As an especially rich source of information for a risk assessment, inspection and integrity assessment results warrant special attention.
Inspections include visual examinations and many NDE techniques such as UT measurements and scans; magnetic particle; dye penetrant; X-ray; MFL, and many others.
Integrity assessments, especially as defined in IMP regulations and guidance documents, include ILI, pressure testing, and methodologies that link inferential evidence with direct examination, such as ECDA, ICDA, and SCCDA.
Use of Inspection and Integrity Assessment Data
The first and primary use of inspection and integrity assessment data, including investigations from failures and damage incidents, is in determining resistance. A secondary, but also very important use of this information is in revisiting previous assumptions used in the risk assessment. Since this latter use permeates so many inputs into a risk assessment, this topic is explored here in an early chapter.
When inspection does not find damages where they had been predicted by the risk assessment, a common cause is conservatism in the risk estimates. However, one should not discount the possibility of damages present but undetected by the inspection. In the case of ILI, such disconnects may warrant a re-examination of factors such as:
- Assumed detection capabilities to various ILI types regarding various anomaly types and configurations.
- Assumed reductions in detection capabilities to various types of ILI excursions.
When an inspection detects corrosion or cracking damage, it is logical to conclude that damage potential existed at one time and may still exist. When there is actual damage, but risk assessment results do not indicate a significant potential for such damage, then a conflict seemingly exists between the direct and the indirect evidence. Such conflicts are discussed in , especially .
Identifying the location of the inconsistency is necessary. The conflict could reflect an overly optimistic assessment of effectiveness of mitigation measures (coatings, CP, etc.) or it could reflect an underestimate of the harshness of the environment. Another possibility is that detected damages do not reflect active mechanisms but only old and now-inactive mechanisms. For instance, replacing anode beds, increasing current output from rectifiers, eliminating interferences, and re-coating are all actions that could halt previously active external corrosion. Finally, the apparent disconnect might not be a disconnect at all. It could simply be an actually very rare occurrence whose time had come. Even very low probability events will occur eventually.
The degradation estimates in a risk assessment should always include the best available inspection information. The risk assessment should preferentially use recent direct evidence over previous assumptions, until the conflicts between the two are investigated.
For example, suppose that, using information available prior to an ILI, the assessment concluded a low probability of subsurface corrosion because both coating and CP were estimated to be fully effective. If the ILI recent inspection, indicates that some external metal loss has occurred, then the subsurface corrosion assessment would be suspect, pending an investigation. The previous assessment based on indirect evidence should probably be initially overridden by the results of the ILI pending an investigation to determine the cause of the damage—how the mitigation measures may have failed and how the risk assessment failed to reflect that.
If the risk assessment is modified based upon un-verified ILI results, it can later be improved with results from more detailed examinations, that is, excavation, inspection, and verifications that anomalies are present and represent loss of resistance. If a root cause analysis of the detected damages concludes that active corrosion is not present, the original risk assessment may have been correct. The root cause analysis might demonstrate that corrosion damage is old and corrosion has been mitigated and values may have to again be revised.
A similar approach is used for integrity assessments such as pressure tests. If test results were not predicted by the risk assessment, investigation is warranted.
Techniques to assimilate ILI and other direct inspection information into risk estimates are discussed in .
Introduction
Integrity assessment verifies, within inaccuracy bounds, the structural integrity of the component(s) being assessed. Various methods are available, with varying degrees of integrity assurance.
Integrity assessment most directly informs our estimates of Resistance, as part of the overall estimation of PoF.
- Selecting an integrity assessment method
- Optimizing The Use of Inspection/Assessment Information
- Chap 10 Resistance Estimation
ILI
Results from an ILI impacts risk assessment in several ways. Firstly, a measure of remaining strength is generated from the ILI. Secondarily some knowledge about exposure and mitigation for certain failure mechanisms may also be generated. For the primary role of ILI– resistance measurements– two important aspects are sometimes overlooked. The ILI must characterize anomalies in a consistent way to make the risk assessment able to efficiently use the information. The risk assessment must also understand the limitations of the ILI. Since a largest remaining defect estimate is the ultimate goal from the ILI, it must be completely understood what the ILI might have missed or inaccurately sized.
- In a nutshell, here is what modern risk assessment gets from an ILI:
- • Indications of reduced resistance to certain failure mechanisms. Risk increases at these locations.
- • ‘Resetting the clock’ for previously assumed degradations, when absence of such degradations is confirmed. Perceived risk is reduced with this confirmation of ‘no damage’.
- • Indirect information regarding exposure to and mitigation from certain failure mechanisms. This supplements other inputs to the risk assessment.
Considerations
- Types
- Accuracy / Limitations
- “Excursions”
- Validation
- Integration into risk assessment
- TTF
- Articles:
- “Don’t Worry, We Did an ILI”
- ILI vs DA
- Training
- Input ILI into risk assessment
Pressure Testing
As one method of verifying integrity, a pressure test is intended to demonstrate the component(s) strength, measured as its ability to withstand a certain set of forces generated by internal pressure.
