Fri. Sep 24th, 2021

City gas distribution

Transporting future fuel

#21 T4S – Technical Standards & Specifications including safety standards for city or local natural gas distribution networks

12 min read

PNGRB has notified regulations covering the pipeline transportation of natural gas and CGD.

Intent of the T4S regulation:

(a) It is intended to apply these regulations to all new and such aspects of already existing networks as design, fabrication, installation, testing at the time of construction and commissioning. However, if an entity has laid, built, constructed or expanded the CGD infrastructure based on some other standard or is not meeting the standards specified in these regulations, the entity needs to carry out a detailed technical audit of its infrastructure through a Board authorized or approved third party agency by the Board. The entity thereafter shall submit the recommendations made by the third party along-with its time-based mitigation plan and implementation schedule to the Board for authorization within six months from the date of notification of these regulations.

(b) The continuation of operation of existing CGD network shall be allowed only if it meets the following requirements, namely:-

  1. The CGD system downstream of the city gate station shall have been tested initially at the time of commissioning in accordance with ASME B 31.8 Chapter IV (with a minimum test pressure of 1.4 times of MAOP for steel network and 1.4 time MAOP or 50 PSI whichever is higher for PE network). The entity should have proper records of the same. Such a test record shall have been valid for the current operation. Alternatively, if such a record is not available, the entity should produce an in-service test record of the CGD network having tested at a pressure of 1.1 times of MAOP as per ASME B 31.8;
  2. The CGD system has a leak detection system in position and is operative. For pipeline network it shall be odorisation based and for enclosures such as CGS, above ground DPRS, it shall be gas leak detection based.
  3. The CGD system has in position necessary pressure relief valves; and
  4. There shall be the protection of the system against third party damages both in respect to steel pipe, PE pipe, and copper tubing. Provided that-

(a) The entity shall submit self-certification in support of meeting the above requirements within a month of notification of these regulations and in addition the certification by the approved or authorized the third party shall be made available to the Board within six months of notification;

(b) Certifications referred to in para (a) shall be done both for operation and maintenance and infrastructure of the entity and shall be submitted to the Board with mitigation plan and implementation schedule;

(c) The critical components of the system as identified by the Board for such existing networks shall comply with these regulations within a period specified at Appendix-I and the authorized entity shall maintain the integrity of the existing system at all times; and

(d) Provisions of these regulations related to operation and maintenance procedures shall also be applicable to all such existing installations.


(a) These regulations cover the design, materials, fabrication, installation, inspection and testing, commissioning, operation, maintenance, modifications, and abandonment of CGD network for domestic, commercial, and industrial users.
(b) Requirements of these regulations shall apply to all pipelines, distribution mains, and piping facilities downstream of the inlet isolation valve of city gate station (CGS) up to and including consumer meter for the commercial or industrial customer and up to final isolation valve including connecting hose to gas appliance for the domestic consumer.
(c) Design, materials, fabrication, installation, inspection and testing, commissioning, operation, maintenance, modifications, and abandonment of steel pipeline between city gate station and natural gas pipeline (sub-transmission pipeline) shall be as per separate regulations.
(d) The CNG Station, CNG Mother Station, CNG On-Line Station and CNG Daughter Station shall be designed, operated, and maintained in line with the requirements of the Chief Controller of Explosives as detailed in the Gas Cylinder Rules, 2004 as modified or amended from time to time. This includes compression, handling, and transportation activities of compressed natural gas.
(e) These regulations also cover safety aspects of operation and maintenance of CGD network and the requirements covered herein these regulations are meant to supplement the safety requirements already covered under ASME B 31.8.

Technical standards and specifications including safety standards for city or local natural gas distribution networks are as specified in Schedule-I which cover material and equipment (Schedule-1A), welding (Schedule-1B), piping system components and fabrication (Schedule- 1C), design, installation and testing (Schedule-1D), operating and maintenance procedures (Schedule-1E), corrosion control (Schedule-1F) and miscellaneous (Schedule-1G).

