ISO 8575:2024

Aerospace series - Fluid systems - Hydraulic system tubing

This document provides information relating to the sizes and materials of tubing for use in aerospace hydraulic pressure and return and suction lines. For pressure lines, the requirements apply to the pressure and temperature ranges covered by pressure class D, E and J and temperature type 13 and type 20 as specified in ISO 6771.

Série aérospatiale — Systèmes de fluides — Tubes pour systèmes hydrauliques

General Information

• Status: Published
• Publication Date: 21-Mar-2024
• ICS: 49.080 - Aerospace fluid systems and components
• Technical Committee: ISO/TC 20/SC 10 - Aerospace fluid systems and components
• Drafting Committee: ISO/TC 20/SC 10 - Aerospace fluid systems and components
• Current Stage: 6060 - International Standard published
• Start Date: 22-Mar-2024
• Due Date: 18-Nov-2024
• Completion Date: 22-Mar-2024

Relations

• Revises: ISO 8575:2016 - Aerospace - Fluid systems - Hydraulic system tubing
• Effective Date: 19-Nov-2022

Overview

ISO 8575:2024 - Aerospace series - Fluid systems - Hydraulic system tubing - specifies the sizes, materials and verification requirements for tubing used in aerospace hydraulic pressure, return and suction lines. The third edition updates material references and aligns tubing options with the pressure and temperature classes defined in ISO 6771 (pressure classes D, E, J and temperature types 13 and 20). Dimensions are provided in SI units with inch equivalents for industry convenience.

Key topics and technical requirements

• Scope: Guidance on tubing for hydraulic pressure lines (high‑pressure), return lines and suction lines used in aircraft hydraulic systems.
• Materials: Acceptable tubing materials are listed (examples from Table 1):
  • Corrosion‑resistant stainless steel (e.g., 304 variants),
  • High‑strength stainless alloys (e.g., 21‑6‑9),
  • Stabilized stainless (UNS S32100),
  • Titanium alloys (Ti‑3Al‑2.5V, TiCP),
  • Aluminium alloy 6061‑T6.
    Annex A maps corresponding national/industry standards for these alloys.
• Tube sizes: Both inch (fractional) and metric (DN) tubing dimensions and wall thicknesses are provided across pressure/temperature classes (Tables 2–5). Note: values below 0.5 mm wall can be critical for manufacture.
• Qualification & testing: Tubing combinations listed in the normative tables must be verified by tests per ISO 8574 (qualification tests for bent tubes). If a particular diameter/material/wall thickness is not tabulated, a suitable wall thickness must be selected and validated by testing.
• Design guidance: Inclusion of a dimension does not automatically guarantee fitness for all applications - aircraft systems designers should confirm tube assemblies with stress authorities.

Applications and users

ISO 8575 is intended for:

• Aircraft systems designers and hydraulic engineers selecting tubing for pressure, return and suction lines.
• Tubing manufacturers and material suppliers who must meet aerospace material and dimensional criteria.
• Maintenance, repair and overhaul (MRO) organizations and certification bodies that verify tubing installations. Practical uses include specifying tubing for hydraulic actuators, flight control systems, landing gear, brakes and other high‑pressure aircraft hydraulic circuits where reliability under defined pressure/temperature classes is critical.

Related standards

• ISO 6771 - Pressure and temperature classifications for aerospace fluid systems (referenced for class definitions).
• ISO 8574 - Qualification tests for bent tubes (required for verification).
• ISO 2964 - Metric tubing conventions (referenced for metric tubing).

Keywords: ISO 8575, aerospace hydraulic tubing, hydraulic system tubing, tube sizes, tubing materials, pressure lines, suction and return lines, ISO 6771, ISO 8574.

Standards Content (Sample)

International
Standard
ISO 8575
Third edition
Aerospace series — Fluid systems
2024-03
— Hydraulic system tubing
Série aérospatiale — Systèmes de fluides — Tubes pour systèmes
hydrauliques
Reference number
© ISO 2024
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Requirements . 1
4.1 General .1
4.2 Pressure lines .2
4.2.1 Tubing material.2
4.2.2 Tube sizes .2
4.2.3 Qualification .2
4.3 Suction and return lines .2
4.3.1 Tubing material.2
4.3.2 Tube sizes .2
Annex A (informative) Aerospace hydraulic tubing materials . 8
Bibliography . 9

iii
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 document 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).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
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 8575:2016), which has been technically
revised.
The main changes are as follows:
— in Table A.1 corresponding national standards for tubing materials have been updated.
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.

