This report provides the Petroleum Technology Alliance Canada (PTAC) with initial scoping of several topics within a broader planning level discussion regarding pipeline abandonment and management of long-term risk associated with pipe abandonment in place. The request by PTAC was the 013 work package entitled “Analysis of Pipeline Exposure Data and Scoping Review of Exposure Scenarios.” The work involved four topics:
- Interpretation of pipe exposure data to estimate the likelihood of future pipe exposure of abandoned pipelines.
- Description of expected buoyancy control longevity for various practices, and recommendations of future studies to improve predictions of buoyancy control longevity.
- Preparation of a recommended work plan to evaluate low impact pipe removal methods for sensitive ecological areas.
- Preparation of a recommended work plan to measure the potential for pipe exposure due to frost heave.
The following is a brief summary of the study results.
An estimate of exposed pipeline frequency after abandonment was derived from published incident data for operating pipelines in several world regions. About one pipe exposure per 100 years per 1,000 km of pipe could be used for planning purposes after abandonment, assuming intervention or mitigation of long-term hazards at the time of abandonment. In Canada, this would equate to about 8 pipe exposures per year along the 840,000 km of operating transmission, gathering and distribution pipelines. Most of these “incidents” are expected to occur at water crossings. Mountainous areas and erodible soils are expected to have a relatively higher frequency of exposures. Removal of pipe at selected hazard locations may reduce the frequency of pipe exposures. The estimate is qualitative because regulatory agencies do not yet publish the exposed pipe frequency of abandoned pipelines.
Most buoyancy control measures will likely outlive the integrity of the steel wall of abandoned pipelines, unless the pipeline continues to be cathodically protected (in which case, the pipe steel may last longer). The corroded pipe will therefore likely fill with water and eliminate the buoyancy force prior to the degradation of the buoyancy control measure. The buoyancy control measure that may be most at risk from degradation is steel anchors. Anchor degradation over the long term will depend significantly on the initial thickness of the various steel components, on whether they were coated, on local soil corrosivity, on the groundwater level, and on groundwater mineral content. Other buoyancy control measures such as concrete weighting and geotextile bags are expected to last many decades, even after pipe abandonment.
At sensitive ecological locations such as river crossings and wetlands, the report describe several removal methods. It states that pipelines will be removed in locations where rivers are progressively eroding or the alignment is unstable, and where a future degraded pipe may result in a drainage diversion. The proposed next steps include a workshop to more fully explore the environmental considerations and potential consequences of removing abandoned pipes for various site conditions.
This report also describes the potential for frost action to impact abandoned buried pipelines, and concludes that this is highly unlikely. A work plan is described to confirm this conclusion, and a detailed assessment of a previous PTAC report explains the conclusions.