The pressure test yields inferential evidence that is used, usually along with other evidence, to estimate current component wall thickness (actually, effective wall thickness).
safety margin, maop vs test level, press reversals
Pressure Testing
The advantages of pressure testing is that the entire line is assessed and provides proof positive that the line is capable of withstand the operating pressures. The other advantage of pressure testing is that it is the one method that assesses for all time-dependent and time-stable threats, something that no other assessment method can claim.
Pressure Testing Disadvantages
The single largest disadvantage is that it requires the pipeline to be taken out of service for the length of the test. In addition, if water is being used to pressurize the line, then the water needs disposed of afterward and the line de-watered and dried to ensure water is not left in the line that can cause internal corrosion issues. Pressure testing can be done with inert or natural gas as well with very specific safety precautions. Pressure testing also provides only limited information about the future operational ability of the pipeline.
DA (Direct Assessment: ECDA, ICDA, SCCDA)
ILI vs DA
Comparisons
Article: ILI vs Direct Assessment: The Risk View
press test vs ILI (and other NDE)
ILI to RA training video
“Don’t Worry, We did an ILI”
“Don’t worry, we did an ILI”
Since its development and introduction to the pipeline integrity industry, With ILI now a mainstream tool for most pipeline operators, the risk reduction benefits of ILI technology and the paradigm around its application may be leading to a problematic mindset. begun to shift.
This article discusses the role of historical use of ILI from a risk perspective and its intended application, offering insight into the concerning implications of this paradigm not properly characterizing that role. This is a timely topic, given the record attendance at the recent Pipeline Pigging and Integrity Management Conferences and Exhibition which take place annually in Houston. That conference showcases all the great advances in inline inspection (ILI) technologies and related activities including NDE, non-destructive evaluation, imaging, mapping, and many others. Seeing all the high high-tech equipment and listening to the discussions of the complex analyses improvements, it is natural that we continue to gain confidence and raise expectations around this relative newcomer to our industry.
Now, that phrase, ‘relative newcomer’, might raise some eyebrows. Many newbies in our industry have never been without the ability to use ILI on a pipeline. ILI is now considered a normal and essential part of owning and operating many pipelines;. However, we should take a moment to make sure we are not losing perspective. .
Let’s recall our origins. When ILI first became a practical tool, it was generally considered a final confirmation that damage was indeed being prevented. It was the last chance to interrupt a failure sequence – finding and halting damage before it progressed to failure. . A It was a useful tool, but also recognised as the last chance to interrupt a failure sequence.
There are now some troubling notions emerging, as evidenced by conference presentations and just academic and expert discussions, as well as general conversations among pipeline operators. In some minds, ILI is now no longer the last chance but rather the primary way to prevent failure.
Let’s examine that idea. ILI does not prevent damage – it is not a mitigation. I; it only allows us to intervene. As valuable as that is, it does nothing to protect the pipeline from any damage mechanism. Even if it was a perfect tool – one that does not miss nor mis-size any defect – ILI is still problematic as the primary failure prevention strategy.
The ‘pig and dig’ approach for avoiding failure can be seen as ‘let it degrade, I can fix it before it fails’. This philosophy is essentially relying on the monitoring of damage as it progresses so that intervention can be performed before the damage becomes critical. So, those who adopt the ‘“I can pig and dig my way out of trouble”’ philosophy are suggesting that allowing their assets to deteriorate is no longer troubling. They will naturally rebut with “oh, sure, we do x, y, z, etc to prevent damage too”. But again, the inclination to view ILI as the primary failure avoidance action is the a concern.
A good risk assessment helps us regain perspective on the role ILI plays in risk reductions. It shows exactly the benefits and limitations of ILI. .
An ILI can directly tell us about the strength of the inspected pipeline – and its ability to resist various failure mechanisms. Indirectly, it also tells us some things about exposure to and mitigation of certain failure mechanisms. .
For instance, at every external metal loss location, we know that, at some point in the past, there was sufficient electrolyte to cause corrosion and that all of our mitigations (coating and cathodic protection) failed. We don’t know how ‘strong’ the electrolyte was/ or is, when the mitigation failed, if all mitigation failed simultaneously, if mitigation is intermittently effective, and many other questions that a good risk assessment seeks answers to.
However, the new knowledge of resistance (strength) gained from an ILI often makes a dramatic difference in risk. In a nutshell, here is what modern risk assessment gets from an ILI:
• Indications of reduced resistance to certain failure mechanisms. Risk increases at these locations.
• ‘Resetting the clock’ for previously assumed degradations, when absence of such degradations is confirmed. Perceived risk is reduced with this confirmation of ‘no damage’.
• Indirect information regarding exposure to and mitigation from certain failure mechanisms. This supplements other inputs to the risk assessment.
All ILI indications must be adjusted for run-specific detection and sizing accuracies. This includes the often- hard- to- quantify effects of excursions from the ILI’s run specifications (such as, speed-, excursions, magnetisation- excursions, loss of sensors, and more). A sound risk assessment shows us the great value of ILI but keeps its role in perspective. It is always preferable to prevent damage, rather than monitor damage and then intervene before it becomes critical.
Let’s keep our focus on protection of pipeline assets and recognise that ‘pig and dig’ is among our last opportunities to avoid failure.
Optimizing the Use of Inspection Results