- The selection of design for city gas distribution network shall be based on the gas properties, required flow rates, operating pressures and the environment.
A typical CGD Network should comprise of one or more or all of the following:
- A medium Pressure Distribution System comprising of Pipelines, normally constructed using steel pipes and connects one or more Transmission Pipeline to respective CGS or one or more CGS to one or
- The maximum velocity in the pipeline network should be limited to 100 ft / sec (30 m/sec) immediately after pressure regulating instrument.
- As far as practical, primary network should be fed through more than one city gate stations / sources of supply.
- A low Pressure Distribution System comprising of Gas Mains usually constructed using thermoplastic piping (MDPE) and connects DPRS to various service regulators at commercial, industrial, and domestic
- The network shall be sized for maximum flow velocity of 100 ft / sec (30 m/sec).
- A service Pressure Distribution System comprising of Service
Lines, Service Regulators and customer/ consumer Meter Set Assemblies constructed using a combination of thermoplastic (MDPE) piping and GI/ copper tubing components.
City gate station (CGS): typically comprising of, but not limited to, the following facilities:
- Separators (if required).
- Metering facilities.
- Heater (if required)
- Pressure reduction skid comprising active and monitor combination with a minimum 50% redundancy with stream discrimination arrangement, including slam shut valve for over and under pressure protection and creep relief valves
- Online odorization equipment designed to minimize fugitive emissions during loading, operation and maintenance.
Distribution Pressure Regulating Station or District Regulating Station (DPRS): Located at various demand centers for domestic / commercial users typically consists of:
- Gas filter
- Heater (if required)
- Pressure reduction skid comprising active and monitor combination with minimum 50% redundancy with stream discrimination arrangement, including slam shut valve for over and under pressure protection with additional feature of under pressure protection if required
- Inlet and outlet isolation valves.
Individual Pressure Regulating Station (IPRS):
- Located at the premises of an individual customer and having facilities similar to DPRS however, monitor regulator may or may not be provided.
- Metering facilities may or may not be part of this station.
- Usually located at customer premises for maintaining supply pressure and designed to maintain safe condition even in the event of rupture in the regulator downstream section.
Network Design Requirements:
The design of CGD Networks and its components shall be such that it ensures:
- Supply of gas at constant volume into a system, which fluctuates in pressure between pre-determined upper and lower limits in the distribution network, or
- Supply of gas at a constant pressure at consumer end, and
- The design should recognize the need for safe guard against malfunction of any equipment and provide sufficient redundancy to ensure that the supply is secured against such malfunctions.
Facilities forming part of CGD networks shall be designed considering:
- Range of flow rates and pressures required in various sections of the network
- Quality of gas, including cleanliness in respect of both solid and liquid particles.
- Metering requirements.
- Noise control and
- Corrosion Protection
Necessary calculations shall be carried out to verify structural integrity and stability of the pipeline for the combined effect of pressure, temperature, bending, soil/pipe interaction, external loads and other environmental parameters as applicable, during all phases of work from installation to operation. Such calculations shall include, but not limited to, the following:
- Buoyancy control and stability of pipeline in areas subjected to flooding / submergence,
- River crossing to be installed by trench less techniques, wherever soil data is favorable for such installations,
- Damage potential for steel pipeline from hazards associated with earthquake, if applicable.
- Layout of Station Facilities
The following aspects are to be considered in deciding layout of facilities at CGS, DPRS, IPRS, etc.
i. Type and size of equipment.
iii. Utility requirement.
iv. Venting wherever required.
v. Operation and Maintenance philosophy.
City Gate Station:
As far as possible the city gate station (CGS) shall be installed at the periphery of populated area. The entity should make best endeavor to have more than one CGS for supply security. Inter distance between various facilities required at CGS shall be as per Table given below;
Inter distance (mtr) between various facilities required at CGS shall be;
- Properly laid out roads around various facilities shall be provided within the installation area for smooth vehicular access.
- Facility shall be provided with proper boundary wall / fencing with gate(s) in line with MHA (Ministry of Home Affairs) guidelines.
- Buried piping inside the CGS area shall have a minimum depth of cover of 1.2 m. Where buried pipes come out of the ground, the underground coating on the pipe will continue for a length of at least 300 mm above ground.
