EN ISO 6570:2004

Natural gas - Determination of potential hydrocarbon liquid content - Gravimetric methods (ISO 6570:2001)

This International Standard describes the principles of, and general requirements for, two gravimetric methods for
the determination of the potential hydrocarbon liquid content of natural gas, or similar gas, at a given pressure and
temperature. Two methods are specified in this International Standard to determine the amount of condensate in a
sample gas:
_ Method A: a manual weighing method;
_ Method B: an indirect automatic weighing method based on the indication of the pressure difference caused by
the accumulation of condensate in a vertical tube.
The manual weighing method is a reference method for the indirect automatic method (Method B). The indirect
automatic method (Method B) is suitable for semi-continuous control.
NOTE Unless otherwise specified, gas volumes are in cubic metres at 273,15 K and 101,325 kPa.

Erdgas - Bestimmung des potentiellen Gehaltes an flüssigem Kohlenwasserstoff - Gravimetrische Verfahren (ISO 6570:2001)

Die vorliegende Internationale Norm beschreibt die Prinzipien und Grundanforderungen von zwei gravimetrischen Verfahren zur Bestimmung des potenziellen Gehaltes an flüssigen Kohlenwasserstoffen in Erdgas oder einem ähnlichen Gas bei vorgegebener Temperatur und vorgegebenem Druck. In dieser Internationalen Norm werden zwei Verfahren zum Bestimmen der Kondensatmenge in einem Probegas festgelegt:
-   Verfahren A: ein manuelles Wägeverfahren;
-   Verfahren B: ein indirektes automatisches Wägeverfahren, das auf der Anzeige der durch die Kondensatansammlung in einem senkrechten Rohr hervorgerufenen Druckdifferenz beruht.
Das manuelle Wägeverfahren ist ein Bezugsverfahren für die indirekte automatische Messung (Verfahren A). Das indirekte automatische Verfahren (Verfahren B) ist für die halbkontinuierliche Überwachung geeignet.
ANMERKUNG   Sofern nicht anderweitig festgelegt, bezieht sich das in Kubikmeter angegebene Gasvolumen auf 273,15 K und 101,325 kPa.

Gaz naturel - Détermination de la teneur en hydrocarbures liquides potentiels - Méthodes gravimétriques (ISO 6570:2001)

Zemeljski plin – Določevanje potencialne vsebnosti tekočih ogljikovodikov – Gravimetrijske metode (ISO 6570:2001)

General Information

• Status: Published
• Publication Date: 07-Sep-2004
• ICS: 75.060 - Natural gas
• Technical Committee: CEN/TC 238 - Test gases, test pressures and categories of appliances
• Drafting Committee: CEN/SS N21 - Gaseous fuels and combustible gas
• Current Stage: 6060 - Definitive text made available (DAV) - Publishing
• Start Date: 08-Sep-2004
• Completion Date: 08-Sep-2004
• Ref Project: SIST EN ISO 6570:2004 - Natural gas - Determination of potential hydrocarbon liquid content - Gravimetric methods (ISO 6570:2001)

Overview

EN ISO 6570:2004 - Natural gas: Determination of potential hydrocarbon liquid content - Gravimetric methods (ISO 6570:2001) specifies two gravimetric procedures to measure the potential hydrocarbon liquid content (PHLC) or condensate that can form from natural gas at a given pressure and temperature. The standard is intended for representative gas samples and defines both a manual weighing reference method (Method A) and an indirect automatic weighing method (Method B). Unless otherwise stated, gas volumes are expressed in cubic metres at 273.15 K and 101.325 kPa.

Key topics and technical requirements

• Two defined methods
  • Method A (manual weighing): direct collection and gravimetric determination of condensate; used as the reference method.
  • Method B (indirect automatic weighing): semi-continuous method that infers condensate mass from the pressure difference caused by liquid accumulation in a vertical tube; calibrated against Method A.
• Principle: pressurize a representative sample, heat before pressure reduction to avoid premature condensation, then cool isobarically to the measurement temperature and collect formed liquid.
• Apparatus and installation: requirements for sample lines (stainless steel tubing), cyclone separators, measuring tubes, differential pressure gauges and safe instrumentation for hazardous areas.
• Sampling and sample handling: conditions for direct and indirect sampling and guidance to ensure representative samples (normative reference to ISO 10715 sampling guidelines).
• Procedure and results: step-by-step measurement, expression of results, and reporting requirements.
• Quality and metrology: uncertainty of measurement, calibration examples (Annex C), checks for correct installation, and factors affecting precision (leakage, bath liquid, wet gas).
• Informative annexes: selection of measurement temperature/pressure (Annex A), apparatus line-up examples (Annex B), calibration and example measurements (Annixes C and D).

