Locating Transmission pipelines for HCA’s and MCA’s determinations
PHMSA’s integrity management rules mandate that gas transmissions lines must have a baseline assessment conducted if they are within an HCA or MCA. If companies do not conduct the baseline assessments in the true HCA/MCA areas, they can face fines from PHMSA and/or state regulatory agencies.
HCA’s and MCA’s are determined by the distance of structures intended for human occupancy to the centerline of the pipeline, some operators determine these distances with the aid of a GIS system. If the centerline is not depicted correctly, then the delineation of the HCA’s and MCA’s will be inaccurate. The information loaded into these systems are the results of many different datasets.
The data sets operators use could include data from intuitional knowledge but due to workforce turnover in operating companies staff the knowledge of centerline locations are being lost as employees leave or retire. Operators could use legacy pipelines constructed before 2000 that relied on bearing and angles for documenting the location of the pipelines. This causes inaccurate as-building and difficulty determine exact location of pipeline. An operator could have used a dataset that was collected by a company employee(s) who used navigation grade GPS units to capture the pipeline location. These units could be as inaccurate as plus or minus 30 feet. The best and most accurate dataset an operator could use is by obtaining correct pipeline locations with pipe locators and documenting it with sub-meter GPS accurate coordinates.
Other issues that hamper operator’s ability to accurately represent the precise location of their pipeline centerline is that when relying on existing pipeline markers and cleared right of ways the pipeline location can be in error. Over the years while clearing the right of way the contractor(s) starts shifting the centerline. In addition to misrepresenting the HCA/MCA areas, encroachments can also be an issue. This is due to the line being marked in the wrong location and the companies and subcontractors using the line markers as to where the pipeline centerline is located. These mis located lines can lead to the public placing/building encroachments over the actual pipeline centerline. Finally locating the centerline of a pipeline can be difficult if there are multiple pipelines in the area.
The six-step solution to this problem starts with a review of any existing maps and as-builts of the pipeline with the operator before locating activities begin. During this operation all pipelines are verified to be in the correct location. Once the locations are verified using the maps and as-builts in the field location verifications can begin by connected transmitter(s) directly to the pipeline at aboveground feature(s) and test point(s). This will reduce the amount of current lost and will increase the accuracy of the pipeline locating. This locating is conducted by physically locating the pipeline using a sensitive pipeline locator and most importantly a qualified technician to ensure that the pipeline is being marked correctly. Once the pipeline has been located properly the use of sub-meter GPS equipment is utilized by a technician to accurately document the location of the pipeline. After the GPS shots are collected the data is post-processed and a quality assurance check is completed to ensure the accuracy is within sub-meter quality. The final and easiest step is for the operator to then upload the correct centerline data into their GIS database.
Operators spend money clearing ROW over the pipelines for maintenance activities. Clearing the correct areas would allow them to clear the right of way over the pipeline. Having a clear right of way over the pipeline enables maintenance activities to be conducted according to O&M manuals and PHMSA guidelines. Correctly locating the pipeline centerline thus, the right of way limits makes sure that trees are not allowed to thrive in the right of way and thus eliminating potential environmental issues. An added benefit to clearing the correct right of way is the decrease in time and money spent to conduct these maintenance activities due to overgrowth.
Once the proper centerline and corresponding right of way has been cleared the operators can move incorrect pipeline marker(s) to the correct location therefore reducing the chance of encroachments and having a better chance of continuing to clear the correct areas in the future. While operators are many times reluctant to change pipeline centerline in their GIS systems due to station equations, legacy compliance reports and uncertainty of the quality of data, which can all lead to inaccurate centerlines and thus erroneous HCA/MCA determinations. With the process that JRGO uses the operators can be sure that the data they are uploading into their GIS systems are more precise and accurate than current data and that the HCA/MCA locations for baseline assessments can be defended in a PHMSA audit.
Numerous times JRGO has been in areas where previous contractors and operators have purportedly located the pipeline and have found the line to be up to 300 feet off. The assumed centerline was found to be incorrect regarding pipeline markers and past evidence of clearing. Working with operators the correct centerline was determined, clearing operations conducted and pipeline markers moved.
JRGO uses state of the art pipeline locators and well-trained technicians to ensure the correct pipeline centerline is located accurately. This is followed by technicians using sub-meter GPS units to capture the location of the pipeline over the centerline. The data is then post-processed and verified to ensure that the data is accurate and then the conversion to operators GIS system(s) is seamless.
JRGO arrives at the jobsite to conduct a survey after the gas company had the right of way cleared.
to clearing operations.