ISO 10785:2025

International
Standard
ISO 10785
Second edition
Space systems — Bellows — Design
2025-08
and operation
Systèmes spatiaux — Soufflets — Conception et fonctionnement
Reference number
© ISO 2025
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ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Abbreviated terms . 6
5 Requirements . 6
5.1 General .6
5.2 Design requirements .7
5.2.1 Loads, pressures and environments .7
5.2.2 Strength .7
5.2.3 Stiffness .7
5.2.4 Thermal effects . .8
5.2.5 Stress analysis .8
5.2.6 Leak-before-burst (LBB) failure modes .8
5.2.7 Fatigue life .8
5.2.8 Leakage .9
5.2.9 Damage tolerance life .9
5.2.10 Miscellaneous .9
5.3 Material requirements.10
5.3.1 Material selection .10
5.3.2 Material evaluation .10
5.3.3 Material characterization .10
5.4 Fabrication and process control requirements .10
5.4.1 General .10
5.4.2 Contamination control and cleanliness requirements .10
5.5 Quality assurance requirements .11
5.5.1 Quality assurance programme .11
5.5.2 Inspection plan .11
5.5.3 Inspection techniques .11
5.5.4 Inspection data .11
5.5.5 Acceptance test requirements .11
5.6 Operation and maintenance requirements . 12
5.6.1 Operating procedures . 12
5.6.2 Safe operating limit . 12
5.6.3 Inspection and maintenance . 12
5.6.4 Repair and refurbishment . . 13
5.6.5 Storage . 13
5.6.6 Documentation. 13
5.6.7 Reactivation . 13
5.7 Specific qualification test requirements . 13
Bibliography .15

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
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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).
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This document was prepared by Technical Committee ISO/TC 20, Aircraft and space vehicles, Subcommittee
SC 14, Space systems and operations.
This second edition cancels and replaces the first edition (ISO 10785:2011), which has been technically
revised.
The main changes are as follows:
— clarification of the Scope;
— updates of the normative references and their citations in the text;
— updates of the terms and definitions to harmonize with the other ISO structural related standards;
— harmonization of requirements with ISO 24638 and ISO 21347.
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 bellows for space systems is usually used under severe conditions, such as high pressure, extremely
low temperatures, large deflection, or high inner flow speed. The design safety factor of the bellows
tends to be small to satisfy two different function requirements simultaneously. One is the function of the
pressure bearing component, which all pressure components have; and the other is the special function to
accommodate installation misalignment, thermal expansion or contraction and displacement induced by
large deformation of the pressurized propellant tank.
There are many items to be considered for design and manufacture such as hoop stress, bulging stress,
buckling strength, flow-induced vibration, and cyclic deflection.
This document aims to ensure safe and reliable bellows hardware and operations.
Some examples of the design safety factors are shown in Annex A.
The requirements in this document are not intended to be different from the requirements also applicable
for bellows included in ISO 24638.

v
International Standard ISO 10785:2025(en)
Space systems — Bellows — Design and operation
1 Scope
This document specifies general and detailed requirements for bellows used in space systems. It establishes
requirements regarding material, design, analysis, fabrication, material, testing, inspection, and operation
for space use.
This document is applicable to metallic bellows which are used as pressure bearing components and are
integrated into a pressure system. This document is not applicable to engine bellows or valve bellows.
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 14623, Space systems - Pressure vessels and pressurized structures — Design and operation
ISO 21347, Space systems — Fracture and damage control
ISO 24638, Space systems — Pressure components and pressure system integration
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
acceptance test
required formal test conducted on flight hardware to ascertain that the materials, manufacturing processes
and workmanship meet specifications and that the hardware is acceptable for intended usage
[SOURCE: ISO 14623:2003, 2.2]
3.2
bellows
corrugated single-layer or multi-layer elastic casing, when integrated into a duct assembly, capable of
performing linear, shear and angular movements
Note 1 to entry: A bellows consists of both a convolution section and a mechanical linkage section (3.23), which serves
as a bellows restraint. The most common mechanical linkage types are gimbal-type and braided-type. In some cases, a
bellows contains an internal liner or flow tube for the purpose of improving flow capability.
Note 2 to entry: See Figure 1.