Applications and users

This standard is practical for professionals involved in:

• Gas producers and processing plants - design and verification of condensate recovery and treatment systems.
• Transmission and distribution network operators - assessing condensate formation risk and sizing of separators and pigging/drainage systems.
• Metering and custody-transfer laboratories - calibrating or validating continuous dew-point/condensate monitors.
• Instrument manufacturers and calibration labs - developing or validating semi-continuous condensate measurement equipment (Method B).
• Regulatory and compliance teams - documenting test reports and measurement uncertainty for operational or contractual requirements.

Related standards

• ISO 10715 (Natural gas - Sampling guidelines) is normative for sampling practice referenced in EN ISO 6570:2004.
• Other gas-property calculation standards (e.g., ISO 6976, ISO 12213 series) are relevant when reporting volumes, compression factors and derived properties.

This standard is essential for accurate determination of condensable hydrocarbon liquids in natural gas and for calibrating instruments that estimate dew point or potential liquid content.

Standards Content (Sample)

SLOVENSKI STANDARD
01-november-2004
=HPHOMVNLSOLQ±'RORþHYDQMHSRWHQFLDOQHYVHEQRVWLWHNRþLKRJOMLNRYRGLNRY±
*UDYLPHWULMVNHPHWRGH,62
Natural gas - Determination of potential hydrocarbon liquid content - Gravimetric
methods (ISO 6570:2001)
Erdgas - Bestimmung des potentiellen Gehaltes an flüssigem Kohlenwasserstoff -
Gravimetrische Verfahren (ISO 6570:2001)
Gaz naturel - Détermination de la teneur en hydrocarbures liquides potentiels - Méthodes
gravimétriques (ISO 6570:2001)
Ta slovenski standard je istoveten z: EN ISO 6570:2004
ICS:
75.060 Zemeljski plin Natural gas
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN ISO 6570
NORME EUROPÉENNE
EUROPÄISCHE NORM
September 2004
ICS 75.060
English version
Natural gas - Determination of potential hydrocarbon liquid
content - Gravimetric methods (ISO 6570:2001)
Gaz naturel - Détermination de la teneur en hydrocarbures
liquides potentiels - Méthodes gravimétriques (ISO
6570:2001)
This European Standard was approved by CEN on 22 July 2004.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European
Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national
standards may be obtained on application to the Central Secretariat or to any CEN member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CEN member into its own language and notified to the Central Secretariat has the same status as the official
versions.
CEN members are the national standards bodies of Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France,
Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia,
Slovenia, Spain, Sweden, Switzerland and United Kingdom.
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EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36  B-1050 Brussels
© 2004 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 6570:2004: E
worldwide for CEN national Members.

Foreword
The text of ISO 6570:2001 has been prepared by Technical Committee ISO/TC 193 "Natural
gas” of the International Organization for Standardization (ISO) and has been taken over as EN
ISO 6570:2004 by CMC.
This European Standard shall be given the status of a national standard, either by publication of
an identical text or by endorsement, at the latest by March 2005, and conflicting national
standards shall be withdrawn at the latest by March 2005.

According to the CEN/CENELEC Internal Regulations, the national standards organizations of
the following countries are bound to implement this European Standard: Austria, Belgium,
Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary,
Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland,
Portugal, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.

Endorsement notice
The text of ISO 6570:2001 has been approved by CEN as EN ISO 6570:2004 without any
modifications.
NOTE Normative references to International Standards are listed in Annex ZA (normative).

Annex ZA
(normative)
Normative references to international publications
with their relevant European publications

This European Standard incorporates by dated or undated reference, provisions from other
publications. These normative references are cited at the appropriate places in the text and the
publications are listed hereafter. For dated references, subsequent amendments to or revisions of
any of these publications apply to this European Standard only when incorporated in it by
amendment or revision. For undated references the latest edition of the publication referred to
applies (including amendments).

NOTE Where an International Publication has been modified by common modifications, indicated
by (mod.), the relevant EN/HD applies.

