Civil Profile of Failure Risk (Step 7)

Find below additional details for Step 7 of the Civil RBI Methodology.

Age-Related Failures

The time-dependency of likelihood can be used to define a profile of the future risks. This is obviously only applicable for age-related failures. The likelihood class can be determined from the likelihood matrix as shown below. In this method, it is assumed that the degradation rate is constant.The likelihood class can be determined from the likelihood matrix.

Failure Risk for Non-Age-Related Failures

The key question here is: “What is the failure risk at the present time?”

Note that in this context the present time means “the failure risk as evaluated at this time using the data from the most recent inspection”.

Failure risk is a combination of consequence of failure and likelihood of failure. As indicated earlier the RAM is used to determine the present risk, see below.

Risk Assessment Matrix.

The risk matrix distinguishes four risk levels. R1 denotes Low, R2 denotes Medium and R3 denotes High and R4 Very High. Site management should decide for each level whether the risk is as low as practicable (ALARP). Depending on the failure consequence, it may be decided to have a managed run-to-failure approach for certain assets or have a PM plan with upkeep tasks. Note that strictly speaking ALARP is on an asset by asset basis – especially in the R3 and R4 areas and for this reason practitioners are invited to do the economic PM task first to see if it is worth the funds.

When an operating unit uses a different risk assessment matrix, then it may be possible to map the outcome of the Shell RAM in IMS with the site-specific RAM.