Natural gas - Quality designation (ISO 13686:2013)

This International Standard specifies the parameters required to describe finally processed and, where required, blended natural gas. Such gas is referred to subsequently in this text simply as "natural gas". The main text of this standard contains a list of these parameters, their units and references to measurement standards. Informative annexes give examples of typical values for these parameters, with the main emphasis on health and safety. In defining the parameters governing composition, physical properties and trace constituents, consideration has also been given to existing natural gases to ensure their continuing viability. The question of interchangeability is dealt with in annex A clause A.2.

Erdgas - Bestimmung der Beschaffenheit (ISO 13686:2013)

Die vorliegende Internationale Norm legt Parameter zur Beschreibung von fertig aufbereitetem Erdgas und, wo dies erforderlich ist, von Erdgasgemischen fest. Dieses Gas wird nachstehend als „Erdgas“ bezeichnet.
Der Hauptteil der vorliegenden Norm enthält eine Liste dieser Parameter mit Einheiten und Verweisen auf Messnormen. Darüber hinaus werden in informativen Anhängen zu dieser Norm Beispiele für typische Werte dieser Parameter gegeben, wobei das Hauptaugenmerk auf Gesundheit und Sicherheit gelegt wird.
Bei der Festlegung von Parametern für die Gaszusammensetzung, die physikalischen Eigenschaften und Spurenbestandteile wurden zur Sicherstellung ihrer Gültigkeit vorhandene Erdgase entsprechend berück-sichtigt.
Das Thema Austauschbarkeit wird in Anhang A (siehe A.2) behandelt.

Gaz naturel - Désignation de la qualité (ISO 13686:2013)

L'ISO 13686:2013 traite des paramètres requis pour décrire le gaz naturel dans son état de traitement final et après ajustement, si nécessaire. Ce type de gaz est désigné par la suite dans le texte sous l'appellation «Gaz naturel».
Le texte principal de l'ISO 13686:2013 contient une liste de ces paramètres, leurs unités et références aux normes de mesurage. Les annexes informatives donnent des exemples de valeurs types de ces paramètres, avec un accent principal sur la santé et la sécurité.

Zemeljski plin - Specificiranje kakovosti (ISO 13686:2013)

Ta mednarodni standard določa parametre, ki so potrebni za opredelitev dokončno predelanega in, kjer je to potrebno, mešanega zemeljskega plina. Takšen plin je v nadaljevanju tega besedila naveden kot „zemeljski plin“. Glavno besedilo tega standarda vsebuje seznam teh parametrov, njihove enote in reference merilnih standardov. V informativnih dodatkih so primeri običajnih vrednosti za te parametre, pri čemer sta izpostavljena predvsem zdravje in varnost. Pri opredelitvi parametrov, ki urejajo sestavo, fizične lastnosti in sledi sestavin, so bili upoštevani tudi obstoječi naravni plini ter njihova nadaljnja rentabilnost. Vprašanje zamenljivosti je obravnavano v Dodatku A, točki A.2.

General Information

Status
Published
Public Enquiry End Date
16-Aug-2011
Publication Date
14-Jul-2013
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
20-Jun-2013
Due Date
25-Aug-2013
Completion Date
15-Jul-2013

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SLOVENSKI STANDARD
SIST EN ISO 13686:2013
01-september-2013
1DGRPHãþD
SIST EN ISO 13686:2005
Zemeljski plin - Specificiranje kakovosti (ISO 13686:2013)
Natural gas - Quality designation (ISO 13686:2013)
Erdgas - Bestimmung der Beschaffenheit (ISO 13686:2013)
Gaz naturel - Désignation de la qualité (ISO 13686:2013)
Ta slovenski standard je istoveten z: EN ISO 13686:2013
ICS:
75.060 Zemeljski plin Natural gas
SIST EN ISO 13686:2013 en

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN ISO 13686:2013
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SIST EN ISO 13686:2013
EUROPEAN STANDARD
EN ISO 13686
NORME EUROPÉENNE
EUROPÄISCHE NORM
June 2013
ICS 75.060 Supersedes EN ISO 13686:2005
English Version
Natural gas - Quality designation (ISO 13686:2013)

Gaz naturel - Désignation de la qualité (ISO 13686:2013) Erdgas - Bestimmung der Beschaffenheit (ISO

13686:2013)
This European Standard was approved by CEN on 29 May 2013.

