ISO 24638:2008

Space systems — Pressure components and pressure system integration

ISO 24638:2008 establishes the baseline requirements for the design, fabrication and testing of space flight pressure components. It also establishes the requirements for assembly, installation, test, inspection, operation and maintenance of the pressure systems in spacecraft and launch vehicles. These requirements, when implemented on a particular space system, ensure a high level of confidence in achieving safe and reliable operation. ISO 24638:2008 applies to all pressure components other than pressure vessels and pressurized structures in a pressure system. It covers lines, fittings, valves, bellows, hoses and other appropriate components that are integrated to form a pressure system.

Systèmes spatiaux — Intégration des composants sous pression et des systèmes sous pression

General Information

• Status: Withdrawn
• Publication Date: 04-Nov-2008
• Withdrawal Date: 04-Nov-2008
• ICS: 49.140 - Space systems and operations
• Technical Committee: ISO/TC 20/SC 14 - Space systems and operations
• Drafting Committee: ISO/TC 20/SC 14 - Space systems and operations
• Current Stage: 9599 - Withdrawal of International Standard
• Completion Date: 13-May-2021

Relations

• Revised: ISO 24638:2021 - Space systems — Pressure components and pressure system integration
• Effective Date: 15-Jul-2017

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 24638
First edition
2008-11-15

Space systems — Pressure components
and pressure system integration
Systèmes spatiaux — Intégration des composants sous pression et des
systèmes sous pression




Reference number
ISO 24638:2008(E)
©
ISO 2008

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ISO 24638:2008(E)
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©  ISO 2008
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ISO 24638:2008(E)
Contents Page
Foreword. iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions. 1
4 Abbreviated terms . 5
5 General requirements. 5
5.1 General. 5
5.2 Design requirements . 5
5.3 Material requirements. 7
5.4 Fabrication and process requirements . 7
5.5 Contamination control and cleanliness requirements. 8
5.6 Quality assurance programme requirements . 8
5.7 Qualification test requirements. 10
5.8 Operation and maintenance requirements . 10
6 General pressurized-system requirements. 12
6.1 System analysis requirements . 12
6.2 Design features . 13
6.3 Component selection . 14
6.4 Design pressures. 15
6.5 Mechanical-environment design . 16
6.6 Controls . 16
6.7 Protection . 17
6.8 Electrical . 17
6.9 Pressure relief . 17
6.10 Control devices . 19
6.11 Accumulators . 19
6.12 Flexhose . 20
7 Specific pressure system requirements.20
7.1 General. 20
7.2 Hydraulic systems . 20
7.3 Pneumatic-system requirements . 23
Annex A (informative) Recommended minimum safety factors. 24
Annex B (informative) Open line force calculation factors . 25

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ISO 24638:2008(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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
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.
ISO 24638 was prepared by Technical Committee ISO/TC 20, Aircraft and space vehicles, Subcommittee
SC 14, Space systems and operations.
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ISO 24638:2008(E)
Introduction
Space vehicles and their launch systems usually have a series of engines to use for both primary propulsion
and secondary propulsion functions, such as attitude control and spin control.
Different engines have different propellant feed systems; for example, the gas-pressure feed system is
typically used for liquid propellant engines, and it consists of a high-pressure gas tank, a fuel tank and an
oxidizer tank, valves and a pressure regulator. All these components are referred to as pressurized hardware.
Due to their specific usage, the liquid propellant tanks and the high-pressure gas bottles are often referred to
as pressure vessels, while valves, regulators and feed lines are usually called pressure components.
ISO 14623 sets forth the standard requirements for pressure vessels in order to achieve safe operation and
mission success. However, the requirements for pressure components are not covered in ISO 14623.
Furthermore, the standard requirements for pressure system integration are lacking.
Significant work has been done in the area of design, analysis and testing of pressure components for use in
space systems. This International Standard establishes the preferred methods for these techniques and sets
forth the requirements for assembly, installation, test, inspection, operation and maintenance of the pressure
systems in spacecraft and launch vehicles.

