Improving pipeline Class Location analysis
How connected routes strengthen sliding mile calculations
Why it matters
Traditional route boundaries can affect Class Location accuracy
Connected pipelines require more comprehensive sliding mile analysis
Network-aware calculations help maintain consistency across pipeline connections
Pipeline Class Location analysis plays an important role in natural gas pipeline safety and integrity management. By evaluating population density along a pipeline, operators can better understand potential risks to people and property in the event of a pipeline failure.
But traditional Class Location analysis can produce inconsistent results when pipelines are divided into separate routes, even when those routes remain physically connected.
Accounting for these connections provides a more comprehensive way to evaluate Class Locations across natural gas transmission and gathering systems.
Understanding the sliding mile approach
Pipeline Class Location is determined through an analysis of population density along a pipeline. Class Location values range from Class 1, representing low-density rural areas, to Class 4, representing high-density urban areas.
The analysis uses a method commonly called the sliding mile algorithm.
At each point along a pipeline, the algorithm evaluates the number of dwelling units in buildings intended for human occupancy (BIHOs) within a 660-foot radius and a one-mile span of the pipeline.
As the analysis progresses, the one-mile window moves along the pipeline, producing dwelling unit counts used to determine Class Location.
Originally developed for pipeline safety design, Class Location analysis is now integral to federally mandated pipeline integrity management requirements.
Traditionally, operators perform this analysis on individual pipeline routes. These routes are typically continuous, non-branching sections of pipeline, often extending between compressor stations.
However, analyzing routes independently can create challenges when those routes are connected.
Why traditional route boundaries create challenges
Pipeline routes are not always defined by physical changes that affect operating pressure or product flow.
Some operators divide routes at administrative boundaries, such as operating divisions, district limits or state lines, even when gas continues flowing across those boundaries.
Other route divisions may occur at pigging launcher and receiver stations. Although these stations temporarily separate pipeline sections during pigging operations, product flow can continue between routes during normal operations.
These divisions can cause traditional Class Location analyses to evaluate connected pipeline segments independently, potentially overlooking the broader context of the network.
The challenge becomes more complex in gas gathering systems, which often include highly branched and interconnected pipelines.
Some Pipeline and Hazardous Materials Safety Administration (PHMSA) and state inspectors have raised concerns about Class Location results when analysis stops at artificial route boundaries or fails to account for interconnected routes.
Where pressure and product flow remain continuous, their position is that sliding mile analysis should extend beyond individual route boundaries.
This creates a need for approaches that account for physically connected pipeline segments rather than treating each route as an isolated system.
How networked Class Location analysis works
A network-aware approach addresses these challenges by tracing connections between pipeline routes and extending the sliding mile analysis across those connections.
The Gas HCA Tool incorporates this approach through an enhanced algorithm that automatically identifies where two pipeline routes meet.
At each identified junction, the algorithm generates an artificial super route extending at least one mile in either direction beyond the connection point.
The sliding mile algorithm is then applied to both the original routes and the newly generated super routes.
Dwelling unit counts from the super routes are overlaid onto the sliding mile counts calculated for the original routes.
Where these counts overlap, the highest dwelling unit count determines the Class Location for the original route.
This approach allows the analysis to account for population density beyond an individual route boundary, reducing the risk of overlooking relevant information from connected pipeline segments.
The algorithm also maintains relationships between each super route and its parent routes.
This traceability allows operators to identify when a Class Location determination on an original route is based on the dwelling unit count from a connected super route.
Addressing short pipeline laterals
Connected route considerations are particularly important for pipeline segments shorter than one mile.
Traditional approaches to analyzing short laterals can produce inconsistent Class Location results.
One method involves prorating sliding mile dwelling unit counts to account for the shorter pipeline length. However, this can result in a short lateral receiving a higher Class Location than the main line to which it connects.
Another approach assigns the main line's Class Location directly to the connected lateral. While simpler, this method can overlook actual Class Location changes along the lateral itself.
Networked analysis provides an alternative by tracing from short laterals into connected mainlines and, where applicable, other nearby laterals.
This allows the sliding mile calculation to account for connected pipeline segments rather than relying solely on the short lateral's length or the main line's classification.
The approach also avoids the inconsistencies that can arise from previous methods, producing consistent Class Location values across pipeline connection points.
Supporting more consistent pipeline integrity analysis
Accurate Class Location determinations are an important part of pipeline integrity management.
When pipeline routes are analyzed independently, administrative boundaries, short laterals and complex network connections can affect the consistency of results.
Networked analysis addresses these challenges by incorporating physically connected routes into sliding mile calculations.
By tracing connections, generating super routes and comparing overlapping dwelling unit counts, operators can evaluate Class Locations using a more comprehensive representation of their pipeline systems.
The result is a methodology that provides greater consistency across connected pipeline segments while supporting the Class Location analysis used in pipeline safety and integrity management.
Key takeaways
Traditional Class Location analysis can produce inconsistent results when physically connected pipeline routes are evaluated independently
Networked sliding mile analysis uses super routes to account for population density across connected pipeline segments
Incorporating connected routes improves Class Location consistency, particularly for short laterals and complex gathering systems
