Pipeline Inspection, Surveying, and Analysis
Pipelines require ongoing inspection, surveying, and analysis for maintenance and optimum performance. Global Mapper and other Blue Marble Geographics programs provide methods to collect, edit, and share data pertaining to any planned or implemented pipeline infrastructure.
The national network of oil and gas pipelines in the United States is continually expanding to accommodate the increasing demand for energy resources across the country. Looking at the network of natural gas pipelines at a national level provides an overview of this implemented infrastructure. However, viewing a specific pipeline or segment in a local context provides useful information for the businesses and residents in the immediate area.
Focusing on a smaller portion of this larger pipeline network also breaks the network into manageable sections that local offices and teams can monitor and track to ensure functionality and safety.
Field Data Collection
When working with a section of the deprecated nationwide pipeline dataset, it is possible that the exact coordinate location of the pipeline is not as accurate as the local municipal office would like. In order to update local information, Global Mapper Mobile can be used to take current pipeline maps into the field, survey the locations, and gather data on condition and status.
Setting Up the Project
Working in the desktop version of Global Mapper to start, layers of data for the local area are loaded. In this example, the reference data includes local streets, imagery, parcels, and the pipeline line features from the national dataset. Altering the style of this data to best display on a smaller mobile device will help teams in the field differentiate layers in order to more easily orient to local features.
Before deploying this data to multiple field inspectors for updating, a Feature Template in Global Mapper can be used to standardize the data collection parameters. A Feature Template is a plan for data collection that assigns a feature type, and sets up the structure for the attributes that should be collected with each data point. Set up in the Configuration dialog box, this feature template for a point layer contains required attributes including the pipeline ID, condition, and depth of the pipeline. Users in the field can add additional information as additional attributes or as a multi-line text notation.
To transfer the data displayed in Global Mapper desktop to the field inspectors, the map data, including the added template layer, is exported to a Global Mapper Mobile Package file and transferred to the field technicians’ Android or iOS devices via email or a shared drive, like Google Drive, MS Teams, or Dropbox.
Data Collection
Using Global Mapper Mobile, inspectors can open the shared file and interact with the data. Not only can the data be viewed on a mobile device, Global Mapper Mobile can be used to edit and add data to the project. In this example, field technicians use the embedded feature template layer to collect data points at key locations along the pipeline.
With the Pro version of Global Mapper Mobile active on a device, there are several additional options for data interaction and collection. Key to this workflow is the ability to connect and use an external GPS receiver and to apply Real-Time Kinematic (RTK) correction to the raw GPS location data. The use of these Pro version tools result in more accurately positioned data points when collecting data with a GPS-based feature creation mode. The NTRIP client built into Global Mapper Mobile Pro allows users to log into their desired NTRIP caster in order to apply the RTK corrections to data points as they are being collected.
To collect the needed data, field inspectors using external GPS receivers with Global Mapper Mobile move to key locations along the pipeline and collect data points by placing them in the layer created from the feature template. Using a GPS receiver attached to a pole, and with the pole height accounted for in Global Mapper Mobile, inspectors can collect high-accuracy points along the pipeline.
Since the pipeline is partially underground, a continuous line along the pipeline path cannot be collected, but points at accessible locations will be collected and processed in the desktop version of Global Mapper. At locations where the pipeline is above ground, a direct 3D GPS-created point will be used. In places where the point is below ground, sounding equipment is used to gather a depth measurement for the 3D GPS point that is created. The depth reading is saved as an attribute value, and the true elevation of the pipeline will be calculated by subtracting the depth from the ground elevation minus the depth. This computation along with other coordinate transformation work will be done in Global Mapper desktop.
Data Processing
After field inspectors have collected the needed data in Global Mapper Mobile, the updated Global Mapper Mobile Package files are saved and shared with the in-office team. The updated data can then be loaded into Global Mapper for further processing and analysis. When loading the shared data packages into the workspace, the Global Mapper user can choose which data layers to load into the project. With this option the import of redundant reference data layers is avoided and only the newly collected data is loaded into the Global Mapper workspace.