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INTERNATIONAL STANDARD ISO 24638:2008(E)

Space systems — Pressure components and pressure system
integration
1 Scope
This International Standard establishes the baseline requirements for the design, fabrication and testing of
space flight pressure components. It also establishes the requirements for assembly, installation, test,
inspection, operation and maintenance of the pressure systems in spacecraft and launch vehicles. These
requirements, when implemented on a particular space system, ensure a high level of confidence in achieving
safe and reliable operation.
This International Standard applies to all pressure components other than pressure vessels and pressurized
structures in a pressure system. It covers lines, fittings, valves, bellows, hoses and other appropriate
components that are integrated to form a pressure system.
The requirements for pressure vessels and pressurized structures are set forth in ISO 14623.
This International Standard does not apply to engine components.
2 Normative references
The following referenced documents are indispensable for the application 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
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
A-basis allowable
mechanical strength value above which at least 99 % of the population of values is expected to fall, with a
confidence level of 95 %
NOTE See also B-basis allowable (3.3).
3.2
applied load
applied stress
actual load (stress) imposed on the hardware in the service environment
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ISO 24638:2008(E)
3.3
B-basis allowable
mechanical strength value above which at least 90 % of the population of values is expected to fall, with a
confidence level of 95 %
NOTE See also A-basis allowable (3.1).
3.4
component
functional unit that is viewed as an entity for the purpose of analysis, manufacturing, maintenance, or record
keeping
3.5
critical condition
most severe environmental condition in terms of loads, pressures and temperatures, or combinations thereof,
imposed on systems, subsystems, structures and components during service life
3.6
damage tolerance
ability of a material or structure to resist failure due to the presence of flaws, cracks, delaminations, impact
damage or other mechanical damage for a specified period of unrepaired usage
3.7
damage tolerance analysis
safe-life analysis
fracture mechanics-based analysis that predicts the flaw growth behaviour of a flawed hardware item which is
under service load spectrum with a pre-specified scatter factor
3.8
design burst pressure
burst pressure
ultimate pressure
differential pressure that pressurized hardware needs to withstand without burst in the applicable operational
environment
NOTE Design burst pressure is equal to the product of the maximum expected operating pressure or maximum
design pressure and a design burst factor.
3.9
design safety factor
design factor of safety
factor of safety
multiplying factor to be applied to limit loads and/or maximum expected operating pressure (or maximum
design pressure)
3.10
detrimental deformation
structural deformation, deflection or displacement that prevents any portion of the structure or other system
from performing its intended function
3.11
fittings
pressure components of a pressurized system used to connect lines, other pressure components and/or
pressure vessels within the system
3.12
hazard
existing or potential condition that can result in an accident
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ISO 24638:2008(E)
3.13
hydrogen embrittlement
mechanical-environmental failure process that results from the initial presence or absorption of excessive
amounts of hydrogen in metals, usually in combination with residual or applied tensile stresses
3.14
limit load
highest predicted load or combination of loads that a structure can experience during its service life, in
association with the applicable operating environments
NOTE The corresponding stress is called “limit stress”.
3.15
lines
tubular pressure components of a pressurized system provided as a means for transferring fluids between
components of the system
NOTE Flexhoses are included.
3.16
loading spectrum
representation of the cumulative loading anticipated for the structure under all expected operating
environments
NOTE Significant transportation and handling loads are included.
3.17
maximum allowed working pressure
MAWP
maximum differential pressure of a component designed to withstand safety and continue to operate normally
when installed in any pressure system
3.18
maximum design pressure
MDP
highest differential pressure 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
3.19
maximum expected operating pressure
MEOP
highest differential pressure that a pressurized hardware item is expected to experience during its service life
and yet retain its functionality, in association with its applicable operating environments
NOTE In this International Standard, the use of the term “maximum expected operating pressure (MEOP)” also
signifies “maximum design pressure (MDP)”, “maximum operating pressure (MOP)” or “maximum allowed working
pressure (MAWP)”, as appropriate, for a specific application or programme.
3.20
maximum operating pressure
MOP
maximum differential pressure at which the component or the pressure system actually operates in an
application
NOTE MOP is synonymous with MEOP.
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ISO 24638:2008(E)
3.21
pressure component
component in a pressure system, other than a pressure vessel, or a pressurized structure that is designed
largely by the internal pressure
EXAMPLE Lines, fittings, pressure gauges, valves, bellows and hoses.
3.22
pressure vessel
container designed primarily for the storage of pressurized fluids, which either contains gas/liquid with high
energy level, or contains gas/liquid that will create a mishap (accident) if released, or contains gas/liquid with
high pressure level
NOTE 1 This definition excludes pressurized structures and pressure components.
NOTE 2 Energy and pressure levels are defined by each project and approved by the procuring authority (customer). If
appropriate values are not defined by the project, the following levels are used:
