IS 15729: Natural gas pressure regulating and metering terminal - Code of practice

2007·2.1 MB·English

by  Bureau of Indian Standards

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IS 15729 (2007): Natural gas pressure regulating and
metering terminal - Code of practice [MED 17: Chemical
Engineering Plants and Related Equipment]
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IS 15729:2007

Indian Standard
NATURAL GAS PRESSURE
REGULATING AND METERING TERMINAL —
CODE OF PRACTICE
ICS 75.200

(3 BIS 2007
BUREAU OF INDIAN STANDARDS
MANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG
NEW DELHI 110002

Febt-uary 2007
Price Group 8
Chemical Engineering Plants and Related Equipment Sectional Committee, ME 17
FOREWORD
This Code was adopted by the Bureau of Indian Standards, after the draft finalized by the Chemical Engineering
Plants and Related Equipment Sectional Committee had been approved by the Mechanical Engineering Division
Council.
The transportation and distribution ofnatural gas through cross-country pipelines are the major business ofthe oil
and gas companies. It was felt that pipeline supplies were rapidly being laid to feed distribution systems for
various users and that there was aneed for adocument embodying recommendations to ensure the utmost reliability
and continuity of supply at pressures that are acceptable to and safe for the downstream pipeline or distribution
system. Assistance has been derived from lGE/TD/ 13 ‘Pressure regulating installations for transmission and
distribution systems’ covering installation with inlet pressures between 0.7 to 10.0 MPa.
Considering the importance of metering, regulation, data acquisition and safety of gas transmission, this Code for
regulating stations has been prepared.
This Code does not restrict the use of new and better techniques developed and proved in due course of time.
The composition of the Committee responsible for the formulation of this standard is given inAnnex D.
For the purpose of deciding whether a particular requirement of this standard is complied with, the final value,
observed or calculated, expressing the result of a test or analysis, shall be rounded off in accordance with
[S2:1960 ‘RuIes for rounding off numerical values (revised)’. The number of significant places retained in the
rounded off value should be same as that of the specified value in this standard.
1S 15729:2007
Indian Standard
NATURAL GAS PRESSURE
REGULATING AND METERING TERMINAL —
CODE OF PRACTICE
1 SCOPE 3.6 Dead Time — The time taken by aslam-shut valve
to sense a pressure signal.
This Code covers the commissioning, operation and
maintenance and safety aspects of natural gas pressure 3.7 Gas
regulating and metering terminal.
3.7.1 First Family Gas — Gas of Wobbe number 24.4
This standard shall be used in conjunction with to 28.8 MJ/m3 commonly known as ‘town gas’.
1S 15677.
3.7.2 Second Family Gas — Gas of Wobbe number
2 REFERENCES 48.2 to 53.2 MJ/m3 commonly known as ‘natural gas’.
The standards listed in Annex A contain provisions 3.8 Holiday — A flaw in the protective coating of a
which, through reference in this text, constitute pipe or component which may expose the underlying
provisions ofthis standard. Atthetime ofpublication, surface.
the editions indicated were valid. All standards are
3.9 Impulse — The pressure sensed at the selected
subject to revision and parties to agreements based on
point inthe gas stream.
this standard are encouraged to investigate the
possibility of applying the most recent editions of the 3.10 Lower Flammable Limit (L~) — The
standards indicated atAnnex A. concentralation of flammable gas, vapour of mist in
air above which combustion can be sustained.
3 TERMINOLOGY
This term may be considered equivalent to the term
3.1 Cathodic Protection (CP) — A method of
‘Lower Explosive Limit’ (LEL).
protecting ametallic pipeline/structure from corrosion
by making it a cathode so that direct current flows on 3.11 Non-destructive Testing (NDT) — Testing of
to the pipeline/structure from the surrounding pipework and components by methods, such as
electrolytic environment. radiography, ultrasonic and magnetic crack detection

