Algorithms are simply equations that calculate various aspects of risk. A set of algorithms receives information and outputs risk estimates.
Risk algorithms calculate risk values. This separates risk assessments from risk analysis tools. The two are often confused. Risk analysis tools can provide valuable inputs into a risk assessment, can help with visualization and communications of risk, and can also sometimes produce narrowly-focused estimates of risk. However, they are not intended to produce efficient, robust total estimates of risk, especially for long linear assets such as pipelines.
Some key features of a modern risk assessment approach are described below:
- Assessment recognizes all known failure mechanisms, i.e., time dependent failure mechanisms of fatigue and corrosion and time independent failure mechanisms including third party damage, sabotage, human error (incorrect operations), geohazards, and others.
- Failure mechanisms are assessed via independent examination of three aspects: Exposure (attack), Mitigation (defense), and Resistance (survivabililty)
- Time-independent failure mechanisms are assumed to either cause immediate failure or create a defect that leads to a time-dependent failure mechanism.
- Time-dependent (degradation) failure mechanisms of corrosion and fatigue are measured in mils-per-year (mpy) (or mm/yr) pipe wall metal loss. This mpy is used to determine the time to failure (TTF) with the assumption that failure occurs just below the wall thickness required for maximum internal pressure (rupture) or when wall is breached (leak).
- Integrity verification re-sets the clock at the measured wall thickness. Mpy is then applied to the new measured wall thickness to determine again when failure theoretically occurs.
- A previous incident impacts the degree of belief about future failure potential in proportion to its relevance as a predictor. Historical incident information, properly adjusted for relevance, is used to initially tune or calibrate the model’s frequency of failure (FoF) estimates when absolute estimates of risk are needed.
- Increased uncertainty is treated the same as increased risk. This is conservative, ensures model credibility, and shows the value of acquiring information.
Older techniques miss some of these important elements and therefore should be avoided. A short and simple list of essential elements allows us to differentiate superior risk assessment techniques. Risk assessment methodologies can be audited and certified using this simple list.
PoF Training Video