Pipeline integrity management (PIM) involves ensuring safe, reliable, spill-free and incident-free operation of natural gas pipelines. To ensure the integrity of pipelines, a city gas distribution (CGD) operator must constantly assess the risks that are associated with a pipeline and then devise risk mitigation programmes to offset them.
Need for a strong PIM system
The natural gas pipeline industry has seen a number of pipeline failures. These include major incidents such as the 2014 explosion at GAIL India Limited’s 18 inch underground gas pipeline at Nagaram in East Godavari district of Andhra Pradesh. Such accidents result in tremendous loss of lives and property, besides disrupting gas supply to consumers. Thus, a strong PIM system is necessary to minimise the impact of pipeline failures on the lives of people and the environment.
Laying the right foundation
For setting up a PIM system, operators should begin by selecting the right pipeline route, and proper material for the mainline pipe and its associated pipe fittings. This should be followed by designing the station and the mainline in a suitable manner. Intricacies such as selecting a proper coating for the pipeline, adding the necessary safety equipment during pipeline design like valves, launching and receiving barrels, understanding the environmental and external factors causing risks to the pipeline and devising safety measures that are vital for laying a strong pipeline infrastructure should also be considered. For example, operating a pipeline in a desert involves a higher safety factor than operating a pipeline in an urban area, where the lower safety factor must be considered as failures in urban areas could be more perilous.
The PIM process can be broadly classified into four steps:
- Risk assessment and integrity management planning: Integrity management begins with assessing the various types of risks associated with pipeline operations using a risk matrix-based assessment method. Risk is calculated numerically as a product of the consequence of failure and the probability of failure of a pipeline. Any project that falls in the red zone of the risk assessment matrix is flagged off as a high-risk project and suitable mitigation measures are accordingly put in place.
- Inspection, monitoring and testing: Once the risks have been assessed, the pipeline operator has to prepare an inspection plan for the pipeline. Based on the inspection plan, the operator defines the inspection, monitoring and testing processes needed for the pipeline.
- Integrity assessment: Based on surveys such as direct current voltage gradient (DCVG) and current interruption potential survey (CIPS) undertaken by engineering auditors, the operator analyses the integrity of a pipeline.
- Mitigation, intervention and repair: After the integrity of a pipeline has been assessed, it is checked if the pipeline can be operated within the specified parameters. If the integrity check identifies the need for any repair, then the operator repairs the pipeline and modifies its inspection plans accordingly.
Key threats to PIM
A number of physical threats including mechanical factors and material defects. can cause internal and external damage to pipelines. Some of the major threats are:
- Corrosion, which leads to metal loss or cracking.
- Mechanical damage to the pipeline, which causes fatigue, dents, gouges, buckles and third-party damage. For example, while laying a pipeline, other pipelines in the same right of way could get damaged.
- Material defects such as those caused due to faulty manufacturing or welding/fabrication.
- Other defects caused due to pilferage, wash-out, sabotage as well as miscellaneous operational errors.
Ensuring pipeline integrity
Ensuring pipeline integrity is a two-stage process. Under stage I, the operator has to select a proper design, and suitable material, and then undertake high quality construction of the pipeline. Once the pipeline has been laid, the operator must ensure smooth operation and regular maintenance of the same. To ensure integrity of their pipelines, operators can make use of the following tools:
- Inline inspection: This is done by using a geometric tool such as a pipeline inspection gauge. The device collects data in the form of mechanical inputs, which can be used to detect anomalies, and identify the areas of corrosion and other defects in the pipeline.
- Direct assessment: This includes directly assessing the pipeline using standard tests such as current attenuation test (CAT), DCVG, CIPS, bell hole inspection or pressure tests, which directly highlight the defect in the pipelines.
- Socio-economic methods: Under this, an operator visits residential areas near the pipeline route and makes people aware of the risks associated with pipelines. This method can also help in identifying pilferage and illegal tapping. Residents may have constructive information, which may lead to the detection of natural gas thefts.
- Other methods: Pipeline integrity can be managed by performing XYZ graph mapping, which shows the areas adjoining the main pipeline plotted on a graph so that the necessary risk mitigation measures can be taken to avoid any failures near residential or other sensitive areas. Optical fibre cable-based intrusion systems can also be used to detect any significant activity near the pipeline such as vehicular activity, drilling or walking near the pipeline. This allows the operator to assess any threats in real time. Other methods such as using corrosion coupons for checking external corrosion and electrical resistance probes for assessing internal corrosion can be used to detect corrosion in the pipeline.
As per the Vision 2030 document released by the Petroleum and Natural Gas Regulatory Board, the regulator is planning to have over 30,000 km of natural gas pipelines in the country at a design capacity of over 800 million metric standard cubic metres per day by 2030. A large part of this pipeline infrastructure is planned to be set up near residential areas, where the consequences of a pipeline failure could be very dangerous. With such large-scale pipeline infrastructure being planned, it becomes imperative for CGD operators across the country to maintain the integrity of pipelines on a continuous basis through a strong and robust PIM system.