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• Status: Withdrawn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
• Start Date: 13-May-2021
• Completion Date: 13-Dec-2025

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 2008
PDF disclaimer
This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but
shall not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In
downloading this file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat
accepts no liability in this area.
Adobe is a trademark of Adobe Systems Incorporated.
Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation
parameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In
the unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below.

©  ISO 2008
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,
electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or
ISO's member body in the country of the requester.
ISO copyright office
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail [e-mail]
Web www.iso.org
Published in Switzerland
ii © ISO 2008 – All rights reserved

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

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

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.

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
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

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.
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

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.
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

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.
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 filtered; and
j) when the clogging of small orifices could cause a hazardous malfunction or failure of the system, each
orifice shall be protected by a filter element (including servo valves) designed to prevent clogging.
5.6 Quality assurance programme requirements
5.6.1 General
A quality assurance (QA) programme shall be established to ensure that the product and engineering
requirements, drawings, material specifications, process specifications, workmanship standards, design
review records, failure mode analysis, non-destructive inspection (NDI) and acceptance tests are effectively
used, such that the completed flight pressure system meets its specified requirements.
8 © ISO 2008 – All rights reserved

The programme shall ensure
⎯ that materials, parts, subassemblies, assemblies and all completed and refurbished hardware conform to
applicable drawings and process specifications,
⎯ that no damage or degradation has occurred during material processing, fabrication, inspection,
acceptance tests, shipping, storage, operational use and refurbishment, and
⎯ that defects which could cause failure are detected, evaluated and corrected.
5.6.2 QA programme inspection plan requirements
An inspection master plan shall be established prior to the start of system assembly and installation. The plan
shall specify appropriate inspection points and inspection techniques for use throughout the programme,
beginning with material procurement and continuing through fabrication, assembly, acceptance testing,
operation and refurbishment, as appropriate. In establishing inspection points and inspection techniques,
consideration shall be given to the material characteristics, fabrication processes, design concepts and
structural configuration. Acceptance and rejection criteria shall be established as part of the plan for each
phase of inspection and for each type of inspection.
5.6.3 QA inspection technique requirements
Inspections shall include both visual inspection with appropriate magnification and NDI, as necessary.
5.6.4 QA inspection data requirements
As a minimum, inspection data shall be dealt with as follows:
a) inspection data, in the form of flaw histories, shall be maintained throughout the life of the flight pressure
system;
b) these data shall be reviewed and assessed periodically to evaluate trends and anomalies associated with
the inspection procedures, equipment, personnel, material characteristics, fabrication processes, design
concept and structural configuration; and
c) the result of this assessment shall form the basis of any required corrective action.
5.6.5 Acceptance test requirements
5.6.5.1 General
Prior to first use, all newly assembled flight pressurized systems shall pass, in the following order,
⎯ a proof pressure test,
⎯ a leak test,
⎯ a grounding test, and
⎯ a functional test.
This test sequence shall be repeated after the system's arrival at the launch processing facility. The system-
level proof pressure tests can be excluded when there is sufficient successful experience and all the
components have been proof-tested at the component level.
