ISO 21014:2006
(Main)Cryogenic vessels — Cryogenic insulation performance
Cryogenic vessels — Cryogenic insulation performance
ISO 21014:2006 defines practical methods for determining the heat-leak performance of cryogenic vessels. The methods include measurement on both open and closed systems. ISO 21014:2006 neither specifies the requirement levels for insulation performance nor when the defined methods should be applied. These requirements may be defined in design or operational standards/regulations.
Récipients cryogéniques — Performances d'isolation cryogénique
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Standards Content (Sample)
INTERNATIONAL ISO
STANDARD 21014
First edition
2006-08-01
Cryogenic vessels — Cryogenic
insulation performance
Récipients cryogéniques — Performances d'isolation cryogénique
Reference number
ISO 21014:2006(E)
©
ISO 2006
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ISO 21014:2006(E)
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ISO 21014:2006(E)
Contents Page
Foreword. iv
Introduction . v
1 Scope . 1
2 Terms and definitions. 1
3 General conditions for all methods . 2
4 Measuring the heat leak by the loss of product method . 3
4.1 General. 3
4.2 Test procedure . 3
4.3 Determination of the heat leak in units of energy per unit time . 4
4.4 Determination of the heat leak as a percentage loss of product per 24 h. 4
5 Determination of the holding time for open systems from heat-leak data . 4
6 Holding times for closed systems . 5
6.1 Determination of the equilibrium holding time from heat-leak data. 5
6.2 Calculation of the equilibrium holding time from heat-leak data . 5
6.3 Static experimental holding time . 6
7 Test report . 7
Annex A (normative) Conversion of measured volumetric gaseous flow to mass flow . 8
Annex B (normative) Correction of measured mass flow rate with regard to deviation from
reference conditions. 9
Annex C (normative) Equivalent loss determination for products other than the test product . 14
Bibliography . 15
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ISO 21014:2006(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 21014 was prepared by Technical Committee ISO/TC 220, Cryogenic vessels.
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ISO 21014:2006(E)
Introduction
Traditionally, there have been different methods of defining the insulation performance of cryogenic vessels.
It is therefore necessary to harmonize such methods for different cryogenic vessels.
Figure 1 shows a logic diagram to help in the understanding of this International Standard.
Figure 1 — Logic diagram
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INTERNATIONAL STANDARD ISO 21014:2006(E)
Cryogenic vessels — Cryogenic insulation performance
1 Scope
This International Standard defines practical methods for determining the heat-leak performance of cryogenic
vessels. The methods include measurement on both open and closed systems.
This International Standard neither specifies the requirement levels for insulation performance nor when the
defined methods should be applied. These requirements may be defined in design or operational
standards/regulations.
2 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
2.1
open system
〈during test〉 system kept at a constant pressure (e.g. atmospheric pressure) in which the gas produced by the
evaporation of the test fluid is continuously released to atmosphere
2.2
closed system
〈during test〉 system in which the mass of the contents is kept constant with no input or output of product
2.3
heat-leak rate
quantity of heat transferred per unit time from the ambient air to the contents of the inner vessel
NOTE In an open system, the heat leak causes a loss of product; in a closed system, it causes a rise in pressure.
2.4
holding time
〈open system〉 time expected to elapse, for a specified degree of filling, from initial filling level until the vessel
is empty (no more liquid) calculated from heat-leak data
2.5
holding time
〈closed system〉 time elapsed, for a specified degree of filling, from establishing the initial filling condition until
the pressure has risen, due to heat leak, to the set pressure of the pressure-limiting device
NOTE 1 For transportable vessels, this holding time is determined without the effects of stratification.
NOTE 2 A pressure-limiting device can be a safety valve, a rupture disc, a back-pressure regulator, or any other device
installed to limit the system pressure under normal operating conditions.
2.5.1
equilibrium holding time
holding time calculated from a specified heat leak assuming that liquid and vapour are constantly in
equilibrium (without stratification)
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ISO 21014:2006(E)
2.5.2
longest equilibrium holding time
equilibrium holding time calculated from heat-leak data for a vessel when filled with the quantity of product
giving the longest holding time
2.5.3
static experimental holding time
time it takes starting from atmospheric pressure, or from a stated pressure in the case of fluids where the
starting pressure cannot be atmospheric pressure (e.g. 10 bar for CO ), to reach the set pressure of the
2
pressure-limiting device with the tank initially filled to its maximum allowable filling mass
2.6
maximum allowable filling mass
initial mass that results in the tank becoming hydraulically full (98 % for all fluids except helium and 100 % for
helium) at the point that the pressure-limiting device operates
NOTE For fluids in a supercritical condition, the maximum allowable filling mass will be a function of the holding time
and will be stated.
3 General conditions for all methods
The measurements specified in this International Standard shall be carried out under the following conditions.
3.1 The cryogenic fluid used for testing shall be agreed upon between the involved parties. Liquid nitrogen
may normally be used, except in cases where the vessel to be tested is designed for a specific cryogenic fluid.
3.2 The liquid and gaseous phases shall be in equilibrium at the beginning of a test. When a test is carried
out at a higher pressure than atmospheric pressure, it is important that the liquid equilibrium pressure is not
lower than this test pressure.