Publication Year Title EN Year

ISO 10715 1997 Natural gas - Sampling guidelines EN ISO 10715 2000

INTERNATIONAL ISO
STANDARD 6570
First edition
2001-06-15
Natural gas — Determination of potential
hydrocarbon liquid content — Gravimetric
methods
Gaz naturel — Détermination de la teneur en hydrocarbures liquides
potentiels — Méthodes gravimétriques
Reference number
ISO 6570:2001(E)
©
ISO 2001
ISO 6570:2001(E)
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ii © ISO 2001 – All rights reserved

ISO 6570:2001(E)
Contents Page
Foreword.iv
Introduction.v
1 Scope .1
2 Normative references .1
3 Principle.2
4 Apparatus requirements .2
4.1 Measurement installation.2
4.2 Check for correct installation operation .5
5 Sampling.10
5.1 General.10
5.2 Sampling conditions .10
5.3 Sample line.10
5.4 Direct sampling.10
5.5 Indirect sampling .10
6 Procedure .11
6.1 Determination of potential hydrocarbon liquid content.11
6.2 Determination of water formation .12
7 Expression of results .12
7.1 Method A — Manual weighing method.12
7.2 Method B — Indirect automatic method.14
8 Uncertainty of measurement .15
8.1 Achievable uncertainty .15
8.2 Gas leakage.15
8.3 Bath liquid .16
8.4 Wet gas .16
8.5 Condensate leakage .16
8.6 Variations in bath temperature and pressure in the gas/liquid cyclone separator .16
8.7 Premature condensation.16
9 Test report .16
Annex A (informative) Selection of measurement temperature and pressure.17
Annex B (informative) Examples of the line-up of the apparatus .18
Annex C (informative) Example of calibration of the differential pressure gauge for the indirect
automatic method — Method B.19
Annex D (informative) Example of an indirect automatic measurement — Method B.21
ISO 6570:2001(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 3.
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 International Standard may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights.
International Standard ISO 6570 was prepared by Technical Committee ISO/TC 193, Natural gas, Subcommittee
SC 1, Analysis of natural gas.
This first edition cancels and replaces ISO 6570-1:1983 and ISO 6570-2:1984, which have been technically
revised.
Annexes A to D of this International Standard are given for information only.
iv © ISO 2001 – All rights reserved