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 CEN-CENELEC Management Centre 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 CEN-CENELEC Management Centre has the same

status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,

Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,

Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and United

Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: Avenue Marnix 17, B-1000 Brussels

© 2013 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 13686:2013: E

worldwide for CEN national Members.
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SIST EN ISO 13686:2013
EN ISO 13686:2013 (E)
Contents Page

Foreword ..............................................................................................................................................................3

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SIST EN ISO 13686:2013
EN ISO 13686:2013 (E)
Foreword

This document (EN ISO 13686:2013) has been prepared by Technical Committee ISO/TC 193 "Natural gas".

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 December 2013, and conflicting national standards shall be withdrawn

at the latest by December 2013.

Attention is drawn to the possibility that some of the elements of this document may be the subject of patent

rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights.

This document supersedes EN ISO 13686:2005.

According to the CEN-CENELEC Internal Regulations, the national standards organizations of the following

countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech

Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece,

Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal,

Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United Kingdom.

Endorsement notice

The text of ISO 13686:2013 has been approved by CEN as EN ISO 13686:2013 without any modification.

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SIST EN ISO 13686:2013
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SIST EN ISO 13686:2013
INTERNATIONAL ISO
STANDARD 13686
Second edition
2013-06-15
Natural gas — Quality designation
Gaz naturel — Désignation de la qualité
Reference number
ISO 13686:2013(E)
ISO 2013
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SIST EN ISO 13686:2013
ISO 13686:2013(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2013

All rights reserved. Unless otherwise specified, no part of this publication 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 at the address below or ISO’s member body in the country of

the requester.
ISO copyright office
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Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
Web www.iso.org
Published in Switzerland
ii © ISO 2013 – All rights reserved
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SIST EN ISO 13686:2013
ISO 13686:2013(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction ..................................................................................................................................................................................................................................v

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 2

4 Symbols, abbreviations and units ....................................................................................................................................................... 6

4.1 Symbols ......................................................................................................................................................................................................... 6

4.2 Abbreviations ........................................................................................................................................................................................... 6

4.3 Subscripts .................................................................................................................................................................................................... 6

5 Quality designation parameters........................................................................................................................................................... 7

5.1 General ........................................................................................................................................................................................................... 7

5.2 Gas composition ..................................................................................................................................................................................... 7

5.3 Gas properties .......................................................................................................................................................................................... 8

6 Sampling ........................................................................................................................................................................................................................ 9

Annex A (informative) Introduction to informative annexes ...................................................................................................10

Annex B (informative) German Regulation Code of Practice DVGW G 260:2008, Extract of the

relevant parts for natural gases .........................................................................................................................................................18

Annex C (informative) European Standard EN 437 “Test gases, test pressures and categories of

appliances” ..............................................................................................................................................................................................................22

Annex D (informative) Interchangeability AGA index method ...............................................................................................25

Annex E (informative) British Gas Hydrocarbon Equivalence Method ..........................................................................32

Annex F (informative) Weaver index method ...........................................................................................................................................37

Annex G (informative) French method for determining gas interchangeability (Delbourg method)

(guide for determining the interchangeability of second family gases) .................................................39

Annex H (informative) Spanish regulation code (Detail Protocol-01 — Measurement) — Extract of

the relevant parts for natural gases ..............................................................................................................................................45

Annex I (informative) Harmonization of gas property data for cross-border transportation ..............46

Bibliography .............................................................................................................................................................................................................................48

© ISO 2013 – All rights reserved iii
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SIST EN ISO 13686:2013
ISO 13686:2013(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.