- Platforms and crossovers shall be provided for ease of operation and maintenance of equipment and piping where required.
- Provision should be made for venting, purging and draining all sections of pipe work and equipment that may have to be isolated during construction or maintenance.
- All vents shall be routed to a safe area and in a manner that gas vented out is blown away from the nearest building. Height of vent shall be minimum three (3) meters above working level. Distance between vent and boundary wall / fence shall be minimum five (5) meters.
- Gas detectors shall be installed at strategic locations covering to detect any gas leakage.
- In case fired gas heaters are installed for heating of gas, all other facilities handling gas should be located down wind from heaters.
Distribution Pressure Regulating Station (DPRS) and Individual Pressure Regulating Station (IPRS):
- DPRS facilities can be located above ground or below ground.
In case DPRS is located below ground, the facilities shall either be inside a enclosed chamber with a provisions for entry of authorized personnel or be a buried hermetically sealed module type with proper cathodic protection.
- [In case butterfly valves are used in underground DPRS, the same shall conform to the requirements given in Annexure – I of T4S. Further, a dedicated isolation valve shall be installed upstream of such underground skid.]
- For below ground installations, the vent line shall be terminated at a minimum height of three (3) meters above the ground level.
- IPRS shall normally be located above ground.
- DPRS/IPRS installed above ground shall be provided with proper security fencing as per requirement of local authorities. The distance between fencing and the wall of nearest building / structure shall not be less than two (2) meters.
- For Wall mounted regulating system, safety features like crash guards, caging of facilities and like other facilities shall be provided. Further, the maximum outlet pressure shall be restricted up to 2.0 bar.
- The consumer, shall be responsible for ensuring the separation distances for customer owned IPRS.
- Customer shall ensure that IPRS installation has been independently approved by certified third party agency before the entity supplies the gas.
- The consumer shall ensure recertification once in 3 years.
Requirements for Electrical Installations in CGD Network
All electrical equipment / installations shall meet following requirements:
- Electrical area classification of Installation, as basis for selection of Electrical Equipment, shall follow IS-5572.
- The specification of Electrical equipments shall be in line with IS-5571, “Guide for selection of Electrical Equipment for Hazardous Area”.
- Fire protection in Electrical installations shall be provided as per requirements specified in this standard.
- All electrical equipment, systems, structures and fencing, etc. shall be suitably earthed in accordance with IS 3043.
- The earthing system shall have an earthing network grid with required number of electrodes. All Electrical equipment operating above 250 volts shall have two separate and distinct connections to earth grids. Separate earthing grid shall be provided for instrument and electrical power.
- Lightening protection shall be provided as per the requirements of IS:2309.
- Self conducting structures having metal thickness of more than 4.8mm may not require lightning protection with aerial rod and down conductors. They shall, however, be connected to the earthing system, at least, at two points at the base
Instrument and Control System:
- Instrumentation and control system for the CGD networks, shall in general meet the requirement of API Standards: API- RP-551, 552, 553, 554, 555 and 556 “Manual on Installation of Refinery Instruments and Control Systems” to the extent applicable.
Additional Requirement for Nominal Wall Thickness : Consideration shall also be given to loading due to following while selecting nominal wall thickness t as per ASME B 31.8 as appropriate:
- Overburden loads
- Dynamic and seismic loads
- Cyclic and vibratory loads
- Internal pressure fluctuations
- Geo-technical loads (including slides, differential settlement of piping, loss of support, and thermal effect of the pipeline on soil properties)
In any case minimum thickness of pipe permitted as per this standard shall not be less than 6.4 mm, irrespective of the grade of the pipe material.
[In any case minimum nominal thickness of pipe permitted as per this standard shall be 6.4 mm for pipe size 4 inch nominal dia. and above, irrespective of the grade of the pipe material.
In all existing cases where thickness of pipe is less than 6.4 mm for pipe size 4 inch and above, Quantitative Risk Assessment shall be carried out and the risk level shall be reduced to ALARP (As low as reasonably possible). For both aboveground and underground pipe size less than 4 inch nominal dia., the minimum nominal thickness shall be as per ASME B36.10 M.