Key
1 internal pressure
Figure 1 — Bellows
3.3
bellows stiffness
ratio between an applied force and the resulting bellows (3.2) displacement
3.4
bulging stress
meridional or axial stress at the convolution section induced by pressure
3.5
component
set of materials, assembled according to defined and controlled processes, which cannot be disassembled
without destroying its capability and which performs a simple function that can be evaluated against
expected performance requirements
[SOURCE: ISO24638:2021, 3.4]
3.6
damage tolerance life
safe life

design criterion under which failure due to the presence of flaws (3.15) does not occur in the expected
environment during the service life (3.29)
Note 1 to entry: In this design criterion, a flaw (3.15) is assumed consistent with the inspection process specified
and it is shown that the largest undetected flaw that can exist in the structure will not grow to failure in durations
multiplying life factors (3.19) to service lifetimes when subjected to the cyclic and sustained loads in the environments
encountered.
3.7
damage tolerance life
safe life

required period during which a structural item, even containing the largest undetected flaw (3.15), is shown
by analysis or testing not to fail catastrophically under the expected service load and environment
3.8
deflection
contraction or expansion along its longitudinal axis, angular rotation, or lateral offset
Note 1 to entry: See Figure 2.

Key
1 axial deflection
2 angular rotation
Figure 2 — Deflection
3.9
design burst factor
multiplying factor applied to maximum expected operating pressure (MEOP) (3.22) or maximum design
pressure (MDP) (3.21) to obtain the design burst pressure (3.10)
3.10
design burst pressure
burst pressure
differential pressure that pressurized hardware must withstand without bursting in the applicable
operational environment
Note 1 to entry: Design burst pressure is equal to the product of the maximum expected operating pressure (MEOP)
(3.22) or maximum design pressure (MDP) (3.21) and a design burst factor (3.9).
[SOURCE: ISO 24638:2021,3.7]
3.11
design safety factor
safety factor
design factor of safety
factor of safety
multiplying factor to be applied to limit loads (3.20) and/or maximum expected operating pressure (MEOP) (3.22)
Note 1 to entry: The factor is defined in order to account for the statistical variations of loads and structural strength,
and inaccuracies in the knowledge of their statistical distributions.
Note 2 to entry: In this definition, the word maximum expected operating pressure (MEOP) (3.22) may be replaced by
maximum design pressure (MDP) (3.21).
[SOURCE: ISO 24638:2021, 3.8, modified — "or maximum design pressure (MDP)" has been removed, and
Note 1 and Note 2 to entry have been added.]
3.12
detrimental deformation
structural deformation, deflection or displacement that prevents any portion of the structure or other
system from performing its intended function or that jeopardizes mission success
[SOURCE: ISO 24638:2021, 3.9]
3.13
fatigue
process of progressive localized permanent structural change occurring in a material/structure subjected to
conditions which produce fluctuating stresses and strains at some point or points and which may culminate
in cracks or complete fracture (3.16) after a sufficient number of fluctuations
[SOURCE: ISO 14623:2003, 2.23]
3.14
fatigue life
number of cycles of stress or strain of a specified character that a given structure or component of a structural
assembly can sustain [without the presence of flaws (3.15)] before failure of a specified nature occurs
[SOURCE: ISO 10786:2011, 2.24]
3.15
flaw
local discontinuity in a structural material
EXAMPLE Crack, cut, scratch, void, delamination disbond, impact damage and other kinds of mechanical damage.
[SOURCE: ISO 10786:2011, 3.23]
3.16
fracture
break occurring due to unstable extension of a flaw (3.15)
3.17
hoop stress
circumferential stress at the convolution section induced by pressure
3.18
leak-before-burst
LBB
design concept which shows that at maximum expected operating pressure (MEOP) (3.22) potentially critical
flaws (3.15) will grow through the wall of a metallic pressurized hardware item and cause pressure relieving
leakage rather than burst or rupture (catastrophic failure)
3.19
life factor
factor by which the service life (3.29) is multiplied to obtain total fatigue life (3.14) or damage tolerance life (3.7)
Note 1 to entry: Life factor is often referred to as a scatter factor that is normally used to account for the scatter of a
material’s fatigue or crack growth rate data.
Note 2 to entry: It can also account for the dispersion of loading spectra parameters and other uncertainties, when
appropriate.
[SOURCE: ISO 21648:2008, 2.1.24, modified —Note 1 to entry has been separated to Note 1 to entry and
Note2 to entry.]
3.20
limit load
design limit load
maximum load, or combination of loads, which a structure or a component in a structural assembly is
expected to experience during its service life, in association with the applicable operating environments
Note 1 to entry: Load is a generic term for thermal load, pressure, external mechanical load (force, moment, or enforced
displacement) or internal mechanical load (residual stress, pretension, or inertial load).
Note 2 to entry: The corresponding stress or strain is called limit stress or limit strain.
[SOURCE: ISO 24638:2021, 3.13]

