It takes a lot to become a highly qualified nondestructive testing technician. Candidates must have a growth mindset, readiness to learn, and subject themselves to a number of hours of training and education. As with most professions, a large part of understanding nondestructive testing as a practice is understanding the language of the field. Here, we will dive deep into the terminology of NDT with an explanation of a key term: Probability of Detection or POD.
In the simplest of definitions, probability of detection is a way to measure just how reliable the nondestructive testing inspection will be for a given asset.
Detection uncertainty is a crucial component of the nondestructive testing practice. According to the Materials Research Institute, detection uncertainty is the process of determining whether or not a flaw is detected. While the entire practice of nondestructive testing is for the sake of detecting flaws and inconsistencies, this is not quite as cut and dry as it may appear.
Taken at face value, detecting a flaw would indicate that any asset or material that is not manufactured and maintained in its purest condition is unfit for use. Certainly, there are a number of imperfections that a component may have and still function perfectly well. Detection uncertainty and probability of detection are both concepts that lay the foundation for determining whether a flaw truly exists within a component under inspection.
Generally, there are four outcomes of a test that constitute the matrix of POD,
An item is flawed and the NDT method detects it (True Positive)
No flaw exists and the NDT method indicates a flaw present (False Positive)
An item is flawed and the NDT method does not detect it (False Negative)
No flaw exists and the NDT method has no indication of a flaw (True Negative)
Developed by NASA in the 70s, probability of detection is the attempt to articulate a minimum flaw size that can be reliably detected by the NDT technique.
According to the Material Research Institute, “This is best done by plotting the accumulation of flaws detected against the flaw size of all the flaws "detected" or that produce a response over some threshold. Ideally all flaws over some critical size will be detected and flaws smaller than that are not "detected". The tool most commonly used for POD description is the POD curve.”
Ultimately, the confidence level must take into account the implications of the full matrix for POD where the potential for false calls is present.
Much like the entire field of nondestructive testing, concepts such as probability of detection are complex and nuanced. It takes a lot more than reading an article to sufficiently understand and implement these practices. This is precisely why achieving NDT certification requires quality education through ndt courses that offer hands-on instruction from experts who know this terminology backwards and forwards.
Becoming an expert technician starts with high caliber training at an NDT school like TXNDT. Since the requirements of an NDT technician can change from job to job, the expert instructors at TXNDT ensure that all prospective technicians are qualified to take on whatever their next job throws at them.
From introductory NDT courses to NDT level 3 certification, we take an active approach to educating all of our students and encourage all prospective technicians to take an active role in their own learning.
If you or your staff are looking for ways to expand your skills and broaden your career opportunities through nondestructive testing courses, consider NDT certification. Don’t trust just any NDT school. If you’re looking for a top-tier experience, give us a call today at 281-231-0001 or check out our website for more information.