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INTERNATIONAL STANDARD

NORME INTERNATIONALE

Natural gas — Vocabulary

Gaz naturel — Vocabulaire


©ISO 2001

ISO 14532:2001 (E/F)

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Contents Page

Foreword v

Introduction vii

1 Scope 1

2 Terms and definitions 1

2.1 General definitions 1

2.1.1 Natural gas 1

2.1.2 Pipeline network 6

2.2 Measurement methods 7

2.2.1 General definitions 7

2.2.2 Specific methods 9

2.3 Sampling 11

2.3.1 Sampling methods 11

2.3.2 Sampling devices 12

2.3.3 Conditioning device 13

2.3.4 Other definitions 14

2.4 Analytical systems 15

2.5 Analysis 18

2.5.1 Metrology 18

2.5.2 Calibration and quality control 21

2.5.3 Gas analysis 24

2.5.3.1 General definitions 24

2.5.3.2 Analysed components 26

2.5.3.3 Trace component [constituent] 28

2.5.3.4 Analyser response 31

2.5.3.5 Calibration gas mixtures 35

2.5.3.5.1 General definitions from metrology 35

2.5.3.5.2 Definitions relevant to gas mixtures 38

2.5.4 Statistics 39

2.6 Physical and chemical properties 40

2.6.1 Reference conditions 40

2.6.2 Behaviour of ideal and real gas 41

2.6.3 Density 43

2.6.4 Combustion properties 44

2.6.5 Dew points 46

2.6.5.1 Water dew point 46

2.6.5.2 Hydrocarbon dew point 47

2.6.6 Other definitions 47

2.7 Interchangeability 48

2.8 Odorization 49

Annex A (informative) Subscripts, symbols and units 51

Bibliography 59

Index 65


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 (lEC) 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 14532 was prepared by Joint Technical Committee ISO/TC 193, Natural gas.

Introduction

ISO Technical Committee 193, Natural Gas, was established in May, 1989, with the task of creating new International Standards, and updating existing International Standards relevant to natural gas. This includes gas analysis, direct measurement of properties, quality designation and traceability.

In these activities, a comprehensive and uniform review of the definitions, symbols and abbreviations used in the International Standards was not previously systematically pursued. The development of International Standards with terminology created to suit specific purposes often resulted in the detriment of uniformity and cohesiveness between International Standards.

Thus, there is the need for harmonization of the terminology used in the International Standards pertaining to natural gas. The intention of this International Standard is to incorporate the reviewed definitions into the ISO/TC 193 source International Standards.

The aim is to create a coherent body of International Standards which support each other with regard to their definitions. Common and unambiguous terms and definitions used throughout all International Standards is the starting point for the understanding and application of every International Standard.

The presentation of this International Standard has been arranged to facilitate its use as follows:

Major headings pertain to specific fields of the natural gas industry. All definitions which fall under these headings, as gleaned from ISO International Standards issued through ISO/TC 193, are listed under that heading. A review of the Contents will serve to facilitate finding specific terms.

Notes are given under numerous definitions where it was deemed important to give informative guidance for a given definition. The notes are not considered a part of the definition.

© !SO 2001 - All rights reserved/Tous droits reserves vii

INTERNATIONAL STANDARD

Natural gas — Vocabulary

1 Scope

This International Standard establishes the terms, definitions, symbols and abbreviations used in the field of natural gas.

The terms and definitions have been reviewed and studied in order to cover all aspects of any particular term with input from other sources such as European standards from CEN (The European Committee for standardization), national standards and existing definitions in the IGU dictionary of the gas industry.

2 Terms and definitions

2.1 General definitions

For the purposes of this International Standard, the following terms and definitions apply.

2.1.1 Natural gas

2.1.1.1 natural gas NG

complex gaseous mixture of hydrocarbons, primarily methane, but generally also including ethane, propane and higher hydrocarbons in much smaller amounts and some non-combustible gases, such as nitrogen and carbon dioxide

NOTE 1 Natural gas generally also includes minor amounts of trace constituents.

NOTE 2 Natural gas is produced and processed from the raw gas or liquefied natural gas and, if required, blended to the extent suitable for direct use (e.g. as gaseous fuel).

NOTE 3 Natural gas remains in the gaseous state under the temperature and pressure conditions normally found in service.

NOTE 4 Natural gas consists predominantly of methane (mole fraction greater than 0,70), and has a superior calorific value normally within the range 30 MJ/m3 to 45 MJ/m3. It contains also ethane (typically up to 0,10 mole fraction), propane, butanes and higher alkanes in steadily decreasing amounts. Nitrogen and carbon dioxide are the principal non-combustible components, each present at levels which typically vary from less than 0,01 mole fraction to 0.20 mole fraction.

Natural gas is processed from the raw gas so as to be suitable for use as industrial, commercial, residential fuel or as a chemical feedstock. The processing is intended to reduce the contents of potentially corrosive components, such as hydrogen sulfide and carbon dioxide, and of other components, such as water and higher hydrocarbons, potentially condensable in the transmission and distribution of the gas. Hydrogen sulfide, organic sulfur compounds and water are then reduced to trace amounts, and high carbon dioxide contents are likely to be reduced to below 0,05 mole fraction.

Natural gas is normally technically free from aerosol, liquid and particulate matter.

In some circumstances, natural gas may be blended with town gas or coke oven gas, in which case hydrogen and carbon monoxide can be present in amounts up to 0,10 mole fraction and 0,03 mole fraction respectively. In this case, small amounts of ethylene may also be present.

Natural gas may also be blended with LPG/air mixtures, in which case oxygen can be present, and the levels of propane and butanes can be considerably enhanced.

NOTE 5 Pipeline quality natural gas is one which has been processed so as to be suitable for direct use as industrial, commercial, residential fuel or as a chemical feed stock.

The processing is intended to reduce the corrosive and toxicity effects of certain components, and to avoid condensation of water or hydrocarbons in the transmission and distribution of the gas.

Hydrogen sulphide and water should only be present in trace amounts, and high carbon dioxide content is likely to be reduced.

2.1.1.2 raw gas

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

NOTE Raw gas can also be partially processed wellhead gas taken from basic upstream processing facilities.

2.1.1.3

substitute natural gas

SNG

manufactured or blended gas which is interchangeable in its properties with natural gas

2.1.1.4

manufactured gas synthetic gas

gas which has been treated and may contain components which are not typical of natural gas

NOTE Manufactured (synthetic) gases may contain substantial amounts of chemical species which are not typical of natural gases or common species found in atypical proportions as in the case of wet and sour gases.

Manufactured gases fall into two distinct categories, as follows:

a) those which are intended as synthetic or substitute natural gases, and which closely match true natural gases in both composition and properties;

b) those which, whether or not intended to replace or enhance natural gas in service, do not closely match natural gases in composition.

In the case a), the composition of the manufactured gas may be such that the gas is indistinguishable from that of a possible true natural gas. However, more often a manufactured gas, even if it contains inert and lower hydrocarbon gases in satisfactory proportions, does not exhibit the distinctive hydrocarbon "tail" of a true natural gas and may additionally contain small but significant amounts of non-alkane hydrocarbons.

Case b) includes gases such as town gas, (undiluted) coke oven gas, and LPG/air mixtures, none of which is compositionally similar to a true natural gas (even though, in the latter case, it may be operationally interchangeable with natural gas).

2.1,1.5 lean gas

natural gas containing more than 0,15 mole fraction of nitrogen or 0,05 mole fraction of carbon dioxide

NOTE According to ASTM D 4150I4S), a lean gas is a natural gas containing little or no hydrocarbons recoverable as liquid product.

2.1.1.6

rich gas

natural gas containing more than 0,10 mole fraction of ethane, or 0,035 mole fraction of propane

NOTE According to ASTM D 4150I(46), a rich gas is a natural gas containing condensable hydrocarbons that can be recovered as liquid product.

2.1.1.7 wet gas

gas which falls short of qualifying as pipeline quality natural gas by the inclusion of undesirable components such as water vapour, free water and/or liquid hydrocarbons, in significantly greater amounts than those quoted for pipeline quality natural gas 1)

2.1.1.8 sour gas

gas failing the qualification as pipeline quality natural gas due to the inclusion of undesirable components such as hydrogen sulphide or carbon dioxide in significantly greater amounts than those quoted for pipeline quality natural gas

NOTE 1 Typically wet and sour gases may be unprocessed (well-head) or partially-processed natural gases and may also contain condensed hydrocarbons, traces of carbonyl sulphide and process fluid vapours such as methanol or glycols.

NOTE 2 According to ASTM D 4150(46), a sour gas is a natural gas containing amounts of sulphur compounds such that it makes it impractical to use, without purification, because of its toxicity or its corrosive effect on piping and equipment. A sweet gas, on the contrary, is a natural gas containing such small amounts of compounds of sulphur that it can be used without purification, with no toxic effects and no deleterious effects on piping and equipment.

NOTE 3 Carbon dioxide in the presence of free water can be an important cause of corrosion damage to pipelines.

1) See also the three notes under 2.1.1.8.

2.1.1.9 dry natural gas

natural gas containing a mole fraction of water of no more than 0,005 % [50 ppm (molar)] in the vapour phase

NOTE Water vapour content in natural gas may be expressed both in terms of water concentration (ppm or mg/m3) and in terms of water dew point. Many relationships can be found in literature correlating water vapour content to dew point. Experimental and theoretical studies on this matter are still being conducted.

The knowledge of water vapour content in natural gas is of particular interest for a safe and efficient transmission and distribution of the gas. Water vapour content in natural gas can be responsible for corrosion phenomena (for example, when in the presence of carbon dioxide, hydrogen sulfide or oxygen) and for hydrate formation. Plugs of liquid water can also hinder transmission operations.

The requirement for gas to be dry may vary significantly depending on the kind of application (transmission, distribution, compressed natural gas for vehicles) and on the location (countries with very cold climates usually have more stringent requirements).

Transmission companies tend to specify very low levels of water content so as to prevent problems which can possibly occur at the high pressures involved. Water content is often specified in terms of water dew point temperature at a defined pressure. These conditions generally correspond to contents ranging from 0,006 % (mole fraction) [60 ppm (molar)] to 0,008 % (mole fraction) [80 ppm (molar)] in water.

At the downstream end of the pipeline, gas is sold to consumers at close to atmospheric pressure, and hence can contain up to about 2 % (mole fraction) of water. Regulations may exist to regulate the cost to the consumer which will depend upon whether the gas is dry or wet under distribution conditions. These regulations will take a very different viewpoint of "wet" and "dry" from those needed for transmission purposes. In the UK, a gas is considered dry if the water content is below about 0,06 % (mole fraction) [600 ppm (molar)] and can be sold by a public gas supplier to the consumer as a gas containing no water. The requirement for distributed gas to be described as dry, where it does exist, may be expected to vary significantly from country to country.