iv
Introduction
The purpose of this document is to provide information relating to the sizes and materials of tubing for use
in aerospace hydraulic pressure and return and suction lines.
International Standards use the International System of units (SI); however, large segments of the aerospace
industry make use of other measurement systems as a matter of common working practice. Although tube
sizes were originally defined (and are frequently cited) using non-SI units, all dimensions used in this
document are given in SI units, with inch units also indicated for the convenience of the user.
The decimal sign used in International Standards is the comma (“,”); however, the comma is not used in
common working practice for inch dimensions. Therefore, in common with many other aerospace standards,
the decimal point is used in this document when providing dimensions in inches.
NOTE The use of non-SI units and the decimal point in this document does not constitute general acceptance of
measurement systems other than SI within International Standards.

v
International Standard ISO 8575:2024(en)
Aerospace series — Fluid systems — Hydraulic system tubing
1 Scope
This document provides information relating to the sizes and materials of tubing for use in aerospace
hydraulic pressure and return and suction lines. For pressure lines, the requirements apply to the pressure
and temperature ranges covered by pressure class D, E and J and temperature type 13 and type 20 as
specified in ISO 6771.
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 8574, Aerospace — Hydraulic system tubing — Qualification tests for bent tubes
ISO 6771, Aerospace — Fluid systems and components — Pressure and temperature classifications
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
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/
3.1
inch tubing
tubing diameters and wall thickness in fractional inch increments and based on industry standards
3.2
metric tubing
tubing diameters and wall thickness in SI-metric units
Note 1 to entry: Metric tubing follows ISO 2964.
4 Requirements
4.1 General
The pipe dimensions quoted are in common use for the stated materials in the different pressure and
temperature classes. Inclusion of a dimension under a pressure and temperature class in this document does
not constitute a guarantee of fitness for the purpose in all circumstances. Aircraft systems designers should
verify each tube assembly application with the appropriate stress authority.

4.2 Pressure lines
4.2.1 Tubing material
Material for tubing used in hydraulic system pressure line shall be in accordance with Table 1 and shall
conform to the appropriate physical properties specified in Table 1.
4.2.2 Tube sizes
The outside diameters, wall thicknesses and materials of tubing used in the manufacture of tube assemblies
shall conform, where applicable, to the relevant requirements given in Table 2 or Table 3 for inch tubing and
Table 4 or Table 5 for metric tubing.
Where no wall thickness is shown in the tables for a particular combination of tube outside diameter and
material and it is desired to use that combination, a suitable wall thickness shall be selected and verified by
testing in accordance with ISO 8574.
4.2.3 Qualification
Tubing having outside diameters, wall thicknesses and materials as specified in Table 2 and Table 3 shall be
verified by testing in accordance with the requirements of ISO 8574.
4.3 Suction and return lines
4.3.1 Tubing material
Materials for tubing used in hydraulic system suction and return lines may be as given in Table 1 and verified
in accordance with ISO 8574 or at the discretion of the aircraft designer.
4.3.2 Tube sizes
Unless otherwise specified, the outside diameters for inch tubing used in suction and return lines shall be
selected from those specified in Table 2 or Table 3 for inch tubing, and from Table 4 or Table 5 for metric tubing.
The corresponding wall thicknesses shall be selected and verified in accordance with Table 2 to Table 5 or at
the discretion of the aircraft designer.

Table 1 — Tubing materials
Percent
Ultimate tensile
Material Yield strength elongation
strength
A
min.
Code R min. min. R min. min.
m p0,2
Description %
no. MPa (psi) MPa (psi)
Cold worked corrosion resistant steel
1 725 (105 000) 515 (75 000) 20
304-1/8H
High strength corrosion resistant steel
2 980 (142 000) 825 (120 000) 20
21-6-9
Re-annealed corrosion resistant steel
3 500 (72 500) 210 (30 500) 40
UNS S32100
Cold-worked and
4 860 (125 000) 720 (105 000) 10
stress relieved
titanium
5 690 (100 000) 655 (95 000) 14
Ti-3AL-2,5V
Unalloyed titanium
6 350 (50 000) 250 (35 000) 28
TiCP
Aluminium alloy (6061),
7 290 (42 000) 240 (34 000) 10
Solution treated and artificially aged (T6)
NOTE While waiting for the publication of International Standards for the materials described in Table 1, national
and industry standards accepted by the corresponding country conforming to the requirements specified in this table
are given in Annex A for information.

Table 2 — Outside diameters, wall thicknesses and materials for hydraulic tubing, pressure lines — Inch tubing
Type 13
a
Temperature
-55 °C to 135 °C (-65 °F to 275 °F)
Class D Class J
a
Pressure class
21 000 kPa 35 000 kPa
Design-operating-pressure (DOP)
(3 000 psi) (5 000 psi)
Material code no. 1 2 4 or 5 4 or 5
Material designation 304-1/8H 21-6-9 Ti-3AL-2,5V Ti-3AL-2,5V
Tube outside diameter Tube wall thickness Tube wall thickness
Type A Type B
Dash size mm (inch
...