⎯ stored energy is at least 19 310 J, based on adiabatic expansion of perfect gas;
⎯ MEOP is at least 0,69 MPa.
3.23
pressurized structure
structure designed to carry both internal pressure and vehicle structural loads
EXAMPLE Launch vehicle main propellant tank, crew cabins, manned modules.
3.24
pressure system
system that consists of pressure vessels or pressurized structures, or both, and other pressure components
such as lines, fittings, and valves, which are exposed to, and structurally designed largely by, the acting
pressure
NOTE The term “pressure system” does not include electrical or other control devices required for system operations.
3.25
proof factor
multiplying factor applied to the limit load or MEOP (or MAWP, MDP and MOP) to obtain proof load or proof
pressure for use in the acceptance testing
3.26
proof pressure
product of MEOP (or MAWP, MDP and MOP) and a proof factor
NOTE The proof pressure is used to provide evidence of satisfactory workmanship and material quality and/or to
establish maximum initial flaw sizes for damage tolerance life (safe-life) demonstration
3.27
scatter factor
multiplying factor to be applied to the number of load/pressure cycles, for the purpose of covering the scatters
that potentially exist in the material’s fatigue or crack growth data
3.28
service life
period of time (or cycles) that starts with the manufacturing of the pressurized hardware and continues
through all acceptance testing, handling, storage, transportation, launch operations, orbital operations,
refurbishment, re-testing, re-entry or recovery from orbit, and reuse that can be required or specified for the
item
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ISO 24638:2008(E)
4 Abbreviated terms
For the purposes of this document, the following abbreviated terms apply.
COPV composite overwrapped pressure vessel
MAWP maximum allowed working pressure
MDP maximum design pressure
MEOP maximum expected operating pressure
MOP maximum operating pressure
NDI non-destructive inspection
QA quality assurance
5 General requirements
5.1 General
This clause presents the general requirements for pressure components in a pressure system regarding
⎯ design and analysis,
⎯ material selection and characterization,
⎯ fabrication and process control,
⎯ quality assurance (QA),
⎯ operation and maintenance (including repair and refurbishment), and
⎯ storage.
The general pressure system requirements are presented in Clause 6. The integration requirements for
specific pressure systems are presented in Clause 7.
5.2 Design requirements
5.2.1 Loads, pressures and environments
The anticipated load-pressure-temperature history and other associated environments throughout the service
life of the pressure system shall be determined in accordance with specified mission requirements. As a
minimum, the following factors and their statistical variations shall be considered appropriate:
a) environmentally induced loads and pressures;
b) environments acting simultaneously with these loads and pressures with their proper relationships;
c) frequency of application of these loads, pressures and environments, and their levels and durations.
These data shall be used to define the design load/environment spectra, which shall be used for both design
analysis and testing. The design spectra shall be revised as the structural design develops and the loads
analysis matures.
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ISO 24638:2008(E)
5.2.2 Strength
Pressure components and their interconnections in a pressure system shall possess sufficient strength to
withstand limit loads and MEOP in the expected operating environments throughout the service life without
incurring detrimental deformation. The pressure components shall sustain proof pressure without leaking or
incurring detrimental deformation. They shall also withstand ultimate loads and design burst pressure in the
expected operating environments without rupturing or collapsing.
The minimum proof test factor for pressure components shall be 1,5. The minimum design burst factor varies
depending on the type of pressure component. Table A.1 presents recommended minimum proof test factors
and design burst factors for various pressure components.
A pressure system shall possess sufficient strength at the component interfaces, attachments, tie-downs and
other critical points. The pressure system shall sustain proof pressure without experiencing leakage and
incurring detrimental deformation.
5.2.3 Stiffness
The mounting and arrangement of all components in a pressure system shall provide adequate stiffness not to
generate destructive vibration, shock and acceleration, and to prevent excess stresses at the interfaces
between components and at mounting brackets when subjected to limit loads, MEOP and deflections of the
supporting structures in the expected operating environments. Connections between adjacent components
shall be designed to prevent excessive stresses at their interfaces from combined effects of limit loads, MEOP
and deflections of the supporting structures in the expected operating environments.
5.2.4 Thermal effects
Thermal effects, including heating and cooling rates, temperatures, thermal gradients, thermal stresses and
deformations, and changes with temperature of the physical and mechanical properties of the material of
construction, shall be factored into the design of the flight pressure system. Thermal effects shall be based on
temperature extremes that simulate those predicted for the operating environment, plus a predefined design
margin. The design margin shall be based on national industry heritage, including experience in thermal
effects that are important to a specific pressure component.
5.2.5 Stress analysis
A detailed stress analysis shall be performed on the pressure components and assembled and installed
pressure system to demonstrate acceptable stress levels and deflections at the interfaces between
components, at component attachments and tie-downs to support structures, and at other critical points in the
system. The effects of flexure of lines, as well as supporting structures being acted on by the flight loads,
pressures and temperature and thermal gradients, shall be accounted for in the analysis. The stress analysis
