ISO/FDIS 23335

FINAL DRAFT
International
Standard
ISO/TC 193/SC 3
Natural gas — Upstream area
Secretariat: SAC
— Determination of hydrate
Voting begins on:
equilibrium temperature
2026-05-06
Gaz naturel — Zone en amont — Détermination de la
Voting terminates on:
température d’équilibre des hydrates
2026-07-01
RECIPIENTS OF THIS DRAFT ARE INVITED TO SUBMIT,
WITH THEIR COMMENTS, NOTIFICATION OF ANY
RELEVANT PATENT RIGHTS OF WHICH THEY ARE AWARE
AND TO PROVIDE SUPPOR TING DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
Reference number
FINAL DRAFT
International
Standard
ISO/TC 193/SC 3
Natural gas — Upstream area
Secretariat: SAC
— Determination of hydrate
Voting begins on:
equilibrium temperature
Gaz naturel — Zone en amont — Détermination de la
Voting terminates on:
température d’équilibre des hydrates
RECIPIENTS OF THIS DRAFT ARE INVITED TO SUBMIT,
WITH THEIR COMMENTS, NOTIFICATION OF ANY
RELEVANT PATENT RIGHTS OF WHICH THEY ARE AWARE
AND TO PROVIDE SUPPOR TING DOCUMENTATION.
© ISO 2026
IN ADDITION TO THEIR EVALUATION AS
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
or ISO’s member body in the country of the requester.
TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland Reference number
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
5 Test solution and gas . 2
5.1 Test solution .2
5.2 Test gas .2
6 Apparatus . 2
7 Procedure . 4
7.1 Calibration and air tightness test .4
7.2 Purging .5
7.3 Sample preparation .5
7.4 Data acquisition .5
7.5 Cooling process .5
7.6 Hydrate formation .5
7.7 Heating process .5
7.7.1 General .5
7.7.2 Ramp heating .5
7.7.3 Stepwise heating .6
7.8 End of the test .6
7.9 Overview .6
8 Calculation . 7
9 Precision . 8
10 Test report . 8
Annex A (informative) Method of temperature setting of gas hydrate test .10
Annex B (informative) Statistical analysis of precision experiments .11
Bibliography .20

iii
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.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO documents should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 193, Natural gas, Subcommittee SC 3, Upstream
area.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

iv
Introduction
Natural gas hydrate is a crystalline structure formed under specific conditions (high pressure and low
temperature), in which gas molecules (primarily methane) are surrounded by water molecules. Due to
its immense potential energy value and environmental significance, research on natural gas hydrates has
been ongoing internationally. The phase equilibrium point is a crucial parameter for the formation and
decomposition of natural gas hydrates and its determination is of great importance for hydrate management.
Common methods for measuring the phase equilibrium point of hydrates are mainly divided into the
observation method and the pressure, volume and temperature (PVT) method.
The observation method requires a high-pressure resistant transparent material (e.g. sapphire) for the
reaction device to clearly observe the formation and decomposition process of the hydrate. With this
method, the formation and decomposition process of the hydrate is directly observed and the results are
intuitive and reliable. However, this method is limited by the pressure resistance and transparency of the
reaction device.
The PVT method measures the phase equilibrium of hydrates by varying any two of the parameters of PVT
in the reaction system while keeping the other parameter constant. Depending on the parameter that is
kept constant, it can be categorized into constant pressure, constant volume and constant temperature
methods. The constant volume method is suitable for measuring the phase equilibrium of hydrates in multi-
component systems and under complex conditions. It provides more comprehensive phase equilibrium
information but requires precise instrument control and data analysis. This document is compiled to meet
the demand for measuring the phase equilibrium point of hydrates in natural gas hydrate research under
the constant volume method.
v
FINAL DRAFT International Standard ISO/FDIS 23335:2026(en)
Natural gas — Upstream area — Determination of hydrate
equilibrium temperature
1 Scope
This document specifies a method for determining the phase equilibrium point of natural gas hydrates in
a laboratory setting under constant volume conditions, including the principle, reagents and materials,
apparatus, procedure, expression of results, test report and precision.