5.6.5.2 Proof pressure test requirements
The flight pressure system shall be tested at the system-level proof pressure prior to first use. For systems
with zones operating at different pressures, each zone shall be tested to its proof pressure level. Proof
pressure testing shall demonstrate whether the flight pressure system will sustain proof pressure without
distortion, damage, leakage or loss of functionality. The system-level proof pressure tests can be excluded
when there is sufficient successful experience and all the components have been proof-tested at the
component level. The exclusion of system-level proof pressure tests shall be approved by the procuring
authority.
5.6.5.3 Leak test requirements
The flight pressure system shall be leak-tested at the system MEOP prior to first use. For systems with zones
operating at different pressures, each zone shall be at its MEOP for the leak test. The gas used during the
leak test shall be the same as the system operating fluid to the extent possible. Gas with higher permeability
and reliable leakage detection is allowed as the replacement. For the systems or zones intended to be filled
with a liquid, a suitable leak check gas shall be used. For systems intended to operate with hazardous fluids, a
non-hazardous gas may be substituted. All mechanical connections, gasketed joints, seals, weld seams and
other items susceptible to leakage shall be tested. The leak rates through fill and drain valves, thruster valves
and pressure relief valves shall be measured and verified within specification. Any method demonstrated
capable of detecting and/or measuring leakage is acceptable.
5.7 Qualification test requirements
Internal/external pressure testing shall be conducted on all pressure components to demonstrate no failure at
the design burst pressure. Annex A presents recommended minimum design burst factors for various
pressure components.
5.8 Operation and maintenance requirements
5.8.1 Operating procedure
Operating procedures shall be established for the pressurized system. The procedures shall be compatible
with the safety requirements and personnel control requirements at the facility where the operations are
conducted. Step-by-step directions shall be written with sufficient detail to allow a qualified technician or
mechanic to accomplish the operations. Schematics that identify the location and pressure limits of all
components and their interconnections into a system shall be included in the procedure, or shall be available
at the time it is running. Prior to initiating or performing a procedure involving hazardous operations with flight
pressure systems, practice runs shall be conducted on non-pressurized systems until the operating
procedures are well rehearsed. Initial tests shall then be conducted at pressure levels not in excess of 50 % of
the normal operating pressures until operating characteristics can be established and stabilized. Only qualified
and trained personnel shall be assigned to work on, or with, high-pressure systems. Warning signs identifying
the hazards shall be posted at the operations facility prior to pressurization.
5.8.2 Safe operating limits
Safe operating limits shall be established based on the pressure capabilities of all components and the effects
of assembly into a completed system. For flight pressure systems with several zones operating at different
pressure levels, safe operating levels shall be established for each zone. The safe operating limits shall be
summarized in a format that will provide rapid visibility of the important structural characteristics and capability
of the flight pressure system.
5.8.3 Inspection and maintenance
The results of the stress analysis (see 5.2.5) and the fatigue life or damage tolerance life (safe-life) analysis
(see 5.2.6) shall be used in conjunction with the appropriate results from the structural development and
qualification tests to develop a quantitative approach to inspection and repair. The allowable damage limits for
each component of the flight pressure system shall be used to establish the required inspection interval and
repair schedule in order to maintain the hardware to the requirements of this International Standard. NDI
methods and inspection procedures to reliably detect defects and determine flaw size under the condition of
use shall be developed for use in the field and depot levels, as appropriate. Procedures shall be established
for recording, tracking and analysing operational data as they are accumulated in order to identify critical
areas requiring corrective actions. Analyses shall include prediction of remaining life and reassessment of
required inspection intervals.
10 © ISO 2008 – All rights reserved