shall also take into account the ground loads.
5.2.6 Fatigue analysis/damage tolerance (safe-life) analysis
In addition to the stress analysis, conventional fatigue-life analysis shall be performed, as appropriate, on the
pressure component and the assembly. Nominal (average) values of fatigue-life (S-N) data shall be used in
the analysis. A scatter factor of four shall be used on service life as specified in ISO 14623. In some cases,
fatigue analysis shall be replaced by damage tolerance (safe-life) analysis in accordance with ISO 21347.
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ISO 24638:2008(E)
5.3 Material requirements
5.3.1 Metallic materials
5.3.1.1 General
Metallic materials used in the assembly and installation of pressurized system components shall be selected,
evaluated and characterized to ensure all system requirements are met.
5.3.1.2 Metallic material selection
Metallic materials shall be selected on the basis of proven environmental compatibility, material strength, and
fatigue characteristics. Unless otherwise specified, A-basis allowable materials shall be used in any
application where failure of a single load path would result in loss of structural integrity to any part of the
pressurized system. For applications where failure of a redundant load path would result in a safe
redistribution of applied loads to other load-carrying members, B-basis allowable materials may be used.
5.3.1.3 Metallic material evaluation
The selected metallic materials shall be evaluated with respect to material processing, fabrication methods,
manufacturing operations, refurbishment procedures and processes, and other factors that affect the resulting
strength and fracture properties of the material in the fabricated as well as the refurbished configurations.
The evaluation shall ascertain whether the mechanical properties, strengths, and fatigue properties used in
design and analyses will be realized in the actual hardware and verify that these properties are compatible
with the fluid contents and the expected operating environments. Materials that are susceptible to stress-
corrosion cracking or hydrogen embrittlement shall be evaluated by performing sustained load fracture tests
when applicable data are not available.
5.3.1.4 Metallic material characterization
The allowable mechanical and fatigue properties of all selected metallic materials shall be obtained from
reliable sources approved by the procuring authority. Where material properties are not available, they shall
be determined by test methods approved by the procuring authority.
5.3.2 Non-metallic material requirements
Non-metallic materials used in the pressure components and the assembly and installation of flight pressure
components shall be selected, evaluated and characterized to ensure their suitability for the intended
application.
5.4 Fabrication and process requirements
Proven processes and procedures for fabrication and repair shall be used to preclude damage or material
degradation during material processing, manufacturing operations and refurbishment. Special attention shall
be given to ascertaining whether the melting, welding, bonding, forming, joining, machining, drilling, grinding,
repair operations and other processes applied to joining system components and hardware and attaching
mounting hardware are within the state of the art and have been used on similar hardware.
The mechanical and physical properties of the parent materials, weld joints and heat-affected zones shall be
within established design limits after exposure to the intended fabrication processes. The machining, forming,
joining, welding, dimensional stability during thermal treatments and through-thickness hardening
characteristics of the material shall be compatible with the fabrication processes encountered.
Special precautions shall be exercised throughout the manufacturing operations to guard against processing
damage or other structural degradation.
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ISO 24638:2008(E)
Bonding, clamping and joining at the interfaces and mountings of the flight pressure systems shall be
controlled to ensure that all requirements are met.
5.5 Contamination control and cleanliness requirements
5.5.1 General contamination control requirements
Required levels of contamination control shall be established by the actual cleanliness needs and the nature
of the flight pressure system and its components. Contamination includes solid, liquid and gaseous material
unintentionally introduced into the system. General contamination control requirements are as follows:
a) protection from contaminants shall be provided by adequate filtration, sealed modules, clean fluids and a
clean environment during assembly, storage, installation and use;
b) the design shall allow for verification that the lines and other components are clean after flushing and
purging; and
c) the design shall ensure that contaminants and waste fluids can be flushed and purged.
5.5.2 Design considerations
The following considerations shall be factored into the design of flight pressure systems to minimize and
effectively control contamination:
a) contamination shall be minimized from entering or developing within the system;
b) the system shall be designed to include provisions to detect contamination;
c) the system shall be designed to include provisions for removal of contamination and provisions for initial
purge with fluid or gas that will not degrade future system performance;
d) the system shall be designed to be tolerant of contamination;
e) unless otherwise specified, all pressurizing fluids entering the system shall be filtered through a 10 µm
filter, or finer, before entering the system;
f) all pressure systems shall have fluid filters in the system, designed and located to reduce the flow of
contaminant particles to a safe minimum;
g) all of the circulating fluid in the system shall be filtered downstream from the pressure pump, or
immediately upstream from safety critical actuators;
h) entrance of contamination at test points or vents shall be minimized by downstream filters;
i) the bypass fluid or case drain flow on variable displacement pumps shall be fi
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