Unlike the circumstance associated with transmission pipelines, where variables that are attributes of risk are typically widely available in GIS systems or in other databases that are geo-referenced to linear assets, risk data for distribution systems are not typically linearly referenced to what is essentially a network system. Therefore the manner in which risk is calculated and displayed for distribution systems must differ significantly from the way these functions are performed on transmission pipelines. In distribution systems, failure (defined as the loss of containment) and the contributors to the likelihood of failure, is often highly correlated to system-specific circumstances, such as type of material used, installation era, and operating environment. These correlations between cause-and-effect as they relate to failure likelihood in distribution systems are not widely recognized on a universal basis, such as they might be in transmission pipeline environments, but are typically unique to each operating system.
Because system data for distribution networks is not typically available in a manner that can be linearly geo-referenced to pipeline coordinates the way it is for transmission systems, the convention of mapping risk to pipeline dynamic segments as a function of risk attributes that exist within those dynamic segments is not achievable for distribution systems the way that it is for transmission systems. Therefore, the most effective strategy for performing risk assessments in distribution systems is to create a database in which existing incident data can be correlated to system attributes, and then to use those correlations to create cause-and-effect relationships between system attributes and failure likelihood. Consequences are characterized in terms of the operating environment (e.g., wall-to-wall, residential, etc.), leak magnitude, type of facility (mains vs. service lines), and special mitigating or exacerbating factors, such as availability of excess flow valves, or the presence of inside meters.
A risk assessment methodology has been developed that accommodates the above constraints and that meets the stated objectives, and which is well-suited to the distribution system data infrastructure that is typical of most operators. Because the risk assessment approach leverages existing databases and incident reporting structures, it lends itself to automation, and re-evaluation on a regular basis. Reporting is facilitated by a ‘heat map’, which provides immediate insight as to the drivers of risk for each system sub-group having similar design, materials, and operating characteristics.
Risk assessment of the maintenance process for onshore oil and gas transmission pipelines under uncertainty