ISO 6570:2001(E)
Introduction
Under certain conditions, higher hydrocarbons present in natural gas or similar gases may condense and the
condensate formed can cause difficulties in the operation of gas transport and distribution systems.
Dew-point measurements, by condensation on a mirror, may give an indication of the conditions under which
condensation starts. However, these measurements give no further information about the amount of liquid to be
expected under operating conditions.
For proper operation of transport and distribution systems, a knowledge of the quantities of condensate formed as
a function of temperature and pressure is required. This knowledge is also required for the design of production
and treatment systems as well as for subsequent handling and disposal of the liquid.
The methods described in this International Standard are intended for the determination of the quantity of
hydrocarbon condensate formed from a natural gas or similar gas as a function of the temperature and pressure of
the gas.
Instruments based on different measurement principles can give a figure related to potential condensate content or
dew point. The dew point can only be determined by performing measurements at different temperatures followed by
extrapolation of the measurements to a potential hydrocarbon liquid content (� ) value of zero. The methods
PHLC
described in this International Standard can be used to calibrate such instruments.
INTERNATIONAL STANDARD ISO 6570:2001(E)
Natural gas — Determination of potential hydrocarbon liquid
content — Gravimetric methods
WARNING — The use of this International Standard may involve hazardous materials, operations and
equipment. This International Standard does not purport to address all of the safety problems associated
with its use. It is the responsibility of the user of this International Standard to establish appropriate safety
and health practices and to determine the applicability or regulatory limitations prior to use.
1 Scope
This International Standard describes the principles of, and general requirements for, two gravimetric methods for
the determination of the potential hydrocarbon liquid content of natural gas, or similar gas, at a given pressure and
temperature. Two methods are specified in this International Standard to determine the amount of condensate in a
sample gas:
� Method A: a manual weighing method;
� Method B: an indirect automatic weighing method based on the indication of the pressure difference caused by
the accumulation of condensate in a vertical tube.
The manual weighing method is a reference method for the indirect automatic method (Method B). The indirect
automatic method (Method B) is suitable for semi-continuous control.
NOTE Unless otherwise specified, gas volumes are in cubic metres at 273,15 K and 101,325 kPa.
2 Normative references
The following normative documents contain provisions which, through reference in this text, constitute provisions of
this International Standard. For dated references, subsequent amendments to, or revisions of, any of these
publications do not apply. However, parties to agreements based on this International Standard are encouraged to
investigate the possibility of applying the most recent editions of the normative documents indicated below. For
undated references, the latest edition of the normative document referred to applies. Members of ISO and IEC
maintain registers of currently valid International Standards.
ISO 6976:1995, Natural gas — Calculation of calorific values, density, relative density and Wobbe index from
composition
ISO 10715:1997, Natural gas — Sampling guidelines
ISO 12213-1:1997, Natural gas — Calculation of compression factor — Part 1: Introduction and guidelines
ISO 12213-2:1997, Natural gas — Calculation of compression factor — Part 2: Calculation using molar-composition
analysis
ISO 12213-3:1997, Natural gas — Calculation of compression factor — Part 3: Calculation using physical
properties
ISO 6570:2001(E)
3Principle
Determination of the quantity of hydrocarbon condensate which can be formed at a pressure (p) and a temperature
(T) by passing a representative sample of the gas through an apparatus where it is first brought to the pressure (p)
and then cooled to the temperature (T).
The temperature and pressure are selected according to the specific application (see annex A).
Prior to reducing the pressure of the sample of gas to that required for the determination, the gas is heated, so that,
after pressure reduction, the temperature is well above the dew-point temperature of the gas. Downstream of the
reducer, the sample is cooled isobarically in a cooling bath to the required measurement temperature.
The quantity of liquid accumulated during the measurement period is determined by either direct manual weighing of
the collected liquid or weighing of the condensate cyclone separator at the start and at the end of a measurement
period (Method A).
Alternatively, the quantity of liquid accumulated in a vertical measuring tube may be determined automatically (indirect
automatic weighing) by indication of the pressure difference caused by the liquid accumulated in a vertical measuring
tube.
4 Apparatus requirements
WARNING — The instrumentation used for this method shall comply with local legal regulations for
application in hazardous areas.
4.1 Measurement installation
The general arrangement is shown in Figure 1. Examples of the line-up of the apparatus are given in annex B.
4.1.1 Gas-line connecting tubes, made of stainless steel with an internal diameter ranging between 2 mm and
4mm.
If mist is present in the gas, all tubing up to the point where the mist is evaporated or separated shall have an
internal diameter compatible with that of the sample line (4.1.2).
4.1.2 Sample line, the length of which is kept to a minimum and temperature-controlled along its length to at
least the point where it enters the part of the installation where the measurement is made.
An example of a sample line is given in Figure 2.
The sample line can be heated by fitting a plastic hose concentrically around the line through which water flows at the
desired temperature. For this purpose, a temperature-controlled bath can be used from which the water to be
circulated is drawn and to which it returns after circulation. The minimum temperature of the sample line can be
checked easily by measuring the return temperature. The sample valve and its vicinity shall be heated or at least
thermally insulated.
4.1.3 Drying tube (optional), for eliminating water vapour present in sufficiently large quantities in the gas.
Care shall be taken to avoid interferences with the determination of potential hydrocarbon liquid content.
Under certain conditions, the presence of water vapour can lead to the formation of hydrate which is detrimental to the
determination. It is, therefore, necessary that the water dew point of the sample be lowered by passing it through a
drying tube packed with anhydrous calcium sulfate or a similar water absorption agent which does not absorb
hydrocarbons. In such cases, it is necessary to monitor the water dew point downstream to the drying tube so as to
check the degree of saturation of the absorption agent. Install the drying tube upstream of a dust filter in order to
prevent particles of the drying agent from entering the measurement installation.
2 © ISO 2001 – All rights reserved