This document applies to laboratory simulations of hydrate formation and decomposition processes. It
involves the analysis of collected temperature and pressure data to determine the phase equilibrium
temperature of hydrates.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements 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 5725-2, Accuracy (trueness and precision) of measurement methods and results — Part 2: Basic method for
the determination of repeatability and reproducibility of a standard measurement method
ISO 10715, Natural gas — Gas sampling
ISO 14532, Natural gas — Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 14532 and the following terms
apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
hydrate
solid crystalline substance resembling ice formed by gas molecules and water molecules
1)
[SOURCE: ISO 14532:20— , 3.1.16, modified — The preferred term has been modified from "gas hydrate" to
"hydrate".]
3.2
equilibrium
limit state of each phase change in a multiphase system, where all phases in the reaction system reach
balance
1) Under preparation. Stage at the time of publication: ISO/DIS 14352:2026.

3.3
phase equilibrium point
intersection of the cooling curve and the heating curve in the phase diagram formed by temperature and
pressure data
4 Principle
The formation and decomposition of natural gas hydrates follow the basic principle of phase equilibrium.
For multiphase systems, the mutual transformation between phases, the formation of new phases and the
disappearance of old phases are related to temperature, pressure and composition. Under constant volume
conditions, the process of hydrate formation and decomposition is simulated. Throughout the entire testing
process, changes in temperature and pressure are recorded. After data processing, a pressure-temperature
[1]
(P-T) diagram is plotted to identify the phase equilibrium point .
5 Test solution and gas
5.1 Test solution
Determine the best testing medium in accordance with the experimental design. The test solution complies
with the following recommendations and requirements:
a) For formation water in field test simulation, the formation water samples should be taken whenever
possible.
b) For prepared water in field test simulation, when formation water samples are unavailable, the
composition of formation water shall be analysed and prepared.
c) Distilled water should be used in laboratory experiment.
d) Other reagents of analytical grade shall be used.
5.2 Test gas
Determine the best testing medium in accordance with the experimental design. The test gas complies with
the following recommendations and requirements:
a) For produced gas in field test simulation, the produced gas samples shall be taken as the methods
specified in ISO 10715.
b) For prepared gas in field test simulation, when produced gas samples are unavailable, the composition
of produced gas shall be analysed and prepared.
c) For prepared gas in laboratory experiment, all test gas component purity should be ≥ 99,9 %.
6 Apparatus
The apparatus for determining the hydrate equilibrium temperature should be constructed in accordance
with Figure 1.
Key
1 material supply unit
2 pressurizing unit
3 mixing unit
4 temperature control unit
5 reaction device
6 liquid feed unit
7 data acquisition unit
NOTE This diagram only shows the composition of the main apparatus. The specific pipeline connections and
valve settings are not shown here.
Figure 1 — Example illustrating the components of apparatus
6.1 Material supply unit, which shall be used to supply test materials.
6.2 Pressurizing unit, which meets the following recommendations and requirements:
a) The pressure range should meet the experimental requirements and achieve a high-pressure condition.
NOTE 1 High-pressure conditions are one of the essential requirements for hydrate formation. In field
production, the pressure ranges usually from several megapascals to several tens of megapascals.
b) The pressure accuracy shall be ±0,01 MPa.
c) Pressurizing devices and pipelines shall be corrosion resistant in a sour gas testing environment.
NOTE 2 For more information about hydrogen sulfide resistant materials, see ISO 15156-1.
6.3 Mixing unit, which meets the following recommendations and requirements:
a) The mixing unit shall be capable of providing effective mixing to facilitate both hydrate formation and
decomposition.
b) Mechanical stirring, magnetic stirring, rocking or gas disturbance techniques should be used depending
on the experimental conditions.
c) High agitation shall be used for mixing. The higher the agitation, the faster the equilibrium is reached.
NOTE 1 The primary functions of the mixing are to enhance mass transfer, intensify heat transfer, promote
nucleation and simulate flow conditions.

NOTE 2 For more information about high agitation, see Reference [3].
6.4 Temperature control unit, which meets the following recommendations and requirements:
a) The temperature range should meet the experimental requirements and achieve a low-temperature
environment, with a recommended range of 253,2 K to 323,2 K.
b) The temperature accuracy shall be at least ±0,1 K.
c) Water bath, air bath or other temperature control methods should be used depending on the
experimental conditions.
d) The maximum overshooting of temperature control shall be lower than 0,1 K.
