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#79 Determining Capacity of City or Local Natural Gas Distribution Network as per PNGRB Regulation, 2015

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PNGRB has issued a notice of regulation namely ” Petroleum and Natural Gas Regulatory Board (Determining Capacity of City or Local Natural Gas Distribution Network) Regulation” on 19th May 2015.

Before understanding the regulation, we must know of the following points;

  • These regulations may be called the Petroleum and Natural Gas Regulatory Board (Determining Capacity of City or Local Natural Gas Distribution Network) Regulations, 2015.
  • Act” means the Petroleum and Natural Gas Regulatory Board Act, 2006;
  • appointed day” means the date of October 1, 2007 when the Central Government notified the establishment of the Petroleum and Natural Gas Regulatory Board;
  • authorized area” means the area as defined under the Petroleum and Natural Gas Regulatory Board (Authorizing Entities to Lay, Build, Operate or Expand City or Local Natural Gas Distribution Networks) Regulations, 2008;
  • authorised entity” means an entity that is authorised to lay, build, operate or expand a city or local natural gas distribution network in a geographical area (GA) under the Act and the relevant regulations made thereunder;
  • Board” means the Petroleum and Natural Gas Regulatory Board
  • capacity assessment group” means a group comprising representatives of two authorised entities other than the entity of which the CGD network capacity is to be certified and a representative of the Board as decided by the Board on case to case basis or any agency or entity or authorized person or any approved third party authorized by the Board for determining the capacity of the CGD network;
  • CGD network capacity” means the maximum quantity in standard cubic meters per hour (SCMH) of natural gas that can be injected into or off taken from the steel pipeline network at specific points, meeting all the technical and operational parameters fixed in steel network at steady state conditions, that is, all parameters like flow, pressure, temperature, are in harmony and vary only along the steel network but not with time or the aggregate rated capacity (in SCMH) of all City Gate Stations (CGS) connected to steel network, whichever is lower. For cases, where any entry points (CGS/DPRS/custody metering systems) are connected directly to the medium density poly ethylene (MDPE) network without involvement of any steel network, the rated capacity of such entry points shall be considered;
  • CGD declared capacity” means the capacity (in SCMH) that the steel pipeline network is capable of distributing under the steady state operating conditions determined based on the approved flow equation and the selected software package or the aggregate rated capacity (in SCMH) of all City Gate Stations connected to steel network, whichever is lower. For cases, where any entry points (CGS/DPRS/custody metering systems) are connected directly to the MDPE network without involvement of any steel network, the rated capacity of such entry points shall also be declared;
  • city or local natural gas distribution network” means an inter-connected network of gas pipelines and the associated equipment used for transporting natural gas from a bulk supply high pressure transmission main to the medium pressure distribution grid and subsequently to the service pipes supplying natural gas to domestic, industrial or commercial premises and CNG stations situated in a specified geographical area.
  • CNG Station Capacity” shall be the maximum rated capacity of running compressors at respective stations or the maximum capacity determined at the inlet flange of the compressors whichever is lower;
  • domestic  consumer”  means  a  consumer  who  is  provided  PNG connection for the purpose of cooking or for other own domestic use and not for commercial use;
  • commercial consumer” means a consumer who is provided PNG connection for commercial purpose;
  • industrial  consumer” means an industrial establishment which is provided PNG connection within the authorized CGD network;
  • CNG consumer” means consumer who is supplied CNG for use as fuel for vehicle through CNG station.
  • operator” means an entity that operates CGD network with authorization of the Board;
  • selected software package” means the software package used by the entity for determination of capacity of the CGD network;
  • steady state condition” means calculation carried out based on time-invariant pressure, temperature and flow profiles throughout a steel pipeline network using specified boundary conditions and network element set points that are entered. In other words, the steady-state run calculates the hydraulic state of a network operating at equilibrium;
  • steel pipeline network” means the steel pipeline laid and commissioned originating from the source (primarily at tap-off point from any transportation / transmission /primary network or city gate station) up to the Distribution Pressure Regulating Station or District Regulating Station (DPRS or DRS), Metering and Regulating Station (MRS) and inlet flange of CNG compressor station;
  • third party contracted capacity” means the quantity (in SCMH) of natural gas contracted with any third party for transportation through a pipeline system;
  • These regulations shall apply to an entity which is laying, building, operating or expanding or which proposes to lay, build, operate or expand a city or local natural gas distribution network.
  • These regulations cover the procedure, parameters both constant and variable and frequency of declaration of CGD network capacity in SCMH for CGD network.
  • These regulations shall not be applicable to sub-transmission pipelines, MDPE network system downstream of DPRS/DRS and service lines, including GI/copper piping of CGD network.
  • It is intended to apply these regulations to all CGD networks for the purpose of declaration of CGD network capacity.
  • The capacity of the CGD network so determined shall be used for providing access to shipper on non-discriminatory basis under the Petroleum and Natural Gas Regulatory Board (Access Code for City or Local Natural Gas Distribution Networks) Regulations, 2011.