Pipelines or Mains on Bridges
- Pipeline on bridges should be avoided. Under unavoidable conditions, pipeline installed on railroad, vehicular, pedestrian, or other pipeline bridges, a design factor of 0.40 shall be used for Location Class 4.
- In cities where crossing the river through HDD crossing is not possible, pipeline laying on river bridges is permitted.
- Upstream dry gas filter(s) shall be installed when rotary or turbine meters are used.
Pressure / Flow Control Facilities
Protection against over pressure of pipeline or mains downstream of city gate station (CGS) shall be provided as follows:
- The provision of Active / Monitor Regulator System (i.e. monitor regulator in series with a controlling (active) regulator) shall be the principal method of controlling pressure.
[Note: To avoid problems associated with a regulator being at rest for prolonged periods it is recommended that the monitor regulator is so impulsed that it can also operate as a first stage regulator.]
- Adequately sized pressure relief valve(s) could be used for overpressure protection downstream of controlling regulator(s) provided Quantitative Risk Assessment is made for environmental hazards (fire / explosions) associated with large release of gas volume of gas release and the risks are found within acceptable level.
- Pressure relief valve(s) should be carefully sized to meet their required duty and to minimize the volume of gas released. The speed of relief valve opening should be adequate and they should re-seat cleanly when normal pressures are restored. The relief valve should be installed and provided with test connections in the impulse pipe work in such a way as to enable them to be set up and tested in-situ.
- Over pressure of shut-off valve(s) or Slam-Shut Valve(s) upstream of the controlling regulators are preferred as overpressure protective devices instead of pressure relief valves. Being ultimate overpressure protection for the pipeline system, it is essential that the Slam-Shut valves are fast closing, highly reliable and secure valve.
- The isolation valve of the sensing lines of regulators and slam shut valves should have provision for locking in open position.
- Additionally suitable gas heaters upstream of regulators / control valves/ pressure reduction system should be provided in case after pressure let down operating conditions would result in low temperatures beyond design conditions of downstream facilities.
- Sound pressure levels shall be limited to the values prescribed by Environmental Authorities but in no case it shall exceed 110dbA.
- Gas velocities in piping up to 20 m/sec before filter and 40 m/sec (120 ft / sec) after filter, at peak flow conditions, may be permitted provided care is taken to ensure that allowable sound pressure values are not exceeded and materials selected are suitable to prevent erosion at such high velocities. However, the gas velocity shall not cross the recommended velocity given by the Original Equipment Manufacturer for the equipment used in the PRI.
- Gas filtration facilities with 100% redundancy shall be provided to avoid damage to instrumentation and other facilities
- Immediately downstream of regulators or control valves, use of conical reducers is recommended.
- In order to prevent over pressurization of piping downstream of regulators / control valves, creep relief valve should be provided, if required.
- For isolation of the CGS during emergency, quick closing valve (with remote operation facility in case of unmanned station) shall be installed at the inlet of CGS.
Protection of pipelines and mains from hazards
- When steel pipelines or mains are installed in areas that are normally under water, anti-buoyancy measures adopted shall be such that specific gravity of resulting installation is 1.10 or more.
- Pipelines and mains installed on bridges and other locations where they are exposed to accidental damages due to vehicular traffic, suitable barricades / crash guards shall be installed for their protection.
- The pipeline in close proximity to unstable structures, landfill sites or where construction could lead to damage to pipeline, should be avoided.
- Pipelines and mains installed in the areas normally under water or subject to flooding (i.e. lakes, bays, or swamps etc.) shall be provided with addition anti-buoyancy measures such as concrete weight coating, geo-textile bags filled with graded stones or anchorages, etc. to prevent floatation. Minimum specific gravity of installation shall be 1.2 after providing anti-buoyancy measures.
Cover, Clearance and Casing Requirements for Buried Steel Pipelines and Mains
Minimum depth of cover for buried steel pipelines shall be as per the table given below;
|Location||Min. Cover (m)|
|Normal / rocky terrain||1.0|
|Minor river / unlined canal / nala crossings,|
tidal areas and other watercourses
|Major river crossings||2.5|
|Rivers with rocky bed||1.5|
|Lined canals / drains / nalas etc.||1.5|
|Drainage ditches at roadways and railroads||1.0|
|Cased / uncased road crossing||1.2|
|Cased railroad crossings||1.7|
- Cover shall be measured from the top of coated pipe to the top of the undisturbed surface of soil or the top of graded working strip, whichever is lower. The fill material in the working strip shall not be considered in the depth of cover.
