Risk = consequence of failure X probability of failure (Oil & Gas UK, Mooring Integrity Guidance)
When assessing risk of an operation, the UK Oil and Gas considers both the consequences of failure and the probability of failure. Each plays a crucial role in determining the attention that should be paid in preventative action. Consequence of failure is the outcome of a possible hazard (What happens if…) where the probability considers how likely it is that something will go awry (How likely is this to happen?).
Welaptega’s lead business development manager for North and South America spent some time rock climbing in beautiful Kentucky this past month. Rock climbing is a sport of constant risk assessment, where the consequence and likelihood of falling is always changing. For example, the higher you climb the more catastrophic a “ground fall” would be; however, the likelihood of hitting the ground simultaneously decreases as you clip the rope higher and higher. Conversely, as a cliff gets more steep/overhanging, the difficulty (and therefore likelihood that you will fall off) increases while the consequence decreases because you will fall into free space – free from hitting the wall or a ledge on the way down.
Every day, in every aspect of life, we assess the consequences and likelihood of different situations and making decisions. Driving on the highway has high consequences if an accident were to occur (lowered over the years through airbags and crumple zones); however, the likelihood of an accident is low, so we drive to work.
When it comes to offshore moorings it is easy to think that the probability of failure is low. Unfortunately, the evidence proves otherwise. In a recent paper at OTC (OTC-25841 Permanent Mooring Reliability & Mooring Risk Management Plan (MRMP): A Practical Strategy to Manage Operational Risk) the author notes that, for mooring systems designed to API’s 100-year return period environment, the design expectation of notional annual probability of expected line failure should be less than 2.1 x 10-5. Notional annual probability of expected first line failure due to overload should be less than about 10-3. In reality, failures of at least one line are actually occurring at a rate of 1.7 x 10-2, an order of magnitude more. There are many ways to slice the data, but it is important to note that mooring lines are being preemptively replaced or failing before their intended design life at a rate far higher than industry targets. Much like in climbing the likelihood of failure is not a constant, it changes as components degrade differently than the design intended, unexpected metocean conditions, or due to installation errors. Accurately assessing the consequence of failure is the straight forward part – gathering the best data for determining likelihood is where Welaptega comes in.
Welaptega’s vast experience allows us to bring expert eyes to safety critical subsea architecture. Our 20 years of experience allows us to train our offshore specialists in how moorings are designed, how they are meant to perform and how they ultimately fail. We can help you to assess both the consequence and likelihood of a particular mooring component failing. By capturing real world data and combining this with the inspection and tracking of degradation in-situ you have a winning formula to understand and assess your mooring risks.
Climbing photographer: Matt MacPhee