etc, that are not destructive.
3.2 CP Related Terminology
3.12 Pig — Adevice which can be propelled through
3.2.1 lt~sula~ing Flanges — Flanges which permit
apipeline by fluid pressure, used for various purposes,
mechanical continuity but break the electrical
for example, cleaning, swabbing, inspection, etc.
continuity.
3.13 Pig Trap — A vessel connected to the end of a
3.2.2 Isola?illg Joint — Electrically insulating
section of pipeline, having abreech loading/unloading
component such as monoblock insulating joint,
arrangement for launching and receiving pigs.
insulating flange, isolating coupling, etc, inserted
between two lengths of pipeline/structure to prevent 3.14 Pressure Related Terminology
electrical continuity between them.
3.14.1 Design Pressure — The design pressure should
3.3 Closing Time — The time taken by a slam-shut be higher than the maximum pressure to which the
valve between commencing and completing the closing system could be subjected during operation. The value
action of its internal valve element. selected as the design pressure should take account of
3.4 Creep (asApplied to Gas Control Equipment) — any foreseeable overpressure condition, particularly
The minor leakage volume of gas which aregulator or where this iscoincident with adverse temperature and/
other control unit may be unable to contain in its or fatigue conditions and of the performance of any
nominally closed state. overpressure protection devices in the system.
3.5 Creep (asApplied toPolymeric Material) — The 3.14.2 Maximum Working Pressure (MWP) — The
phenomenon ofgrowth or displacement ofthe material maximum pressure to which apipe or component may
resulting from applied stress, aging or other factors. be subjected in normal operation.
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IS 15729:2007
3.14.3 Z'.\r/'r[.s.~/{rc-Thep ressuret o\$rllichcopponents 3.15.12 Lock-Up — The act of closure of a regulator
or complete installations aresubjected for acceptance when gas demand falls to zero.
purposes,
3.15.13 Wicking — Aterm used to describe the escape
3.15 ReguIato rRelate dTerminology of gas within a pressurized, fabric-reinforced rubber
diaphragm when the leakage path is along the fabric
3.15.1 Rc,qr{[[{tor- A device whose function is to
interstices.
automatically control pressure or volume flow at a
3.15.14 Relief Valve (Relief Regulator) — A valve or
selected point in a gas stream.
regulator incorporated to protect a system, or a
3.15.2 Pr~'.s.sllr(R' c'gul(~tor- Aregulatorwhich nlaintains component part thereof, against excessive pressure. Its
a preset constant pressure atapoint on itsoutlet. function isto vent, usually to atmosphere, when apre-
determined pressure is attained.
3.15.3 Vc]l!4inttric(Cotlstatlt V[)[Lltne)Regu[utcjr —A
regulator which maintains a preset constant rate of 3.16 Slam-Shut Valve — Avalve-that is designed to
volume flow irrespective ofinlet pressures. close quickly in the event of an abnormal (usually
excess) pressure being detected at aselected point in a
3.15.4 Mo}]itor/Active Regulation -Anarrangement
gas stream.
of two regulators in series whose pressure settings are
stepped so as to allow one regulator (active) normally 3.17 Thermowell — Ametal pocket protruding into
to control the outlet pressure and the other (monitor) the gas stream tohouse atemperature-measuring device.
to assutme control in the event of failure of the active
unit towards the open position. 4 PLANNING, LAYOUT AND SECURITY
3.15.5 Pilor Control — A subsidiary regulating Any natural gas pressure regulating and metering
Imechanism that generally employs the pressure terminal must be designed, located, constructed and
upstream of the main regulator orother control unit operated taking into consideration the safety and
as a power source to exert control over the main environmental requirements of applicable legislation.
regulator.
4.1 Planning
3.15.6 Size ofu Regulator — Size of the regulator is
Consideration should be given to the layout and other
defined asthe nominal diameter ofthe regulator’s inlet
uses of the station, for example, gas storage, the need
connection.
for security ofthe station and anyhousing forthe natural
3.15.7 Capacity of a Regulator — The maximum gas pressure regulating and metering.
volume flow which a regulator will pass at given inlet
Consideration should be given to the possibility of
and outlet pressure under specific gas measurement
flooding and, inthe case ofanunderground installation,
conditions for which the regul ator is designed whilst
the Iikelihood of arising water table.
maintaining stable control of that flow.
4.2 Station Location
3.15.8 Ratlgeubility of aRegulator — The ratio ofthe
maximum capacity of regulator to the minimum When selecting the location for a natural gas pressure
capacity. The maximum capacity can usually be regulating and metering, care should be taken to avoid
obtained from the manufacturer’s catalogue, making the following:
due allowance forthe specific gravity ofthe gas handled
a) Proximity toresidential properties orareas that
and the pressure recovery appropriate to the particular
may be subject to residential development;
installation. The minimum capacity isthat volume flow
down to which the regulator is designed to maintain b) Proximity totall buildings where eddy currents
stable control. around the building may cause problems with
gas dispersal;
3.15.9 Rcpe[ttobility of Actuation — The limits of
c) Positioning the natural gas pressure regulating
deviation from pressure set point within which aslam-
and metering beneath or close to overhead
shut valve isable, repeatedly without failure, to actuate
power lines; and
closure from its normally open state.
d) Vulnerable sites where traffic accidents, etc,
3.1 S.10 /J\tt[//~~ic fc~forfnat~ce — The transient
could result in damage to the natural gas
behaviour of aregulator inControlling pressure or flow
pressure regulating and metering.
following deviation from set-point.
4.3 Station Layout
3.15.11 Trim — A term embracing the internal flow
control elements within the body of aregulator, valve 4.3.1 The area of the station should be adequate to
or other control unit. accommodate the equipment and provide access for