3.21
maximum design pressure
MDP
highest pressure, as defined by maximum relief pressure, maximum regulator pressure and/or maximum
temperature, including transient pressures, at which a pressurized hardware item retains two-fault
tolerance without failure
[SOURCE: ISO 24638:2021, 3.16]
3.22
maximum expected operating pressure
MEOP
maximum allowed working pressure
MAWP
maximum operating pressure
MOP
highest differential pressure which a pressurized hardware item is expected to experience during its service
life and retain its functionality, in association with its applicable operating environments
Note 1 to entry: MEOP includes the effects of temperature, transient peaks, relief pressures, regulator pressure,
vehicle acceleration, phase changes, transient pressure excursions, and relief valve tolerance.
Note 2 to entry: Some projects may replace MEOP with maximum design pressure (MDP) (3.21), which takes into
account more conservative conditions.
Note 3 to entry: The terms MAWP and MOP are used when required to replace the term MEOP in a specific application.
[SOURCE: ISO 24638:2021, 3.17]
3.23
mechanical linkage section
section within bellows (3.2) assembly that will serve as the bellows restraint for thrust force by pressure,
deflection, or other factors
3.24
proof factor
multiplying factor applied to the limit load (3.20) or maximum expected operating pressure (MEOP) (3.22) or
maximum design pressure (MDP) (3.21) to obtain proof load or proof pressure (3.25) for use in acceptance test (3.1)
[SOURCE: ISO 24638:2021, 3.22, modified —The wording, “acceptance testing” has been replaced by
“acceptance test”.]
3.25
proof pressure
product of MEOP (3.22) [or MDP (3.21)] and a proof factor (3.24)
Note 1 to entry: The proof pressure is used to provide evidence of satisfactory workmanship and material quality
and/or to establish maximum initial flaw (3.15) sizes for damage tolerance life (3.7) demonstration.
[SOURCE: ISO 24638:2021, 3.23, modified— The wording, “damage tolerance life (safe life)” has been
replaced by “damage tolerance life”.]
3.26
qualification test
required formal contractual test conducted to demonstrate that the design, manufacturing, and assembly
have resulted in hardware conforming to specification requirements
Note 1 to entry: Qualification tests are conducted on a flight-quality article at load levels and durations sufficient
to demonstrate that all design requirements have been met under the specified environmental conditions. Both
protoflight and prototype tests are considered qualification tests.
Note 2 to entry: The qualification test may also validate the planned acceptance programme, including test techniques,
procedures, equipment, instrumentation, and software.

[SOURCE: ISO 10795:2019, 3.187, modified — The word, “used “, has been replaced by “conducted”. Note 1 to
entry and note 2 to entry have been added.]
3.27
refurbishment
renovation and restoration to intended use condition
3.28
repair
action on a nonconforming product or service to make it acceptable for the intended use
Note 1 to entry: A
...