Optimize Your Inspection Plan for the Greatest Probability of Detection (POD)
Oftentimes, asset owners do not give sufficient weight to the probability of detection (POD) in their asset integrity management programs. Yet, the continued operation of critical assets and the prevention of failures depends on correctly identifying damage, modeling, and predicting corrosion rates. This relies on the effectiveness of an inspection methodology for a given piece of equipment. Understanding the maximum POD for an inspection method is vital.
An example of a very simple, typical inspection plan:
- Per the code, or someone advising it is time, it is decided XYZ piece of equipment is due for an inspection.
- A work order is then issued to an inspection contractor.
- The inspection contractor uses a method they have previously used to inspect XYZ piece of equipment, obtain a reading, issue their report, and move on to the next job.
Some identifiable and correctable limitations to using this approach:
- It assumes inspection is occurring in the right place, to begin with. In many cases, condition monitor locations (CML) have not been modified in 10+ years.
- It assumes that the inspection contractor knows and understands what damage mechanism(s) to look for.
- It assumes that the technician understands and is able to find said damage mechanism when present.
- It assumes the gage or technology selected is appropriate for the given task.
- It assumes that the method of reporting will provide what the inspector or engineer is looking for.
Ultimately, a lot is assumed. However, quality inspection planning eliminates as many assumptions as possible. This yields a higher POD and therefore higher reliability of the plant and equipment. Some of the factors of a quality program are outlined below:
The inspection plan and the amount of real estate covered.
Have historical bad actors, the age of equipment, IOW excursions, and change in material been taken into consideration? What exact flaws are being looked for? Does the allocated budget allow for a thorough job to be completed?
The technology and inspection equipment you are using, including calibration.
Is the inspection equipment adequate and in good working order? What are the sensitivities and limitations of a particular piece of technology? Are available screening technologies with volumetric displays being used, to maximize POD?
The training and ability of the technicians performing the tests, including physical condition, experience with a particular damage mechanism, mental state, etc.
What kind of training and experience do the contracted technicians have? How thorough and reliable are they based on their history? Is there a clear understanding of the damage mechanism? Does the technician demonstrate that they can find that type of damage? More often than not, the answer is no. Technicians have been certified to ASNT Level 2 or 3, but rarely demonstrate their abilities on all important and high consequence damage mechanisms.
The testing environment, including weather and other stressors such as working at height and/or extreme heat or cold.
Humans are all prone to performance variation given increasing stressors. Has this been taken into account when considering the probability of detecting damage? Especially when working on high consequence of failure equipment? Are there any hazards in the environment that can skew results or prevent 100% coverage of what the inspection plan calls for? Are there any potential safety issues that need to be addressed before technicians can go in? Have all of the stressors been reduced as much as possible? And where not, has the reliability of the inspection results been appropriately discounted?
When considering all of these factors together, the overall quality of inspection can be revealed. The probability of actually detecting damage mechanisms, and therefore controlling them and ensuring plant reliability and personnel safety, is a multiple of these factors. Time and effort spent in optimizing each factor leads to a better inspection and ultimately concise reporting with actionable insights into the condition of the components in the end.
If you have any questions or would like to know more about how to optimize your probability of detection, please contact one of our inspection specialists today!
