Originally published in World Pipelines Magazine, August 2023 issue.*
Pipelines have long been the safest way to transport gas, but what are crucial components of modern energy infrastructure still have weaknesses despite their necessity. Safety has always been the main priority for the natural gas sector, with an understanding that any accident could have a significant impact on public safety and the environment.
This was certainly the case in 2018 when a series of gas explosions shook Merrimack Valley, Massachusetts. One person died because of the fires, another 21 were injured, and 8,000 were forced to evacuate their homes following the accidental over-pressurization of a low-pressure natural gas distribution system.
Any natural gas incident is one too many. But unfortunately, incidents such as Merrimack Valley have increased in frequency over the last decade, according to research by the Pipeline Safety Trust.
While the incident in Massachusetts was rare in its scale and such events are unlikely to be commonplace, it led to pipeline operators forcing through change to drastically improve safety standards in the sector. Two years after the Merrimack Valley incident, the United States Congress passed the "Protecting Our Infrastructure of Pipelines and Enhancing Safety (PIPES) Act of 2020" (Pipes Act 2020). For operators, it means that they must now assess the risks that could lead to or result from the operation of a distribution system at a pressure, too low or high, that makes the operation of any connected low-pressure gas burning equipment unsafe.
Ensuring safe pressure levels
Gas utilities have relied on pressure regulator stations for over 200 years to maintain constant pressure across their distribution networks. With downstream distribution networks designed to operate at lower pressures, regulating pressure to appropriate levels is essential to avoid catastrophic overpressure events or costly gas outages, either of which would impact thousands of customers.
However, challenges such as differences in the station and regulator types and their configurations, site-specific differences compounded by limited data and multiple failure mechanisms in regulator stations mean traditional risk management methods and models are often inadequate.
Understanding regulations
The safe and reliable operation of gas pipelines and management of over-pressurization or network outages is not only important for the industry and the communities they serve, but it is also heavily regulated by governments worldwide. There are several regulations in place to manage over-pressurization in gas pipelines. Regulations vary by country and region, and pipeline operators must be aware of and comply with all relevant regulations in their area.
Here are some of the recent regulations that underscore the importance of a robust over-pressurization management plan for gas pipelines:
- 49 CFR 192.195: This is a regulation enforced by the Pipeline and Hazardous Materials Safety Administration (PHMSA) in the United States. It requires operators of gas transmission pipelines to perform a risk assessment of their pipelines and implement integrity management programs that address the risks identified in the assessment, including overpressure incidents.
- 49 CFR 192.622: This regulation, also enforced by PHMSA, requires operators of gas transmission pipelines to have and implement a written emergency response plan, including procedures for responding to overpressure incidents.
- PIPES Act of 2020: The PIPES Act of 2020 aims to improve the safety and security of gas and hazardous liquid pipelines by strengthening the regulatory oversight of pipeline operators, enhancing incident response and emergency preparedness, and providing additional resources to support pipeline safety research and development. Per the PIPES Act of 2020, operators are directed to:
- Assess each regulator station for the risk of overpressure and upgrade as appropriate.
- Assess the risks that could lead to or result from the operation of a low-pressure distribution system at a pressure that makes the operation of any connected and properly adjusted low-pressure gas-burning equipment unsafe.
- Address methane emissions and replacement or remediation of pipeline facilities that are susceptible to leaks or failure.
- The statute also requires the operations and maintenance plan to contain written procedures for responding to overpressure indications.
How best to tackle over-pressurization
A focused and combined approach, leveraging the power of risk, integrity, and hydraulic analysis, is key to robust regulator station risk and overpressure management.
While many operators use simplified estimates to model regulator station overpressure consequences, leveraging a hydraulic model allows for the identification of more accurate consequence factors, such as the number of impacted customers and the over-pressurized pipeline length associated with the failure of each regulator station in a network. Juxtaposing this information with the integrity and reliability of each station to establish the probability of failure as well as the ultimate chance of ignition allows for a more accurate estimate of the risk of an overpressure event at a specific regulation station. This marks a significant step forward in the management of these critical assets.
A deeper understanding of network outages
While network outages do not often pose a significant threat to public safety, they remain a credible risk to pipeline operators and the public they serve. By leveraging hydraulic models, operators gain a detailed understanding of the potential downstream impact of a failed regulator station to plan for these events more accurately in terms of emergency and restoration response and targeted public communication during and after an incident. Combining this enhanced consequence information with the probability of these events for each regulator station gives operators the knowledge they need to minimize the risk of these events.
So, what is being done to move this school of thought forward?
DNV's effective regulator station risk model and over-pressurization and outage management systems provide a comprehensive risk profile for each regulator station by combining the powers of hydraulic and integrity assessments.
Figure 1 DNV - Combining the power of risk, integrity, and hydraulic analysis.
While the Overpressure Analysis and Outage Analysis applications in Synergi Gas analyze the downstream impact of an event, the integrity and risk management software, Synergi Pipeline, assesses the stations based on reliability, probability of failure and potential impact. When used with the organization's other probabilistic models, it provides visibility of the regulator station risk liability versus other asset classes, such as main and service pipelines.
With its accurate picture at that moment or under future conditions, the system provides operators with flexibility. By combining the likelihood and consequence of failure, the tool provides them with a clear gauge of potential damages, allowing for effective monetizing of risk across all stations and subsequent prioritizing of resources. This information allows engineers to identify the regulator stations most at risk and implement mitigation measures such as overpressure protection, the replacement of outdated regulators and increased inspection frequencies through asset management programs. Time can also be saved, with decisions that previously may have taken weeks or months now being taken in minutes.
An example of the model in action
In the aftermath of the Merrimack Valley incident, one of America's largest operators implemented the DNV's combined solution to assess the risk of leaks and ruptures of each station and the risks associated with overpressure and outage events.
One of the first companies to adopt the programme, it worked closely with DNV experts to create a risk model that accounted for each station's configurations and associated historical operational reliability. Primarily, the solution has helped the operator:
- Meet DIMP (Distribution Integrity Management Program) regulatory requirements, including PIPES Act 2020.
- Evaluate the consequence and impact on customers.
- Identify the highest-risk regulator stations and station types.
- Understand regulator station risk compared to other assets when used in conjunction with DNV's other probabilistic models.
- Drive mitigative measures based on risk through DIMP.
- Guide future regulator station design and construction.
The operator has found that their decision-making ability has considerably improved regarding maintenance, upgrades, and replacement of regulator station equipment. Beyond operational tasks, the client relies extensively on the solution for planning, saying that it is fundamental to their capital investment planning process.
Moving forward with confidence
With utilities prioritizing efforts and expenses, being proactive in gauging risk is essential. The Merrimack Valley explosion highlighted the impact of such an incident on public health, safety, and property and the sheer cost that this can generate.
In 2020, the world consumed around 3.7 trillion cubic meters of natural gas, according to the International Energy Agency statistics. That translates to nearly 10 billion cubic meters of natural gas being transported daily from production sites to homes, businesses, and power plants worldwide.
Given the proven risk of overpressure and outage incidents, proactive mitigation should be on the agenda for companies to safeguard their interests as well as the well-being of the wider community. Implementing strategies that proactively address these risks in pipelines can go a long way in preventing potential disasters and ensuring a safer environment for all stakeholders involved.
*To view the original article, visit World Pipelines Magazine.