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. www.iso.org/directives

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. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received. www.iso.org/patents

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.
The committee responsible for this document is ISO/TC 193, Natural gas.

This second edition cancels and replaces the first edition (ISO 13686:1998), which has been

technically revised.
iv © ISO 2013 – All rights reserved
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SIST EN ISO 13686:2013
ISO 13686:2013(E)
Introduction

The need for an International Standard concerning the designation of natural gas quality was a basic

reason for the establishment of ISO/TC 193 in 1989. Standardization of the designation of quality is

specifically stated in the scope of ISO/TC 193. Natural gas, supplying 20 % of the world’s primary energy,

is likely to increase its market share greatly. Yet there is currently no generally accepted definition of

natural gas quality.

To meet this need, it was decided that a general statement of the parameters (i.e. components and

properties) recommended should be established and that the resulting International Standard would

not specify values of, or limits for, these parameters.

Furthermore, it was decided that general-purpose natural gas transmitted to local distribution systems

(LDS), referred to as “natural gas”, should be the first consideration. Thus, this International Standard

was developed. Informative annexes are attached as examples of actual natural gas quality specifications

that already exist.

This International Standard does not impose any quality restrictions on raw gas transported via

pipelines or gathering systems to processing or treating facilities.

It should be understood that this International Standard covers natural gas at the pipeline level prior to

any treatment by LDS for peakshaving purposes. This covers the vast majority of the natural gas that is

sold in international trade and transmitted for custody transfer to local distribution systems.

© ISO 2013 – All rights reserved v
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SIST EN ISO 13686:2013
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SIST EN ISO 13686:2013
INTERNATIONAL STANDARD ISO 13686:2013(E)
Natural gas — Quality designation
1 Scope

This International Standard specifies the parameters required to describe finally processed and, where

required, blended natural gas. Such gas is referred to subsequently in this text simply as “natural gas”.

The main text of this International Standard contains a list of these parameters, their units and references

to measurement standards. Informative annexes give examples of typical values for these parameters,

with the main emphasis on health and safety.

In defining the parameters governing composition, physical properties and trace constituents,

consideration has also been given to existing natural gases to ensure their continuing viability.

The question of interchangeability is dealt with in Annex A (see Clause A.2).
2 Normative references

The following documents, in whole or in part, are normatively referenced in this document and are

indispensable for its application. For dated references, only the edition cited applies. For undated

references, the latest edition of the referenced document (including any amendments) applies.

ISO 6326-1, Natural gas — Determination of sulfur compounds — Part 1: General introduction

ISO 6326-3, Natural gas — Determination of sulfur compounds — Part 3: Determination of hydrogen sulfide,

mercaptan sulfur and carbonyl sulfide sulfur by potentiometry

ISO 6326-5, Natural gas — Determination of sulfur compounds — Part 5: Lingener combustion method

ISO 6327, Gas analysis — Determination of the water dew point of natural gas — Cooled surface

condensation hygrometers

ISO 6570, Natural gas — Determination of potential hydrocarbon liquid content — Gravimetric methods

ISO 6974-1, Natural gas — Determination of composition and associated uncertainty by gas

chromatography — Part 1: General guidelines and calculation of composition

ISO 6974-2, Natural gas — Determination of composition and associated uncertainty by gas

chromatography — Part 2: Uncertainty calculations

ISO 6974-3, Natural gas — Determination of composition with defined uncertainty by gas chromatography —

Part 3: Determination of hydrogen, helium, oxygen, nitrogen, carbon dioxide and hydrocarbons up to C8

using two packed columns

ISO 6974-4, Natural gas — Determination of composition with defined uncertainty by gas chromatography —

Part 4: Determination of nitrogen, carbon dioxide and C1 to C5 and C6+ hydrocarbons for a laboratory and

on-line measuring system using two columns

ISO 6974-5, Natural gas — Determination of composition and associated uncertaint y by gas chromatography —

