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
Replaced
Publication Date
04-Nov-2008
Withdrawal Date
04-Nov-2008
Current Stage
9599 - Withdrawal of International Standard
Completion Date
05-Nov-2008
Ref Project

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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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ii © ISO 2008 – All rights reserved
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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

© ISO 2008 – All rights reserved iii
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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.
iv © ISO 2008 – All rights reserved
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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.
© ISO 2008 – All rights reserved v
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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
© ISO 2008 – All rights reserved 1
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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
2 © ISO 2008 – All rights reserved
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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.
© ISO 2008 – All rights reserved 3
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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
4 © ISO 2008 – All rights reserved
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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.
© ISO 2008 – All rights reserved 5
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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.

6 © ISO 2008 – All rights reserved
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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.
© ISO 2008 – All rights reserved 7
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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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