Note: The determination of capacity for the CGD network shall be based on selected software package and flow equation approved by the Board under these regulations. It is not necessary for the entities to buy and install any specific software package. The entities may continue to use or operate the system based on the previously installed software but shall have to determine the capacity of the system based on the flow equation approved by the Board in any of the selected software package for the purpose of these regulations. The entity while submitting the capacity of the CGD network to the Board, shall furnish a declaration that the capacity has been calculated using the approved flow equation. The entity shall also submit the detailed report of the capacity and indicate the software used for the purpose within ninety days of the notification of these regulations and thereafter as per the periodicity for determining capacity of CGD network defined in regulation 7.

The parameters for running the steady state simulation for determining the CGD network capacity shall be considered as given below, namely:-

  1. Constant Parameters
  2. Variable Parameters

Constant Parameters:

  1. Internal diameter (ID) – The internal diameter shall be determined by deducting twice the thickness from outer diameter of steel pipes used in the CGD network. Further, the internal diameter shall be determined based on weighted average of internal diameters based on different pipe thicknesses used in different sections in the pipeline system.
  2. Length – The actual length (for already installed pipeline) or proposed length (for yet to be installed pipeline) of the pipe in the pipeline system.
  3. Roughness – This is a fixed value for a pipe which determines the unevenness inside a pipe. Depending on the pipe material, the below given value for roughness factor shall be used;
Type of MaterialRoughness (micron)
Steel – New Pipe (up to ten years old)
– With internal coating10-15
– Without internal coating25-45
Steel–Old Pipe (more than ten years old)
– With internal coating15-20
– Without internal coating45-100
  1. For old pipelines already operating, roughness factor shall be determined by duly calibrating actual field data in the approved flow equation. These factors shall be assessed by the capacity assessment group. For new pipelines, roughness factor used shall be decided keeping in view the operating conditions and pipeline feature like bends, valves, or any other restrictions present in the system: Provided that the entity shall declare in advance the roughness factor considered for the pipes with relevant operating data to support the value chosen.

Efficiency factor

Steel Pipeline: Efficiency factor within the range of 0.85 to 1.0 shall be used. For old pipelines already operating, efficiency factor shall be determined by duly calibrating actual field data in the approved flow equation. These factors shall be assessed by the capacity assessment group. For new pipelines efficiency factor used shall be decided keeping in view the operating conditions and pipeline feature like bends, valves, life of pipeline or any other restrictions present in the system: Provided that the entity shall declare in advance the efficiency factor considered for the pipes with relevant operating data to support the value chosen giving complete analysis. The Board may direct the entity to improve upon such design.

Formula – For determination of flow rate and pressure drop in the pipeline, the following flow equation shall be used:

Type of NetworkName of Flow equation
Steel NetworkColebrook White / Fundamental pipe equation with flow dependent (Colebrook White) friction factor

Velocity – The maximum allowable velocity of the gas in the steel pipeline section of CGD network shall be 30 m/s.

Note: The steel pipeline network capacity shall be determined at maximum operating pressure (MOP) for the CGD network and with the following standard Pressure and Temperature conditions:
Standard pressure – 1.01325 bar (a).
Standard temperature – 15.56 degree Celsius

Variable Parameters

Operating temperature – For the purpose of determining the capacity and for annual capacity declaration to the Board, the summer temperature of 30 ºC shall be considered by all the entities.

  1. Inlet temperature – This is the actual inlet temperature (º C) of the gas from the source into the CGD network.
  2. Outlet temperature– This is the actual outlet temperature (º C) of the gas at the delivery point.
  3. Inlet pressure – The maximum pressure (in barg) that is available at the entry point to the CGD network and shall be declared by the CGD entity during capacity declaration.
  4. Outlet pressure – The minimum pressure (in barg) that is required by the consumer at the delivery or exit point as per access arrangement entered into by the shipper and the authorised entity.
  5. Maximum operating pressure (MOP) – This is the highest pressure (in barg) at which a CGD Network operates during normal operating cycle and shall be declared by the CGD entity for capacity determination. However, in case an entity is operating the CGD network at certain pressure which is at variance from above for more than or equal to five years, need to submit calculation carried in line with the Petroleum and Natural Gas Regulatory Board (Technical Standards and Specifications including Safety Standards for City or Local Natural Gas Distribution Networks) Regulations, 2008 and ASME B31.8 (Latest edition) supporting the revised MOP considered in determination of CGD network capacity. For the purpose of determining MOP, the Board shall be guided by incoming pressure at city gate station or custody transfer point.
  6. Minimum committed pressure (MCP) – This is the minimum pressure (in barg) at the exit points and shall be declared by the CGD entity during capacity declaration.
  7. Source supply flow – This is the maximum flow (in SCMH) that can be available from the source (primarily a Tap-off point from any Transportation / Transmission / Sub-Transmission Pipeline or City Gate Station).
  8. Delivery flow – This is the maximum flow (in SCMH) that is required by the consumers at the exit point as per access arrangement entered into by the shipper and the operator.
  9. Elevation difference – Depending on the terrain of the ground profile, this factor will be considered from the mean sea level of the area.
  10. Gas composition – The gas composition indicating all components totaling 100% by volume is to be given with the level of impurities as per the Petroleum and Natural Gas Regulatory Board (Access Code for City or Local Natural Gas Distribution Networks) Regulations, 2011. From this, necessary input to the flow equation shall be worked out. In case of more than one source, the weighted average composition of commingled natural gas beyond the second source of entry point shall be considered.
  11. In case of CGD network, the gas quality at exit point shall be as per the Petroleum and Natural Gas Regulatory Board (Access Code for City or Local Natural Gas Distribution Networks) Regulations, 2011.