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IS 15729:2007
maintenance purposes andlor the location ofemergency a) Two or more high pressure inlet filters with
facilities, for example, fire extinguishers. suitable valves and connections to permit
NOTE — Itisdesirabletoprovidehardaccess uptoand within design throughput to be maintained with one
thestation toaccommodate maintenance andemergency service unit out of action.
vehicles. b) Means to avoid the entrapment of liquids in
4.3.2 An emergency exit should be provided, if the gas entering a pressure regulator and if
appropriate. necessary, suitabIe provision made for their
removal.
4.3.3 Vulnerable pipework or equipment should be
It isparticularly important that the gas supply
protected, where necessary.
to valve control instruments should be tlee of
4.3.4 Any hazardous area should be taken into account liquids and dust and suitable filters/separators
when determining the station boundary. shall be installed as appropriate.
c) Two or more streams of pressure regulators,
4.3.5 The combustion airintake ofartygasheater orother
burner equipment should be located so as to minimize each stream to contain at least one pressure
any hazard arising from any source of gas leakage or regulator. For critical installation,
consideration may be given for one monitor
emission, forexample, from afilter, relief valve vent, etc.
and one active regulator ineach stream. Where
4.3.6 Consideration should be given to: the installation is not a big gas despatch
terminal, consideration may be given to the
a) access for pigging operation and equipment,
provision of a single stream of pressure
b) minimizing noise,
regulators only.
c) access for maintenance activities,
d) Upstream slam-shut valves shall be fitted on
d) excess for fire fighting, and
all streams of pressure regulators.
e) gas detection.
e) Installations should be designed to withstand
NOTE — Where gas is not odorized, enhanced maximum inlet pressure conditions to be at
arrangementsmaybeneeded,such asprominent notices metering station. Where this isnot reasonably
and/or additional detection equipment.
practicable, the design should include inter-
4.4 Station Security state relief valves ineach stream where more
than one stage, if pressure reduction is
4.4.1 Any station should be secured against entry by involved. Such relief valves should be at least
unauthorized persons. of sufficient capacity to offset the effects of
4.4.2 If a station security fence is used, equipment gas passing due to failure of regulators to
‘lock-up’ at times of no flow.
should be sited at a sufficient distance from the fence