6.5 Reaction device, which meets the following requirements:
a) The reaction device shall be capable of forming a sealed, pressure-resistant space and exchanging heat
with the external environment to achieve temperature control.
b) The materials of reaction device shall not react with the test solution (5.1) or test gas (5.2).
c) The reaction device shall meet the test conditions, including the pressure range (6.2), temperature
range (6.4) and the data acquisition (6.7) requirements.
d) The reaction device, whether in the form of a reactor or a rocking cell, shall be capable of connecting to
the data acquisition unit (6.7) to meet the data collection requirements during the testing process.
e) Reaction devices with or without viewports shall be both acceptable for use.
6.6 Liquid feed unit. If the reaction device is easy to seal and open, a liquid feed unit is not required and
the material supply unit (6.1) should be used, instead.
6.7 Data acquisition unit. The data acquisition unit complies with the following recommendations and
requirements:
a) The temperature sensors shall be accurate to 0,01 K.
b) The temperature probes should be positioned in the central or lowe
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ISO/TC 193/SC 3/WG 3
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Secretariat: SAC
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Date: 2026-01-2704-22
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Natural gas — Upstream area — Determination of hydrate
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equilibrium temperature
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Gaz naturel — Zone en amont — Détermination de la température d’équilibre des hydrates
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St l D fi iti
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All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication
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may be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying,
or posting on the internet or an intranet, without prior written permission. Permission can be requested from either ISO
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at the address below or ISO’s member body in the country of the requester.
Header distance from edge: 1.27 cm, Footer distance
from edge: 0.5 cm
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: + 41 22 749 01 11
Formatted: French (Switzerland)
EmailE-mail: copyright@iso.org
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Website: www.iso.orgwww.iso.org
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Published in Switzerland
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ii
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Contents Page
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single, No page break before, Don't keep with next,
Foreword . v
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Introduction . vi
stops: Not at 17.2 cm
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
5 Test solution and gas . 2
5.1 Test solution . 2
5.2 Test gas . 2
6 Apparatus . 3
7 Procedure . 6
7.1 Calibration and air tightness test . 6
7.2 Purging . 6
7.3 Sample preparation . 6
7.4 Data acquisition . 6
7.5 Cooling process . 6
7.6 Hydrate formation . 7
7.7 Heating process . 7
7.8 End of the test . 7
7.9 Overview . 7
8 Calculation . 9
9 Precision . 11
10 Test report . 11
Annex A (informative) Method of temperature setting of gas hydrate test . 12
Annex B (informative) Statistical analysis of precision experiments . 14
Bibliography . 25

Foreword . iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
5 Reagents and materials . 2
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5.1 Test solution . 2
5.2 Test gas . 2
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6 Apparatus . 2
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6.1 General. 2
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6.2 Material supply unit . 3
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6.3 Pressurizing unit . 3
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iii
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6.5 Temperature control unit . 4
6.6 Reaction device . 4
6.7 Liquid feed unit . 4
6.8 Data acquisition unit . 4
7 Procedure . 5
7.1 Calibration and air tightness test . 5
7.2 Purging . 5
7.3 Sample preparation . 5
7.4 Data acquisition . 5
7.5 Cooling process . 5
7.6 Hydrate formation . 6
7.7 Heating process . 6
7.7.1 General . 6
7.7.2 Ramp heating . 6
7.7.3 Stepwise heating . 6
7.8 End of the test . 6
7.9 Overview . 6
8 Calculation . 7
9 Precision . 8
10 Test report . 8
Annex A (informative) Method of temperature setting of gas hydrate test . 9
Annex B (informative) Statistical analysis of precision experiments . 10
Bibliography . 18

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iv
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Foreword
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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.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types of
ISO documents should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directiveswww.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent rights
in respect thereof. As of the date of publication of this document, ISO had not received notice of (a) patent(s)
which may be required to implement this document. However, implementers are cautioned that this may not
represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents.www.iso.org/patents. ISO shall not be held responsible for identifying any or all such
patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.htmlwww.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 193, Natural gas, Subcommittee SC 3, Upstream
area.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.htmlwww.iso.org/members.html.
Formatted: Font: 10 pt
Formatted: Font: 10 pt
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v
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Formatted: HeaderCentered
Introduction
Natural gas hydrate is a crystalline structure formed under specific conditions (high pressure and low
temperature), in which gas molecules (primarily methane) are surrounded by water molecules. Due to its
immense potential energy value and environmental significance, research on natural gas hydrates has been
ongoing internationally. The phase equilibrium point is a crucial parameter for the formation and
decomposition of natural gas hydrates, and its determination is of great importance for hydrate management.
