About Pipelines
What is Risk Assessment?
Risk assessment is a process used to evaluate unwanted consequences and the likelihood of those consequences occurring. The purpose of risk assessment is to develop information that allows organizations to make decisions that reduce or eliminate unwanted consequences by changing their likelihood, their adverse impacts, or both.
For instance, aircraft manufacturers analyze the performance effects of different aircraft designs to minimize the likelihood of crashes. Government agencies evaluate the effects of emissions from industrial plants, or motor vehicles, in order to develop regulations that limit emissions and minimize adverse impacts to the public and the environment.
The terms “risk analysis” and “risk evaluation” are often used interchangeably with “risk assessment”.
What is risk?
Risk is a concept that describes and measures the combination of the likelihood of a negative outcome and the severity of consequences that result from that outcome. The higher the risk number, the more “risky” is the combined likelihood and severity of a particular event.
Likelihood is measured as probability ( a number between 0 and 1 that represents the chance of some consequence occurring) or as frequency (a number that represents how many times a consequence occurs during a fixed time period).
Consequence is measured in a variety of ways, depending on the nature of the consequences being considered. For example, if the consequences involve human health or safety, then consequences may be measured by fatalities or injuries. If consequences involve environmental damage, they may be measured by the cost required to repair the damage and restore the affected environment.
How do pipeline operators use risk assessment to enhance pipeline safety?
Risk assessment is used to address issues pertaining to safety, environmental protection, financial management, project or product development, and many other areas of business performance. In the pipeline industry, risk assessments are utilized for many of these same reasons. For the purposes of this fact sheet, however, we are addressing risk assessment related to pipeline safety – that is, protecting the public, property, and the environment from pipeline failures.
Risk assessments of this kind begins by looking at the different ways a pipeline can fail and release its contents – such as oil or natural gas – into the environment. Factors that can lead to pipeline failure are referred to as pipeline failure threats . For example, a pipeline can leak because corrosion weakens the steel in the pipe. Failures also occur as a result of excavation equipment striking the pipe. Identifying potential threats to a pipeline requires looking at the factors that cause failures as well as looking for unique factors that could lead to failure at a particular location, whether or not that particular failure has occurred or been observed before.
The next step in risk assessment is to assess the likelihood that each threat could lead to a failure at a particular location on the pipeline. This assessment is performed by looking at the specific characteristics of the pipeline at any given location, along with the unique characteristics of the area around the pipeline. For example, the susceptibility of the pipeline to failure due to corrosion is dependent on numerous characteristics, such as the type and condition of the pipe’s coating, the effectiveness and operability of the operator’s corrosion control equipment, and the soil conditions surrounding the pipe.
As another example, the susceptibility of a pipeline to third-party excavation damage is dependent on characteristics such as the extent and type of excavation or agricultural activity along the pipeline right-of-way, the effectiveness of the One-Call System in the area, the amount of patrolling of the pipeline by the operator, the placement and quality of right-of-way markers, and the depth of cover over the pipeline. In all cases, different threats will exist at different locations along the pipeline.
The next step is to assess the types of consequences that could result from a pipeline release at a specific location, along with the potential severity of those consequences. For example, failures of pipelines in remote areas, where people do not live or congregate, will likely result in lower impacts than failures in areas of dense residential or commercial development. Similarly, failures in areas sensitive to environmental damage, such as the locations of drinking water sources or endangered species’ habitats, have higher environmental consequences than areas without these features.
The final step in risk assessment for a pipeline is to use the results of the likelihood and consequence assessments to determine the overall risk at each pipeline location. This allows the operator to ensure that sections identified as having the highest risk are assigned top priority for actions that will reduce the likelihood of a release, reduce its potential consequences, or both.
The results of the likelihood assessment also provide the operator with information on the significance of different pipeline threats at different locations, allowing them to carry out actions that reduce the likelihood of a pipeline failure. For example, an operator may choose to conduct internal inspections on those pipeline sections that are shown to be most susceptible to corrosion, to identify where corrosion might be occurring, and to repair any damage before the pipe fails.
The results of the consequence assessment provide the operator with information on the significance of consequences of accidents at different locations, so that operators can carry out steps to reduce or eliminate those consequences. For example, an operator may place specialized emergency response equipment at an environmentally sensitive site to allow for quick response should a pipeline release occur.
What are the requirements for risk assessment by pipeline operators?
It is important for pipeline operators to be keenly aware of threats and potential consequences of accidents along the entire length of their pipelines, and to employ rigorous assessment as a tool to manage those risks.
The federal pipeline integrity management regulations for hazardous liquid pipelines ( §195.452) and natural gas pipelines ( §192.901- §192.951) require operators to perform risk assessments of their pipelines to:
- Ensure that integrity assessment methods (internal inspection, pressure testing, direct assessment, etc.) are employed to address significant threats on pipeline segments.
- Ensure that integrity assessments of the highest risk segments are scheduled with priority over lower risk segments.
- Ensure that assessments of threats and potential consequences are conducted to define, evaluate, and implement additional measures that address significant threats to the pipeline (e.g., conducting depth-of-cover surveys and correcting any deficiencies), or reduce potential consequences of failures (e.g., installing additional valves on the pipeline to reduce the amount of liquid or gas that might be released should a failure occur).
Date of Revision: 12012011