ISO 7661:2024

Aerospace fluid systems - Clamp blocks for tube lines having axial alignment - Design requirements and qualification testing (metric series)

This document describes clamp blocks for tube lines having axial alignment, with or without electrical grounding, designed for a range of tube outside diameters from 4 mm to 36 mm selected from ISO 2964. This document specifies the dimensions of clamp blocks and the test methods for qualification testing.

Systèmes de fluides pour l'aéronautique et l'espace — Peignes supports de tuyauteries à alignement axial — Exigences de conception et essais de qualification (série métrique)

General Information

• Status: Published
• Publication Date: 10-Oct-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: 11-Oct-2024
• Due Date: 21-Nov-2024
• Completion Date: 11-Oct-2024

Relations

• Revises: ISO 7661:1984 - Aerospace - Fluid systems - Clamp blocks for tube lines having axial alignment - Design standard and qualification testing - Metric series
• Effective Date: 06-Jun-2022

Overview

ISO 7661:2024 - "Aerospace fluid systems - Clamp blocks for tube lines having axial alignment - Design requirements and qualification testing (metric series)" specifies dimensional requirements and qualification test methods for clamp blocks used to support axially aligned tubing on aerospace vehicles. The standard covers clamp blocks for tube outside diameters from 4 mm to 36 mm (selected from ISO 2964), and applies to both modular and monobloc clamp-block designs, with or without electrical grounding.

Key topics and technical requirements

• Scope and classification
  • Supports tube ODs 4–36 mm; clamp blocks are classified into Class A, B, and C based on OD ranges and maximum heights.
  • Two main designs: monobloc (two monobloc parts) and modular (removable parts and optional inserts).
• Dimensions
  • Standardized nominal radii, maximum heights per class, removable part widths (two models providing 3 mm or 5 mm clearance), and bolt spacing rules (modular spacing = sum of removable parts and inserts + 10 mm).
• Temperature service classes
  • Design for Type I (−55 °C to +70 °C), Type II (−55 °C to +135 °C) and Type III (−55 °C to +200 °C) environments in accordance with ISO 6771.
• Qualification tests
  • Electrical tests (for grounded blocks): measure contact resistance before and after mechanical/climatic tests using 1–4 A DC. Contact resistance ≤ 150 mΩ is required.
  • Mechanical tests: sliding test under temperature (3 samples, specified tube sizes, ±3 mm displacement at 1 Hz, 50 000 cycles at defined temperatures), sliding-force initial range (15–30 N), final requirement (> 5 N), and wear limits (aluminium 40 μm; stainless steel and titanium 15 μm). Vibration tests and other mechanical assessments are specified.
  • Climatic and flame-resistance tests: procedures include low/high temperature cycles, salt spray and flame-resistance apparatus and acceptance criteria (see clauses 7.3–7.4).
• Test documentation
  • Measurement procedures (e.g., electrical contact resistance, sliding force, wear measurements) are explicitly defined for qualification.

Practical applications

• Use ISO 7661:2024 when designing, specifying, procuring, qualifying or approving clamp blocks for aerospace fluid systems:
  • Aircraft and spacecraft integrators specifying tube supports
  • Component manufacturers producing monobloc or modular clamp blocks
  • Certification and quality teams performing qualification testing and acceptance
  • Maintenance and repair organizations assessing replacement components

Related standards

• ISO 2964 (tube outside diameters selection)
• ISO 6771 (pressure and temperature classifications)
• ISO 7137 (environmental conditions and test procedures for airborne equipment)
• ISO 2685 (flight test procedures referenced for flame/resistance context)

Using ISO 7661:2024 ensures consistent clamp-block geometry, reliable mechanical and electrical performance, and repeatable qualification testing across aerospace fluid-system applications.

Standards Content (Sample)

International
Standard
ISO 7661
Second edition
Aerospace fluid systems —
2024-10
Clamp blocks for tube lines
having axial alignment — Design
requirements and qualification
testing (metric series)
Systèmes de fluides pour l'aéronautique et l'espace — Peignes
supports de tuyauteries à alignement axial — Exigences de
conception et essais de qualification (série métrique)
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
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Classification of clamp blocks . 3
5 Dimensions of clamp blocks . 4
5.1 Maximum height .4
5.2 Nominal radius .4
5.3 Width of removable parts .4
5.4 Clamp block bolt spacing .5
5.4.1 Modular clamp block.5
5.4.2 Monobloc clamp block .5
6 Temperature conditions . 5
7 Qualification tests . 5
7.1 Electrical tests (for clamp blocks with electrical grounding) .5
7.1.1 Measurement of the electrical contact resistance .5
7.2 Mechanical tests .6
7.2.1 Sliding test under temperature .6
7.2.2 Sliding test combined with contamination .7
7.2.3 Vibration test .8
7.3 Climatic tests . .9
7.3.1 General .9
7.3.2 Low temperature test .9
7.3.3 High temperature test .9
7.3.4 Salt spray test .9
7.4 Flame resistance test .9
7.4.1 General .9
7.4.2 Test apparatus .9
7.4.3 Test procedure.10
7.4.4 Acceptance criteria .10
Bibliography .12

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,
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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 second edition cancels and replaces the first edition (ISO 7661:1984), which has been technically
revised.
The main changes are as follows:
— the reference to ISO/TR 2685 has been updated in 7.4 and in the bibliography because ISO/TR 2685 has
been replaced by ISO 2685;
— Clause 2, normative references, has been updated;
— Clause 3, terms and definitions, has been updated;
— the upper limit of the tube outside diameters range has been increased from 32 mm to 36 mm.
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
International Standard ISO 7661:2024(en)
Aerospace fluid systems — Clamp blocks for tube lines having
axial alignment — Design requirements and qualification
testing (metric series)
1 Scope
This document describes clamp blocks for tube lines having axial alignment, with or without electrical
grounding, designed for a range of tube outside diameters from 4 mm to 36 mm selected from ISO 2964.
This document specifies the dimensions of clamp blocks and the test methods for qualification testing.
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 6771, Aerospace — Fluid systems and components — Pressure and temperature classifications
ISO 7137, Aircraft — Environmental conditions and test procedures for airborne equipment
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
axial alignment
axes of supported tubings located in the same plane
3.2
clamp block for tubing
device used on aerospace vehicles for fixing tubings, the dimensions of which may be different and which
are constituted from different materials.
Note 1 to entry: These clamp blocks permit the fastening of tubes, used for different purposes in fluid systems.
3.2.1
monobloc clamp block
clamp block for tubing (3.2) consisting of two monobloc parts
EXAMPLE See Figure 1.
Dimensions in millimetres
Key
1 upper part
2 lower part
R radius of tube support
H height of clamp block
a
See ISO 5855-2.
b
Bolt spacing ±0,125.
c
Width of tube support.
Figure 1 — Monobloc clamp block
3.2.2
modular clamp block
clamp block for tubing (3.2) consisting of removable parts (3.3), with or without insert(s) (3.4)
EXAMPLE See Figure 2.
Key
1 upper part
2 lower part
R radius of tube support
H height of clamp block
L length of part X
x
L length of part Y
y
L length of part Z
z
a
See ISO 5855-2.
b
Bolt spacing ±0,125.
c
Width of tube support.
Figure 2 — Modular clamp block (without insert)
3.3
removable part
part of a modular clamp block (3.2.2) which ensures a standardized clearance between two adjacent tubings
3.4
insert
part that can be assembled between two removable parts (3.3) in order to obtain the required centre-to-
centre distance, standardized or not, between tubes
4 Classification of clamp blocks
The clamp blocks are divided into three classes, A, B an
...