Common methods for measuring the phase equilibrium point of hydrates are mainly divided into the
observation method and the pressure, volume and temperature (PVT) method.
The observation method requires a high-pressure resistant transparent material (e.g. sapphire) for the
reaction device to clearly observe the formation and decomposition process of the hydrate. With this method,
the formation and decomposition process of the hydrate is directly observed and the results are intuitive and
reliable. However, this method is limited by the pressure resistance and transparency of the reaction device.
The PVT method measures the phase equilibrium of hydrates by varying any two of the parameters of PVT in
the reaction system while keeping the other parameter constant. Depending on the parameter that is kept
constant, it can be categorized into constant pressure, constant volume and constant temperature methods.
The constant volume method is suitable for measuring the phase equilibrium of hydrates in multi-component
systems and under complex conditions. It provides more comprehensive phase equilibrium information but
requires precise instrument control and data analysis. This document is compiled to meet the demand for
measuring the phase equilibrium point of hydrates in natural gas hydrate research under the constant volume
method.
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vi
DRAFT International Standard ISO/FDIS 23335:2026(en)

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single
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Natural gas — Upstream area — Determination of hydrate
and Asian text, Adjust space between Asian text and
equilibrium temperature
numbers
1 Scope Formatted: Left: 1.5 cm, Right: 1.5 cm, Bottom: 1 cm,
Header distance from edge: 1.27 cm, Footer distance
from edge: 0.5 cm
This document specifies a method for determining the phase equilibrium point of natural gas hydrates in a
laboratory setting under constant volume conditions, including the principle, reagents and materials,
apparatus, procedure, expression of results, test report and precision.
This document applies to laboratory simulations of hydrate formation and decomposition processes. It
Formatted: Default Paragraph Font
involves the analysis of collected temperature and pressure data to determine the phase equilibrium
Formatted: Default Paragraph Font
temperature of hydrates.
Formatted: Default Paragraph Font
2 Normative references
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The following documents are referred to in the text in such a way that some or all of their content constitutes
Adjust space between Asian text and numbers, Tab
requirements of this document. For dated references, only the edition cited applies. For undated references,
stops: Not at 0.7 cm + 1.4 cm + 2.1 cm + 2.8 cm +
the latest edition of the referenced document (including any amendments) applies.
3.5 cm + 4.2 cm + 4.9 cm + 5.6 cm + 6.3 cm + 7 cm
ISO 5725--2, Accuracy (trueness and precision) of measurement methods and results — Part 2: Basic method Formatted: Default Paragraph Font
for the determination of repeatability and reproducibility of a standard measurement method
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ISO 10715, Natural gas — Gas sampling
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ISO 14532, Natural gas — Vocabulary
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3 Terms and definitions
Formatted: Adjust space between Latin and Asian text,
For the purposes of this document, the terms and definitions given in ISO 14532 and the following terms apply.
Adjust space between Asian text and numbers
Formatted: Default Paragraph Font
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
Formatted: Default Paragraph Font
— — ISO Online browsing platform: available at https://www.iso.org/obphttps://www.iso.org/obp
Formatted: Adjust space between Latin and Asian text,
Adjust space between Asian text and numbers, Tab
— — IEC Electropedia: available at https://www.electropedia.org/https://www.electropedia.org/
stops: Not at 0.7 cm + 1.4 cm + 2.1 cm + 2.8 cm +
3.5 cm + 4.2 cm + 4.9 cm + 5.6 cm + 6.3 cm + 7 cm
3.1 3.1
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hydrate
and Asian text, Adjust space between Asian text and
solid crystalline substance resembling ice formed by gas molecules and water molecules
numbers
1 1)
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[SOURCE: ISO 14532:20— , , 3.461.16, modified — The preferred term has been modified from "gas
hydrateshydrate" to "hydrate".]
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Under preparation. Stage at the time of publication: ISO/DIS 14352:2025.
1)
Under preparation. Stage at the time of publication: ISO/DIS 14352:2026. Formatted: Footer, Left, Space After: 0 pt, Tab stops:

Not at 17.2 cm
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3.2 3.2
equilibrium
limit state of each phase change in a multiphase system, where all phases in the reaction system reach balance
3.3 3.3
phase equilibrium point
intersection of the cooling curve and the heating curve in the phase diagram formed by temperature and
pressure data
4 Principle
The formation and decomposition of natural gas hydrates follow the basic principle of phase equilibrium. For
multiphase systems, the mutual transformation between phases, the formation of new phases and the
disappearance of old phases are related to temperature, pressure and composition. Under constant volume
conditions, the process of hydrate formation and decomposition is simulated. Throughout the entire testing
process, changes in temperature and pressure are recorded. After data processing, a pressure-temperature
[1] [1]
(P-T) diagram is plotted to identify the phase equilibrium point . .