- For river / watercourses that are prone to scour and / or erosion, the specified cover shall be measured from the expected lowest bed profile after scouring / erosion. Where scour level cannot be established, an additional cover of minimum 1 meter shall be provided from the existing bed of the river/water course.
- The cover shall be measured from the top of road or top of rail, as the case may be.
- Whenever the above provisions of cover cannot be provided due to site constraints, additional protection in form of casing/ concreting etc. shall be provided.
Clearance between Pipelines or Mains and other underground structures
- When a buried steel pipeline or main has to cross any existing underground pipeline, cable, drain or other services, the pipeline shall be laid at least 300 mm below from such services.
- When laid parallel to any existing underground cable, drain or other utilities, the pipeline or main shall be laid with a clear distance of at least 300 mm from existing utility.
- As far as practical, a minimum separation of three (3) meter should be maintained between the steel pipeline or main and footing of transmission tower.
- A clearance sufficiently large to avoid electrical fault current interference shall be maintained between the pipeline and the grounding facilities of electrical transmission lines.
- Clear distance between new steel pipeline or main running parallel to existing pipeline should be minimum 5.0 meters when heavy conventional construction equipment is expected to be utilized. This distance may be reduced, after careful assessment of construction methodologies, to three (3)meters, provided it does not result in unsafe conditions during construction. Existing pipeline should be clearly marked on the ground during construction. Bi-language (local language and Hindi / English) caution signs should be installed while working in such areas.
- While laying more than one new hydrocarbon pipelines or mains in the same trench, clear separation of minimum 500 mm shall be maintained between adjacent pipelines.
- No steel pipeline or main should be located within three (3) meters of any habitable dwelling or any industrial building unless it is provided with at least 300 mm of cover over and above minimum cover specified under Table above or special protective measures such as concrete slab, steel casing are provided.
Casing Requirements under Railroads, Highways, Roads or Streets
Steel casing at road/railway crossings, when provided to meet statutory requirements, shall be designed in accordance with API 1102. Casing pipe diameter shall be minimum two pipe sizes bigger than carrier pipe. In case of PE, the casing can be RCC pipe of min NP3 class.
Bends, Elbows and Miters in Steel Pipelines and Mains
- Miters bends and wrinkle bends are not permitted in pipelines and mains used in CGD networks regardless of operating hoop stress.
- Cold field bend radius for pipes of size NPS 20 and larger shall be minimum 40 times the pipe diameter.
- As far as possible use of short radius elbows should be avoided.
- Split tees designed to fully encircle the pipe shall be used for making hot taps. The split Tees shall be designed considering a minimum design factor F = 0.40.
- However, in case of Hot taps of size upto 1/4th of the nominal bore of the main pipeline, use of weldolets is permitted in place of split tees.
- Full bore ball valve shall be used when making branch connections using hot taps.
- Recommendations as per API RP 2201– Recommended Practice for Safe Hot Tapping Practices in the Petroleum and Petrochemicals Industry shall be followed while carrying out hot tapping works.
- Where it is not possible to maintain the clearances, cover, vent locations etc. mentioned in this standard, the entity shall carryout special design and construction methodologies through experienced personnel/consultant and seek clearance from the Board.
Testing after Construction
- Proper communication facilities shall also be arranged for during testing.
- Testing equipment / instruments shall be properly inspected and shall have valid calibration certificates before they are used for testing.
- Test Required to Prove Strength of Pipelines and Mains to operate at Hoop Stresses of 30% or more of Specified Minimum Yield Strength of Pipe.
- All buried steel pipelines and mains shall be pressure tested after installation using water as a test medium. Minimum test pressure shall be equal to 1.4 times Maximum Allowable Operating Pressure.
- Test procedure as per ASME B 31.8 Appendix N “Recommended Practice for Hydrostatic Testing of Pipelines in Place” shall be followed.
- Hold-up time for the pressure testing shall be minimum 24 hours for underground and four hour aboveground pipeline.
Safety During Tests
- Relevant Warning Signs shall be displayed at the test area.
