ISO 24490:2005

INTERNATIONAL ISO
STANDARD 24490
First edition
2005-04-15

Cryogenic vessels — Pumps
for cryogenic service
Récipients cryogéniques — Pompes pour service cryogénique




Reference number
ISO 24490:2005(E)
©
ISO 2005

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ISO 24490:2005(E)
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ISO 24490:2005(E)
Contents Page
Foreword. iv
1 Scope. 1
2 Normative references. 1
3 Terms and definitions. 1
4 Requirements for pump. 2
4.1 General. 2
4.2 Materials. 2
4.3 Design. 3
5 Test procedures. 6
5.1 Prototype testing. 6
5.2 Production testing. 7
6 Cleanliness. 7
7 Marking. 7
Annex A (informative) Guidance on installation design. 8
Annex B (informative) Acceptable materials for construction of centrifugal pumps for liquid
oxygen. 10
Bibliography . 14

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ISO 24490:2005(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 24490 was prepared by Technical Committee ISO/TC 220, Cryogenic vessels.

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INTERNATIONAL STANDARD ISO 24490:2005(E)

Cryogenic vessels — Pumps for cryogenic service
1 Scope
This International Standard specifies the minimum requirements for the design, manufacture and testing of
pumps for cryogenic service.
This International Standard is applicable to centrifugal pumps. However the principles may be applied to other
types of pump (e.g. reciprocating pumps).
This International Standard also gives guidance on the design of installations (see Annex A).
It does not specify requirements for operation or maintenance.
NOTE For cryogenic fluids, see ISO 21029-1, ISO 20421-1 and/or ISO 21009-1.
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 5198:1987, Centrifugal, mixed flow and axial pumps — Code for hydraulic performance tests — Precision
grade
ISO 21010, Cryogenic vessels — Gas/materials compatibility
ISO 21028-1, Cryogenic vessels — Toughness requirements for materials at cryogenic temperature — Part 1:
Temperatures below – 80 °C
ISO 21028-2, Cryogenic vessels —Toughness requirements for materials at cryogenic temperature — Part 2:
Toughness requirements for temperatures between – 80 °C and – 20 °C
ISO 23208, Cryogenic vessels — Cleanliness for cryogenic service
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
nominal size
DN
alphanumeric designation of size for components of a pipework system, which is used for reference purposes.
NOTE 1 It comprises the letters DN followed by a dimensionless whole number which is indirectly related to the
physical size, in millimetres, of the bore or outside diameter of the end connections.
NOTE 2 The number following the letters DN does not represent a measurable value and should not be used for
calculation purposes except where specified in the relevant standard.
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ISO 24490:2005(E)
NOTE 3 In those standards which use the DN designation system, any relationship between DN and component
dimensions should be given, e.g. DN/OD or DN/ID.
NOTE 4 Adapted from ISO 6708.
3.2
nominal pressure
PN
alphanumeric designation used for reference purposes related to a combination of mechanical and
dimensional characteristics of a component of a pipework system
NOTE 1 It comprises the letters PN followed by a dimensionless number equal to at least the maximum allowable
pressure.
NOTE 2 For a pump, PN can be different for inlet and outlet.
3.3
specified minimum temperature
lowest temperature for which the pump is specified
3.4
duty point
performance point defined by pressure or head and volume or mass flow rate
3.5
net positive suction head
NPSH
inlet total head increased by the head (in flowing liquid) corresponding to the atmospheric pressure at the test
location and decreased by the sum of the head corresponding to the vapour pressure of the pump liquid at the
inlet temperature and the inlet impeller height
NOTE See also ISO 5198:1997, Table 1.
4 Requirements for pump
4.1 General
It is a requirement of this International Standard that a cryogenic pump shall first comply with appropriate
general International Standards. In the event of conflict, the requirements of this International Standard shall
take precedence over the general International Standards.
4.2 Materials
4.2.1 General
Materials of construction shall be selected taking into consideration that cryogenic pumps operate at low
temperature, often in a damp environment, and at times with liquid oxygen or flammable fluids.
The minimum requirements given in 4.2.2, 4.2.3 and 4.2.4 shall apply.
4.2.2 Mechanical properties at low temperature
Metallic materials which are under stress at low temperature and which exhibit a ductile/brittle transition (such
as ferritic steels) shall have minimum toughness values in accordance with ISO 21028-1 or ISO 21028-2 as
appropriate.
Metallic materials which can be shown to have no ductile/brittle transition do not require impact testing.
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ISO 24490:2005(E)
Non-metallic materials are generally used only for seals or heat barriers. If such materials are to be used for
structural parts, the stress levels and material impact values shall be shown to be acceptable for the intended
use.
4.2.3 Corrosion resistance
Materials should be resistant to, or protected from, atmospheric corrosion. Where this is not achievable, a
suitable corrosion allowance shall be considered.
4.2.4 Oxygen compatibility
If the specified minimum service temperature is equal to or less than the boiling point of air, or the pump is
intended for oxygen service, the materials which are, or are likely to come, in contact with oxygen or oxygen-
enriched air shall be oxygen-compatible in accordance with ISO 21010.
If the pump is employed for oxidising cryogenic fluids, e.g. nitrous oxide, the requirements for oxygen