In general practice in the United States, natural gas is considered to be "dry" with a water content of about 0,015 % (mole fraction) [7 lb/106ft3 or about 150 ppm (molar) at standard reference conditions or 0,014% (mole fraction) 140 ppm (molar) at normal reference conditions].

2.1.1.10 high pressure natural gas

natural gas with a pressure exceeding 200 kPa

NOTE In many national standards, high pressure gas is specified at a pressure exceeding 100 kPa. For laboratory use, the value is set at 200 kPa for practical reasons.

2.1.1.11 low pressure natural gas

natural gas having a pressure between 0 kPa and 200 kPa

NOTE These ranges are in accordance with ISO-10715[31].

2.1.1.12 compressed natural gas

CNG

natural gas used as a fuel for vehicles, typically compressed up to 20 000 kPa in the gaseous state

2.1.1.13

liquefied natural gas

LNG

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

NOTE Liquid natural gas is revaporized and introduced into pipelines for transmission and distribution as natural gas.

2.1.1.14 gas quality

attribute of natural gas defined by its composition and its physical properties

2.1.2 Pipeline network

2.1.2.1 pipeline grid

system of interconnected pipelines, both national and international, which serve to transmit natural gas to local distribution systems

2.1.2.2

local distribution system

LDS

gas mains and services which supply natural gas directly to consumers

2.1.2.3

delivery point

location where the natural gas is transferred from the pipeline grid to the local distribution system

2.1.2.4 injection point

location where a supplier of natural gas feeds into the pipeline grid

2.1.2.5 feeding station

system of pipelines, measurement and regulation (pressure control), and ancillary devices at the injection point of the pipeline grid used for the custody transfer of natural gas

2.1.2.6 outlet station

system of pipelines, measurement and regulation (pressure control), and ancillary devices for the delivery of natural gas from the pipeline grid into the local distribution system

NOTE 1 Outlet stations are often called gate stations.

NOTE 2 The custody transfer of natural gas into a pipeline grid and from transmission pipeline grid to local distribution systems requires equipment designed and installed to meet the physical needs of both parties, and to provide for accurate energy measurement to the satisfaction of both.

2.2 Measurement methods

2.2.1 General definitions

2.2.1.1

absolute measurement

measurement of a property from fundamental metrological quantities

NOTE For example, the determination of the mass of a gas using certified masses.

2.2.1.2

direct measurement

measurement of a property from quantities which, in principle, define the property

NOTE For example, the determination of the calorific value of a gas using the thermometric measurement of the energy released in the form of heat during the combustion of a known amount of gas.

2.2.1.3

indirect measurement

measurement of a property from quantities which, in principle, do not define the property, but have a known relationship with the property

NOTE For example, the determination of the calorific value from measurements of the air-to-gas ratio required to achieve stoichiometric combustion which is related linearly to the calorific value.

2.2.1.4

inferential measurement

measurement of a property from quantities by comparison or interpolation of readings produced by an instrument calibrated using accepted reference materials

NOTE For example, the determination of the calorific value from measurement of the rise in temperature of a heat-exchange fluid caused by the combustion of a gas and calibrated using a substance having a known calorific value. Inferential measurements may be either direct or indirect.

2.2.1.5

measurement method for direct measurement of properties

method for determining the physical properties of natural gas which does not require a detailed component analysis of the gas

NOTE Such measurements take into consideration the "whole" sample of gas. Some instruments rely upon the absence of certain components for proper operation and may require secondary analytical knowledge to ascertain this absence.

Various measurement methodologies exist, however the distinctions between these categories are not always clear. It is possible for a measurement to belong to more than one category.

2.2.1.6

relative measurement

measurement of a property by means of comparison or difference from a normal value of the property taken from an accepted reference material

NOTE For example, determining gas density from the quotient of the mass of gas contained in a given volume to that of air contained in the same volume at the same temperature and pressure and multiplying by the density of air at that temperature and pressure.

2.2.2 Specific methods

2.2.2.1 gas chromatographic method

method of analysis by which the components of a gas mixture are separated using gas chromatography

NOTE The sample is passed, in a stream of carrier gas, through a column which has different retention properties relative to the components of interest. Different components pass through the column at different rates and are detected as they elute from the column at different times.

2.2.2.2 potentiometric method

method of analysis by which a known quantity of gas is first passed through a solution, where a specific gas component or a group of components is (are) selectively absorbed, then the absorbed analyte(s) in the solution is(are) evaluated by potentiometric titration

NOTE The result is a titration curve showing the potentiometric end points for the components being sought versus the titration solutions required. From this data, the concentrations of the various components can be calculated.

2.2.2.3 potentiometric titration

method where the reaction of the gas component with the titrant is proportional to its concentration and is measured by the variation of potential inside the cell

NOTE The volume increments of titrant (titration solution) added determine the difference in potential to be measured. Different volume increments of titrant, specifically smaller volume increments close to end points, can permit a better evaluation of the end points.

2.2.2.4 turbidimetric titration

method to determine the content of sulfate ions whereby a barium salt solution is added to an absorption solution and the turbidity caused by the formation of any insoluble barium sulfate detected

NOTE 1 This method is valid for solutions having a total sulfur content below 0,1 mg.

NOTE 2 A photometer with galvanometer readout is employed with the titration procedure to determine the inflection point. From these data, the total sulfur content in mg/m3 can be calculated.

2.2.2.5 combustion method

method by which a gas sample undergoes total combustion and the specific combustion products are measured to determine the total concentration of an element in the sample, e.g. sulfur

NOTE 1 Wickbold method:

The Wickbold combustion method uses the combustion and complete thermal decomposition of compounds at a high temperature in a hydrogen/oxygen flame. It is performed with a special instrument (see ISO 4260I2!).

NOTE 2 Lingener method:

The Lingener combustion method uses air, and it ss performed using a special instrument (see ISO 6326-519)).

2.2.2.6 absorption

extraction of one or more components from a mixture of gases when brought into contact with a liquid

NOTE 1 The assimilation or extraction process causes (or is accompanied by) a physical or chemical change, or both, in the sorbent material.

NOTE 2 The gaseous components are retained by capillary, osmotic, chemical, or solvent action.

EXAMPLE Removal of water from natural gas using glycol.

2.2.2.7 adsorption

retention, by physical or chemical forces, of gas molecules, of dissolved substances, or of liquids by the surfaces of solids or liquids with which they are in contact

NOTE For example, retention of methane by carbon.

2.2.2.8 desorption

removal of a sorbed substance by the reverse process of adsorption or absorption

2.2.2.9 aliquot part

part of a whole that is to be analysed

NOTE When analysing an aliquot part, i.e. a part of a whole sample which is homogenous, there is no need to use multiplication to obtain the concentration in the whole sample, because the concentration is the same in the sample and its part.

2.3 Sampling

2.3.1 Sampling methods

2.3.1.1

direct sampling

sampling in situations where there is a direct connection between the medium to be sampled and the analytical unit (i.e. in-line or on-line instrument)

2.3.1.2

indirect sampling

sampling in situations where there is no direct connection between the medium to be sampled and the analytical unit (i.e. off-line instrument)

NOTE In the case of indirect sampling, depending on the fluctuations of composition and/or properties, the following sampling techniques can be used:

periodical sampling where a spot sample is periodically taken from the gas stream and brought to the analytical unit;

incremental sampling which accumulates gas samples into one composite sample then brought to the analytical unit.

2.3.1.3

in-line instrument2)

instrument whose active element is installed inside the pipeline and makes measurements under pipeline conditions

2.3.1.4

on-line instrument2)

instrument that samples gas directly from the pipeline, but is installed externally to the pipeline

2.3.1.5

off-line instrument

instrument that has no direct connection to the pipeline

2.3.1.6 spot sample

sample of specified volume taken under operating conditions from a specified place in a gas stream

2) French makes no distinction between "in-line" and "online" installation of the instrument.

2.3.2 Sampling devices

2.3.2.1

floating piston cylinder

container which has a moving piston separating the sample from a buffer gas

NOTE The pressures are in balance on both sides of the piston.

2.3.2.2

proportional-flow incremental sampler

sampler that collects gas over a period of time and at a rate that is proportional to the flowrate in the sampled pipeline

2.3.2.3 incremental sampler

sampler that accumulates a series of spot samples into one composite sample

NOTE There are two general classes of commercial incremental samplers:

pressure increment: a specially designed pressure regulator increases the pressure of the collected sample in a sample cylinder from zero to a maximum of line pressure during the sample period;

volume increment: the sample is displaced by a pump into a floating piston cylinder at constant line pressure during the sampling period.

2.3.2.4

sample container

container for collecting the gas sample when indirect sampling is necessary

NOTE The sample container should not alter the gas composition in any way or affect the proper collection of the gas sample. The materials, valves, seals, and other components of the sample container should all be specified with this principle.

2.3.2.5 sample line

line provided to transfer a sample of the gas to the sampling point

NOTE It may include devices which are necessary to prepare (he sample for transportation and analysis.

2.3.2.6 sample probe

device inserted into the gas line to be sampled and to which is connected a sample line

NOTE The most elementary sample-probe design is the straight-tube probe. The other type of probe design is the regulated probe. These probes are designed to deliver the gas to the analytical system or sample container at reduced pressure.

2.3.2.7 transfer line

line for carrying the sample to be analysed from the sample point to the analytical unit

2.3.2.8 fast loop

hot loop

bypass loop that returns to the process line in a closed configuration and used for environmental and safety considerations

NOTE The loop requires a pressure differential from collection point to discharge so as to ensure a constant and steady flowrate through the sampling equipment located in the loop.

2.3.2.9 bypass line

line ultimately vented to the atmosphere that is used where it is impractical to provide a sufficient pressure differential

NOTE The flowrate and pressure loss in the open-ended line need to be controlled so as to ensure that sample accuracy cannot be affected from any cooling and condensation.

2.3.3 Conditioning device

2.3.3.1 condenser

apparatus used to transform the condensable fraction (consisting of water vapour and/or of the higher hydrocarbons) of the vapour phase present in natural gas into a liquid phase by cooling

2.3.3.2

gas-liquid separator

drip pots

unit in the gas sample line used to collect liquid fallout

2.3.3.3 regulator

reducer

device used to reduce and to control gas pressure entering or moving through a piping system

NOTE It has the ability to maintain a near constant outlet pressure regardless of fluctuations in inlet pressure or flowrate within its design parameters. The regulator can be mechanical or pilot-controlled depending on the application. It operates on the basic principle of the expansion of gas through an orifice against a seat whose positioning is controlled by the downstream pressure acting against a diaphragm linked to the seat.

