ISO/DIS 9938
(Main)Aerospace -- Polytetrafluoroethylene (PTFE) hose assemblies, classification 204 °C/28 000 kPa -- Procurement specification
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
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DRAFT INTERNATIONAL STANDARD
ISO/DIS 9938
ISO/TC 20/SC 10 Secretariat: DIN
Voting begins on: Voting terminates on:
2020-09-16 2020-12-09
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'approvisionnementICS: 49.080; 83.140.40
THIS DOCUMENT IS A DRAFT CIRCULATED
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ISO/DIS 9938:2020(E)
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NOTIFICATION OF ANY RELEVANT PATENT
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PROVIDE SUPPORTING DOCUMENTATION. ISO 2020
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ISO/DIS 9938:2020(E)
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ii © ISO 2020 – All rights reserved
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ISO/DIS 9938:2020(E)
Contents Page
Foreword ..........................................................................................................................................................................................................................................v
1 Scope ................................................................................................................................................................................................................................. 1
2 Normative references ...................................................................................................................................................................................... 1
3 Terms and definitions ..................................................................................................................................................................................... 1
4 Requirements ..........................................................................................................................................................................................................2
4.1 Qualification .............................................................................................................................................................................................. 2
4.2 Materials ....................................................................................................................................................................................................... 2
4.2.1 General...................................................................................................................................................................................... 2
4.2.2 Metals ........................................................................................................................................................................................ 2
4.3 Construction .............................................................................................................................................................................................. 2
4.3.1 General...................................................................................................................................................................................... 2
4.3.2 Inner tube .............................................................................................................................................................................. 3
4.3.3 Reinforcement .................................................................................................................................................................... 3
4.3.4 Fittings ...................................................................................................................................................................................... 3
4.4 Inner tube requirements ................................................................................................................................................................ 3
4.4.1 Density and relative density .................................................................................................................................. 3
4.4.2 Tensile strength ................................................................................................................................................................ 3
4.4.3 Elongation .............................................................................................................................................................................. 3
4.4.4 Tube roll .................................................................................................................................................................................. 4
4.4.5 Tube proof-pressure ..................................................................................................................................................... 4
4.4.6 Electrical conductivity ................................................................................................................................................ 4
4.5 Hose .................................................................................................................................................................................................................. 4
4.5.1 Dimensional requirements ..................................................................................................................................... 4
4.5.2 Physical requirements ................................................................................................................................................ 4
4.5.3 Bore check ............................................................................................................................................................................. 4
4.6 Screw threads........................................................................................................................................................................................... 4
4.7 Part numbering of interchangeable parts ....................................................................................................................... 4
4.8 Identification of products .............................................................................................................................................................. 4
4.8.1 General...................................................................................................................................................................................... 4
4.8.2 Fittings ...................................................................................................................................................................................... 6
4.8.3 Hose assembly ................................................................................................................................................................... 6
4.9 Workmanship ........................................................................................................................................................................................... 6
4.9.1 General...................................................................................................................................................................................... 6
4.9.2 Dimensions and tolerances ..................................................................................................................................... 6
4.9.3 Cleaning ................................................................................................................................................................................... 6
4.10 Hose assembly — Test and performance requirements ..................................................................................... 6
4.10.1 Proof pressure .................................................................................................................................................................... 6
4.10.2 Elongation and contraction .................................................................................................................................... 6
4.10.3 Volumetric expansion .................................................................................................................................................. 6
4.10.4 Leakage .................................................................................................................................................................................... 7
4.10.5 Thermal shock ................................................................................................................................................................... 7
4.10.6 Impulse ..................................................................................................................................................................................... 7
4.10.7 Assembly flexibility ....................................................................................................................................................... 7
4.10.8 Stress degradation .......................................................................................................................................................... 7
4.10.9 Pneumatic surge ............................................................................................................................................................... 7
4.10.10 Pneumatic effusion ........................................................................................................................................................ 9
4.10.11 Repeated installation ................................................................................................................................................... 9
4.10.12 Burst pressure at room temperature ............................................................................................................. 9
4.10.13 Electrical conductivity ................................................................................................................................................ 9
4.10.14 Fire resistance .................................................................................................................................................................... 9
5 Quality assurance .............................................................................................................................................................................................10
5.1 Responsibility for inspection ...................................................................................................................................................10
5.2 Classification of inspections .....................................................................................................................................................10
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ISO/DIS 9938:2020(E)
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 ...............................................................................................................................................................13
5.4.3 Sampling tests .................................................................................................................................................................13
5.4.4 Periodic control tests ................................................................................................................................................13
5.4.5 Rejection and re-test..................................................................................................................................................14
5.4.6 Changes in inspection procedures .................................................................................................................14
5.4.7 Destructive test sample ...........................................................................................................................................14
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 ...........................................................................................................................15
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 .....................................................................................................................................17
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ISO/DIS 9938:2020(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 second edition cancels and replaces the first edition (ISO 9938:1994), which has been technically
revised.The main changes compared to the previous edition are as follows:
— clause 2, Normative references, was updated;
— references in the whole document were updated;
— column "Material No." was added to Table 1;
— note in 4.3.4.1 General (Fittings) 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.© ISO 2020 – All rights reserved v
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DRAFT INTERNATIONAL STANDARD ISO/DIS 9938:2020(E)
Aerospace — Polytetrafluoroethylene (PTFE) hose
assemblies, classification 204 °C/28 000 kPa —
Procurement specification
1 Scope
This International Standard 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.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 International Standard are exceeded, or in
which the application is not covered specifically by this International Standard, for example for oxygen,
shall be subject to the approval of the purchaser.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 2685, Aircraft — Environmental test procedure for airborne equipment — Resistance to fire in
designated fire zonesISO 2859-1, Sampling procedures for inspection by attributes — Part 1: Sampling schemes indexed by
acceptance quality limit (AQL) for lot-by-lot inspectionISO 5855-3, Aerospace — MJ threads — Part 3: Limit dimensions for fittings for fluid systems
ISO 6772, Aerospace — Fluid systems — Impulse testing of hydraulic hose, tubing and fitting assemblies
ISO 7258, Polytetrafluoroethylene (PTFE) tubing for aerospace applications — Methods for the
determination of the density and relative densityISO 8829-1:2009, Aerospace — Test methods for polytetrafluoroethylene (PTFE) inner-tube hose
assemblies — Part 1: Metallic (stainless steel) braid3 Terms and definitions
No terms and definitions are listed in this document.
