3  Materials
4.3.1  General
The hose assembly materials shall be as described in this document. All materials not specifically
described in this document shall be of the highest quality and suitable for the purpose intended.
4.3.2 Metals
Metals used in the hose and fittings shall be corrosion-resistant or titanium and shall conform to the
applicable specifications described in Table 1.
Table 1 — Metals to be used in hose assemblies
Form Metal Material No.
Austenitic, annealed or as-rolled, corrosion-resistant steel AMS 5639 (304)
AMS 5645 (321),
Austenitic, annealed or as-rolled, stabilized, corrosion-resistant steel
AMS 5646 (347)
Bars
AMS 5643 (17-4),
and
forgings
Precipitation-hardening, corrosion-resistant steel AMS 5644,
AMS 5743
Titanium 6Al - 4V AMS 4928 (6-4)
Austenitic, seamless or welded, annealed, corrosion-resistant steel
MIL-T-8504 (304),
Steel, corrosion-resistant, seamless or welded hydraulic tubing,
AMS 5567 (304)
19 Cr - 10 Ni, solution heat treated
MIL-T-8808 (321),
Tubing Austenitic, seamless or welded, stabilized, corrosion-resistant steel
MIL-T-8808 (321),
Steel, corrosion and heat-resistant, seamless or welded hydraulic
tubing, 18,5 Cr - 10,5 Ni - 0,40 Ti, solution heat treated
AMS 5557 (321)
Cold-worked, stress-relieved titanium alloy AMS 4945
AMS 5689,
Austenitic, cold-drawn, corrosion-resistant steel AMS 5690,
Wire
AMS 5697
Steel, corrosion-resistant, wire, 18 Cr - 9,0 Ni, spring temper AMS 5688 (302)
4.4  Construction
4.4.1  General
The hose assembly shall consist of
— a seamless PTFE inner tube (see 4.4.2),
— corrosion-resistant steel-wire reinforcement (see 4.4.3), and
— corrosion-resistant steel and/or titanium end-fittings (see 4.4.4),
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ISO 9938:2022(E)
as required to meet the construction and performance requirements laid down in this document and as
required for its intended use.
4.4.2  Inner tube
The inner tube shall be of a seamless construction of virgin PTFE resin of uniform gauge; it shall have
a smooth bore and shall be free from pitting or projections on the inner surface. Additives may be
included in the compound from which the tube is extruded with no more than 2 % of such additives
being retained in the mixture.
4.4.3  Reinforcement
The reinforcement shall consist of corrosion-resistant steel wire conforming to the applicable
specifications given in 4.3.2. The wires shall be arranged on the outside surface of the inner tube so as
to provide sufficient strength to ensure conformity to the requirements laid down in this document.
Broken or missing reinforcing wires or buckled wires more than 1,5 mm above the outside diameter
surface shall be cause for rejection. Overlapping or crossed-over reinforcing wires shall not be cause for
rejection of the flexible hose assembly.
4.4.4  Fittings
4.4.4.1  General
It shall be proven that all fittings conform to the requirements laid down in this document. Unless
otherwise specified by the purchaser, the hose assemblies shall have flareless fittings (24° cone
coupling).
4.4.4.2  Insert fittings
Insert fittings shall be manufactured in one piece wherever possible. Those made of other than one-
piece construction shall be butt-welded, unless otherwise agreed by the purchaser, fabricated from
corrosion-resistant steel tubing or titanium. Welded and redrawn tubing (materials No. 8 and No. 9)
may be used for corrosion-resistant steel.
4.5  Inner tube requirements
4.5.1  Density and relative density
The relative density of the hose inner tube shall not exceed 2,155, when tested in accordance with
ISO 7258, either method A or method B (as specified in ISO 8829-1). The density shall not exceed
3
2,204 g/cm , when tested in accordance with ISO 7258, method C (as specified in ISO 8829-1).
4.5.2  Tensile strength
When tested in accordance with ISO 8829-1:2009, 4.2, the longitudinal tensile strength for all sizes of
21)
tubes shall be at least 15,1 N/mm .