2.3.3.4 back-pressure regulator

device used to maintain a selected pressure in a system from which gas is being vented to a lower pressure (commonly atmospheric pressure)

NOTE It maintains constant upstream pressure regardless of flowrate or variations in downstream pressure, provided that this does not exceed the selected pressure.

2.3.3.5 heating device

device to ensure that the sample gas remains at, or above, the gas-line temperature, keeping the heavy, end components in the gas phase so as to allow them to be accurately accounted for when the gas is analysed

NOTE Heating elements may be installed on the sample probe and sample lines. In some cases, heating the sample cylinder is also required. It is particularly important where Joule-Thomson cooling occurs as a result of pressure reduction.

2.3.4 Other definitions

2.3.4.1 purging time

time interval necessary to purge a piece of equipment before the gas sample is analysed

2.3.4.2 representative sample

sample having the same composition as the material sampled when the latter is considered totally homogeneous

2.3.4.3 residence time

time interval necessary for a gas sample to flow through a piece of equipment

2.3.4.4 sampling point

location in the gas stream where a sample is obtained

2.3.4.5 gas sorption effects

processes whereby some gases are adsorbed onto or desorbed from the surfaces of a solid

NOTE The force of attraction between some gases and solids is purely physical and depends on the nature of the participating material. Natural gas may contain several components which exhibit strong sorption effects. Special care should be taken when determining trace concentrations of heavy hydrocarbons, water, sultur compounds and hydrogen.

2.4 Analytical systems

2.4.1

measuring system

complete set of measuring instruments and other equipment assembled to carry out specified measurements

NOTE System comprising, in general, a sample transfer and introduction unit, a separation unit, a detector and an integrator or a data processing system.

2.4.2 introduction unit

unit for introducing a constant, or a measured amount of material to be analysed into the analyser

NOTE 1 Gas chromatographic analysers are comparative rather than absolute. Therefore, the introduction of equal quantities of calibration mixture and of sample allows quantitative measurement of sample components.

NOTE 2 In gas analysis, the introduction device is frequently a multi-port valve, in which a fixed volume of calibration mixture or sample is isolated, and, by operation of the valve, passed into the analyser.

NOTE 3 Equimolar quantities can be obtained by controlling the pressure and temperature of the introduction device.

2.4.3 gas chromatograph

chromatograph that physically separates components of a mixture and measures them individually with a detector whose signal is processed

NOTE 1 A chromatograph consists of the following main parts: an introduction unit, a separation unit and a detector. The separation unit consists of one or more chromatographic columns through which carrier gas flows and into which samples are introduced. Under defined and controlled operating conditions, components can be qualitatively identified by their retention time, and quantitatively measured by comparing their detector response to that of the same or a similar component in a calibration mixture.

NOTE 2 In gas analysis, the range of components and their properties frequently cause more than one separation mechanism to be required. These can be and often are combined in a single separation unit or chromatograph.

NOTE 3 A gas chromatograph capable of temperature programming is a chromatograph whose columns are placed in an oven whose temperature is programmable in a defined and repeatable manner over the period of analysis.

2.4.4 carrier gas

pure gas introduced so as to transport a sample through the separation unit of a gas chromatograph for analytical purposes

NOTE Typical carrier gases are hydrogen, nitrogen, helium and argon.

2.4.5 auxiliary gases

gases required for detector operation, e.g. hydrogen and air for flame detectors

2.4.6

chemiluminescence detector

CD

detector that uses a reducing reaction in which molecules give rise to characteristic luminous emissions which are measured by a photomultiplier and the associated electronic devices

NOTE Chemiluminescence detector is used in gas chromatography mainly to detect components which contain particular elements, e.g. nitrogen oxide (NO) and sulphur (S).

2.4.7

electrochemical detector

ED

detector consisting of an electrochemical cell which responds to certain substances contained in the carrier gas eluting from the column

NOTE The electrochemical process may be an oxidation, reduction or a change in conductivity. The detection can be very specific depending on the electrochemical process involved.

2.4.8

flame ionization detector

FID

detector in which hydrocarbons are burned in a hydrogen-air flame and the resulting ions are measured electrically between two electrodes

NOTE The flame ionization detector is used in gas chromatography mainly to detect hydrocarbon compounds.

2.4.9

thermal conductivity detector TCD

hot wire detector HWD

detector that measures the difference in thermal conductivity between two gas streams when a sample (gas mixture) passes through the sample channel

NOTE 1 The HWD is a dual channel detector, requiring a reference flow of pure carrier gas through the reference channel.

NOTE 2 The use of helium or hydrogen is recommended as carrier gas except when the sample contains either of these two substances to be measured.

NOTE 3 The detector consists of a bridge circuit; the change in resistance in the sample channel during the passage of the sample produces an out-of-balance signal that is the basis of the detection. The detector responds to all components except the carrier gas and it is non-destructive.

2.4.10

flame photometric detector

FPD

detector that uses a reducing flame in which individual elements give rise to characteristic colours which are measured by a photomultiplier

NOTE The detector is used in gas chromatography mainly to detect components which contain particular elements, e.g. phosphorous (P) and sulphur (S).

ISO 14532: 2001 (E/F)

2.4.11

integrator

device which quantitatively measures the response signal of a detector to a component in a mixture

NOTE By comparing the integrator output to the same component in a calibration mixture and in a sample, the concentration in the sample can be calculated. If the detector response has a time element, as in chromatography. then the instantaneous response is integrated with respect to time.

2.4.12 photometry

determination of the concentration of a dissolved substance in a solution by using the absorption of light by this substance

2.4.13 absorption cell

device put into the light path of the photometer

NOTE The lower the concentration of the dissolved substance, the thicker the absorption cell has to be.

2.5 Analysis

2.5.1 Metrology

2.5.1.1

accuracy of measurement

closeness of the agreement between a measurement result and a true value of the measurand

NOTE 1 The term accuracy, when applied to a set of measurement results, describes a combination of random components and a common systematic error or bias component.

NOTE 2 Because the true value is seldom known, accuracy often refers to the agreement between measurement results and an accepted reference value.

2.5.1.2

trueness

closeness of agreement between the average value obtained from a large series of measurement results and the true value of the measurand

NOTE The measure of trueness is usually expressed in terms of bias.

2.5.1.3

bias

systematic difference between the expectation of the measurement results and an accepted reference value

2.5.1.4

precision

closeness of agreement between independent measurement results obtained under prescribed conditions

NOTE 1 Precision depends only on the distribution of random errors and does not relate to the true value.

NOTE 2 Precision is a qualitative term relating to the dispersion between the results of measurements of the same measurand, carried out under specified conditions of measurement. Quantitative measures of precision such as variance or standard deviation critically depend on the variation implied by the specified measurement conditions.

2.5.1.5 repeatability limit

value below which the absolute difference between two single measurement results obtained using the same method, on identical measurement material, by the same operator, using the same apparatus, in the same laboratory, within a short interval of time, (repeatability conditions), may be expected to lie with a specified probability

NOTE 1 In the absence of other indication the probability is 95 %.

NOTE 2 The rigorous way of calculating the repeatability limit of component measurement, r(xi), is:

where

t

is taken from the two-sided t-distribution table at the 5 % significance level with the number of degrees of freedom appropriate to the number of data points from which the standard deviation s(xi) has been calculated; and

reflects the fact that two measurements are being compared. However, the confidence interval for the standard deviation is likely to be so large that such distinctions are unjustified, and the repeatability can in all cases be expressed as:

r(xi) = 2,8 · s(xi)

2.5.1.6 reproducibility limit

value below which the absolute difference between two single measurement results obtained using the same method, on identical measurement material, by different operators, using different apparatus, in different laboratories, (reproducibility conditions), may be expected to lie with a specified probability

NOTE In the absence of other indication the probability is 95 %.

2.5.1.7 uncertainty

estimate attached to a measurement result which characterizes the range of values within which the true value is asserted to lie

NOTE 1 Uncertainty of measurements comprises, in general, many components. Some of these components may be estimated on the basis of the statistical distribution of the results of a series of measurements and can be characterized by experimental standard deviation. Estimates of other components can only be based on experience or other information.

NOTE 2 Uncertainty should be distinguished from an estimate attached to a measurement result which characterizes the range of values within which the expectation is asserted to lie. This latter estimate is a measure of precision rather than of accuracy and should be used only when the true value is not defined. When the expectation is used instead of the true value the expression "random component of uncertainty" should be used.

NOTE 3 Since the terminology relating to accuracy and/or uncertainty of measurement has recently undergone substantial changes, a short comment on the meaning of the main terms shall be given.

Accuracy, trueness and precision are qualitative terms used to express the smallness of expected measurement errors. Hereby accuracy as the more general term refers to the total measurement error, trueness to the systematic components), and precision to the random component (s) of measurement error.

Uncertainty, systematic uncertainty and random uncertainty (dispersion) are qualitative terms used to express the extent of expected measurement errors, as the counterparts of accuracy, trueness, and precision, respectively. Accuracy and uncertainty are reciprocal terms: high accuracy is equivalent to small uncertainty, and the same is true for both the other pairs of reciprocal terms, i.e. trueness with systematic uncertainty and precision with random uncertainty (dispersion).

For quantitative expressions of accuracy or uncertainty the common measures, derived from the results of repeated measurements, are:

bias for systematic uncertainty; and

standard deviation for random uncertainty (dispersion).

2.5.2 Calibration and quality control

2.5.2.1

material measure

device intended to reproduce or supply, in a permanent manner during its use, one or more known values of a given quantity

NOTE The quantity concerned may be called the supplied quantity.

2.5.2.2 calibration

set of operations that establish, under specified conditions, the relationship between values of quantities indicated by a measuring instrument or measuring system, or values represented by a material measure or a reference material, and the corresponding values obtained using working standards

NOTE 1 Adapted from the VIM[45].

NOTE 2 The result of a calibration permits either the assignment of values of measurements to the indicated reading or the determination of the corrections with respect to indicated readings.

NOTE 3 A calibration may also determine other metrological properties that affect the result of the measurement, i.e. influence quantities.

NOTE 4 The result of a calibration may be reported in a document, sometimes called a calibration certificate or a calibration report.

NOTE 5 The measuring instrument can be calibrated over its entire working range or simply in a specific portion of its range.

NOTE 6 A laboratory which performs calibrations can be accredited for this activity. In order to assess the traceability of the calibrations reported, protocols covering the relevant uncertainty analysis and other quality assurance elements are required.

NOTE 7 Calibration includes the adjustment and/or correction of instruments giving readings during calibration that are outside acceptable limits.