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/
© ISO 2020 – All rights reserved 1
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ISO/DIS 9938:2020(E)
4 Requirements
4.1 Qualification
Hose assemblies supplied in accordance with this International Standard shall be representative of
products which have been subjected to and which have successfully passed the requirements and tests
specified in this International Standard.4.2 Materials
4.2.1 General
The hose assembly materials shall be as described in this International Standard. All materials not
specifically described in this International Standard shall be of the highest quality and suitable for the
purpose intended.4.2.2 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)
AMS 5643 (17-4),
Bars 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)
MIL-T-8808 (321),Tubing Austenitic, seamless or welded, stabilized, corrosion-resistant steel
MIL-T-8808 (321)
Cold‑worked, stress‑relieved titanium alloy AMS 4945
AMS 5689,
Wire Austenitic, cold-drawn, corrosion-resistant steel AMS 5690,
AMS 5697
4.3 Construction
4.3.1 General
The hose assembly shall consist of
— a seamless PTFE inner tube (see 4.3.2),
— corrosion‑resistant steel‑wire reinforcement (see 4.3.3) and
— corrosion‑resistant steel and/or titanium end‑fittings (see 4.3.4),
as required to meet the construction and performance requirements laid down in this International
Standard and as required for its intended use.2 © ISO 2020 – All rights reserved
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ISO/DIS 9938:2020(E)
4.3.2 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.4.3.3 Reinforcement
The reinforcement shall consist of corrosion-resistant steel wire conforming to the applicable
specifications given in 4.2.2. The wires shall be arranged on the outside surface of the inner tube so as to
provide sufficient strength to ensure compliance with the requirements laid down in this International
Standard.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.4.3.4 Fittings
4.3.4.1 General
It shall be proven that all fittings comply with the requirements laid down in this International
Standard. Unless otherwise specified by the purchaser, the hose assemblies shall have flareless fittings
(24° cone coupling).4.3.4.2 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.4.4 Inner tube requirements
4.4.1 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
2,204 g/cm , when tested in accordance with ISO 7258, method C (as specified in ISO 8829‑1).
4.4.2 Tensile strengthWhen tested in accordance with ISO 8829-1:2009, 4.2, the longitudinal tensile strength for all sizes of
2 1)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 and
larger shall be at least 12,4 N/mm ; for sizes under DN16, the transverse strength need not be tested.
4.4.3 ElongationWhen tested in accordance with ISO 8829‑1:2009, 4.2, the elongation shall be at least 200 %.
1) 1 N/mm = 1 MPa.© ISO 2020 – All rights reserved 3
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ISO/DIS 9938:2020(E)
4.4.4 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, 4.3.2.4.4.5 Tube proof-pressure
After being subjected to the tube roll test sequence (see 4.4.4), 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.
4.4.6 Electrical conductivityWhen tested in accordance with ISO 8829-1:2009, 4.4, the electrical current shall be equal to or
greater thana) 10 µA for sizes DN06 to DN12 (inclusive);
b) 20 µA for sizes DN16 and over.
4.5 Hose
4.5.1 Dimensional requirements
The hose assembly dimensions, except for length, shall be as specified in Figure 1 and Table 2.
4.5.2 Physical requirementsHose assemblies shall comply with the physical and linear density (weight) requirements specified in
Table 3.4.5.3 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
elbow fittings, see Footnote a) in Table 2.4.6 Screw threads
Unless otherwise specified (see 4.3.4), 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.4.7 Part numbering of interchangeable parts
All parts complying with this International Standard and having the same manufacturers or standard
part number shall be functionally and dimensionally interchangeable.4.8 Identification of products
4.8.1 General
The hose assembly and its component parts shall be permanently marked.
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ISO/DIS 9938:2020(E)
Key
a See footnote b) to 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 diam- Outside Inside diam- Outside
length
a b
tube
eter diameter eter 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
Minimum inside diameter through the elbow area may be 85 % of the values given for d .
Width across corners of nut and socket hexagon may exceed the values given for D .
Table 3 — Physical requirements of hose assemblies and linear density (weight) of hose
Burst pressure BendHose Operating Proof radius at Volumetric
a Room tem- High tempe
...
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