Part 5: Isothermal method for nitrogen, carbon dioxide, C1 to C5 hydrocarbons and C6+ hydrocarbons

ISO 6974-6, Natural gas — Determination of composition and associated uncertainty by gas

chromatography — Part 6: Determination of helium, oxygen, nitrogen, carbon dioxide and C1 to C10

hydrocarbons using capaillary columns
ISO 6975, Natural gas — Extended analysis — Gas-chromatographic method
© ISO 2013 – All rights reserved 1
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SIST EN ISO 13686:2013
ISO 13686:2013(E)

ISO 6976:1995, Natural gas — Calculation of calorific values, density, relative density and Wobbe index

from composition

ISO 6978-1, Natural gas — Determination of mercury — Part 1: Sampling of mercury by chemisorption on iodine

ISO 6978-2, Natural gas — Determination of mercury — Part 2: Sampling of mercury by amalgamation on

gold/platinum alloy

ISO 10101-1, Natural gas — Determination of water by the Karl Fischer method — Part 1: Introduction

ISO 10101-2, Natural gas — Determination of water by the Karl Fischer method — Part 2: Titration procedure

ISO 10101-3, Natural gas — Determination of water by the Karl Fischer method — Part 3: Coulometric procedure

ISO 11541, Natural gas — Determination of water content at high pressure
ISO 13443, Natural gas — Standard reference conditions
ISO 14532, Natural gas — Vocabulary

ISO 15970:2008, Natural gas — Measurement of properties — Volumetric properties: density, pressure,

temperature and compression factor

ISO 15971:2008, Natural gas — Measurement of properties — Calorific value and Wobbe index

ISO 18453, Natural gas — Correlation between water content and water dew point

ISO 19739, Natural gas — Determination of sulfur compounds using gas chromatography

ISO 23874, Natural gas — Gas chromatographic requirements for hydrocarbon dewpoint calculation

3 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO 14532 and the following apply.

3.1
natural gas

gaseous fuel obtained from underground sources and consisting of a complex mixture of hydrocarbons,

primarily methane, but generally also including ethane, propane and higher hydrocarbons in much

smaller amounts

Note 1 to entry: It also includes some inert gases, such as nitrogen and carbon dioxide, plus minor amounts of

trace constituents.

Note 2 to entry: Natural gas remains in the gaseous state under the temperature and pressure conditions normally

found in service. It is produced by processing raw gas or from liquefied natural gas and, if required, blended to give

a gas suitable for direct use. As pipeline quality natural gas, it can then be transmitted within a local distribution

system, within a country, or across national borders. It is subject to contractual requirements between buyer and

seller, and in some cases to national or state requirements as to quality (see Clause A.1).

3.2
liquefied natural gas

natural gas which, after processing, has been liquefied for storage or transportation purposes

Note 1 to entry: Liquefied natural gas is revaporized and introduced into pipelines for transmission and

distribution as natural gas.
3.3
substitute natural gas

manufactured or blended gas with properties which make it interchangeable with natural gas

Note 1 to entry: Substitute natural gas is sometimes called synthetic natural gas.

2 © ISO 2013 – All rights reserved
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SIST EN ISO 13686:2013
ISO 13686:2013(E)

Note 2 to entry: This also includes gases manufactured by thermal process from biomass.

3.4
raw gas

unprocessed gas taken from well heads through gathering lines to processing facilities

3.5
local distribution system
gas mains and services which supply natural gas directly to consumers
3.6
gas quality

attribute of natural gas by its composition (major components, minor components and trace components)

and its physical properties (calorific value, Wobbe index, compression factor, relative density and dew points)

3.7
reference conditions

standard reference conditions of temperature, pressure and humidity (state of saturation) to be used for

measurements and calculations carried out on natural gases, natural gas substitutes and similar fluids

in the gaseous state

Note 1 to entry: Standard reference conditions are denoted by the subscript “s”: p = 101,325 kPa; T = 288,15 K.

s s
Note 2 to entry: Adapted from ISO 13443.
3.8
calorific value

amount of heat which would be released by the complete combustion in air of a specified quantity of gas,

in such a way that the pressure at which the reaction takes place remains constant, and all the products

of combustion are returned to the same specified temperature as that of the reactants

Note 1 to entry: It is divided into two types: superior calorific value and inferior calorific value.