2.5.2.3 calibration interval

period of time during which the analytical system would normally be used between calibrations

2.5.2.4 single-point calibration

establishment of the calibration function using one (only) calibration point, below which the estimated value of the property is expected to lie

NOTE 1 Notes 2, 3 and 4 are applicable to analytical systems,

NOTE 2 This is a calibration in which the response of the analyser to a measured component maintains an exact proportion to the concentration of the component over the entire working range.

NOTE 3 The response can be described as being linear through the origin. A plot of the analyser response against the concentration of the component would show a straight line intercepting the (0, 0) point of the plot. In such circumstances, the use of a single calibration mixture containing the component at a concentration within the working range (single-point calibration) is appropriate, as the ratio of response to concentration remains constant at all points.

NOTE 4 Where a more complex response function, such as a second or third order polynomial, has been defined by the use of multiple calibration mixtures, and the different elements of this function, e.g. the coefficient of the polynomial, have been shown to maintain a constant relationship to each other, then a single-point calibration can be used to adjust all the elements of the function on a short term basis (for example, daily).

2.5.2.5 bracketing

method consisting in principle in reducing the interval over which the linearity of the calibration function is assumed as much as possible

NOTE This leads to surrounding the value of the unknown quantity by two values of reference materials (RMs) as tightly as possible (or bracketing).

2.5.2.6

multi-point calibration

establishment of a calibration function using several (more than two) calibration points which define a range within which the estimated values of the properties are expected to lie

NOTE 1 Notes 2 and 3 are applicable to analytical systems.

NOTE 2 In multi-point (also called "multi-level") calibrations, the response curves of the detector are determined for each component over the ranges to be analysed.

NOTE 3 To define the response curves, it is necessary to obtain results at a number of different concentration levels for each component. The number of concentration levels needed depends on the order of the polynomial (response curve) that has to be fitted. The minimum number of concentration levels needed is the same as the number of polynomial coefficients in the response curve to be fitted. However, it is advisable to analyse a few extra concentration levels than strictly necessary. In most cases, the order of fit of the response curves is unknown beforehand. Therefore a few extra points for fitting the response curve will decrease the influence of the measurement errors made during calibration. Consequently, it is advisable to perform the analysis of at least seven concentration levels so as to detect third order detector behaviour with a high degree of detection sensitivity.

The concentration levels shall correspond to at least seven different certified reference gas mixtures.

These concentration levels should be equally spaced across the specified working range of each component. The lowest concentration level should be slightly below the lowest concentration level of the working range, the highest concentration level should be slightly higher than the highest concentration level of the working range.

2.5.2.7 transformation

correction of future measurements if both the accepted values of the RMs and the observed values have the same units or a translation from the units of the observed measurements to the units of the RMs

2.5.2.8 verification

process to specify procedures and equipment for limited tests performed over a restricted range with traceable materials or instruments on a regular basis or upon indication of need in order to detect whether the system is behaving normally or erratically with no adjustment or correction of the measurement system

2.5.2.9

control method control chart

method which monitors the measurement system on a regular basis so as to detect quickly when the method has deteriorated, or the calibration shifted, or both

NOTE 1 Detection is achieved by using control charts for each component. A control gas of known composition, typical of the natural gases for which the method is to be used, is required (or the preparation of a control chart.

Before the first use, the control gas is analysed at least 10 times for precision data to be calculated (mean concentration and standard deviation for each component in the test gas).

For each component in the control gas, a control chart is constructed with the mean value for the component and concentrations representing the mean ± 2 standard deviations and the mean ± 3 standard deviations marked on the y-axis. Lines parallel to the x-axis are drawn from these points. Each time the control gas is analysed, the value is plotted using the x-axis as a time scale.

The plotted values from each analysis of the control gas are compared with the mean value and the lines for ± 2 standard deviations and ± 3 standard deviations.

Assuming that the composition of the control gas is stable and that the analytical results for the control gas follow a normal distribution, then for a system behaving normally, it may be expected that any individual result for the control gas can possibly fall outside the limit of ± 2 standard deviations on 1 occasion in 20. This means that if individual results fall outside the warning limits (± 2 standard deviations) more frequently than this, it can be an indication that the system is steering out of control with a systematic tendency for results to be too high (or too low) or the random error for measurement of that component to increase.

NOTE 2 This control method can be applied to various other instruments apart from an analyser.

2.5.3 Gas analysis

2.5.3.1

General definitions

2.5.3.1.1 mass [volume] [mole] fraction

quotient of the mass [volume (under specified conditions of pressure and temperature)] [number of moles] of each component to the sum of the masses [sum of the volumes (intended prior to mixing under specified conditions of pressure and temperature)] [sum of the moles] of all components of the gas mixture

NOTE According to ISO 7504[26], the sum of the volumes of all components of the gas mixture prior to mixing is replaced by the volume of the gas mixture.

For a real gas, the sum of the volumes of all components of the gas mixture does not give in general the volume of the mixture since mixing of different components generally results in changes of intermolecular forces which in turn cause an increase or decrease of total volume. The sum of the masses or numbers of moles of all components of the gas mixture gives the mass or number of moles of the mixture.

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 for the reason mentioned above.

The mass and mole fractions are independent of pressure and temperature of the gas mixture. The volume fraction depends on pressure and temperature of the gas mixture.

The percentage is calculated from the fraction multiplied by 100.

2.5.3.1.2 mass [molar] concentration

quotient of the mass [number of moles] of each component to the volume of the gas mixture under specified conditions of pressure and temperature

NOTE The mass and molar concentrations depend on the pressure and temperature of the gas mixture.

2.5.3.1.3 mole

amount of substance of any chemical species which contains the relative molecular mass

NOTE A table of recommended values of relative molecular masses is given in ISO 6976[22].

2.5.3.1.4

gas composition

fractions or percentages of the main components, associated components, trace components and other components determined from natural gas analysis

2.5.3.1.5 gas analysis

test methods and techniques for determining the gas composition

2.5.3.1.6

direct chromatographic measurement of components

individual components or groups of components determined by comparison with identical components in the working reference gas mixture (WRM)

NOTE Main and associated components are determined using direct measurement.

2.5.3.1.7 indirect chromatographic measurement of components

individual components or groups of components determined using relative response factors to a reference component in the WRM

NOTE Trace components are determined using indirect measurement.

2.5.3.2 Analysed components

2.5.3.2.1

main component

major component

component whose content influences the calculation of physical properties

NOTE Main components of natural gases generally include: nitrogen, carbon dioxide and saturated hydrocarbons from methane through n-pentane.

2.5.3.2.2

associated component

minor component

component whose content does not significantly influence the calculation of physical properties

NOTE Associated components generally include: helium, hydrogen, argon and oxygen.

2.5.3.2.3

trace component

trace constituent

component present at very low levels

NOTE Trace components generally include hydrocarbons or groups of hydrocarbons above n-pentane and the components listed in 2.5.3.3.

2.5.3.2.4

group of components

individual components whose similar properties make analytical separation too poor for individual determination and are thus considered and treated as a group of components in the mixture

NOTE 1 The property of the group, rather than each individual property, is used to evaluate the properties of the mixture.

NOTE 2 The group may be physically combined as a result of the analytical procedure, as with backflushing in chromatography, or individually measured and combined by calculation. If they are physically combined, the precision of

the measurement of the group is likely to be superior to the precision of measurement of the individual components.

NOTE 3 It is important to recognize when it is appropriate to consider groups of components, and when it is not. For calculation of calorific value or relative density, all hydrocarbons of carbon number six (C6) and higher can be considered as a group (C6+) with relatively little resulting error. However, such simplification gives rise to large calculation errors of the hydrocarbon dew point.

NOTE 4 When a number of hydrocarbons are identified and quantified as a group or groups, the following options are possible:

the total is reported as though the group extends from the lowest carbon number of that group (e.g. C6+, which indicates all hydrocarbons of carbon number six and above);

separate groups are reported as the total of each carbon number (e.g. total C6, total C7, etc.);

the above groups, reported as total of each carbon number, can be further broken down to component types (e.g. C6 alkanes, as distinct from benzene and C6 cycloalkanes or naphthenes).

In the above mentioned cases, the response of the group is the sum of the responses of the normal hydrocarbon components) and its (their) isomers. The relative response of the group is equal to the relative response of the normal alkane of the group (C6 for C6+).

2.5.3.2.5

other component

other constituent

component possibly being present in the gas, which is either measured directly using other analytical methods or its content in the gas is assumed to remain constant and set to a value based on past measurements or valid estimations

2.5.3.2.6

reference component

bridge component

component present in the WRM used as a reference to define the relative response factors of sample components which are not present in the WRM

NOTE The response function of the reference component and of the sample components measured relative to it should be linear and pass through the origin.

2.5.3.3 Trace component [constituent]

2.5.3.3.1 alkane thiol

alkyl mercaptan

organic sulfur compound with the general formula R-SH (where R is the alkyl group), either naturally present or added as an odorant to natural gas

NOTE 1 They are classified as primary, secondary and tertiary thiols (mercaptans) according to whether the a!kyl group attached to the thiol (mercaptan) group is a primary, secondary or tertiary group, respectively. The number o( carbons attached to the carbon atom bearing the thiol group distinguishes primary, secondary and tertiary thiols.

In a primary alkyi group, one or none carbon is attached to the carbon atom under consideration. [Examples of primary thiols (mercaptans): methane thiol (methyl mercaptan) CH3-SH, ethane thiol (ethyl mercaptan) CH3CH2-SH].

In a secondary alkyi group, two carbons are attached to the carbon atom under consideration. (Example of a secondary thiol (mercaptan): 2-propane-thiol (isopropyl mercaptan) (CH3)2CH-SH).

In a tertiary alkyi group, three carbons are attached to the carbon atom under consideration. (Example of a tertiary thiol (mercaptan): 2-methylpropane-2-thiol (tertiary-butyl mercaptan) (CH3)3C-SH).

NOTE 2 Thiols (mercaptans) are the sulfur analogues of the alcohols.

2.5.3.3.2 alkyi sulfide

thioether

organic sulfur compound with the general formula R-S-R' (where R and R' are alkyi groups), either naturally present or added as an odorant to natural gas

NOTE 1 The alkyi groups are identical (R = R') in symmetrical sulfides (e.g. diethyl sulfide: C2H5-S-C2H5) or different (R =/ R'), in asymmetrical sulfides (e.g. methyl ethyl sulfide: CH3-S-C2H5).

NOTE 2 Sulfides are the sulfur analogues of the ethers and are also known as thioethers.