In case of default & consequences:

(1) There shall be a system for ensuring compliance to the provision of these regulations through the conduct of technical and safety audits during the construction, commissioning and operation phase, as well as on an on-going basis as may be specified from time to time.
(2) The Board shall monitor the compliance to Technical Standards and Specifications including Safety Standards either directly or by an accredited third party through separate regulations on third-party conformity assessment.
(3) In case of any deviation or shortfall, in achieving the targets for implementing the specified standards, the entities shall be liable to face the following consequences, namely:-
(i) in case of critical activities at Appendix-I, the entity shall be given a single notice by the Board specifying the time limit to remove the specified shortcoming and ensure compliance and if the entity fails to comply within the specified time limit, immediate suspension or termination, as deemed appropriate, of authorization shall be done;
(ii) in other cases, the Board may issue a notice to defaulting entity allowing it a reasonable time to remove the specified shortcoming and ensure compliance and in case the entity fails to comply within the specified time or in case the entity defaults on more than three occasions, its authorization to lay, built, operate or expand the CGD network shall be liable for suspension or termination apart from taking legal action under the provision of the Act and regulations thereunder.

As stated above the T4S regulations specify the standards in the form of Schedules (Schedule 1A to 1G) which are dedicated to a different aspects of the design construction and safety of CGD.

Schedule – 1BWELDING;

Schedule 1A covers material and equipment covering the specification of the material used for CGD in normal high & cold climates. This schedule also specifies the standards for various materials used for CGD.

Schedule 1B specifies welding used for CGD covering qualification and procedure qualification for welders, welding process, inspection for welds. This schedule also specifies the standards for various welding materials and processes used for CGD.

Schedule 1C specifies the piping system component and fabrication details covering valves, pressure reducing devices, flanges and other fittings of PE including bolting and special fittings. This schedule also specifies the standards for various material used for piping system and component in CGD.

Schedule 1D specifies the design, installation, and testing of CGD. It also provides an understanding of the primary network, secondary network, and tertiary network. The primary network consists of a ring main or steel network, the secondary network is of MDPE with medium pressure up to 7 bar, and the tertiary network is low pressure up to 121 milli bar. This schedule also addresses various installation like CGS, DPRS, etc. Further, the schedule describes safety distance or distance between various facilities at CGS. The schedule further covers all facets of design for electrical instrumentation & control, steel pipe, metering facilities, etc. This schedule also specifies the standards for various materials, a system used for CGD, and class location for laying pipelines. It also takes a reference from ASME and other standards for tabulating the requirement of steel and PE network including SDR rating for PE pipe. For the ease of laying pipeline, this schedule also specifies the inter distances of the utilities buried in the same pit and also the protection by concrete slab or reinforcement for the pipelines covers.

Schedule 1E covers operating and maintenance procedures for CGD. In this schedule the issue like

i) Operating & maintenance procedure affecting the safety gas transmission and distribution facilities.

ii) External corrosion control

iii) Odorization

The schedule further emphasizes on GIS-based assets management system and development of emergency plan & procedure. The provision of markers, patrolling and leakage surveys are also described in the schedule. This schedule also provides requirements for abandoning, disconnecting, and reinstalling distribution facilities. To ensure quick & safe containment of gas within the distribution network, the procedure for squeezing-off MDPE pipe, repair of plastic pipe & tubing has also been provided in the schedule. For any incident, a reporting procedure has been defined and annexed in the schedule.

Schedule 1F covers the corrosion control system for the CGD network. It is important to note that the corrosion control in CGD is more different than that of the transmission pipeline because of fast-changing resistivity of the soil in CGD and crossing of several utilities including high tension electrical cables by the transmission mains. This schedule also specifies the standards for various materials used for corrosion control including its thickness for coating used in CGD.

Schedule 1G covers miscellaneous provision such as odorization, personnel protection system etc. This schedule also specifies the standards for various materials & system used in CGD such as gas transmission & distribution piping – ASME B31.8, welding procedure – API 1104, Valves – ASTM A-395, BS EN 331 etc.

Another provision in the T4S Regulations are provided as Annexure which gives specific information pertaining to important areas of CGD project:

a) Annexure-I gives the list of specifications of piping material used in CGD network covering steel pipe, GI pipe, copper tubing, plastic pipes, plastic fittings, SS tubing, brace valves, etc.

b) Annexure-II provides a list of specifications for equipment used in CGD networks such as pressure safety valve, filters, metering equipment, pressure measuring equipment, electro fusion machines, etc.

c) Annexure – III provides additional requirements for electric welded pipe such as the reverse bend tests, minimum requirements for GI pipe, and tubing for CGD. It is also advisable that a ready handbook is produced by the entity to draw the attention of all employees, contact persons and the visitors about do & don’t for safety & security.

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