to prevent interference from outside. Protection may also be afforded by providing
an auxiliary trip switch for the slam-shut valve
4.4.3 Consideration should be given to the provision
referred to in (d) above.
of a locking device for valves, including auxiliary
f) In certain circumstances failure of apressure
valves located external to a natural gas pressure
reduction installation to ‘lock-up’ at periods
regulating and metering housing.
of low flow may cause the normal working
4.4.4 Consideration should be given to installing pressure of the system into which it delivers
intruder detection devices. to be exceeded, the use of a relief valve and
vent of sufficient capacity to offset this
4.4.5 Where the presence of vehicular tratlic could
failure to lock-up maybe considered, if the
cause a hazard, the use of safety barriers should be
operation of the slam-shut system is
considered.
unacceptable.
4.4.6 Prominent signs should be displayed, prohibiting g) It is necessary to consider whether pre-
smoking and other ignition sources. heating of the gas is required to avoid
unacceptably low temperature in the
4.4.7 Apermanent notice should be displayed clearly,
downstream pipe network and auxiliary
showing an emergency telephone number which may
systems due to pressure reduction. If heaters
be used by the public or others.
are installed then they shall be controlled in
5 COMPONENTS OF NATURAL GAS such away as to avoid high gas temperature
DESI?ATCH TERMINAL which may damage any seal, diaphragm or
valve seat in equipments like regulators,
The natural gas terminal shall generally include:
meters, relief valves, etc.
3
IS 15729:2007
To meet the above requirement the main components c) Horizontally positioned baskets shall be
of natural gas terminals are as follows: adequately supported. Baskets of cantilever
design are not acceptable.
a) Gas filtration system;
d) All baskets/elements shall be designed to
b) Gas heating system;
withstand the effects of any vibration under
c) Pressure regulators;
all operating conditions.
d) Pressure relief valves, vent and drains;
5.1.1.1 The recommended differential pressure before
e) Valves and actuators;
cleaning or changing and the maximum differential
f) Slam shut valves; pressure which the element can withstand before
g) Thermowell; collapse shall be specified by the filter manufacturer
h) Meter and associated piping; in the data sheet.
j) Electrical system; and 5.1.1.2 The filter body shall beprovided with supports
k) Supervisory control and data acquisition when specified in the data sheet. In case saddle type
system. supports are provided, these shall be either welded to
NOTE — The applicable aspects of EN 12186 maybe used the body or of the loose clamp type. Supports shall
as reference for functional requirements of gas pressure make designed displacement in either direction in
regulating stations andtheir operation, maintenance andsafety
addition to fill axial movement toallow for movement
recommendations.
of the pipework.
5.1 Gas Filtration System
5.1.1.3 Vent and drain connections shallbe provided
Filters, scrubbers and separators or composite units on the body of the filter. Unless otherwise specified,
should be installed onthe inlet ofgas Despatch terminal different pressure tappings shall also be provided on
to clean the gas to a standard required for satisfactory the body.
operation of the downstream equipments.
5.1.1.4 All”flangesshallbefittedsothat their bolt holes
Certain filter elements shall withstand high differential are off the vertical and horizontal centre line.
pressures which could be sufilcient to shut off the
5.1.2 Mechanical Design
supply of gas through the installation. In some cases
such conditions could not be tolerated and alternative 5.1.2.1 The design pressure for the filter shall be as
types of fiIters with internal components designed to desired by the buyer and same shall be stated in the
collapse and/or relieve high differential pressures data sheet.
may be preferred; the selection of downstream
5.1.2.2 For the ambient temperature range of –20°
equipment should therefore take account of the
to 50”C, the lower design temperature for the
choice made.
determination ofimpact properties ofmetallic materials

The filter shall be so designed that the desired degree shall betaken as–1O°C.For other operating temperature
of filtration is achieved in the normal operating ranges, the lower design temperature shall be as stated
conditions. Maximum pressure loss across the inleti by the buyer.
outlet flanges of filter shall not be more than that
5.1.2.3 The design pressure shall be such that during
specified in process parameters of product data sheet.
the hydrostatic pressure test, the design stress shall not
The filter element shall be suitable for any reverse flow exceed 90 percent of the specified yield stress.
of gas. Filter design shall be such that only the element
5.1.3 Manufacturing, Inspection and Tests
itself shall require replacement when blocked/chocked.
5.1.3.1 All flanges left for connection by others shall
The end closure should be such that filter element could
besquare tothe centre line ofthe vessel within 0.25 mti
I-seaccessed.
100 mm of flange outside diameter.
5.1.1 The design of the filter assembly shall take into
5.1.3.2 The peripheries ofthe flanges shall be machined
account the following:
within the following tolerances:
a) Ease of replacement of basket (for example
a) Up to and including 200 mm
the baskets should be bolted toasupport ring).
nominal size +0.5 mm
b) If welded to the pressure shell, the basket
b) Greater than 200 mm
support ring shall be of such a design as to
nominal size +1.Omm
avoid shrinkage stress (for example, segment
construction), with a suitable gasket 5.1.3.3 The completed vessel, including the end closure,
arrangement to prevent bypass. shall be pressure tested hydrostatically.