2.5.3.3.3 alkyi disulfide

organic sulfur compound with the general formula R-S-S-R' (where R and R' are alkyi groups)

NOTE 1 The alkyi groups are identical (R = R') in symmetrical disulfides (e.g. dimethyl disulfide:

CH3-S-S-CH3) or different (R =/ R') in asymmetrical disulfides (e.g. methyl ethyl disulfide: CH3-S-S-C2H5).

NOTE 2 Disulfides are formed by oxidation of thiols (mercaptans). Their odour intensity is insufficient to be used as gas odorants.

2.5.3.3.4 carbonyl sulfide

COS

sulfur compound found in natural gas, which contributes to the total sulfur content

NOTE Under particular conditions, it can be formed from, or be converted to, H2S.

2.5.3.3.5

carbonyl sulfide sulfur

amount of sulfur in natural gas found in the form of carbonyl sulfide (COS) and determined, for example, by potentiometry (ISO 6326-3[7])

2.5.3.3.6 cyclic sulfide

thioether

cyclic organic sulfur compound with one sulfur atom incorporated into a saturated hydrocarbon ring

EXAMPLE Tetrahydrothiophene (thiophane or thiacyclopentane), i.e. C4H8S, which is added as an odorant to natural gas.

2.5.3.3.7 glycol

liquid binary alcohol (R-CHOH-CH2OH) used as an anti-freeze and in some processing operations as a dehydrating agent

2.5.3.3.8

hydrogen sulfide

H2S

colourless, toxic gas with an odour similar to rotten eggs

NOTE H2S is an undesirable constituent of natural gas, and should be reduced to tolerable concentrations by processing. A low concentration of hydrogen sulfide provides safety for personnel and customer, mitigates corrosion in pipeline and distribution systems, prevents objectionable products, of combustion, and protects sensitive industrial operations.

ISO 14532:2001 (E/F)

2.5.3.3.9

mercaptan

see alkane thiol (2.5.3.3.1) [(alkyl mercaptan)

(2.5.3.3.1)]

2.5.3.3.10 mercaptan sulfur

see thiol sulfur (2.5.3.3.15)

2.5.3.3.11 methanol

light, volatile, flammable, poisonous, liquid alcohol (CH3OH) used to prevent hydrate formation in wet, high-pressure gas lines

2.5.3.3.12 organic sulfur

term commonly used to designate all of the sulfur compounds in natural gas with the exception of hydrogen sulfide and sulfur oxides

EXAMPLES These sulfur compounds consist of carbon disulfide (CS2), carbon oxysulfide, also called carbonyl sulfide (COS), thiophene (C4H4S) and its homologues, alkane thiols (alkyi mercaptans) such as methane thiol (methyl mercaptan) (CH3-SH) and ethane thiol (ethyl mercaptan) (C2H5-SH), and various other sulfur compounds present in very small traces, such as the thioethers and the alkyi disulfides.

2.5.3.3.13 sulfide

see alkyl or cyclic sulfide (2.5.3.3.6)

2.5.3.3.14 thioether

see sulfide (2.5.3.3.13)

2.5.3.3.15

thiol [mercaptan] sulfur

amount of sulfur bonded in the form of a thiol [mercaptan] in natural gas

NOTE The amount of thiol sulfur may be determined by an analytical method which does not differentiate between individual thiols [mercaptans] (e.g. potentiometry using ISO 6326-3171).

2.5.3.3.16 thiol

see alkane thiol (2.5.3.3.1) [(alkyi mercaptan) (2.5.3.3.1)]

2.5.3.3.17

total sulfur

total amount of sulfur found in natural gas

NOTE The total amount of sulfur, both organic and inorganic, may be determined by an analytical method not differentiating between individual sulfur compounds [e.g. Wickbold (ISO 4260(21) or Lingener (ISO 6326-5191) combustion methods].

2.5.3.4 Analyser response

2.5.3.4.1 response

output signal for a component that is measured as peak area or peak height

NOTE Response is expressed in counts.

2.5.3.4.2 response factor

ratio of the non-normalized mole fraction of the component in the WRM to its response

NOTE 1 The response factor for this component is defined on the assumption that the detector behaviour for a certain component intercepts the origin and is linear for a small range around the point which is calibrated; in this case, a single-point calibration is used.

NOTE 2 In this case the non-normalized mole fraction of this component in the sample is given by the product of the response factor of this component with the response of the same component in the sample:

where

is the non-normalized mole fraction for component i in the sample;

is the non-normalized mole fraction for component i in the WRM;

is the response factor, expressed in counts, for component; in the sample;

is the response factor, expressed in counts, for component i in the WRM.

2.5.3.4.3 relative response factor

ratio of the molar amount of the component analysed to the molar amount of reference component present in the working reference gas mixture (WRM) which produces an equal response from the analyser

NOTE 1 It is necessary to use the relative response (actor to calculate the non-normalized mole fraction of sample components not present in the WRM.

NOTE 2 The relative response factor for a certain component can also be defined as the ratio of the response factor of this component to the response factor of the reference component.

NOTE 3 When using an FID detector, the relative response factor is calculated as the ratio of the carbon number of the reference component to the carbon number of the sample component.

NOTE 4 It is assumed that the detector response curve, calibrated using the reference component, intercepts the origin and is linear for a small range around the point obtained for the sample component. The non-normalized mole fraction of the sample component not present in the WRM can be calculated by the following equation:

where

is the non-normalized mole fraction for component i in the sample which is not present in the WRM;

is the non-normalized mole fraction for the reference component in the WRM;

is the response factor, expressed in counts, for component i in the sample;

is the response factor, expressed in counts, for component for the reference component in the WRM;

the relative response factor (or the reference component with respect to component;'.

2.5.3.4.4 response function

response of the detector after a multi-point calibration performed for a component over the range to be analysed (see the note in the definition of the multi-point calibration in 2.5.2.6)

NOTE 1 It is not possible to make the assumption that the detector response function calibrated for a certain component intercepts the origin and is linear for a small range around the measured point.

NOTE 2 In this case, the non-normalized mole traction of the component in the sample is given by the product of the response function of the component in the sample with the scaling factor:

where

is the non-normalized mole fraction for component i in the sample;

is the mole fraction for component i in the WRM;

is the response factor, expressed in counts, for component i in the sample;

is the response factor, expressed in counts, for component i in the WRM;

a, b, c, d are the polynomial coefficients.

2.5.3.4.5 normalization

composition data is set to 100 % or to some slightly lesser value if there is a small, constant and recognized contribution from unmeasured other components

NOTE 1 Analysers which have been set up for natural gas analysis, however well configured, will rarely measure the sum of the components in a natural gas to be exactly 100 % (or 1 if expressed in mole fraction). Therefore composition data is normalized to 100 %.

This is based on the obvious premise that the sum of all components in a natural gas adds up to 100% and not some other value:

where

xmc is the mole fraction for main and associated components;

xtc is the mole fraction for trace components;

xoc is the mole fraction for other components;

The normalization is carried out as follows:

where

xOC is the non-normalized mole fraction for component i in the sample;

xi,S is the normalized mole fraction for component i in the sample;

xOC,S is the normalized mole fraction for sum of the other components in the sample;

k is the number of components detected.

NOTE 2 The method should quote limits within which such normalization would be acceptable; a measured total between 0,99 and 1,01 may be deemed to be usual, with analyses producing wider-ranging totals being rejected. Analytical methods which calculate the methane by difference do not normalize in this way, but instead force the total to 1, with the calculated methane value absorbing the errors in all the other component measurements.

2.5.3.4.6 chromatographic resolution

column efficiency characteristic describing the degree of separation of two adjacent peaks in gas chromatography

NOTE The resolution is measured for two eluted components, A and B. as twice the difference of their retention times, measured at their maxima, divided by the sum of the peak widths measured at their baseline. The peak width is measured by drawing tangents to the peaks at half their height and measuring the distance between the intercepts of these two tangent lines at the baseline:

where

RA,B is the resolution between peaks for components A and B;

tR(A), tR(B) retention time of the eluted components A and B;

w(A), w(B) peak widths at the baseline of the eluted components A and B measured with respect to retention time.

In the case where the retention time scale of the chromatogram is linear, chromatogram distances can be measured instead of retention times.

2.5.3.5 Calibration gas mixtures

2.5.3.5.1 General definitions from metrology

2.5.3.5.1.1 reference material

RM

material or substance, one or more of whose property values are sufficiently homogeneous and well established to be used for the calibration of an apparatus, the assessment of a measurement method, or for assigning values to materials

[ISO Guide 30[43]]

NOTE A reference material may be in the form of a pure or mixed gas, liquid or solid.

EXAMPLES Several kinds of reference materials exist. An internal reference material is an RM developed by a user for its own internal use. An external reference material is an RM provided by someone other than the user. A certified reference material (CRM) is an RM issued and certified by an organization recognized as competent to do so.

2.5.3.5.1.2

certified reference material

CRM

reference material, accompanied by a certificate, one or more of whose property values are certified by a procedure which establishes traceability to an accurate realization of the unit in which the property values are expressed, and for which each certified value is accompanied by an uncertainty at a stated level of confidence

[ISO Guide 30[43]]

2.5.3.5.1.3

reference measuring system

represents not only a measuring instrument but the set of procedures, operators and environmental conditions associated with that instrument

2.5.3.5.1.4

traceability

property of the result of a measurement or the value of a standard whereby it can be related to stated references, usually national or International Standards, through an unbroken chain of comparisons all having stated uncertainties

[ISO Guide 30[43]]

NOTE 1 The concept is often expressed by the adjective traceable.

NOTE 2 It should be noted that traceability only exists when scientifically rigorous evidence is collected on a continuing basis showing that the measurement is producing documented results for which the total measurement uncertainty is quantified (NIST Technical Note 1297:1994 Edition).

NOTE 3 The unbroken chain of comparisons is called a traceability chain.

2.5.3.5.1.5

measurement standard etalon

material measure, measuring instrument, reference material or measuring system intended to define, realize, conserve or reproduce a unit of one or more values of a quantity to serve as a reference

[VIM][45]

2.5.3.5.1.6 group standard series of standards

set of standards of specially chosen values which individually or in suitable combination reproduce a series of values of a quantity over a given range

NOTE Adapted from the VIM[45].

2.5.3.5.1.7 primary standard

standard that is designated or widely acknowledged as having the highest metrological qualities and whose value is accepted without reference to other standards of the same quantity

[VIM][45]

NOTE 1 The concept of primary standard is equally valid for base quantities and derived quantities.

NOTE 2 A primary standard is never used directly for measurements other than for comparison with duplicate or reference standards. In general the National Standards

Laboratory is responsible for the conservation of a primary standard in a country.