- The test area shall be properly cordoned to prevent any accidents.
- A proper Emergency Response Plan shall be in place and emergency contact numbers of relevant agencies should be visible
Commissioning of Facilities
- Appropriate Work Permit should be issued based on the kind of activity.
- Fire fighting equipment should be available during commissioning.
- Proper communication facilities should also be arranged for.
- A proper Emergency Response Plan should be in place and emergency contact number of relevant agencies should be available.
Ductile Iron Piping System Requirements
Use of ductile iron piping is not permitted for CGD networks as per this standard.
Design of Plastic Piping
Plastic pipe shall not be used for Pipeline and Distribution Mains operating at pressure in excess of 100 psig.
Use of thermosetting plastic piping is not permitted as per this standard.
Plastic Pipe and Tubing Design Formula
[The design pressure for plastic gas piping systems or the nominal wall thickness for a given design pressure shall be determined by the following formula:]
P = 2S * (t / (D-t)) * 0.32
D = Specified outside diameter in mm
P = Design pressure in psig
t = Nominal wall thickness in mm
S = Long term hydrostatic strength in barg (psig) determined in accordance with applicable pipe specification at temperature equal to 73°F, 100°F or 120°F.
The design pressure shall not exceed 100 psig (7 bar).
Thermoplastic pipe, tubing and fittings shall not be used where operating temperature of the materials will be:
1) Below 32°F (0 degree centigrade) or
2) Above 120°F (50 degree centigrade) or temperature at which long term hydrostatic strength used in design formula in para 842.31 of ASME B 31.8 is determined, (whichever is lower).
Minimum thickness shall not be less than 2.3 mm.
Pipe wall thickness selected shall be such that it corresponds to Standard Dimension Ratio indicated in Table below. Pipes with non standard SDR should not be used.
Design Pressure of Plastic Fitting
- All fittings used shall be electro fusion type. Other types of fittings are not permitted.
- All PE fittings shall conform to ISO 4437 Part 3 or EN 1555 Part 3.
- The wall thickness of the fittings shall be more or equal to the wall thickness of the pipe jointed.
Plastic Pipe and Tubing Joints and Connections
- Threaded joints in plastic pipe are not permitted.
- Plastic piping joints shall be made by Electro Fusion fittings only.
- Jointing of plastic piping by butt fusion method, solvent cement method, adhesive method, heat fusion method or by means of compression couplings or flanges is not permitted.
- Recommendations of the fitting manufacturer shall be followed in this regard.
- All electro fusion fittings shall be bar coded and the control unit shall be equipped with bar code reader to directly transfer fusion data to control unit. Bar coding shall be long lasting even when the joint is buried in corrosive soil, alternatively each fitting shall have a data card which can be read by the computer and thereafter the card is positioned with the joint.
Installation of Plastic Piping
- Use of thermoplastic piping in above ground piping is not permitted unless the piping is completely protected against deterioration (e.g. high temperature ultra violate degradation) by corrosion protected metallic or reinforced concrete or Glass Reinforced Plastic (GRP) enclosure.
- Directly buried thermoplastic pipe shall have a minimum thickness of 2.3mm.
- Trench width shall be at least 300 mm.
- The bed of the trench shall be free of sharp objects, stones etc.
- In rocky areas trench shall be padded with soft soil or sand to minimum depth of 150 mm below the pipe.
Bends and Branches
Branch connections shall be made only by socket type electro fusion tees or electro fused Saddle connections.
Use of special saddle or split tee type electro fusion fittings for hot tapping is permitted.
Testing Plastic Piping after Construction
Testing equipment / instruments shall be properly inspected and shall have valid calibration certificates before they are used for testing. Proper communication facilities shall be available during testing.
- Thermoplastic piping shall not be tested at material temperature above 120°F (50 degree centigrade).
- Test medium shall be air or nitrogen for test pressure up to 100 psig. For test pressure higher than 100 psig, water shall be used as test medium.
- Test duration shall be minimum 24 hours for plastic distribution mains of length greater than 1 km and minimum 4 hours for length shorter than 1 km.
- In case water is used as test medium, test duration shall start after achieving thermal stabilization.
- Suitable relief valve set at 5% higher than test pressure shall be fitted at the test heads to avoid over pressurization during testing.
