ISO 21013-3:2006

INTERNATIONAL ISO
STANDARD 21013-3
First edition
2006-01-01
Cryogenic vessels — Pressure-relief
accessories for cryogenic service —
Part 3:
Sizing and capacity determination
Récipients cryogéniques — Dispositifs de sécurité pour le service
cryogénique —
Partie 3: Détermination de la taille et du volume

Reference number
©
ISO 2006
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ii © ISO 2006 – All rights reserved

Contents Page
Foreword. iv
1 Scope . 1
2 Normative references . 1
3 Calculation of the total quantity of heat transferred per unit time from the hot wall
(outer jacket) to the cold wall (inner vessel). 2
3.1 General. 2
3.2 Under conditions other than fire . 3
3.3 Under fire conditions. 4
4 Calculation of the mass flow Q to be relieved by the pressure-relief devices. 5
m
5 Rule for installation of pressure-relief devices . 7
6 Sizing of pressure-relief devices. 7
6.1 General. 7
6.2 Pressure-relief valves. 7
6.3 Bursting disc . 7
Bibliography . 8

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
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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 21013-3 was prepared by Technical Committee ISO/TC 220, Cryogenic vessels.
ISO 21013 consists of the following parts, under the general title Cryogenic vessels — Pressure-relief
accessories for cryogenic service:
⎯ Part 1: Reclosable pressure-relief valves
⎯ Part 2: Non-reclosable pressure-relief devices
⎯ Part 3: Sizing and capacity determination
iv © ISO 2006 – All rights reserved

INTERNATIONAL STANDARD ISO 21013-3:2006(E)

Cryogenic vessels — Pressure-relief accessories for cryogenic
service —
Part 3:
Sizing and capacity determination
1 Scope
This part of ISO 21013 provides separate calculation methods for determining the required mass flow to be
relieved for each of the following specified conditions.
⎯ Vacuum-insulated vessels with insulation system (outer jacket + insulating material) intact under normal
vacuum; outer jacket at ambient temperature; inner vessel at temperature of the contents at the relieving
pressure.
⎯ Vacuum-insulated vessels with insulation system (outer jacket + insulating material) intact under normal
vacuum; outer jacket at ambient temperature; inner vessel at temperature of the contents at the relieving
pressure; pressure regulator of the pressure build-up system functioning at full potential.
⎯ Vacuum-insulated vessels with insulation system remaining in place but with loss of vacuum, or non-
vacuum-insulated vessels with insulation system intact; outer jacket at ambient temperature; inner vessel
at temperature of the contents at the relieving pressure; vacuum or non-vacuum-insulated vessels with
insulation system remaining fully or partially in place, but with loss of vacuum in the case of vacuum-
insulated vessels, and fire engulfment; inner vessel at temperature of the contents at the relieving
pressure.
⎯ Vessels with insulation system totally lost and fire engulfment.
Good engineering practice based on well-established theoretical physical science shall be adopted to
determine the required mass flow where an appropriate calculation method is not provided for an applicable
condition.
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 4126-1, Safety devices for protection against excessive pressure — Part 1: Safety valves
ISO 4126-6:2003, Safety devices for protection against excessive pressure — Part 6: Application, selection
and installation of bursting disc safety devices
3 Calculation of the total quantity of heat transferred per unit time from the hot wall
(outer jacket) to the cold wall (inner vessel)
3.1 General
P (in bar abs) is the actual relieving pressure inside the vessel, which is used for calculating the required mass
flow through pressure-relief devices.
T (in K) is the maximum ambient temperature for conditions other than fire (as specified, for example, by a
a
regulation or standard).
T (in K) is the external environment temperature under fire conditions, which is taken to be 922 K in this part
f
of ISO 21013.
T (in K) is the relieving temperature in the vessel to be taken into account:
a) for subcritical fluids, T is the saturation temperature of the liquid at pressure P;
b) for critical or supercritical fluids, T is calculated from 4.3.
The quantity of heat transferred per unit time (in watts) by supports and piping located in the interspace to be
included in W , W and W is calculated as follows:
1 2 3
W = (T − T) (w + w + … + w + …)
c a 1 2 n
where
w is the heat leak per degree K contributed by one of the supports or the pipes, in W/K,
n
A
n
w = k
n n
l
n
where
k is the thermal conductivity of the support or pipe material between T and T , in W/(m⋅K);
n a
A is the support or pipe section area, in m ;
n
l is the support or pipe length in the vacuum interspace, in m.
n
2 © ISO 2006 – All rights reserved
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