2.5.3.5.1.8 secondary standard

standard whose value is assigned by comparison with a primary standard of the same quantity

[VIM][45]

2.5.3.5.1.9

international measurement standard

standard recognized by an international agreement to serve internationally as the basis for assigning values to other standards of the quantity concerned

[VIM][45]

2.5.3.5.1.10 national measurement standard

standard recognized by a national decision to serve, in a country, as the basis for assigning values to other standards of the quantity concerned

[VIM][45]

NOTE A. National Standards Laboratory assures that the national standards are primary standards.

2.5.3.5.1.11 reference standard

standard generally having the highest metrological quality available at a given location or in a given organization, from which measurements made there are derived

[VlM][45]

2.5.3.5.1.12 working standard

standard that is used routinely to calibrate or check material measures, measuring instruments or reference materials

NOTE A working standard is usually calibrated against a reference standard.

[VIM][45]

2.5.3.5.1.13 transfer standard

standard used as an intermediary to compare standards

[VIM][45]

2.5.3.5.2 Definitions relevant to gas mixtures

2.5.3.5.2.1

primary standard gas mixture

PSM

gas mixture whose component quantity levels have been determined with the utmost accuracy and can be used as a reference gas for determining the component quantity levels of other gas mixtures

2.5.3.5.2.2

secondary standard gas mixture

gas mixture whose component quantity levels have been validated by direct comparison with a PSM

NOTE A secondary standard gas mixture is a CRM. It is used for the determination of the response curves of the measuring system and can also be used for its regular calibration. It can be a binary or multi-component mixture and can be prepared gravimetrically in accordance with IS06142I3) and verified in accordance with IS06143!4]. The quantity levels of the components can be determined by comparison with a PSM of closely related composition in accordance with ISO 61431[4].

2.5.3.5.2.3

working reference gas mixture

WRM

gas mixture whose component quantity levels have been validated by direct comparison with a secondary standard gas mixture

NOTE A WRM is used regularly to calibrate the measuring system. A WRM can be a binary or a multi-component mixture and can be prepared gravimetrically in accordance with IS06142[3] and verified in accordance with ISO 6143[4]. The quantity levels of the components can be determined by comparison with a CRM of closely related composition in accordance with ISO 6143[4].

2.5.3.5.2.4 control gas

gas mixture of known composition containing all the components present in the working reference gas mixture

NOTE A control gas can be either a sample gas with a composition determined in accordance with ISO 6143I4! or a multi-component mixture prepared in accordance with ISO 6142[3]. A control gas is used to calculate the mean (µ) and standard deviation (σ) of the quantity levels of the components detected so as to prepare the relevant control charts.

2.5.4 Statistics

2.5.4.1 sequential F-test

statistical test used sequentially to compare the goodness of fit to data of two polynomial curves of different order varying from third order (the highest order of interest) to possibly first order so as to determine the curve that best fits the data

NOTE 1 If the third order polynomial fits the data, it is accepted. If not, the second order is similarly compared with a first order and, if necessary, the first order is compared with the first order through the origin.

NOTE 2 The sequential f-test can be used for fitting a polynomial to the data. After calculating the four possible response curves of interest for a component (first order polynomial through the origin, first, second or third order polynomials), it is necessary to choose the most appropriate curve. This decision can be based on the use of a sequential F-test.

2.5.4.2 critical value

tabulated value from a particular table against which a measured statistic is compared

NOTE The tables cover the t- and F-distributions and data for Grubbs' and Cochran's tests. The critical value is read from the table at the chosen level of probability, and at the degree or degrees of freedom equivalent to the parameters involved in the test. In some cases, more than one critical value may be required, and the test statistic compared with, for example, both 95 % and 99 % levels.

2.5.4.3 outlier

extreme value of the measured values which exceeds the tabulated value at the chosen significance level

2.5.4.4 straggler

extreme value of the measured value which exceeds the tabulated value at the 5 % significance level

2.6 Physical and chemical properties

2.6.1 Reference conditions

2.6.1.1 combustion reference conditions

specified conditions of pressure and temperature at which natural gas is notionally (see note) burned

NOTE "Notionally" has the meaning in this context of speculative or imaginary. Since ISO 6976[22] refers to calculation of calorific value from composition, the metering and combustion temperatures refer to those which would exist if combustion calorimeter had been used instead.

2.6.1.2 metering reference conditions

specified conditions of pressure and temperature at which the amount of natural gas to be burned is notionally (see note in 2.6.1.1) determined

NOTE 1 There is no a priori reason for these conditions to be the same as the combustion reference conditions.

NOTE 2 See ISO 6976[22].

2.6.1.3

normal reference conditions

reference conditions of pressure, temperature and humidity (state of saturation) equal to: 101,325kPa and 273,15 K for a dry, real gas

2.6.1.4

standard reference conditions

reference conditions of pressure, temperature and humidity (state of saturation) equal to: 101,325kPa and 288,15 K for a dry, real gas

NOTE 1 Good practice requires that the reference conditions be incorporated as part of the symbol, and not of the unit, for the physical quantity represented.

EXAMPLE

where

is the superior calorific value on volumetric basis;

pcrc is the pressure of the combustion reference conditions;

Tcrc 7- is the temperature of the combustion reference conditions;

V(pmrc, Tmrc)is the volume at the temperature and the pressure of the metering reference

conditions.

NOTE 2 Standard reference conditions are also referred to as metric standard conditions.

NOTE 3 The abbreviation s.t.p. (standard temperature and pressure) replaces the abbreviation N.T.P. (Normal Temperature and Pressure), as formerly used, and is defined as the condition of pressure and temperature equal to: 101,325 kPa and 288,15 K. No restriction is given on the state of saturation.

2.6.2 Behaviour of ideal and real gas

2.6.2.1 ideal gas

gas that obeys the ideal gas law

NOTE 1 The idea! gas law is given by:

where

p is the absolute pressure;

Vm is the molar volume;

R is the molar gas constant;

T is the thermodynamic temperature.

NOTE 2 No real gas obeys this law; for real gases the above equation should be rewritten as:

where

Z(p, T) is the compression factor.

2.6.2.2

compression factor

Z-factor

gas compressibility factor

quotient of the actual (real) volume of an arbitrary mass of gas, at a specified pressure and temperature, and the volume of the same gas, under the same conditions, as calculated from the ideal gas law

NOTE 1 The formula for the compression factor is as follows:

where

Thus

where

p is the absolute pressure;

T is the thermodynamic temperature;

y is the set of parameters which uniquely characterizes the gas;

Vm is the molar volume;

R is the molar gas constant;

Z is the compression factor.

In principle, v may be the complete molar composition (see ISO 12213-2[36]) or a distinctive set of dependent physicochemical properties (see ISO 12213-3[37]).

NOTE 2 The compression factor is a dimensionless quantity usually close to unity near standard or normal reference conditions. Within the range of pressures and temperatures encountered in gas transmission, the compression factor can significantly differ from unity.

NOTE 3 The supercompressibility factor, f, is defined as the square root of the ratio of the compression factor at reference conditions to the compression factor of the same gas at the conditions of interest:

where Zb is the compression factor at base conditions of pressure and temperature.

Base conditions are temperature and pressure conditions at which natural gas volumes are determined for the purpose of custody transfer. In natural gas measurements the properties of interest are temperature, pressure and composition. Assuming ideal gas properties, for simplicity, tables of pure compounds can be prepared for use in calculating gas properties for any composition at "base conditions". These "base conditions" are chosen near ambient.

In the IGU Dictionary of the Gas Industry the supercompressibility factor is defined as:

The supercompressibility factor is used with measurements made by flow instruments. The volume obtained with a flowmeter should be multiplied by f to obtain the corrected volume.

The compression factor is used with measurements made by displacement methods. In this case the volume should be multiplied by “1/Z” to obtain the correct volume.

2.6.3 Density

2.6.3.1 density

mass of gas divided by its volume at specified conditions of pressure and temperature

NOTE In a mathematical representation the density is given by:

2.6.3.2 relative density

quotient of the mass of a gas, contained within an arbitrary volume, and the mass of dry air of standard composition (defined in ISO 69761221) which would be contained in the same volume at the same reference conditions

NOTE 1 An equivalent definition is given by the ratio of the density of the gas pg to the density of dry air of standard composition pa at the same reference conditions.

where

d is the relative density;

psrc is the pressure at standard reference conditions;

Tsrc is the temperature at standard reference conditions;

ρ(psrc, Tsrc) js the density at the standard reference conditions of temperature and the pressure.

NOTE 2 Density can be expressed in terms of the real gas law;

With this relation the relative density, when both gas and air are considered as real fluids, becomes:

For ideal gas behaviour of the gases, when both gas and air are considered as fluids which obey the ideal gas law, the relative density becomes:

NOTE 3 In former times, the above ratio MglMa was called the specific gravity of a gas, which has the same value as the relative density if ideal behaviour of the gases is assumed. The term relative density should now replace the term specific gravity.

2.6.4 Combustion properties

2.6.4.1 superior calorific value

energy released as heat by the complete combustion in air of a specified quantity of gas, in such a way that the pressure p1 at which the reaction takes place remains constant, and all the products of combustion are returned to the same specified temperature T1 as that of the reactants, all of these products being in the gaseous state except for water formed by combustion, which is condensed to the liquid state at T1

NOTE 1 Where the quantity of gas is specified on a molar basis, the calorific value, expressed in MJ/mol, is designated as:

On a mass basis the calorific value, expressed in MJ/kg, is designated as:

Where the quantity of gas is specified on a volumetric basis, the calorific value, expressed in MJ/m3 is designated as:

where T2, and p2 are the gas volume (metering) reference conditions.

NOTE 2 The terms gross, higher, upper and total calorific value, or heating value, are synonymous with superior calorific value.

2.6.4.2 inferior calorific value

energy released as heat by the complete combustion in air of a specified quantity of gas, in such a way that the pressure pi at which the reaction takes place remains constant, and all the products of combustion are returned to the same specified temperature Ti as that of the reactants, all of these products being in the gaseous state

NOTE 1 Superior calorific value differs from inferior calorific value by the heat of condensation of water formed by combustion.

NOTE 2 Where the quantity of gas is specified on a molar basis, the calorific value, expressed in MJ/mol, is designated as:

On a mass basis the calorific value, expressed in MJ/kg, is designated as:

Where the quantity of gas is specified on a volumetric basis, the calorific value, expressed in MJ/m3, is designated as:

where T2 and p2 are the gas volume (metering) reference conditions.

NOTE 3 The terms net and lower calorific value, or heating value, are synonymous with inferior calorific value.

NOTE 4 Superior and inferior calorific values can also be stated as dry or wet (denoted by the subscript "w") depending on the water vapour content of the gas prior to combustion.