Note 2 to entry: Both superior and inferior calorific values, which differ by the heat of condensation of water

formed by combustion, can be specified on a molar, mass or volumetric basis. For the volumetric basis the pressure

and temperature shall be stated at standard reference conditions.

Note 3 to entry: Calorific values can also be stated as dry or wet, depending on the water vapour content of the

gas prior to combustion.

Note 4 to entry: The effect of water vapour on the calorific values, either directly measured or calculated, is

described in Annex F of ISO 6976:1995.

Note 5 to entry: Normally, the calorific value is expressed as the superior, dry value specified as a volumetric basis

under standard reference conditions.
Note 6 to entry: Adapted from ISO 6976.
3.8.1
superior calorific value

amount of heat that would be released by the complete combustion with oxygen of a specified quantity

of gas, in such a way that the pressure p at which the reaction takes place remains constant, and all the

products of combustion are returned to the same specified temperature t as that of the reactants, all

of these products being in the gaseous state except for water, which is condensed to the liquid state at t

Note 1 to entry: Adapted from ISO 6976.
© ISO 2013 – All rights reserved 3
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SIST EN ISO 13686:2013
ISO 13686:2013(E)
3.8.2
inferior calorific value

amount of heat that would be released by the complete combustion with oxygen of a specified quantity

of gas, in such a way that the pressure p at which the reaction takes place remains constant, and all the

products of combustion are returned to the same specified temperature t as that of the reactants, all of

these products being in the gaseous state
Note 1 to entry: Adapted from ISO 6976.
3.9
density
mass of a gas divided by its volume at specified pressure and temperature
3.10
relative density

density of a gas divided by the density of dry air of standard composition at the same specified conditions

of pressure and temperature

Note 1 to entry: The term “ideal relative density” applies when both gas and air are considered as fluids which

obey the ideal gas law; the term “real relative density” applies when both gas and air are considered as real fluids.

For the standard composition of dry air.
Note 2 to entry: Adapted from ISO 6976.
3.11
Wobbe index

volumetric-basis superior (inferior) calorific value, at specified reference conditions, divided by the

square root of the relative density at the same specified metering reference conditions

Note 1 to entry: The heat input for different natural gas compositions is the same if they have the same Wobbe

index and are used under the same gas pressure.
Note 2 to entry: Adapted from ISO 6976.
3.12
compression factor

compression factor Z is the quotient of the volume of an arbitrary mass of gas, at a specified pressure and

temperature, and that of the same gas under the same conditions as calculated from the ideal gas law

Note 1 to entry: The terms “compressibility factor” and “Z-factor” are synonymous with compression factor.

Note 2 to entry: Adapted from ISO 12213-1.
3.13
water dew point
temperature above which no condensation of water occurs at a specified pressure

Note 1 to entry: For any pressure lower than the specified pressure there is no condensation at this temperature.