Points collected by the inspectors in the field are created and saved in reference to the geographic (WGS84) horizontal coordinate system, and elevations are in reference to Ellipsoidal Height. This is typical for any GPS-collected 3D data. In order to transform the vertical component of this data to the North American Vertical Datum of 1988 (NAVD88), Geographic Calculator will be used in conjunction with Global Mapper. The combination of these two Blue Marble programs allows GeoCalc Mode to be activated in Global Mapper, providing access to a powerful suite of geodetic tools. GeoCalc Mode utilizes the advanced coordinate system transformations in Geographic Calculator within the user interface of Global Mapper.
Calculating Pipeline Elevation
Since the pipeline is underground and the data points have an elevation measurement from the GPS receiver and a depth value recorded on the sounding equipment, the depth measurement needs to be combined with the elevation at each point to calculate the true pipeline elevation. In this case, depth is noted as a positive attribute value. Using Global Mapper’s Attribute Calculator, the Depth is subtracted from the GPS-derived elevation value to determine the true elevation of the underground pipeline.
In order for this new attribute to be used as the elevation value for the set of collected points, it is selected in the Elevations tab of the Layer Options. This ensures that the computed elevation will be used to display the points at a specific elevation, and in any feature editing.
Creating Line Features
With 3D points indicating the path of the pipeline at key locations loaded in Global Mapper, these features can easily be connected into lines. After searching for the required points based on the Pipeline_ID value and selecting all of the points along a specific pipeline, a digitizer option is used to create line features from selected points. Repeating this line creation workflow for all the pipeline identifiers creates a new layer of line features for the pipelines based on the surveyed points. These new lines are created with per vertex elevations inherited from the surveyed points and calculated pipeline elevations.
Vertical Coordinate Transformation
Finally, the pipeline data is transformed from the vertical reference system WGS84 Ellipsoidal Height to NAVD88. This can be done by setting a vertical coordinate system for the workspace in Configuration. After selecting the desired vertical system, a transformation method is selected. The coordinate systems and vertical transformations selected in this example are using the resources and options available from Geographic Calculator through GeoCalc Mode in Global Mapper.
With a new vertical system and transformation selected for each layer in the Configuration dialog, the transformation is completed. Since vertical transformations are more complex than horizontal transformations, and can be difficult for a program to render on the fly, the per vertex elevation values for the 3D pipeline lines are finally converted when the layer is exported and saved to a new external file..
Hazard Analysis
When transporting combustible commodities, such as natural gas, safety is a prime concern. Residents living close to the pipeline need to be aware of its location and should know how to detect and report leaks that may become dangerous. Most natural gas is odorized to alert residents and passers-by of a gas leak. When a leak is detected, residents, businesses, and landowners need to be informed if they need to evacuate.
Evacuation Distance
Based on the known characteristics of the pipelines, such as diameter and pressure, the evacuation distance will vary. These values can be added to the pipeline features as attributes and used to create buffer distances that clearly show the evacuation area for a pipeline leak.
Using the evacuation distance attribute as the buffer distance, polygons are created around each pipeline feature showing the area that would be affected by a pipeline leak. These buffer features can be analyzed in conjunction with the town parcel data using Global Mapper’s Spatial Operations tool to apply the evacuation distance to the municipal data. Executing an Intersect with the Spatial Operations tool yields a layer containing parcels that would need to be evacuated due to a pipeline leak.
The municipal parcel data contains attributes describing the address and land owner(s) for each property. With the impacted parcels isolated, the contact and information about each parcel can be viewed with the attribute editor and exported to a CSV file.
WORK MADE EASY WITH GLOBAL MAPPER
Global Mapper and Geographic Calculator work together to provide a cohesive set of tools for the viewing, collecting, and editing of data related to this pipeline and many other infrastructure assets. With 3D data describing a pipeline, the features can be shared via many file formats to help inform future projects and can be saved for future teams to survey and update.
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References:
Dahlberg, Erik. “Geospatial Technologies Aid in Locating Underground Utilities.” Point of Beginning, Point of Beginning, 14 Feb. 2018, pobonline.com/articles/101210-geospatial-technologies-aid-in-locating-underground-utilities.
“Naturalgas.org.” NaturalGasorg, 3 Sept. 2013, naturalgas.org/naturalgas/transport.
“Recommended Minimum Evacuation Distances For Natural Gas Pipeline Leaks and Ruptures.” Pipeline Association for Public Awareness, pipelineawareness.org.