Formatted: No underline
5 ReagentsTest solution and materialsgas
5.1 Test solution
Determine the best testing medium in accordance with the experimental design. The test solution complies
Formatted: Body Text, Adjust space between Latin and
with the following recommendations and requirements:
Asian text, Adjust space between Asian text and
numbers, Tab stops: Not at 0.7 cm + 1.4 cm + 2.1 cm
a) a) For formation water in field test simulation, the formation water samples should be taken
+ 2.8 cm + 3.5 cm + 4.2 cm + 4.9 cm + 5.6 cm + 6.3
whenever possible;. cm + 7 cm
b) b) For prepared water in field test simulation, when formation water samples are unavailable, the
composition of formation water shall be analysed and prepared;.
c) c) Distilled water should be used in laboratory experiment;.
d) d) Other reagents of analytical grade shall be used.
5.2 Test gas
Determine the best testing medium in accordance with the experimental design. The test gas complies with
Formatted: Body Text, Adjust space between Latin and
the following recommendations and requirements: Asian text, Adjust space between Asian text and
numbers, Tab stops: Not at 0.7 cm + 1.4 cm + 2.1 cm
a) a) For produced gas in field test simulation, the produced gas samples shall be taken as the + 2.8 cm + 3.5 cm + 4.2 cm + 4.9 cm + 5.6 cm + 6.3
methods specified in ISO 10715;. cm + 7 cm
b) b) For prepared gas in field test simulation, when produced gas samples are unavailable, the
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composition of produced gas shall be analysed and prepared;.
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c) c) For prepared gas in laboratory experiment, all test gas component purity should be ≥ 99,9 %.
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6 Apparatus
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6.1 General
The apparatus for determining the hydrate equilibrium temperature should be constructed in accordance
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with Figure 1. Figure 1.
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Key
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1 material supply unit
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2 pressurizing unit
3 mixing unit
4 temperature control unit
5 reaction device
6 liquid feed unit
7 data acquisition unit Formatted: Font: 10 pt
NOTE  This diagram only shows the composition of the main apparatus. The specific pipeline connections and valve settings
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are not shown in here.
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1 material supply unit
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2 pressurizing unit
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3 mixing unit
4 temperature control unit
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5 reaction device
6 liquid feed unit
7 data acquisition unit
NOTE This diagram only shows the composition of the main apparatus. The specific pipeline connections and valve
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settings are not shown here.
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numbers
Figure 1 — Example illustrating the components of apparatus
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6.2 Material supply unit
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6.1 The material supply unit, which shall be used to supply test materials.
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6.3 Pressurizing unit .
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6.1.1 The pressurizing unit complies with, which meets the following recommendations and
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requirements:
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a) a) The pressure range should meet the experimental requirements and achieve a high-pressure
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condition;.
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NOTE 1 High-pressure conditions are one of the essential requirements for hydrate formation. In field
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production, the pressure ranges usually from several megapascals to several tens of megapascals.
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b) b) The pressure accuracy shall be ±0,01 MPa;.
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c) c) Pressurizing devices and pipelines shall be corrosion resistanceresistant in a sour gas testing
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environment.
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[2]
NOTE See 2 For more information about hydrogen sulfide resistant materials in, see ISO 15156-1 .
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6.4 Mixing unit
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6.2 The mixing unit complies with, which meets the following recommendations and requirements:
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a) a) The mixing unit shall be capable of providing effective mixing to facilitate both hydrate
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formation and decomposition;.
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b) b) Mechanical stirring, magnetic stirring, rocking or gas disturbance techniques should be used
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depending on the experimental conditions;.
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c) c) High agitation shall be used for mixing, and the. The higher the agitation, the faster the Formatted: English (United Kingdom)
equilibrium is reached.
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NOTE 1 The primary functions of the mixing are to enhance mass transfer, intensify heat transfer, promote nucleation .
and simulate flow conditions.
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NOTE 2 For more information about high agitation, see Reference [3]. [3]. .
