When you feel sick, you typically go to doctors who check your medical records and history as well as your current condition. The FFP (Fitness-for-Purpose) Assessment could be described as the medical file of a pipeline, making it an important tool for any inspection.
It lets us know whether the line is “sick” or needs adjustments to improve its quality of life, which, in turn, ensures a safe and risk-free operation and mitigates risks that could jeopardize the operation and the lives of humans or entire ecosystems. A FFP analysis, report or assessment tells us the current condition of a specific pipeline and allows us to take appropriate actions to avoid immediate damage or damage in the near future. We must always remember that everybody involved in this process has a great responsibility.
Designing a pipe requires different codes that enlist prescribed acceptance levels to guarantee manufacturing quality and thereby to ensure its operation. However, during construction and operation, pipes are subject to degradation and aging mechanisms, such as the presence of corrosion features. According to design quality standards, these features could not be considered acceptable, even though in some cases they were likely not to affect the integrity of the pipe. Therefore, in the 1960s and 70s, the Batelle Institute in Ohio started to develop a series of equations in order to assess corrosion features and identify whether or not they were acceptable for a safe operation by the time they were detected.
FFP: FITNESS FOR PURPOSE
The main objective of a fitness-for-purpose assessment is to study the features reported by an integrity inspection. In this particular case, we will focus on the features reported during an in-line inspection (ILI).
ILI: RESULTS ANALYSIS
In-line inspections with axial and circumferential Magnetic Flux Leakage (MFL) and RoGeo XT (extended geometry) tools allow us to identify metal loss features associated with corrosion, anomalies introduced into the line during the manufacturing or construction processes, and features that may damage the line geometry. Within the FFP report, a corrosion diagnosis could be considered. This would help us to identify the origin of these features, i.e., whether they had their origin before commissioning or during the operation, or if they were even still active at the time of the ILI. The diagnosis focuses on the characterization of features by their o’clock position along the spool’s circumference, their reported depth or their association with the fittings of the pipeline along its entire trajectory.
This diagnosis can be supported by a mapping tool that takes into account the features’ coordinates to allow geo-referencing throughout the pipeline’s terrain and to identify their distribution within specific areas, such as human settlements, or susceptible areas, such as nature conservation areas or protected ecosystems.
The features’ characterization and mapping plus the data collection from the pipeline can result in a corrosion diagnosis that helps us to identify the initial corrosion likelihood and the current condition of the pipeline.
The objective is also to provide specific recommendations to conduct prevention or mitigation actions on the line.
FFP ASSESSMENT – IMMEDIATE INTEGRITY
As mentioned before, the main objective of a FFP assessment/report is the evaluation of the features reported during the in-line inspection. An immediate integrity assessment will, as its name suggests, allow us to prioritize the features that will fail immediately, i.e., at the time the internal inspection is conducted.
The FFP assessment can include different evaluation methodologies developed through international or national assessment codes (depending on the region). The following are among the main standards:
- ASME B31.G 2012
- API 579
- DVN RP F 101
NOM-009-ASEA-2017 is the valid standard in Mexico.
The main objective of these codes is to identify, by means of an assessment, the risks that each of the features represents, in order to avoid accidents, maintain the operation of the pipeline, and ensure the safety of all those involved, including operators and third parties.
One of the most frequently used corrosion feature codes is ASME B31.G in its original and modified versions. The difference between both methods lies in the use of the approximation area, i.e., the way in which the feature depth is estimated. The modified ASME B31.G is a less conservative method and therefore the one that operators frequently choose to conduct their assessments.
The advantage of working with ASME B31.G is that the assessment data is provided by the ILI, so it is not necessary to conduct extra work to obtain new information. This means the budget will be kept within established limits, without any cost increases for the operator.
Figure 2 – Manual for Determining the Remaining Strength of Corroded Pipelines
It is important to mention that metal loss features not associated with corrosion, i.e., spools manufacturing anomalies or features originated during the construction of the pipeline, can also be assessed – although not by the same methods used for corrosion features. Assessments of these types of anomalies are based on the NG-18 equations, and it is assumed that the failure occurs during plastic collapse, for example features in ductile welds.
The future integrity survey consists of a basic concept: projecting the internal and external corrosion rates (previously estimated) for a number of years – “X”– in order to identify the Remaining Lifetime (RLT), i.e., the estimated time within the next few years by which the anomalies will need attention, verification or repair. With this in mind, we can say that future integrity allows us to create a mitigation and preventive care plan that could reduce the risk of incidents during the time to which the anomalies were projected.