As the desire for more robust pipeline risk management grows, so too does the need for superior risk assessment. A formal risk assessment provides the structure to increase understanding, reduce subjectivity, and ensure that important considerations are not overlooked. Associated decision-making is therefore more consistent and reliable when formal techniques are used. But has pipeline […]
Topic: Modeling
I want to keep using our relative points scoring system. I don’t see why we should change.
Perhaps first question is this: ‘is your scoring system really giving you new knowledge and useful insights into actual risks?’ If not, then that alone should be a compelling reason to change—especially when modern risk assessment is both more efficient and less expensive. See more extensive discussion here.
Cracking doesn’t really progress in a linear fashion. It shouldn’t be modeled that way. Actually, corrosion doesn’t either.
True. You can put in non-linear equations as part of the TTF estimate. A risk assessment should represent the actual underlying science as much as possible/practical.
Ok, so how do I convert from TTF to PoF?
This is one of the more challenging aspects of modern risk assessment. One of the keys is to select the future date for which the PoF is being estimated. This is often ‘next year’ but can really be 5 years, 10 years, 20 years, etc into the future. Another key is to ensure that both likely and […]
Why do I need a PoF for time-dependent failure mechanisms? The TTF is more relevant since it drives integrity re-assessment schedules and other risk mgmt. efforts.
TTF is indeed the more useful metric for many applications. However, the TTF has a probabilistic aspect that must be understood before its use in, for example, setting an integrity reassessment interval. The TTF calculation uses segment lengths since degradation mechanisms are usually related to surface areas. A probabilistic TTF per mile is an intermediate calculation […]
How do I include ‘tank overfilling’ in a risk assessment?
You first choose to include such events in your definition of ‘failure’. Then, the event is assessed like any integrity-threatening event, in terms of exposure, mitigation, and resistance. Perhaps this event can be included as an Incorrect Operations scenario, along with analogous events such as overpressure.
How should I be doing risk assessments in facilities like tank farms, compressor stations, etc?
Exactly the same way as for components on the ROW. You don’t want or need multiple risk assessment approaches. A good risk assessment methodology works equally efficiently on any component or any collection of components. The challenge with facilities will be in segmentation. The more robust assessments will examine very small sub-components (eg, the casing of the pump […]
How do I include flange and screw-connection leaks that are really just ‘wiggling loose’ over time?
This scenario must first be categorized in terms of its underlying failure mechanism. An underlying question to answer when categorizing a failure mechanism as either time independent or time dependent is ‘if there have been no changes in any forces, then why did it fail today instead of yesterday?’. When a fitting or appurtenance has performed […]
Does the CoF hazard zone approach make sense for water pipeline risk assessments?
Absolutely. Even though, unlike its hydrocarbon cousins, no thermal scenarios would be expected from water pipe failures, other consequences are numerous and many are related to the distance from the failure location (hazard zones). Modeling is therefore appropriately done using hazard zones, with both direct and indirect consequence considerations, just as we do for hydrocarbon pipelines.
What’s behind the EE guideline document that DNV and you recently released?
We are advocating a degree of standardisation that serves all stakeholders. This list of essential elements sets forth the minimum ingredients for acceptable pipeline risk assessment. Every RA should have these elements. A specific methodology and detailed processes are intentionally not essential elements, so there is room for creativity and customised solutions. DNV’s recognition of […]