5.8.4 Repair and refurbishment
When inspections reveal structural damage or defects exceeding the permissible levels, the damaged
hardware shall be repaired, refurbished or replaced, as appropriate. All repaired or refurbished flight pressure
systems shall be recertified in accordance with 5.8.8 after each repair and refurbishment, by means of the
applicable acceptance test procedure for new hardware, in order to ensure their structural integrity and to
establish their suitability for continued service.
5.8.5 Storage
A flight pressure system put into storage shall be protected against exposure to environments that could
cause corrosion or other forms of material degradation. It shall be protected against mechanical degradation
resulting from scratches, dents or accidental dropping of the hardware. Induced stresses caused by storage
fixture constraints shall be minimized by suitable storage fixture design. In the event that storage requirements
are violated, recertification specified in 5.8.8 shall be required prior to return to use.
5.8.6 Documentation
Inspection, maintenance and operation records shall be kept and maintained throughout the life of the flight
pressure system. As a minimum, the records shall contain the following information:
a) temperature, pressurization history and pressurizing fluid for both tests and operations;
b) number of pressure cycles experienced, as well as number of pressure cycles allowed in safe-life
analysis;
c) results of any inspection conducted, including inspector, inspection dates, inspection techniques
employed, location and character of defects, and defect origin and cause; this shall include inspection
made during fabrication;
d) storage condition;
e) maintenance and corrective actions performed from manufacturing to operational use, including
refurbishment;
f) sketches and photographs to show areas of structural damage and extent of repairs;
g) acceptance and recertification tests performed, including test conditions and results; and
h) analyses supporting the repair or modification that may influence future-use capability.
5.8.7 Reactivation
A flight pressure system reactivated for use after a period in an unknown, unprotected or unregulated storage
environment shall be recertified according to 5.8.8 in order to ascertain its structural integrity, functionality and
suitability for continued service before reuse.
5.8.8 Recertification
5.8.8.1 Requirements
Any flight pressure system requiring recertification prior to return to service shall meet the following
requirements:
a) the documentation of affected components or portions of the flight pressure system shall be reviewed to
establish the last known condition;
b) the pressure system shall be inspected and subjected to appropriate NDI to detect any previously
unknown flaws;
c) the pressure system shall pass all the acceptance test requirements for new systems in accordance with
5.6.5.
5.8.8.2 Test after limited modification and repair
If any system elements, such as valves, regulators, gauges or tubing, have been disconnected or reconnected
for any reason, the affected system or subsystem shall be leak-tested in accordance with 5.6.5.3 as a
minimum. For more extensive modifications or repairs that may affect its ability to meet the requirements of
this International Standard or its required functions, the flight pressure system shall meet the full recertification
requirements in accordance with 5.8.8.
6 General pressurized-system requirements
6.1 System analysis requirements
6.1.1 System pressure analysis
A thorough analysis of the pressure system shall be performed to establish the correct MEOP, leak rates, etc.
for each pressure component. The effects of the operating parameters of each component on the MEOP shall
be determined. When applicable, pressure regular lock-up characteristics, valve actuation and water hammer
shall be considered for the entire service life of the pressure system.
NOTE Throughout this International Standard, limit load and MEOP are used as the baseline load and pressure. The
terms MAWP and MDP are used when required to replace MEOP in a specific application.
6.1.2 System functional analysis
A detailed system functional analysis shall be performed to determine whether the operation, interaction and
sequencing of components within the pressure system
⎯ are capable of supporting all required actions, and
⎯ lead to damage to flight hardware or ground support equipment.
The analysis shall identify all possible hardware malfunctions, software errors and personnel errors in the
operation of any component that may create conditions leading to an unacceptable risk to operating personnel
or equipment. The analysis shall evaluate any secondary or subsequent occurrence, failure, component
malfunction or software errors initiated by a primary failure, which could result in an unacceptable risk to
operating personnel or equipment.
The analysis shall also show that:
a) all pressures are maintained at safe levels in the event of a process or control sequence being interrupted
at any time during test or countdown;
b) redundant pressure relief devices have mutually independent pressure escape routes during all stages of
operation;
c) when the hazardous effects of safety-critical failures or malfunctions are prevented through the use of
redundant components or systems, all such redundant components or systems shall be operational prior
to the initiation of irreversible portions of safety-critical operations or events.
12 © ISO 2008 – All rights reserved

6.1.3 System hazard analysis
A system hazard analysis shall be performed on all hazardous pressure system components to identify
hazards to personnel and facilities. All prelaunch and launch operations and conditions shall be included in the
analysis. The results of the system functional analysis shall be used in the system hazard analysis to ensure
that all operations and configurations are considered in the system hazard analysis.
Hazards identified by the analysis shall be designated safety-critical and shall be mitigated by one or more of
the following methods:
a) design modifications to eliminate the hazard;
b) operating restrictions to minimize personnel exposure during hazardous periods;
c) specific hazard identification and procedural restrictions to avoid hazardous configurations; or
d) special safety supervision during hazardous operations and systems configurations.
6.2 Design features
6.2.1 Assembly
Components shall be designe
...