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IS 15729:2007
5.2 Gas Heating System complete calculation shall be undertaken having regard
to the composition of the gas to be ,heated and the
Due to reduction in pressure across the control valve/
influence ofpressure onthe specific heats ofthe various
regulator, the temperature of gas reduces, it may be
constituents.
necessary to Ynstall pre-heaters to avoid unacceptable
low temperatures on the outlet of pressure reduction Heating ofthe gas maybe achieved by the use of heater
equipment. Generally itisnot necessary to provide pre- units located inthe installation on the inlet side of the
heater where differential pressure across the installation regulators.
is less than 1.5 Mpa.
The following forms of gas heaters maybe used:
In establishing arequirement for the provision of pre-
a) Water bath heaters — These consist oftubular
heating of gas, the aspects to be seen areas under.
elements, carrying the gas, immersed in a
The ability of the downstream pipe material to retain water bath, which ismaintained atthe required
satisfactory physical characteristics at any reduced constant temperature by the use of a burner
temperature of operation. fitted with standard controls and safety devices
to maintain the desired exit temperature inthe
The possibilities of hydrate or liquid formation which
gas stream.
may inftuence the operation of the equipments.
b) Indirect heaters — These consist of tube-in-
The possibility of frost formation due to Iiozen ground shell heat exchangers located inthe gas stream,
around buried outlet pipe. heated by steam from an external source, or
byhot water circulated from anadjacent boiler
The effectiveoperationofanygasconditioningprocess.
or modular boiler unit.
The number of heaters and their capacity should be
The pressure-containing parts ofallheating installations
determined having regard to the probability of failure
subject to gas pressure shall be constructed and tested
of unit occurring simultaneously with a period of
in accordance with the requirements of IS 2825. Due
extreme demand. If this possibility is low then the
allowance for corrosion shall be made where it is
provision of standby heater capacity to meet the
necessary.
extreme condition may not be necessary.
5.3 Pressure Regulators
Consideration should be given to the reliability of the
heating system in operation, taking into account its 5.3.1 Design
dependence of other services. It maybe necessary to
Regulator bodies, diaphragm chambers and bolting
provide standby water and electricity supplies where
shall be designed to withstand the maximum pressure
continuous operation under all fault conditions is
and temperature variations under fault conditions. Parts

essential.
ofthe regulator normally subject tooutlet pressure only

Any polymeric and elastomeric materials used in the should where practicable, also be designed to the same
installation should be capable of withstanding the standard unless provided with integral pressure relief
maximum temperature that the preheat source can of adequate capacity.
attain. To avoid exceeding the safe operating
For inlet pressure up to 10MPa and size upto DN 400,
temperature of these materials in meters or regulator pressure regulators, the applicable aspects of EN 334
valve seats it may well be necessary to limit the may be used. as reference for the constructional,
maximum temperature of the preheat source. functional and testing requirements.
The heater installation should be equipped with ameter Regulators should be sized on the basis of maximum
and control system which minimizes the energy design flow rate coefficient with demand at minimum
consumed bythe preheater. This isnormally achieved differential pressure and inlet and outlet pressure range
by carefully sensing the temperature of the gas capability. The type selected should have a dynamic
downstream of the regulators to control the operation performance compatible with the characteristics of the
of heaters. system to be supplied; taking into account any
associated metering arrangements.
The chosen set-point should be as low as possible
and this equipment and control system should be Wherever it is known that stream capacity is likely to
designed to maintain a minimum variation from this change, consideration should be given tothe installation
set-point. of regulators with adjustable rangeability.
The determination ofthe heat input required should be It is desirable that a port opening indicator and scale
carefully considered to meet a particular duty. The be incorporated in all main regulators.
5