Test Requirements for DPRS and IPRS Piping
DPRS and IPRS piping shall be subjected to strength test and leak test, before commissioning, as given in table below:
Acceptance criteria shall be no pressure loss after accounting for temperature variation.
Safety During Testing
- Relevant Warning Signs shall be displayed along the test section.
- The test area should be properly cordoned to prevent any accidents.
- A proper Emergency Response Plan shall be in place and emergency contact numbers of relevant agencies should be available.
CONTROL AND LIMITING OF GAS PRESSURE
Control and Limiting of Gas Pressure in High Pressure Steel or PE Distribution System :
- Use of automatic shut-off device (slam shut valves) as a means of accidental over- pressure of high pressure distribution system is preferred over pressure relief valves or weight-loaded relief valves or spring loaded diaphragm type relief valve.
- DPRS/IPRS shall normally be equipped with minimum two safety devices. At least one of them shall be a slam shut valve operating on over pressure for those installations whose inlet operating pressure is more than 60 psig.
- To prevent over pressurization of downstream system during periods of low flow, creep relief valve can be used.
- If a monitor regulator is installed in the system, it shall be such that it is the first acting device in the pressure safety system.
Control and Limiting of Gas Pressure in low Pressure Distribution Systems
- A combined Over Pressure Shut-Off (OPSO) regulator with built-in creep relief is also acceptable device for control and limiting of gas pressure in low pressure distribution system.
- Service regulator with a built-in Under Pressure Shut-Off (UPSO) regulator is also acceptable device for control and limiting of gas pressure to consumer.
- As far as practical, the valves in the distribution mains should be installed below ground with the valve operating device readily accessible.
- A stem extension may be used to elevate the valve operator above ground provided it does not cause obstruction to traffic and / or
pedestrians. In such cases, sealant / lubrication points and vent pipe work shall also be extended above ground for ease of operation.
- Valves of size 4 inches and above shall be fitted with double block and bleed facility.
- Spacing between valves on distribution mains, whether for operating or emergency purpose shall be decided as follows:
(a) High Pressure Distribution System:
Based on operation and maintenance flexibility requirements, valves may be provided on:
- Either side of water body crossings.
- Strategic take-off points including future developments.
Based on risk associated with emergency situations requiring speedy isolation and resulting number and type of customers affected by such emergencies etc.
- In steel distribution mains valve spacing should normally not be more than 3 km.
- In plastic distribution mains valve spacing should normally not be more than 1 km.
- The above spacing, however, may be increased or decreased based on risk assessment and to allow location of valve at an easily accessible location.
(b) Low Pressure Distribution System:
Valves in low pressure distribution system may be provided at locations requiring isolation for ease of maintenance in addition to those required as per following Para.
Distribution System Valves
A valve shall be installed on the inlet and outlet piping of each regulator station controlling flow or pressure of gas in distribution system. The distance between the valve and regulator(s) shall be adequate to allow operation of the valve during emergency (such as large leakage or fire). These valves should be located in a manner that they are easily accessible during emergency.
Accessibility : In case part of Vault or Pit extends above ground (e.g. to avoid water flooding in low lying areas that cannot be avoided), then, it shall be located such that it causes minimum interference / hindrance to the traffic / pedestrians.
CUSTOMERS’ METERS AND REGULATORS
Location for Customers’ and Regulator Installations: Customer meter shall preferably be located on the wall outside the kitchen, however, when customers’ meters and regulators are located inside the building, it should be located in a well ventilated area.
GAS SERVICE LINES
General Provisions Applicable to Steel, Copper and Plastic Service Lines:
Service lines shall be sized for a maximum flow velocity of 15 m / sec.
Installation of Service Lines
- All plastic pipe and fittings shall be laid underground and shall not be exposed.
- The buried service lines shall be provided with a minimum cover of 1.0 m.
- Where it is impractical to provide 1.0 m cover due to physical constraints, additional protective measures such as concrete slabs or high impact resistance plastic sheets shall be installed at least 300 mm above the service line.
- In no case the depth of cover shall be less than 600mm.
- For transition from plastic pipe to GI pipe, transition fittings shall be used. Plastic part of transition fitting protruding above ground shall be protected by encasing it with concrete guard.
