Natural gas is a highly inflammable substance that is transported through city gas distribution (CGD) pipelines at a high pressure. These pipelines often pass through areas having a high population density, which poses a challenge for operators in carrying out routine operations and maintenance of the pipelines. Inspections at regular intervals and adoption of safety measures are necessary to avoid uncalled-for accidents arising out of gas leakages and causing fire or eruptions, besides other external damages. Several precautionary measures such as polyethylene external coating, intermediate pipeline inspection, and cathodic protection against galvanic corrosion of underground pipelines need to be taken in the concerned areas. Besides, an emergency response plan must be prepared to systematically deal with any disaster.
Challenges in maintaining CGD networks
A CGD network is a complex system of pipelines which makes it difficult for operators to maintain them. Constant corrosion and external damages hamper their operational efficiency, which calls for their regular maintenance. However, upkeep of the pipelines becomes difficult due to several reasons. For instance, major damages to the pipeline are caused by third parties either during the course of work or intentionally. Other problems such as difficulty in tracing a damaged pipeline, excavations for road widening works, unauthorised modification of pipelines by the customers and delayed response from operators for repairing further deteriorate their condition. As a result, the gas pipelines become prone to major or minor hazards. These hazards can be in the form of fire accidents and gas leakages, eventually resulting in the loss of life and property. In order to ensure safety, measures have to be taken by the CGD operators.
Precautionary measures or operational preparedness
As various challenges are involved in maintaining the CDG network, proactive measures are necessary to avert an accident. Continuous inspections, risk assessments and mitigation activities are some of the steps which can be taken to avoid mishaps. The following precautionary measures will minimise the impact of an accident on both residents and the environment.
- Ensuring safety of the pipeline at the time of designing the pipeline network. To this end, several techniques can be deployed. For instance, a three-layer polyethylene external coating to the pipeline can help protect against external corrosion.
- Current cathodic protection can be used to prevent the pipeline from electrochemical reactions or electrolysis and galvanic corrosion.
- For carrying out regular inspections, a pipeline inspection gauge can be installed at intermediate distances of the pipeline. Besides, deployments of a slug catcher at compressor stations can help collect the impurities, if any.
- As gases are moving at a high pressure inside pipelines, this can also pose problems. Pressure safety valves and isolation valves can be installed at intermediate pumping stations to monitor excess pressure. In case of any fault in a particular pipeline, isolation valves can be closed, thereby saving the other pipelines from damages.
- Deployment of safety equipment such as automatic fire detection and suitable fire extinguishing systems at compressor stations, intermediate pigging stations, sectional valve stations, gas entry/exit terminals and metering stations will mitigate the effects of a sudden fire.
- At the customer-end terminal, provision of supervisory control and data acquisition (SCADA) has to be ensured for effective and reliable control and management of the gas flow.
Emergency response system
Despite the in-built safety features of the CGD network, the possibility of accidents remains. To efficiently minimise its effect and resulting losses, an emergency preparedness and response system is required. This system aims at ensuring that the gas operator has enough capability, competence and capacity to safely respond to incidents, thereby protecting people, environment and property. This system essentially involves preparation of an emergency response and disaster management plan as per the guidelines of the Petroleum and Natural Gas Regulatory Board.
For risk identification and analysis of the likely cause of disaster, a pre-emergency plan has to be prepared.
Emergency mitigation plan
An emergency mitigation plan essentially involves laying out site plans and deployment of safety management systems. A site plan indicating boundary walls, an entry-exit gate, layout of fire water systems and fire fighting equipment details will immensely help in taking mitigation steps. Besides, a database of internal and external emergency contact numbers and addresses has to be created.
In order to be prepared to deal with a disaster, operators can carry out drills and awareness drives.
Emergency response plans
Plans for responding to an emergency can be executed by liaising with institutions such as hospitals and the fire department, and assigning individual responsibilities. Besides, required infrastructure has to be created. This includes:
- Round-the-clock availability of fully equipped emergency vans with a minimum response time at strategic locations.
- Development of an emergency control room with the facility of a toll-free number with several telephone lines working at one time.
- Provision of man force to carry out patrolling of the pipeline network at least twice a day.
- Deputation of excavation supervisors on major excavation sites to avoid damages to the pipelines.
- Liaising with district officials, and networking with local residents, security guards of buildings and nearby shopkeepers to act promptly in case of a minor leakage.
- Tie-ups with medical emergency services are also required.
Emergency recovery plan
Not only dealing with an accident, but also bearing the after-effects is required. It involves informing statutory authorities, which can then investigate the cause of the accident. Besides, recovery measures can be taken.
The way forward
Although several steps have been taken, hazardous incidents persist, leading to huge losses. Going forward, to eliminate any chance of accidents, a robust legal framework has to be created. The regulations for the Emergency Response and Disaster Management Plan were formulated in 2010, and there is a need to bring in amendments and new policies. International standards like the Oil Industry Safety Directorate, the ASME code and standards for piping and fitting, need to be followed during the design, construction, and operations and maintenance phases. Sizing of the pipeline wall thickness according to the population density of the area and setting up a minimum standard for corrosion allowance of design wall thickness will significantly improve pipeline life.
Information technology-based solutions can also be used by operators to monitor pipelines. For instance, gas management centres for tracking pipeline leakages on a real-time basis using geospatial information have to be developed. A similar initiative has already been taken by GAIL (India) Limited. It has developed a regional gas management centre at Kalamassery in Kerala to monitor the gas flow parameters of the entire gas pipeline network. In case of a leak in the pipeline, an alarm is generated in the monitoring system. The pipeline section is isolated immediately by closing the sectional valve or intermittent pigging stations on the related pipeline section. Other operators can work on similar lines.
Operators are apprehensive about using upgraded technology solutions such as SCADA systems due to the lack of a skilled workforce. Training has to be imparted and awareness created. Deploying such equipment will help increase efficiency and minimise the response time during an emergency situation.