ISO 6570:2001(E)
If the presence of water vapour does not lead to hydrate formation, the drying tube may be omitted and the amount of
water formed under the measurement conditions determined.
If hydrocarbon mist is present in the sample, and a drying tube is used, ensure that the mist is evaporated by heating
before allowing the sample to pass through the drying tube.
4.1.4 Dust filter, preferably of a 5µm pore size, which does not adsorb hydrocarbons.
4.1.5 Heat exchangers, pressure regulators and controllers, installed on the gas line with the heat
exchanger immediately upstream to each pressure regulator so as to ensure that the gas temperature after pressure
reduction remains at least 5 K above the dew point.
The pressure controller can be placed upstream or downstream from the cooling bath in the measurement
installation (see annex B).
4.1.5.1 Heat exchanger (see example in Figure 3), through which water, maintained at the required temperature, is
circulated from a thermostatically controlled bath so as to maintain the temperature constant in the gas line.
4.1.5.2 Pressure regulator and pressure controller, to ensure the maximum variation from its set-point with the
pressure measurement in the gas/liquid cyclone separator is� 10 kPa.
4.1.6 Measurement instruments for temperature and pressure, capable of recording or monitoring the
following:
a) gas temperature and pressure in the gas/liquid cyclone separator;
b) ambient temperature and pressure;
c) gas temperature in the gas transmission line, or in the cylinder from which the sample is taken (optional);
d) gas temperature after pressure reduction (optional);
e) temperature of the bath (optional);
f) gas pressure before pressure reduction (optional);
g) gas pressure after pressure reduction (optional).
If proven experimentally that the difference between the temperature of the gas in the cyclone separator and the
temperature of the cooling bath is less than 0,1 K, the temperature of the cooling bath may be measured instead.
The pressure can be measured in the sample line just before or just after the cyclone separator.
4.1.7 Gas flow meter, capable of making either mass or volumetric measurements for either wet or dry gas. If a
mass flow meter is used, it is necessary that the density of the gas be known.
The flow rate of the gas passing through the installation is limited by the cooling capacity of the bath, the heat
transmission between the cooling coil and bath and the temperature drop to which the sample is subjected. The flow
rate shall, therefore, be limited to a value that will ensure that the gas is cooled to the bath temperature (see 4.1.9.3).
Check the accuracy of the meter at regular intervals. The choice of gas meter shall be made taking into account the
required accuracy, flow rate and the nature of the natural gas. The maximum permissible error in the flow meter shall
be� 1 % of the measured value.
The measured values shall be corrected for temperature and pressure if the values vary during the course of the
period of measurement from reference conditions (273,15 K and 101,325 kPa).
4.1.8 Heated cabinet, used in the case of indirect sampling, of the appropriate shape to contain the sample
cylinder and capable of heating to at least 10 K above the temperature at the sampling point (see 5.5).
ISO 6570:2001(E)
4.1.9 Condenser/separator apparatus, consisting of a cooling coil connected at the end to a cyclone separator
wherecondensatesarecollected(seeFigure4).
The cooling coil and cyclone separator are completely immersed in the cooling bath. The difference in temperature
between the cooling bath and the gas/liquid cyclone separator shall not exceed �0,1 K.
4.1.9.1 Cooling coil, possibly in the form of a coil of stainless steel tubing and meeting the following design
characteristics:
a) capable of providing turbulent flow throughout the measurements;
b) capable of maintaining the temperature difference between the gas leaving the cooling coil and the
temperature of cooling bath to less than 0,25 K;
c) capable of maintaining pressure difference over the cooling coil not exceeding 1 kPa so as to ensure isobaric
conditions;
d) having an internal diameter between 2 mm and 4 mm.
NOTE These specifications can be met for example with a cooling coil of 2,5 m length and a gas flow of 1 m /h.
4.1.9.2 Cyclone separator, permanently connected to the cooling coil, with a specific inlet diameter enabling
sufficient centrifugal action to be obtained as the sample gas enters the cyclone separator barrel.
EXAMPLE A cyclone separator having an inlet diameter of 1 mm can meet these requirements. A provision can be made
for measuring or recording the gas temperature in the barrel.
For the indirect automatic condensate measurement (Method B) a vertical measuring tube is mounted at the bottom
of the cyclone separator. A weighing device (4.1.10.2) is connected to the bottom of the measuring device. This
differential pressure transducer is connected to one side at the bottom of the measuring tube and to the other side at
the lower part of the cyclone separator. Thus, the pressure difference between both sides of the transducer is a
measure for the mass of the liquid in the measuring tube. At the bottom of the measuring tube there is also a drain
line connected. This drain is opened at regular time intervals to release the collected condensate from the measuring
tube.
NOTE For the weighing device an accurate differential pressure gauge should be used (see 4.1.10.2).
4.1.9.3 Cooling bath, well stirred, capable of completely immersing the cooling coil (4.1.9.1) and cyclone separator
(4.1.9.2) as well as maintaining the temperature at any point of the bath by less than 0,25 K.
Proper operation of the co
...