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6.5 Temperature control unit
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6.3 The temperature control unit complies with, which meets the following recommendations and
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requirements:
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a) a) The temperature range should meet the experimental requirements and achieve a low-
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temperature environment, with a recommended range of 253,2 K to 323,2 K;.
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b, c, … + Start at: 1 + Alignment: Left + Aligned at: 0
b) b) The temperature accuracy shall be at least ± 0,1 K;.
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c) c) Water bath, air bath or other temperature control methods should be used depending on the
numbers
experimental conditions;.
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d) d) The maximum overshooting of temperature control shall be lower than 0,1 K.
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6.6 Reaction device
6.4 The reaction device complies with, which meets the following requirements:
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a) a) The reaction device shall be capable of forming a sealed, pressure-resistant space and
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exchanging heat with the external environment to achieve temperature control;.
stops: Not at 0.7 cm + 1.27 cm + 1.4 cm + 2.1 cm +
2.8 cm + 3.5 cm + 4.2 cm + 4.9 cm + 5.6 cm + 6.3
b) b) The materials of reaction device shall not react with the test solution (5.1)(5.1) or test gas
cm + 7 cm
(5.2);(5.2).
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c) c) The reaction device shall meet the test conditions, including the pressure range (6.3),(6.2),
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temperature range (6.5)(6.4) and the data acquisition (6.8)(6.7) requirements;.
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d) d) The reaction device, whether in the form of a reactor or a rocking cell, shall be capable of .
connecting to the data acquisition unit (6.8)(6.7) to meet the data collection requirements during the
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testing process;.
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e) e) Reaction devices with or without viewports shall be both acceptable for use. Formatted
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6.7 Liquid feed unit
6.5 . If the reaction device is easy to seal and open, a liquid feed unit is not required and the material supply
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unit (6.2)(6.1) should be used, instead.
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6.8 Data acquisition unit
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6.6 . The reaction devicedata acquisition unit complies with the following recommendations and
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requirements:
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a) a) The temperature sensors shall be accurate to 0,01 K;.
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b) b) The temperature probes should be positioned in the central or lower-central region of the
reaction device (6.6),(6.5), within the core mixing and reaction zone of the fluid, and should avoid
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placement directly against the inner wall of the reaction device;.
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c) c) The pressure sensor shall be accurate to ±0,1 % full scale at least;.
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d) d) For data processing and recording, it shall use a recorder which is capable of real-time logging
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temperature and pressure data and exporting raw data, or an equivalent electronic data recording device,
such as a computer-based data acquisition system with software that supports pressure-temperature
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curve plotting.
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7 Procedure
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7.1 Calibration and air tightness test
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7.1.1 7.1.1 Calibration of temperature and pressureall apparatus shall comply with international or Formatted
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national measurement standards., e.g. ISO 9001. The basis used for calibration shall be retained as
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documented information.
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7.1.2 7.1.2 The air tightness test should be performed on the reaction device (6.6)(6.5) before starting a
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new test.
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NOTE A new test means the initial testing prior to first use of the equipment, following maintenance or modification,
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or upon restart after prolonged disuse of more than six months.
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7.2 Purging
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7.2.1 7.2.1 Purge with test gas (5.2)(5.2) by pressurising between 1,0 MPa and 3,5 MPa and subsequently .
depressurising to ambient pressure. Purging shall be repeated at least 3 times.
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7.2.2 7.2.2 If applicable, users may use a vacuum pump or depressurization may be used to remove .
residual air from the system based on laboratory equipment availability. The vacuum level should ensure
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residual air content remains below 2,5 % of ambient pressure.
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7.3 Sample preparation
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Sample preparation complies with the following requirements:
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a) a) The test solution (5.1)(5.1) shall occupy 20 % to 50 % of the total volume of the reaction
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device;.
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b) b) The reaction device (6.6)(6.5) shall be pressurized with the test gas (5.2)(5.2) to the designated
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initial test pressure using the pressurizing unit (6.3);(6.2).
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c) c) The system shall be allowed to reach temperature and pressure stabilization after activating .
the mixing unit (6.4).(6.3). If the temperature and pressure deviates from the set value, the deviating
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parameter shall be readjusted and the system shall be allowed to stabilize again.
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NOTE Stabilization typically takes 15 min to 30 min.
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7.4 Data acquisition
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Use the data acquisition unit (6.8)(6.7) to record temperature and pressure data accurately. The minimum
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data acquisition frequency shall be one reading per minute to minimize data errors.
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7.5 Cooling process
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Set the target temperature for cooling at least 5 K lower than the predicted hydrate equilibrium temperature.