3.3 The test environment shall be stable and constant during the test. It shall be as close as possible to the
following reference conditions:
⎯ ambient temperature, 15 °C;
⎯ atmospheric pressure, 1 013 mbar.
For products other than carbon dioxide and nitrous oxide:
⎯ vessel reference pressure, 1 013 mbar.
For carbon dioxide and nitrous oxide:
⎯ vessel reference pressure, 15 bar (gauge).
3.4 The vessel and its contents shall have reached a stable temperature before the beginning of the
measuring period. Equilibrium conditions are obtained after a period of stabilization, the duration of which
depends on the size of the vessel and the type and configuration of the insulation.
3.5 All accessories of the vessel which can influence the result of the measurement shall be clearly defined
and specified in the report.
3.6 All instrumentation used shall be verified by calibration.
3.7 It is not necessary to use the method defined in this International Standard to evaluate the insulation
performance resulting from small modifications; this may be done by simple extrapolation.
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ISO 21014:2006(E)
4 Measuring the heat leak by the loss of product method
4.1 General
There are two methods of measuring the heat leak:
⎯ direct measurement of loss of mass;
⎯ indirect measurement of loss of mass by measuring the gaseous volumetric discharge rate.
+10
The filling level shall be 50 % of the maximum filling level at the start of measurement, unless otherwise
0
stated.
The ambient temperature, ambient barometric pressure and the operating pressure at the top of the vessel
shall be recorded throughout the test so as to be used for correction purposes. The temperature sensor(s)
shall be placed in the immediate proximity of the tank being tested, but sited such that they are unaffected
directly by cold gas discharged from the vents.
The minimum measurement duration shall be 24 h after stable conditions have been reached.
During the test, precautions shall be taken to avoid agitation of the liquid, except for tanks designed for land
transport mode.
When measuring the rate of discharge of gas escaping from the vessel by a flow meter, it is essential that the
entire gas flow passes through the meter. The gas flow rate shall be determined as a mass flow rate by using
either of the following:
⎯ mass flow meter;
⎯ volumetric flow meter (an appropriate method is shown in Annex A).
4.2 Test procedure
The test procedure shall be as follows:
a) precool the vessel;
b) leave for a first stabilization period;
+10
c) adjust the filling to the intended starting level (e.g. 50 % );
0
d) connect the instrumentation (e.g. gas flow meter);
e) leave for a second stabilization period;
f) take a sufficient number of readings to establish an acceptable thermal equilibrium before the start of the
measuring period;
g) determine the mass of the vessel contents at the start of measuring period, if direct measurement of the
mass is used;
h) record readings for a minimum of 24 h;
i) determine the loss of product in mass units (when gaseous flow is measured) in accordance with
Annex A;
j) reduce to reference conditions in accordance with Annex B.
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ISO 21014:2006(E)
4.3 Determination of the heat leak in units of energy per unit time
The rate of product loss (kg/s) during the measurement period, corrected to the reference conditions in
accordance with Annexes A and B, shall be converted to an equivalent heat leak, Q, as given in 4.4.
To calculate the heat leak with a product other than the test product, compensation using linear extrapolation
in accordance with Annex C may be applied, but only if the difference between the boiling temperature of
these products at the reference conditions does not exceed 20 K.
4.4 Determination of the heat leak as a percentage loss of product per 24 h
Based on the result obtained in accordance with 4.3, the heat leak as a percentage loss of product per 24 h is
calculated as follows.
a) Correct the measured heat leak to the reference condition for the test product by linear extrapolation, as
specified in 4.3.
b) Calculate the equivalent loss of the test product per day in accordance with the following formula:
86 400 (vv− )Q
gl
L=×100 %
vh F
gfg
where
F is the maximum allowable filling mass of the test product (kg);
L is the equivalent loss of product as a percentage of F per day;
Q is the heat leak (W);
h is the latent heat of vaporization (J/kg) at the vessel reference pressure (see 3.3);
fg
3
ν is the specific volume of vapour (m /kg) at the vessel reference pressure (see 3.3);
g
3
ν is the specific volume of saturated liquid (m /kg) at the vessel reference pressure (see 3.3);
l
86 400 is the number of seconds per day.
All product-related data shall be taken at correct reference conditions for the specified product. Annex C may
be used to determine the equivalent loss of product as a percentage of full tank content per day, for a product
other than the test product.
5 Determination of the holding time for open systems from heat-leak data
100
The holding time, in days, for open systems is equal to for the specified product.
L
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ISO 21014:2006(E)
6 Holding times for closed systems
6.1 Determination of the equilibrium holding time from heat-leak data
The system is in thermal equilibrium, i.e. the liquid and gas phases are saturated and at a temperature
corresponding to the saturation pressure at all times. The calculation process shall incorporate correctly the
temperature and pressure dependence of the thermodynamic properties. The data source used for
calculations shall be identified and the actual value shall be shown in the calculation. Thermodynamic data
from bibliography items [1], [2] or [3] may be used. The influence of phase change in the system has to be
accounted for in a proper manner.
The thermal mass of the vessel shall be neglected in the calculation, which results in shorter holding times.
For a degree of filling less than that used for the longest holding time, the holding time shall be defined as the
time elapsed between when the initial filling condition is established and when the pressure-limiting device
...
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