When tested in accordance with ISO 8829-1:2009, 4.2, the transverse tensile strength for sizes DN16
2
and larger shall be at least 12,4 N/mm ; for sizes under DN16, the transverse strength doesn't need to
be tested.
4.5.3  Elongation
When tested in accordance with ISO 8829-1:2009, 4.2, the elongation shall be at least 200 %.
2
1) 1 N/mm = 1 MPa.
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ISO 9938:2022(E)
4.5.4  Tube roll
The tube shall not leak, split, burst or show any signs of malfunction, when tested through the sequence
as specified in ISO 8829-1:2009, 4.3.2.
4.5.5  Tube proof‑pressure
After being subjected to the tube roll test sequence (see 4.5.4), the tube, without reinforcing wires, shall
not leak, burst or show any signs of malfunction, when tested as specified in ISO 8829-1:2009, 4.3.3.
4.5.6  Electrical conductivity
When tested in accordance with ISO 8829-1:2009, 4.4, the electrical current shall be equal to or greater
than:
a) 10 µA for sizes DN06 to DN12 (inclusive);
b) 20 µA for sizes DN16 and over.
4.6 Hose
4.6.1  Dimensional requirements
The hose assembly dimensions, except for length, shall be as specified in Figure 1 and Table 2.
4.6.2  Physical requirements
Hose assemblies shall conform to the physical and linear density (weight) requirements specified in
Table 3.
4.6.3  Bore check
When bent to the appropriate minimum bend radius as specified in Table 3, the hose assembly shall
permit the free passage of a solid rigid sphere throughout its length. The diameter of the sphere shall
be 90 % of the appropriate minimum internal diameter of the end fittings as specified in Table 2. For
a
elbow fittings, see footnote in Table 2.
4.7  Screw threads
Unless otherwise specified (see 4.4.4), fitting threads shall be in accordance with ISO 5855-3. A 10 %
increase in the tolerance of the fitting thread of the nut following proof testing shall not be cause for
rejection of the hose assembly.
4.8  Part numbering of interchangeable parts
All parts conforming to this document and having the same manufacturers or standard part number
shall be functionally and dimensionally interchangeable.
4.9  Identification of products
4.9.1  General
The hose assembly and its component parts shall be permanently marked.
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ISO 9938:2022(E)
Key
a b
See footnote in Table 2.
Figure 1 — Hose and fitting dimensions
Table 2 — Hose and fitting dimensions (see Figure 1)
Dimensions in millimetres
Hose (braided) Fitting
Wall thick‑
Attachment
Hose size ness of inner
Inside  Outside  Inside  Outside
length
a b
tube
diameter diameter diameter diameter
(nom.) d D d D l δ
h h f f
min. min. max. min. max. max. min.
DN06 5,4 10,1 12,6 3,4 23 58
0,9
DN10 7,6 14,0 15,8 6,1 26 64
DN12 9,9 17,0 20,9 8,6 31 70 1
DN16 12,3 21,6 24,6 10,4 36 76
DN20 15,3 25,1 30,5 12,9 43 83 1,1
DN25 21,6 30,7 38,1 19,3 51 96
a
Minimum inside diameter through the elbow area may be 85 % of the values given for d .
f
b
Width across corners of nut and socket hexagon may exceed the values given for D .
f
Table 3 — Physical requirements of hose assemblies and linear density (weight) of hose
Burst pressure Bend
Hose Operating  Proof  radius at  Volumetric
a Room  High
weight pressure pressure inside of  expansion
Hose
temperature temperature
bend
size
max. min. min. min. max.
kg/m kPa kPa kPa kPa mm ml/m
DN06 0,4 76 3,2
DN10 0,66 127 4,7
DN12 0,81 146 6,7
28 000 56 000 112 000 84 000
DN16 1,25 165 10,8
DN20 1,7 197 14,8
DN25 2,86 245 37
a
Hose weight shall b
...