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See Annex ASee Annex A for more information on predicting hydrate equilibrium temperature. The cooling
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rate range should be 3 K/h to 5 K/h.
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NOTE A faster cooling rate causes a supercooling effect. Supercooling significantly affects the actual conditions for
hydrate formation. However, it does not affect the determination of the phase equilibrium point. The purpose of cooling
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is to provide conditions for hydrate formation.
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7.6 Hydrate formation
Monitor the pressure and temperature through the data acquisition unit. The extensive formation of hydrates
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is expected to be accompanied by a sharp drop in pressure. Asian text, Adjust space between Asian text and
numbers, Tab stops: Not at 0.7 cm + 1.4 cm + 2.1 cm
NOTE 1 Hydrate formation is an exothermic process, which means the temperature fluctuates.
+ 2.8 cm + 3.5 cm + 4.2 cm + 4.9 cm + 5.6 cm + 6.3
cm + 7 cm
NOTE 2 If the reaction device has a viewport, the extensive formation of hydrates is visually confirmed easily.
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7.7 Heating process
Asian text and numbers
7.7.1 General
The heating process shall gradually increase the temperature to decompose the hydrates to obtain a more
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precise phase equilibrium point. Depending on the heating conditions, the two heating methods outlined in
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7.7.27.7.2 and 7.7.37.7.3 may be used.
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7.7.2 Ramp heating
Heat the reaction device (6.6)(6.5) at a low ramp rate. The ramp heating rate should be 0,1 K/h or lower.
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7.7.3 Stepwise heating
Heat the reaction device (6.6)(6.5) stepwise for each interval. The step size should be 0,1 K. Each interval shall
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be considered to do the next heating step when the pressure variation does not exceed 0,01 MPa within
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30 min.
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7.8 End of the test
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When the pressure returns to the initial pressure of the test, the test end shall comply with the following
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a) a) Stop data acquisition;.
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0 cm, Numbered + Level: 1 + Numbering Style: a, b, c,
b) b) Stop the mixing unit and temperature control unit;.
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Indent at: 0 cm, Adjust space between Latin and Asian
c) c) Disconnect the power supply to the relevant equipment;.
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d) d) Depressurize the system. Sour gases, if any, shall be processed with a buffer solution before
release;.
e) e) Clean the reaction device and system and end the test.
7.9 Overview
See Figure 2Figure 2 for a flow diagram for all procedures.
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Start the test
Calibration and
Yes
End of the test
pressure test
New test?
(7.8)
(7.1)
No
Use a vacuum pump or
depressurization
No
Purging
(7.2.2)
(7.2)
Yes
Stepwise heating
Sample preparation (7.7.3)
(7.3)
No
Data acquisition
Ramp heating?
(7.4)
(7.7.2)
Method of predicting
Yes
hydrate equilibrium
Target temperature
Heating process
temperature
unknown?
(7.7)
(Annex A)
No
Hydrate formation
Cooling process
(7.5) (7.6)
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numbers
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Figure 2 — Flow diagram of the procedure
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+ 2.8 cm + 3.5 cm + 4.2 cm + 4.9 cm + 5.6 cm + 6.3
8 Calculation
cm + 7 cm
After the test, use the collected temperature and pressure data to draw figures. The figure shall have pressure Formatted: English (United Kingdom)
on the vertical axis and temperature on the horizontal axis, as shown in Figures 3.Figures 3. Segment from
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point A to point C represents the cooling process of the test, while the segment from point C back to point A
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represents the heating process. According to the definition, the intersection point by the cooling curve and the
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heating curve shall be determined as the phase equilibrium point of the hydrate under initial pressure
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condition, point E. And T(E) is the hydrate equilibrium temperature.
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NOTE The slower the heating rate, the more accurate the results obtained. To overcome the effect of extreme slow
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dissociation close to hydrate equilibrium temperature or if heating curve do not exactly meet the cooling down curve, a
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regression line is used from the linear part of heating curve and close to the cooling curve. The intersection of the
regression line with the cooling curve is hydrate equilibrium temperature. For more information about regression
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linelines, see Reference [4]. [4].
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A
P (E)
P
E
B
T (E)
C
T
Key
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P(E) phase equilibrium pressure, expressed in MPa
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T(E) phase equilibrium temperature, expressed in K
E phase equilibrium point.
P(E) phase equilibrium pressure, expressed i
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