The effects of water vapour on the calorific values, either directly measurer or calculated, are described in annex F of ISO 6976:1995[22]

NOTE 5 Normally the calorific value is expressed as the superior, dry value specified on a volumetric basis under standard reference conditions.

2.6.4.3

enthalpy of transition

enthalpy of transformation

amount of heat released accompanying the transition of a substance from one state to another

NOTE By convention, positive heat release is numerically equal to an increment of negative enthalpy (for a heat-releasing transition, ΔH<0). The quantities, enthalpy of combustion and enthalpy of vaporization, should have meanings that are evident. The term enthalpic correction refers to the (molar) difference in enthalpy for the transition of a gas from an ideal state to a real state.

2.6.4.4 Wobbe-index

calorific value, on a volumetric basis, at specified reference conditions, divided by the square root of the relative density at the same specified metering reference conditions

NOTE 1 The Wobbe index is specified as superior (denoted by the subscript "S") or inferior (denoted by the subscript "I"), depending on the calorific value, and as dry or wet (denoted by the subscript "w") depending on the calorific value and the corresponding density.

NOTE 2 The Wobbe index is a measure of heat input to gas appliances derived from the orifice flow equation. Heat input for different natural gas compositions is the same if they have the same Wobbe index, and operate under the same gas pressure (see ISO 6976(221).

2.6.5 Dew points

2.6.5.1 Water dew point

2.6.5.1.1 water dew point

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

NOTE For any pressure lower than the specified pressure there is no condensation at this dew point temperature.

2.6.5.1.2 water content

mass concentration of the total amount of water contained in a gas

NOTE 1 Water content is expressed in grams per cubic metre.

NOTE 2 For raw gas, this means water in the forms of both liquid and vapour, but for pipeline gas this means only water vapour.

2.6.5.2 Hydrocarbon dew point

2.6.5.2.1 hydrocarbon dew point

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

NOTE 1 At a given dew point temperature there is a pressure range within which retrograde condensation can occur. The cricondentherm defines the maximum temperature at which this condensation can occur.

NOTE 2 The dew point line is the locus of points for pressure and temperature which separates the single phase gas from the biphasic gas-liquid region.

2.6.5.2.2 retrograde condensation

phenomenon associated with the non-ideal behaviour of a hydrocarbon mixture in the critical region wherein, at constant temperature, the vapour phase in contact with the liquid may be condensed by a decrease in pressure; or at constant pressure, the vapour is condensed by an increase in temperature

NOTE Retrograde condensation of natural gas is the formation of liquid when gas is heated or pressure is reduced.

2.6.5.2.3 potential hydrocarbon liquid content

amount of liquid potentially condensable per unit volume of gas at a given temperature and pressure

2.6.6 Other definitions

2.6.6.1 methane number

rating indicating the knocking characteristics of a fuel gas

NOTE It is comparable to the octane number for petrol. 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 14532:2001 (E/F)

2.7 Intel-changeability

2.7.1 Interchangeability

measure of the degree to which combustion characteristics of one gas are compatible with those of another gas

NOTE Two gases are said to be interchangeable when one gas may be substituted for the other gas without interfering with the operation of gas-burning appliances or equipment.

2.7.2

family of gases

gas family

set of gases having common main constituents

2.7.3

group of gases

gas group

subset of a family of gases, categorized as having similar combustion characteristics with reference to limit gases and test pressures

2.7.4 reference gas

gas with which appliances operate under nominal conditions when supplied at the corresponding normal pressure

NOTE Nominal conditions are the conditions at which appliances have been optimized to give their best performance.

2.7.5 limit gas

gas representative of one of the extreme variations, in terms of the Wobbe Index, categorizing a group of gases

2.7.6

normal pressure

pressure at which appliances operate under nominal conditions when they are supplied with the corresponding reference gas

NOTE Nominal conditions are the conditions at which appliances have been optimized to give their best performance.

2.7.7

test pressure

pressure representative of a possible extreme pressure variation resulting from gas supply conditions of the appliance

2.7.8

flash back

tendency for the flame to contract back towards the burner outlet port resulting in combustion taking place inside the burner

2.7.9

lifting

expansion of the burning surface to the point where burning ceases at the burner outlet port and bums above it

2.7.10 yellow tipping

incomplete combustion where excess hydrocarbons can possibly result in unacceptable levels of carbon monoxide being produced

NOTE This may result in soot deposition and continual deterioration of combustion.

2.8 Odorization

2.8.1 odorization

addition of odorants, generally strongly offensive smelling organic sulfur compounds, to natural gas (normally odourless) to allow gas leaks to be recognized by smell at trace levels (before accumulating to dangerous concentrations in air)

2.8.2 odorant

"strong" smelling organic chemical or combination of chemicals (e.g. sulfur compounds) added to fuel gases to impart a characteristic and distinctive (usually disagreeable) warning odour so as to be enable the detection of gas leaks by smell

2.8.3 odoriferous sulfur compound

organic sulfur compound used for fuel gas odorization

NOTE Odoriferous sulfur compounds belong to one of the following classes of substances:

alkyi sulfides (thioethers);

cyclic sulfides (thioethers);

alkane thiols (alkyi mercaptans).

2.8.4 tetrahydrothiophene

THT

cyclic organic sulfur compound with one suifur atom incorporated in the hydrocarbon ring (C4H8S) and often used for natural gas odorization

Annexe A

(informative)

Subscripts, symbols and units

A.1 Symbols and subscripts

A.1.1 Symbols

a, b, c, d polynomial coefficients

b gas law deviation coefficient (b = 1-Z)

summation factor

d relative density 1

f supercompressibility factor

H molar basis calorific value MJ/mol

H mass basis calorific value MJ/kg

H volumetric basis calorific value MJ/m3

h molar enthalpy J/mol

K relative response factor 1

k number of components detected in the chromatogram

L molar enthalpy of vaporization of water kJ/mol

M mass per mole kg/kmol

p (absolute) pressure kPa

R gas constant (8,314 510) J/(K-mol)

RA,B chromatographic resolution between peaks for components A and B

Rf chromatographic response factor counts

r repeatability

s standard deviation

T thermodynamic (absolute) temperature K

r Celsius temperature °C

t t-statistic

tR (A), tR(B) chromatographic retention time for components A and B min

V volume m3

Vm molar volume . m3/kmol

W Wobbe index MJ/m3

w(A), w(B) chromatographic peak widths at baseline for components A and B min

x mole fraction or normalized mole fraction 1

x* non-normalized mole fraction 1

y volume fraction 1

Z compressibility factor

ρ density kg/m3

ρm molar density kmol/m3


A.1.2 Subscripts

A, B components A and B

a air

crc combustion reference conditions

g gas

I inferior

i component i

m quantity per mole

mc main and associated components

mrc metering reference conditions

oc other components

rc reference component

S superior

s sample

src standard reference conditions

tc trace components

w wet

wrm working reference gas mixture (WRM)


A.2 Conversion factors for pressure, temperature, length and energy


A.2.1 Pressure


To convert from


kPa to bar =>


MPa to bar => bar = MPa·10

atm to bar => 10 bar= atm • 1,013 25

psia to bar =>

psig to bar =>

A.2.2 Temperature

To convert from

K to ºC => ºC=K-273,15

ºF to ºC => ºC=


ºR to ºC => ºC=ºR·1,8 - 273,15

A.2.3 Length

To convert from

foot to m => m = foot • 0,304 8


A.2.4 Energy


To convert from BTU to J => J = BTU • 1,055

A.3 List of abbreviations


ASTM American Society for Testing and Materials


CEN European Committee for International Standardization


IEC International Electrotechnical Commission


IGU International Gas Union


ISO International Organization for Standardization


CD Chemiluminescence detector


CNG Compressed natural gas


CRM Certified reference gas mixtures


ED Electrochemical detector


FID Flame ionization detector


FPD Flame photometric detector


HWD Hot wire detector


LDS Local distribution system


LNG Liquefied natural gas


LPG Liquid petroleum gas


NG Natural gas


RM Reference material


PSM Primary standard gas mixture


SNG Substitute natural gas


TCD Thermal conductivity detector


THT Tetrahydrothiophene


VIM International vocabulary of basic and general terms in metrology (see reference [45] of the Bibliography)


WRM Working reference gas mixtures


Bibliography


[1] ISO 3534-1, Statistics — Vocabulary and symbols — Part 1: Probability and general statistical terms

[2] ISO 4260, Petroleum products and hydrocarbons — Determination of sulfur content — Wickbold combustion method

[3] ISO 6142, Gas analysis — Preparation of calibration gas mixtures — Gravimetric methods

[4] ISO 6143, Gas analysis — Comparison methods for determining the composition of calibration gas mixtures

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

[6] ISO 6326-2, Gas analysis — Determination of sulfur compounds in natural gas — Part 2: Gas chromatographic method using an electrochemical detector for the determination of odoriferous sulphur compounds

[7] ISO 6326-3, Natural gas — Determination of sulfur compounds — Part 3: Determination of hydrogen sul-fide, mercaptan sulfur and carbonyl sulfide sulfur by potentiometry

[8] ISO 6326-4, Natural gas — Determination of sulfur compounds — Part 4: Gas chromatographic method using a flame photometric detector for the determination of hydrogen sulfide, carbonyl sulfide and other suifur-containing odorants

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

[10] ISO 6327, Gas analysis — Determination of the water dew point of natural gas — Cooled surface condensation hygrometers

[11] ISO 6568, Natural gas — Simple analysis by gas chromatography

[12] ISO 6570-1, Natural gas — Determination of potential hydrocarbon liquid content— Part 1: Principles and general requirements

[13] ISO 6570-2, Natural gas — Determination of potential hydrocarbon liquid content — Part 2: Weighing method

[14] ISO 6570-3:19843), Natural gas— Determination of potential hydrocarbon liquid content— Part 3: Volumetric method

[15] ISO 6974-1, Natural gas— Determination of composition with defined uncertainty by gas chromatography — Part 1: Guidelines for tailored analysis

[16] ISO 6974-2, Natural gas — Determination of composition with defined uncertainty by gas chromatography — Part 2: Measuring-system characteristics and statistics for processing of data

[17] 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 Cg using two packed columns

ISO 6974-4, Natural gas— Determination of composition with defined uncertainty by gas chromatogra-pny— part 4: Determination of nitrogen, carbon dioxide and C^ to Cg and Cg+ hydrocarbons for a laboratory and on-line measuring system using two columns

[19] ISO 6974-5, Natural gas— Determination of composition with defined uncertainty by gas chromatogra-phy— Part 5: Determination of nitrogen, carbon dioxide and C-s to Cg and Cg+ hydrocarbons for a laboratory and on-line process application using three columns