- In case carbon steel section beyond transition fitting is below ground, it shall be protected against corrosion by minimum 400 micron thick 2 pack high build epoxy coating.
- Above ground service piping shall be Galvanized Iron or copper or carbon steel protected by anti-corrosive coating.
- Wherever the service line riser is installed in confined spaces like basements, only welded risers shall be used. The gap between riser and wall shall be minimum 25 mm to and shall be supported at every 2 m. Ventilators shall be provided in confined space.
The depth of cover can be further reduced upto 375 mm provided it meets the following requirements:
i. The line pressure shall not exceed 110 mbar.
ii. The diameter of pipe shall not exceed 63mm.
iii. Pipe shall be laid in a trench with Reinforced Cement Concrete (RCC) slab at the top and bottom. The RCC slab of the roof of basement shall be treated as the bottom.
iv. There shall be a sand filling across three sides of the line pipe of 100 mm each.
v. RCC on top shall have minimum thickness of 150mm.
vi. The top side shall be covered by warning mat.
vii. The Quantitative Risk Assessment (QRA) of the site shall be carried out and specific approval from management shall be taken for reducing the depth of cover upto 375 mm.
viii. The site shall be private property i.e. multi-storey buildings / apartments with no movement of heavy vehicles.
Usage of PE pipes to construct above-ground risers is permitted, subject to meeting the following requirements, namely: –
(a) PE pipe employed shall conform to the requirements specified at Annexure 1 of T4S regulations;
(b) The PE pipe shall be used starting from a height of 3 metres from the ground level, up to which GI pipe shall be used ;
(c) The PE pipe shall be entirely protected from exposure to sunlight and any damage due to external impact;
(d) The fittings employed and the jointing method for the PE riser system shall conform to the requirements of GIS / PL3: 2006 standard.
Type of Valves Suitable for Service Line
Valves: Soft seated valves in service lines are not permitted.
Steel Service Lines
Design of Steel Service Lines: All underground steel service lines shall be joined by welding using qualified welding procedure and welders.
Installation of Service Lines into or Under Building
Use of sleeve for laying steel pipe through wall, or under outer wall foundations of building or under the building is not recommended. Such underground lines shall be protected against corrosion by minimum 400 micron thick 2 pack high build epoxy coating.
Ductile Iron Service Lines
Use of ductile iron service lines is not permitted.
Plastic Service Lines
Design of Plastic Service Lines: Only electro fusion fittings shall be used in plastic service piping including pipe to pipe joints.
Installation of Plastic Service Lines
Installation of plastic pipe above ground is not recommended. In case any section of plastic pipe extends above ground, it shall be completely encased in a concrete casing. Use of flexible conduit is not permitted.
Installation of Plastic Service Lines into or Under Buildings
Installation of plastic service lines under or inside the building is not permitted as per this standard.
Service Line Connections to Mains Service Lines Connections to Steel Mains
Service line connection to steel mains shall be as follows:
- In case of plastic service line, connection to underground steel main shall be by use of transition fitting in plastic piping with steel part of transition fitting welded to steel main piping.
- Direct connection of galvanized iron or copper service lines to underground steel mains is not permitted.
Service Lines Connections to Plastic Mains
- In case of plastic service line, connection to plastic main shall by use of electro fusion fittings only.
- Direct connection of galvanized iron or copper service lines to underground plastic mains is not permitted.
PIPING BEYOND CONSUMER METER SET ASSEMBLY TO GAS APPLIANCE
- Piping connecting consumer meter set assembly to consumer gas appliance shall be either GI or copper up to last valve located near actual appliance.
- A metal seated leak detection cum excess flow shut off valve shall be provided near the appliance located at easily accessible location by the authorized entity.
- The valve shall be designed to shut off in case of sudden leakage of gas from the hose or in case of burner flame-off condition.
- Appliance shall be connected to gas line with a flexible and braided hose as per IS 9573.
- The hose shall not be exposed to internal or external temperature exceeding the recommended limits. Care shall be exercised not to exceed permissible bend radius specified in IS: 9573
- Length of this hose shall be kept minimum. However, in no case the length shall be more than 1.5 meters. Both ends of the hose shall be firmly clamped on the nozzle by metallic clamps.