Oil and gas pipelines have been around for well over a century. Although early pipelines were made of wood and plastics, but the vast majority of pipelines in service today, are made of steel. Steel has a higher propensity to dent, buckle, crack and corrode when exposed to the environment, and therefore, proactive pipeline inspections are needed to identify defects before they cause a leak or rupture. The most common form of pipeline integrity conducted is direct assessment.
The demand for direct assessment is ever increasing due to industry regulations and an aging pipeline network. The fact that as much as 70% of North America’s pipelines cannot be or are difficult to pig, also plays a role in the demand for direct assessment. There are three types of anomalies specifically inspected by direct assessment; external corrosion, internal corrosion and stress corrosion cracking. When conducting a direct assessment, four steps to the inspection are followed; a Pre-Assessment, and Indirect Inspection, a Direct Examination and a Post-Assessment.
In the pre-assessment phase of the inspection, all pipeline data, historic and current, is collected in order to determine whether direct assessment is feasible, define direct assessment regions, select indirect inspection tools, and determine if additional integrity data is needed. The second step of the inspection involves the use of non-intrusive and aboveground techniques to assess the buried pipelines. In the direct examination phase, the data collected from the pre-assessment and indirect inspection phases is analyzed in order to select sites for excavation and examination of the pipe surface. Finally, in the post-assessment phase, integrity data collected in the previous three phases is analyzed and integrated to assess the effectiveness of the direct assessment process and determine reassessment intervals.
Through these four phases, the direct assessment process becomes a structured, iterative integrity assessment protocol used by pipeline operators to assess and evaluate the integrity of their pipelines. Direct assessment gives oil and gas pipeline owners, the confidence that they are receiving the best data to make the most precise integrity decisions.