[20] ISO 6974-6:—4^, Natural Gas — Determination of composition with defined uncertainty by gas chromatog-raphy— Pan. 6: Determination of hydrogen, helium, oxygen, nitrogen, carbon dioxide and hydrocarbons up to Co using three capillary columns

[21] ISO 6975, Natural gas — Extended analysis — Gas chromatographic method

[22] ISO 6976:1995, Natural gas— Calculation of calorific values, density, relative density and Wobbe index from composition

[23] ISO 6978-1:—5), Natural gas — Determination of mercury — Part 1: Principles and general requirements

[24] ISO 6978-2:—5), Natural gas — Determination of mercury — Part 2: Sampling of mercury by chemisorption on iodine

[25] ISO 6978-3:—5), Natural gas — Determination of mercury — Part 3: Sampling of mercury by amalgamation on gold/platinum alloy

[26] ISO 7504:—6\ Gas analysis — Vocabulary [27] ISO 10101 –1, Natural gas — Determination of water by the Kart Fischer method — Part 1: Introduction

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

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

[30] ISO 10241, International terminology standards — Preparation and layout

[31] ISO 10715, Natural gas — Sampling guidelines

[32] ISO 10723, Natural gas — Performance evaluation for on-line analytical system

[33] ISO 11095, Linear calibration using reference materials

[34] ISO 11541, Natural gas — Determination of water content at high pressure

[35] ISO 12213-1, Natural gas — Calculation of compression factor — Part 1: Introduction and guidelines

[36] ISO 12213-2, Natural gas— Calculation of compression factor— Part 2: Calculation using a molar-composition analysis

[37] ISO 12213-3, Natural gas — Calculation of compression factor — Part 3: Calculation using physical properties

[38] ISO 13443, Natural gas — Standard reference conditions

[39] ISO 13686, Natural gas — Quality designation

[40] ISO 13734, Natural gas — Organic sulfur compounds used as odorants — Requirements and test methods

[41] ISO 14111, Natural gas — Guidelines for traceability in analysis

[42] ISO 15403, Natural gas — Designation of the quality of natural gas for use as a compressed fuel for vehicles

[43] ISO Guide 30, Terms and definitions used in connection with reference materials

[44] Guide to the expression of uncertainty in measurement (GUM). BIPM, IEC, IFCC, ISO, IUPAC, IUPAP, OIML, 1st ed., corrected and reprinted in 1995

[45] International vocabulary of basic and general terms in metrology (VIM). BIPM, IEC, IFCC, ISO, IUPAC, IUPAP, OIML, 2nd ed., 1993

[46] ASTM D 4150-00, Standard Terminology Relating to Gaseous Fuels

Index


A


absolute measurement 2.2.1.1 absorption 2.2.2.6 absorption cell 2.4.13 accuracy of measurement 2.5.1.1 adsorption 2.2.2.7 aliquot part 2.2.2.9 alkanethiol 2.5.3.3.1 alky! disulfide 2.5.3.3.3 alkyi mercaptan 2.5.3.3.1 alkyi sulfide 2.5.3.3.2 associated components 2.5.3.2.2 auxiliary gases 2.4.5


B


back-pressure regulator 2.3.3.4


bias 2.5.1.3


bracketing 2.5.2.5


bridge component 2.5.3.2.6


bypass line 2.3.2.9


C


calibration 2.5.2.2 calibration interval 2.5.2.3 carbonyl sulfide 2.5.3.3.4 carbonyl sulfide sulfur 2.5.3.3.5 carrier gas 2.4.4 CD 2.4.6 certified reference


material 2.5.3.5.1.2 chemiluminescence detector 2.4.6 chromatographic


resolution 2.5.3.4.6 CNG 2.1.1.12


combustion method 2.2.2.5 combustion reference


conditions 2.6.1.1 compressed natural gas 2.1.1.12 compression factor 2.6.2.2 condenser 2.3.3.1 control chart 2.5.2.9 control gas 2.5.3.5.2.4 control method 2.5.2.9 COS 2.5,3.3.4 critical value 2.5.4.2 CRM 2.5.3.5.12 cyclic sulfide 2.5.3.3.6


D


delivery point 2.1.2.3 density 2.6.3.1 desorption 2.2.2.8




direct chromatographic measurement of components 2.5.3.1.6 direct measurement 2.2.1.2 direct sampling 2.3.1.1 drip pots 2.3.3.2 dry natural gas 2.1.1.9


E


ED 2.4.7


electrochemical detector 2.4.7 enthalpy of transformation 2.6.4.3 enthalpy of transition 2.6.4.3 etalon 2.5.3.5.1.5


F


family of gases 2.7.2


fast loop 2.3.2.8


feeding station 2.1.2.5


FID 2.4.8


flame ionization detector 2.4.8


flame photometric detector 2.4.1


flash back 2.7.8


floating piston cylinder 2.3.2.1


FPD 2.4.1


G


gas analysis 2.5.3.1.5 gas chromatograph 2.4.3 gas chromatographic


method 2.2.2.1 gas composition 2.5.3.1.4 gas compressibility factor 2.6.2.2 gas family 2.7.2 gas group 2.7.3 gas quality 2.1.1.14 gas sorption effects 2.3.4.5 gas liquid separator 2.3.3.2 glycol 2.5.3.3.7


group of components 2.5.3.2.4 group of gases 2.7.3 group standard 2.5.3.5.1.6


H


heating device 2.3.3.5


high pressure natural gas 2.1.1.10


hot loop 2.3.2.8


hot wire detector 2.4.9


HWD 2.4.9


hydrocarbon dew point 2.6.5.2.1


hydrogen sulfide (H^S) 2.5.3.3.8




I


ideal gas 2.6.2.1 incremental sampler 2.3.2.3 indirect chromatographic measurement of components 2.5.3.1.7 indirect measurement 2.2.1.3 indirect sampling 2.3.1.2 inferential measurement 2.2.1.4 inferior calorific value 2.6.4.2 injection point 2.1.2.4 in-line instrument 2.3.1.3 integrator 2.4.11 interchangeabiiity 2.7.1 international measurement


standard 2.5.3.5.1.9 introduction unit 2.4.2


L


lean gas 2.1.1.5


LDS 2.1.2.2


lifting 2.7.9


limit gases 2.7.5


liquefied natural gas 2.1.1.13


LNG 2.1.1.13


local distribution system 2.1.2.2


low pressure natural gas 2.1.1.11


M


main component 2.5.3.2.1 major components 2.5.3.2.1 manufactured gas 2.1.1.4 mass [molar]


concentration 2.5.3.1.2 mass [volume] [mole]


fractions 2.5.3.1.1 material measure 2.5.2.1 measurement reference


system 2.5.3.5.1 measurement method for direct


measurement of


properties 2.2.1.5 measurement standard 2.5.3.5.1.5 measuring system 2.4.1 mercaptan 2.5.3.3.9 mercaptan sulfur 2.5.3.10 metering reference


conditions 2.6.1.2 methane number 2.6.6.1 methanol 2.5.3.3.11 minor component 2.5.3.2.2 mole 2:5.3.1.3 multi-point calibration 2.5.2.6


N


national measurement


standard 2.5.3.5.1.10 natural gas 2.1.1.1 NG 2.1.1.1


normal pressure 2.7.6 normal reference


conditions 2.6.1.3 normalization 2.5.3.4.5


0


odorant 2.8.2 odoriferous sulfur


compound 2.8.3 odorization 2.8.1 off-line instrument 2.3.1.5 on-line instrument 2.3.1.4 organic sulfur 2.5.3.3.12 other components 2.5.3.2.5 other constituents 2.5.3.2.5 outlet station 2.1.2.6 outlier 2.5.4.3


P


photometry 2.4.12 pipeline grid 2.1.2.1 potential hydrocarbon liquid


content 2.6.5.2.3 potentiometric method 2.2.2.2 potentiometric titration 2.2.2.3 precision 2.5.1.4 primary standard 2.5.3.5.1.7 primary standard gas


mixture 2.5.3.5.2.1 proportional-flow incremental


sampler 2.3.2.2 PSM 2.5.3.5.2.1 purging time 2.3.4.1


R


raw gas 2.1.1.2


reducer 2.3.3.3


reference component 2.5.3.2.6


reference gas 2.7.4


reference material 2.5.3.5.1.1


reference measuring


system 2.5.3.5.1.3 reference standard 2.5.3.5.1.11 regulator 2.3.3.3 relative density 2.6.3.2 relative measurement 2.2.1.6 relative response factor 2.5.3.4.3 repeatability limit 2.5.1.5 representative sample 2.3.4.2 reproducibility limit 2.5.1.6 residence time 2.3.4.3 response 2.5.3.4.1




response factor 2.5.3.4.2 response function 2.5.3.4.4 retrograde condensation 2.6.5.2.2 rich gas 2.1.1.6 RM 2.5.3,5.1.1


S


sample container 2.3.2.4 sample line 2.3.2.5 sample probe 2.3.2.6 sampling point 2.3.4.4 secondary standard 2.5.3.5.1.8 secondary standard gaz


mixture 2.5.3.5.2.2 sequential F-test 2.5.4.1 series of standards 2.5.3.5.1.6 single-point-calibration 2.5.2.4 SNG 2.1.1.3 sour gas 2.1.1.8 spot sample 2.3.1.6 standard reference


conditions 2.6.1.4 straggler 2.5.4.4 substitute natural gas 2.1.1.3 sulfide 2.5.3.3.13 superior calorific value 2.6.4.1 synthetic gas 2.1.1.4


T


TCD 2.4.9


test pressure 2.7.7 tetrahydrothiophene 2.8.4 thermal conductivity detector 2.4.9 thioether 2.5.3.3.14,2.5.3.3.2,


2.5.3.3.6 thiol 2.5.3.3.16


thiol (mercaptan) sulfur 2.5-3.3.15 THT 2.8.4


total sulfur 2.5.3.3.17 trace component 2.5.3.2.3 trace constituent 2.5.3.2.3 traceability 2.5.3.5.1.4 transfer line 2.3.2.7 transfer standard 2.5.3.5.1.13 transformation 2.5.2.7 trueness 2.5.1.2 turbidimetric titration 2.2.2.4


U uncertainty 2.5.1.7


V verification 2.5.2.8




W


water content 2.6.5.1.2 water dew point 2.6.5.1.1 wet gas 2.1.1.7 Wobbe-index 2.6.4.4 working reference gas


mixture 2.5.3.5.2.3 working standard 2.5.3.5.1.12 WRM 2.5.3.5.2.3


Y yellow tipping 2.7.10