Network Code
ATTACHMENT 11/A
TECHNICAL SPECIFICATION OF THE CHEMICAL-PHYSICAL
CHARACTERISTICS AND OF THE PRESENCE OF OTHER
COMPONENTS IN NATURAL GAS AND BIOMETHANE
PART I – NATURAL GAS
1
Scope and application
The specification aims to define the chemical-physical characteristics of the
natural gas to be carried in the Snam Rete Gas pipeline network, in accordance
with "Technical regulations on the chemical and physical characteristics and on
the presence of other components in the fuel gas to be carried", in Attachment A
of the Decree of the Ministry of Economic Development of 19th February 2007.
The scope is related to natural gas of the Second Family-Group H, in accordance
with UNI EN 437 "Trial gas - Trial pressure - Categories of equipment", excluding
manufactured gas and liquefied petroleum gas. This specification refers to both
the National Network (NN) and the Regional Network (RN) of the Transporter.
The document in question applies to both the natural gas input and the gas offtaken from all the interconnected networks.
2
Regulatory references






CNR-UNI 10003 “International system of units (SI)”;
Ministerial Decree of 24th November 1984 “Fire-prevention safety rules for
the transportation, storage and usage of natural gas with density lower than
0.8” and Ministerial decree of 3 February 2016 “Approval of the technical
fire prevention regulations on the design, construction and operation of
natural gas deposits with a density of no more than 0.8 and biogas deposits,
including those with a density of over 0.8”;
UNI EN 437 “Trial gas – Trial pressure – Categories of equipment”;
ISO 13443 “Natural gas – Standard reference conditions”;
Decree of 22nd December 2000 “Identification of the national pipeline
network according to Article 9 of the Law Decree no. 164 of 23 May 2000”;
Decree of 19th February 2007 "Approval of the technical regulations on the
chemical and physical characteristics and on the presence of other
components in the fuel gas to be carried."
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3
Reference conditions
The reference conditions adopted for volume units are the following standard
conditions (see ISO 13443), or:
Pressure
Temperature
101.325 kPa
288.15 K (= 15°C)
To determine the physico-chemical characteristics of the natural gas in the
network under this Annex for Gross Calorific Value and for the Wobbe Index, the
following enthalpy reference is adopted:
288.15 K (= 15°C); 101.325 kPa
4
QUALITY PARAMETERS
4.1
Gross Calorific Value (“PCS”) Components
Acceptable
Components
Value
Methane
(*)
Ethane
(*)
Propane
(*)
Isobutane
(*)
Normal-butane
(*)
Isopentane
(*)
Normal-pentane
(*)
Hexane and above
(*)
Nitrogen
(*)
Oxygen
 0.6
Carbon dioxide
3
Measurement
Unit
% mol
% mol
(*) For these components the acceptable values are intrinsically linked with the
acceptable range of the Wobbe Index.
4.2
Trace compounds
Parameters
Hydrogen Sulphide
Sulphur from mercaptan
Total Sulphur
4.3
Acceptable
Value
 6.6
 15.5
 150
Measurement
Unit
mg/ Sm3
mg/ Sm3
mg/ Sm3
Physical properties
Property
Gross Calorific
Acceptable Value
34.95  45.28
Measurement
Unit
MJ/Sm3
Conditions
Network Code
4.4
47.31  52.33
0.5548  0.8
MJ/Sm3
Water Dew Point
 -5
°C
Hydrocarbon Dew
Point
0
°C
Max. temperature
Min. temperature
< 50
>3
°C
°C
At the relative
pressure of 7,000 kPa
In the relative
pressure range 100 
7,000 kPa
Other properties
The gas, during operational conditions, should contain no traces of the following
components:



4.5
Value
Wobbe Index
Relative density
water and hydrocarbons in liquid state;
solid particulate in such quantities that would damage the materials used for
gas transportation;
other gases that may affect the safety or integrity of the transportation
system.
Special cases
For Delivery Points connected to national natural gas production fields that are
not compatible with these Quality Requirements, as described in paragraph 1.1.1
of Chapter 6, Snam Rete Gas will accept the injection of gas with a composition
that does not conform to the quality specification, if the following conditions
occur:
 mixing conditions are feasible in order to obtain a gas mix within the quality
specification;
 these mixing conditions will persist for a sufficiently long period
The requiring party must give to the Transporter – as stated in paragraph 1.1.1 of
Chapter 6 - the chemical and physical characteristics of the gas injected at that
Point, in order to allow Snam Rete Gas to define and communicate to the Shipper
the range of variability of the quality parameters at such Delivery Point: this
variability range defines the limit of maximum variation of the parameters for
which the provisions in paragraph 1.2.2 of Chapter 19.
The acceptance of the injection of gas at Delivery Points connected to national
production with a composition different from the Quality Requirements will be
suspended in the periods where:
 the composition of gas to mix is significantly worse than that defined;
 the gas flowing in the pipeline where the connection is linked is not available
in the quantities needed for the mixing.
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PART II – BIOMETHANE
5
Scope and application
These specifications define the chemical and physical characteristics of the
biomethane to be transported on the Snam Rete Gas network, in accordance with
the provisions laid down in the “Technical regulations on the chemical and
physical characteristics and the presence of other components in the fuel gas to
be transported”, indicated in Annexe A of the Ministry of Economic
Development decree of 19 February 2007 and in the Interministerial decree of 5
December 2013.
The parameters indicated below also conform to Resolution 46/2015/R/gas,
subsection 3.2, which specifies that, before being injected into the network, the
biomethane must be technically free of all the components listed in technical
report UNI/TR 11537, for which the maximum limits have not yet been set by the
regulations.
The field of application concerns the biogas treated and purified so as to make its
chemical and energy characteristics compatible with natural gas of the 2nd
Family-Group H, excluding manufactured gas and liquefied petroleum gas. This
specification refers both to the National Network (RN) and the Transporter’s
Regional Network (RR).
6
Regulatory references
 CNR-UNI 10003 “International System of Units (SI)”;
 Ministerial decree of 24 November 1984 “Fire safety regulations for the
transportation, distribution, storage and use of natural gas with a density of
no more than 0.8” and Ministerial decree of 3 February 2016 “Approval of
the technical fire prevention regulations for the design, construction and
operation of natural gas deposits with a density of no more than 0.8” and
biogas deposits, including those with a density of over 0.8”;
 UNI EN 437 “Test gas – Test pressures – Categories of devices”;
 ISO 13443 “Natural gas – Standard reference conditions”;
 Decree of 22 December 2000 “Identification of the national gas pipeline
network in accordance with Art. 9 of Legislative no. 164 of 23 May 2000”;
 Decree of 19 February 2007 “Approval of the technical regulations on the
chemical and physical characteristics and the presence of other components
in fuel gas to be transported”;
 Interministerial decree of 5 December 2013;
 UNI-TR 11537 “Injection of biomethane in the natural gas transportation and
distribution networks”;
 Resolution of the Authority no. 46/2015/R/gas.
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7
Reference conditions
The reference conditions of the volume unit adopted are standard (ref. ISO
13443), that is:
Pressure
Temperature
101.325 kPa
288.15 K (= 15°C)
To determine the Gross Calorific Value and the Wobbe Index, the following
reference enthalpy is taken:
288.15 K (= 15°C); 101.325 kPa
8
QUALITY PARAMETERS
8.1
Components of the PCS
Component
Methane
Ethane
Propane
Iso-butane
Normal-butane
Iso-pentane
Normal-pentane
Hexane and above
Nitrogen
Oxygen
Carbon dioxide
Hydrogen
Carbon monoxide
Acceptability
values
(*)
(*)
(*)
(*)
(*)
(*)
(*)
(*)
(*)
 0.6
3
≤ 0.5
 0.1
Unit of
measurement
% mol
% mol
% Vol
% mol
(*) For these components, the acceptability values are intrinsically limited by the
acceptability range of the Wobbe Index.
8.2
Trace compounds
Parameters
Hydrogen sulfide
Sulfur from mercaptan
Total sulfur
Mercury
Chlorine
Fluorine
Ammonia
Acceptability
values
 6.6
 15.5
 150
≤1
<1
<3
≤3
Unit of
measurement
mg/ Sm3
mg/ Sm3
mg/ Sm3
μg/Sm3
mg/Sm3
mg/Sm3
mg/Sm3
Network Code
Silicon
Hydrogen
Carbon monoxide
8.3
ppm
% Vol
% mol
Physical properties
Acceptability
values
Unit of
measurement
34.95 – 45.28
MJ/Sm3
47.31 – 52.33
0.5548  0.8
MJ/Sm3
Dew point of water
 -5
°C
Dew point of
hydrocarbons
0
°C
Max. temperature
Min. temperature
< 50
>3
°C
°C
Property
Gross Calorific
Value
Wobbe index
Relative density
8.4
≤5
≤ 0.5
 0.1
Conditions
At a relative
pressure of 7,000 kPa
Within the relative
pressure range of
100 – 7,000 kPa
Other properties
Without prejudice to the provisions laid down in resolution 46/2015/R/gas,
article 3, under operating conditions, the biomethane must not contain traces of
the components listed below:



Water and hydrocarbons in liquid form;
Solid particulate in quantities that could damage the materials used in the
transportation of gas;
Other gases that could have effects on the safety or integrity of the
transportation system.
Biomethane must also be odorizable in accordance with the UNI 7133 standard
and the other applicable standards and not present characteristics that cancel or
cover the effect of the characteristic odorizing substances.