Condition Monitoring Location (CML) Selection is certainly one of the most critical components of a successful Mechanical Integrity program. It’s one of the final steps before beginning inspection activities, but is rarely given sufficient attention. The goal? Find the damage before it finds you, shifting to a proactive mode rather than reactive, while minimizing resource consumption. All of the prerequisites to inspection lose a considerable amount of value if you aren’t looking in the right locations with the right technique.
All of the asset organization, datamining, and risk assessments (if RBI was the chosen strategy) culminate in performing nondestructive examination of assets to determine their current health. If you’re looking in the wrong locations it’s akin to using a dipstick to check tire pressure; in this case it's all for naught.
We continue to see inspection isometrics, for equipment and piping alike, peppered with CMLs in a “shotgun” approach, most being a single point UT reading that is misaligned to the expected degradation. This occurs after years of inspection, with new CMLs being added for different special emphasis efforts or even just because a documented strategy was not available and over application became the “safe” approach. The NDE technique remains the same to keep costs low and there is no program in place to eliminate an in-kind location that shows no degradation.
We recommend an approach that is simple to apply, easy to replicate, and strategically targeted with the only prerequisite being that your program has progressed through a robust damage mechanism identification process. Focusing on the damage mechanism and damage modes, you can target the right components with the appropriate NDE technique to maximize your chances of finding damage while limiting wasteful inspection. More specifically, selecting an RT shot on a high velocity Lean Amine process elbow vs a single point UT reading, or performing UT scanning in your column overhead system where you’re expecting Ammonium Bisulfide salt deposition as well as the potential for liquid water.
Combining the likelihood and type of failure with some consideration for consequence; you can expand or shrink your coverage based on perceived risk. It’s important to note that a full RBI process does not need to be present, merely a consideration for consequence using API-570 piping class will often suffice! Reviewing past inspection data can fortify your damage mechanism assessment and allow you to preserve CML locations that have known high degradation or low remaining life. This doesn’t require Weibull distribution analysis or a high tech black box selection process that ties you to a specific vendor. It’s a simple logic-based approach that can be expanded or minimized based on future findings, by your own inspection department.
Some additional considerations:
All the above is contingent on a robust, documented, and defined CML placement/selection process.
Are there organizational processes in place to ensure CML locations are added and removed when changes are made out in the field? If not, you may find yourself back in the same starting position after a handful of inspection cycles.
Do you have sufficient metadata (component, access requirements, NDE technique etc.) to effectively plan your inspections well in advance? An initial desktop process may be possible that can make your subsequent field efforts much more efficient.
Are there “critical path” assets that would benefit from more advanced NDE or screening tools to minimize unexpected downtime?
We have previously mentioned the importance of CML Selection and precursor integrity management processes in our commentary on the PES Philadelphia disaster: https://www.modusoperationsllc.com/blog/integrity-management. Reviewing CSB reports it may be noted that CMLs were not placed on the failed component in major disasters such as at PES or Richmond California, but they were placed on neighboring components that were of slightly different metallurgy. SME involvement and an in depth understanding of these historical disasters can offer invaluable insight into strategies that reduce the risk of these extremely hazardous loss of containment events.
Ultimately, we want to maximize inspection value while minimizing operations risk and the right CML selection process will help you do both!