Canada, Vermont, New Hampshire, Maine
By federal regulation, Portland Natural Gas Transmission System (PNGTS) is required to regularly assess and report on the integrity of its pipeline. This is accomplished by utilizing a mechanical device (“pig”) that travels inside the pipe collecting data such as wall thickness, weld integrity and geometry of the pipe while providing critical information to address any irregularities.
PNGTS recognized that the existing horizontal and vertical control for the pipeline could not ensure spatial accuracy. Thus, PNGTS engaged SGC to design and survey a Geodetic Control Network that would result in 20 permanent horizontal and vertical control pairs along the 200-mile length of its pipeline. Additionally, SGC’s scope of services included 200 “pig points” that were utilized by the inspection “pig” to ensure spatial accuracy for reporting.
SGC completed this assignment utilizing a combination of static, fast static and real-time kinematic GPS surveying techniques. To meet the aggressive five-week schedule, SGC assigned a Senior Geodesist to manage the project who utilized three experienced GPS crews to collect the field observations. All GPS observations were adjusted utilizing a rigorous parametric least squared algorithm to ensure quality and acceptable relative accuracies for each control point.
In addition, establishment of the geodetic control network had unforeseen benefits. SGC was able to reference exiting as-built pipeline information to the newly established geodetic control network to form the spatial component of PNGTS’ GIS.