Note 2 to entry: Adapted from ISO 6327.
3.14
hydrocarbon dew point

temperature above which no condensation of hydrocarbons occurs at a specified pressure

Note 1 to entry: At a given dew point, there is a pressure range within which condensation occurs except at one

point, the cricondentherm (see A.3.2).
3.15
gas composition

concentrations of the major and minor components and trace components in natural gas as analysed

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SIST EN ISO 13686:2013
ISO 13686:2013(E)
3.16
molar composition

gas composition expressed as a molar (or mole) fraction, or molar (mole) percentage

Note 1 to entry: The mole fraction, x, of component i is the quotient of amount of substance of this component and

amount of substance of the whole mixture. The unit of amount of substance is mole. The mass of one mole of any

chemical species, in grams, is numerically equal to its relative molecular mass. A table of recommended values of

molar masses is given in ISO 6976. For an ideal gas, the mole fraction is identical to the volume fraction, but this

relationship cannot in general be assumed to apply to real gas behaviour.
3.17
gas analysis

use of test methods and other techniques for determining the gas composition, as stated in this

International Standard
3.18
interchangeability

measure of the degree to which the combustion characteristics of one gas resemble those of another gas

Note 1 to entry: Two gases are said to be interchangeable when one gas may be substituted for the other without

affecting the operation of gas burning appliances or equipment.
3.19
odorization

addition of odorants, in most cases intensively smelling organic sulfur compounds, to natural gas to

allow the recognition of gas leaks by smell at very low concentration (before a build up to a dangerous

gas in air concentration can occur)

Note 1 to entry: Natural gas is normally odourless. It is necessary to add an odorant to the gas for safety reasons.

It permits the detection of the gas by smell at very low concentrations.
Note 2 to entry: Odorants in use for gas odorization are specified in ISO 13734.
3.20
methane number
rating indicating the knocking characteristics of a fuel gas
Note 1 to entry: It is comparable to the octane number for petrol.

Note 2 to entry: The methane number expresses the volume percentage of methane in a methane/hydrogen mixture

which, in a test engine under standard conditions, has the same tendency to knock as the fuel gas to be examined.

© ISO 2013 – All rights reserved 5
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SIST EN ISO 13686:2013
ISO 13686:2013(E)
4 Symbols, abbreviations and units
4.1 Symbols
Symbol Meaning and units
d Relative density
Molar basis calorific value (kJ/mol)
ˆ Mass basis calorific value (MJ/kg)
Volumetric basis calorific value (MJ/m )
M Mass per mole (kg/kmol)
p (Absolute) pressure (kPa)
t Celsius temperature (°C)
T Thermodynamic (absolute) temperature (K)
V (Gas) volume (m )
W Wobbe index (number) (MJ/m )
Z Compression factor
D Density (kg/m )
4.2 Abbreviations
Abbreviation Meaning
LDS Local distribution system
NG Natural gas
SNG Substitute (synthetic) natural gas
4.3 Subscripts
d (Gas volume) dry
l Inferior (calorific value)
s (Gas volume) saturated
S Superior (calorific value)
w (Gas volume) wet

Superior calorific value is denoted by Hs; inferior calorific value is denoted by H . The calorific value

shall be specified under the combustion conditions. The volumetric calorific value shall be specified

under standard reference conditions. The calorific value is normally stated as “dry”.

6 © ISO 2013 – All rights reserved
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SIST EN ISO 13686:2013
ISO 13686:2013(E)

EXAMPLE Superior calorific value, specified on a volumetric basis, at standard reference conditions and

stated as wet. For simplicity, the combustion conditions are not specified.
Hp(,T )
S,ws s

The Wobbe index, denoted by W, is expressed on a volumetric basis and given in MJ/m3, where the

volume is stated at standard reference conditions. The Wobbe index can be specified as superior or

inferior, depending on the calorific value and as dry or wet, depending on the calorific value and the

corresponding density.

EXAMPLE Wobbe index, superior, specified an a volumetric basis, at standard reference conditions and

stated as “wet”.
Hp(,T )
S,ws s
Wp(,T )=
S,ws s
dp(,T )
ws s
5 Quality designation parameters
5.1 General

This clause deals with the various parameters which may be referred to in a designation of the quality of

natural gas. The parameters actually selected will depend upon the purpose for which the designation

is required and it is unlikely that all the parameters listed in this International Standard will be used.

5.2 Gas composition
5.2.1 General
Natural gas is compo
...

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