The country’s city gas distribution (CGD) network has expanded manyfold over the years. At present, 31 CGD entities are operating CGD networks in 83 cities. Unlike cross-country pipelines, which run straight for kilometres through open fields, CGD networks are more complex in nature. Further, the pipelines have to pass through congested areas within the city crossing other underground utilities. Due to various activities by third parties within the city area, the risk of damages and accidents is high as compared to cross-country pipelines. All these factors call for sophisticated inbuilt safety systems in the network and special preparedness to handle emergency situations.
Genesis of hazard
The main risk associated with gas supply is leakage or rupture of pipeline, resulting in uncontrolled gas release. Gas leaks can prove to be hazardous if mishandled or not properly disposed of. The possible causes of gas leakage are as follows: Pipeline damage due to construction/material failure, corrosion, mechanical damage, etc; flange leakage due to material failure, wrong gasket (on customer’s premises only); valve leak due to stem seal failure, assembly failure, etc; and Enemy action/Sabotage/Natural calamities such as earthquake and flood.
In a typical CGD network, the main underground lines are optical fibre cable, telephones cables, power cables, sewer and water lines. The main risk to the pipeline integrity is from damage caused by third parties. There are several reasons behind possible safety slippages in CGD networks. At the design and construction phase, factors such as non-compliance of standards and procedures, compromise on network integrity, use of poor quality material, and poor quality checks during construction have been identified as some of the causes of pipeline leakage. Meanwhile, patrolling slippages, poor reach and upkeep, compromise on health surveys, and insufficient skilled workers are a few challenges faced by CGD entities at the pipeline operations and maintenance stage.
Safety practices and mitigation
In order to prevent pipeline leakage and subsequent hazards, pipeline distribution networks must have the required inbuilt safety systems to ensure safe operations. It is important to adopt three-tier safety measures, that is, in design, construction and operations. Some of the other efforts for mitigating pipeline-related hazards are: hazard identification and risk analysis; playing of radio jingles and distribution of pamphlets; display of signboards at compressed natural gas stations; having an emergency response disaster management plan in place; use of mobile training van for on-site awareness; metal plate/registration certificate checking at CNG stations and data creation; implementation of geographic information system; implementation of integrity management system; remote monitoring through CCTV
According to the Natural Gas Pipeline Vision 2030, it is envisaged that the share of natural gas in the primary energy mix will reach 20 per cent by 2030. Further, natural gas demand for the CGD sector is expected to rise due to the addition of gas networks in new cities, price advantage of CNG and increased use of piped natural gas in the domestic, industrial and commercial sectors. Environmental concerns will further boost the use of natural gas, especially in the automotive and industrial segments. Therefore, continuous monitoring and maintenance of existing and new pipelines has become a necessity for ensuring uninterrupted supply of natural gas to consumers and CGD pipeline integrity.
Based on a presentation by Milind Narharshettiwar, Chief General Manager, Maharashtra Natural Gas Limited, during ISGW 2018