compatibility should be taken into consideration.
Materials should be selected that minimise the potential for ignition and inhibit sustained combustion.
Suitable material properties are
 high ignition temperature,
 high thermal conductivity,
 low heat of combustion.
Table B.1 lists materials found through testing and operating experience to be particularly suitable for
centrifugal cryogenic pumps in oxygen service. Materials other than those identified in Table B.1 may be used,
but their selection shall be justified by specific testing or long-term experience in this application.
For (any) parts of the pump which are, or are likely to come, in contact with oxygen and which could be
exposed to energy sources such as friction, aluminium or aluminium alloy including aluminium bronzes shall
not be used. The use of aluminium or aluminium alloy for any other parts shall only be adopted after careful
consideration.
Stainless steel shall not be used for exposed thin components. Exceptions allowed are seal bellows, trapped
shims or gaskets and screw-locking devices of stationary parts where knowledge of past satisfactory
performance is available. However, suitable alternative materials, e.g. nickel or nickel alloy, Monel and Inconel,
should be considered.
NOTE Tin bronze has been found to be most suitable for the main “wetted” pump components. The most common
aluminium bronzes, which typically contain between 6 % and 11 % aluminium, have relatively high heats of combustion
and, if combustion occurs, are practically impossible to extinguish in an oxygen environment.
4.3 Design
4.3.1 General
Pumps for cryogenic service shall met the requirements of ISO 5198.
4.3.2 Pressure-containing parts
The high-pressure side of the pump shall be designed to withstand at least the nominal outlet pressure. The
low-pressure side shall be designed to withstand at least the nominal inlet pressure.
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ISO 24490:2005(E)
The material stress level from pressure may not be the dominant factor in pump design. The allowable stress
level may be calculated at the pressure rating, using ISO 21009-1 for guidance. For any parts subject to
fatigue, material stress levels should not exceed one-half of the infinite fatigue life for the part in question.
4.3.3 Performance
The pump design and installation shall meet the performance requirements specified on a data sheet (or
similar document). Examples of a data sheet can be found in ISO 5199 and ISO 9908.
4.3.4 Clearances
Clearances between moving and stationary parts within the pump shall be as large as practical, consistent
with good hydraulic performance and sealing. Material selection for components should take into account the
often large differences in expansion coefficients to ensure satisfactory clearances and interferences at the
operating temperatures and during cool-down.
4.3.5 Prevention of rubbing
The consequences of bearing failure or the consumption of parts by wear shall be considered, particularly in
pumps designed for liquid oxygen duty.
4.3.6 Fastenings
All internal fasteners shall be secured to prevent them loosening in service (e.g. friction nuts, tab washers).
Consideration shall be given to more adequately securing items which might normally be held in place by an
interference fit only (e.g. wear rings). These components can cool down more quickly than others and become
temporarily loose.
4.3.7 Warm bearings
Rolling-element bearings designed to run warm shall be located or protected such that freezing of the
lubricating grease or oil is avoided. The effect of ice build-up over a period shall be considered. This can result
in overcooling of the bearing and can allow shaft-seal leakage to be forced directly into the driver bearing.
Motor-bearing heaters may be considered for cold standby pumps.
4.3.8 Cold bearings
For bearings designed to run cold, lubricated by the cryogenic fluid, the use of materials and design
arrangements that can safely withstand short-term dry running shall be considered.
4.3.9 Bearing lubrication
For direct-coupled cryogenic pumps, grease and oils shall be suitable for all oxidising and predictable offset
conditions. The lubricants should typically be suitable down to – 40 °C.
Sealed bearings are preferred. Where bearing re-greasing in situ is required, grease drain plugs should be
provided to reduce the risk of accumulations of grease within the motor housing.
Liquid oxygen pumps shall be constructed so that possible oxygen leakage cannot contact any hydrocarbon
lubricant. If this cannot be prevented with certainty, the use of oxygen-compatible lubricants meeting the
requirement of ISO 21010 shall be considered. It should be noted, however, that such oxygen-compatible
lubricants are less able to protect the bearing against corrosion, generally reduce the ability of the bearing to
withstand load and speed, and may have some adverse reaction with some material combinations.
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ISO 24490:2005(E)
4.3.10 Shaft seals
Shaft seals are usually either mechanical rubbing face or labyrinth type. Both have a high possibility of
leakage.
The design of the mechanical seal shall prevent metal-to-metal rubbing between the seal carrier and the
rotating seal ring when the soft face material wears out.
For pumps in oxygen service, a protective sleeve shall be fitted between the bellows of any mechanical seal
and the shaft.
Labyrinth shaft seals shall be treated as systems, engineered for the particular application. For pumps in
oxygen service, injected gas may be an inert gas or oxygen.
Leakage-detection devices should be considered, e.g. a low-temperature trip.
A slinger or other deflection device shall be used to prevent direct impingement of shaft seal leakage on the
driver bearing.
4.3.11 Purging
A tapping for a dry inert gas purge may be used
...