All entities shall declare to the Board the constant parameters and the variable parameters for the CGD network –
(i) on first working day of October every year; and
(ii) whenever there is any addition or deletion of the supply source of natural gas.
The entities shall also provide on first working day of October the network diagram superimposed on the authorized area map for the CGD network.

The methodology for calculation of CGD network capacity shall be as under:

  1. The entire steel pipeline network shall be configured in the selected software package operating offline. The steady state condition of the pipeline hydraulics with variable parameters (pressure, temperature and flow) at entry that is downstream flange of City Gate Station and declared exit points shall be simulated in the selected software package.
  2. Assuming gas at the entry point (single source or multiple source of gas) is unlimited, the selected software shall be run till inlet flange of any industrial PRS, DRS and CNG Compressor connected to the system till it reaches limiting condition of pressure required at any exit point or limiting velocity in steel pipeline network as calculated by software or maximum flow capacity is reached at exit points.
  3. After satisfactory completion of simulation, add dummy load at the farthest exit points of steel network, considering the minimum committed pressure.
  4. Now, simulate the steel pipeline network till inlet flange of any industrial PRS, DRS, CNG Compressor and dummy load connected to the system reaches limiting condition of pressure required or limiting velocity in pipeline as calculated by software or maximum flow capacity is reached at exit points.
  5. The sum of flow (in SCMH) at each exit point (i.e. Inlet flanges of Industrial PRS, DRS and CNG compressor) and dummy load in all the charge areas is the total steel network capacity.
  6. The entity shall submit the details of maximum achievable steel network capacity so derived, under the steady state simulation with the details of variable and constant parameters, to the Board in the specified format at Schedule A along with the hydraulic gradient and system flow diagram for the steel network system. The entity shall submit the details of rated capacity of all entry points (CGS/DPRS/custody metering systems) including entry points, if any, connected directly to the MDPE network without any steel pipeline in between along with details of rated capacity of exit points like DRS/IPRS/CNG station etc. in Annexure-1.
  7. The capacity of CGD network shall be as per the operation days specified in the Petroleum and Natural Gas Regulatory Board (Access Code for City or Local Natural Gas Distribution Networks) Regulations, 2011 for respective system.
  8. If the aggregate CGS capacity is less than the determined steel network capacity, then, the aggregate CGS capacity shall be considered as the steel network capacity.
  9. The steel network capacity so determined shall be the CGD network capacity provided that if any entry point (CGS/DPRS/custody metering systems) is connected directly to the MDPE network without involvement of any steel network, the rated capacity of such entry point shall also be considered for the purpose of capacity declaration.

Declaring capacity of a City or Local Natural Gas Distribution Network by the Board.

  1. The Board, after having analyzed the report submitted by the entity regarding capacity of the CGD network with respect to the provisions of these regulations, shall decide-
    (i) to reject the capacity so determined and direct the entity to revise the capacity calculations based on the revised parameters; or
    (ii) to go ahead with the proposal with or without modification.
  2. The capacity so determined shall be declared by the Board as the capacity of the CGD network. The Board shall declare the capacity of the CGD network in the format specified at Schedule B of this regulation.
  3. The entity, after declaring the CGD network capacity by the Board, shall publish the same in line with the provisions of the relevant Regulations on the Petroleum and Natural Gas Regulatory Board (Access Code for City or Local Natural Gas Distribution Networks) Regulations, 2011, on their website.

Periodicity for determining capacity of city or local natural gas distribution networks.

  1. The capacity of a CGD network shall be determined on first working day of October every year or whenever there is a change in quantity of natural gas plus or minus 10% of previous declared capacity due to any of the following :
    (a) change in quality of gas,
    (b) modification, upgradation, addition or deletion of entry or exit points,
    (c) addition or deletion of loop lines, compressor etc.
  2. The entity shall submit the details of the so re-determined capacity of the pipeline to the Board in line with the provisions of these regulations for the purpose of declaration of capacity.

Note: If any dispute arises with regard to the interpretation of any of the provisions of these regulations, the decision of the Board shall be final. The Board may, either suo moto or on a complaint, refers the issue of determination of the capacity of a CGD network, to any external consultant or expert. Cost in this regard shall be borne by the entity or the complainant or as deemed fit by the Board on a case specific basis. However, the recommendation of the consultant or expert shall be advisory in nature to the Board and shall not be binding. The Board may validate the computed capacity with actual capacity as per the flow regime of the pipeline with actual flow conditions as and when desired.

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