In evaluating the integrity of a system using fracture mechanics analysis, it is necessary to know the maximum size of flaws which are likely to be present. The effectiveness in reliability of nondestructive examination techniques are used to establish the probability of detection curves for different types of flaws and for different flaw characteristics, i.e., size, shape, orientation, tightness, roughness and location. This information on flaws must be known in order to ensure the systems integrity. The U.S. Nuclear Regulatory Commission has instituted a research program to establish the effectiveness and reliability of ultrasonic in-service inspections performed on light water reactor primary typing systems. This paper describes the results obtained to date and proposed methods of evaluating inspection reliability. A method has been developed for evaluating inspection reliability based on the measured variability of the inspection process. Estimates of the current level of inspection reliability have been made. Efforts are currently in progress to verify the results of these predictions and the effectiveness of the predictive model

Becker, L.

Doctor, S.

English

In evaluating the integrity of a system using fracture mechanics analysis, it is necessary to know the maximum size of flaws which are likely to be present. The effectiveness in reliability of nondestructive examination techniques are used to establish the probability of detection curves for different types of flaws and for different flaw characteristics, i.e., size, shape, orientation, tightness, roughness and location. This information on flaws must be known in order to ensure the systems integrity. The U.S. Nuclear Regulatory Commission has instituted a research program to establish the effectiveness and reliability of ultrasonic in-service inspections performed on light water reactor primary typing systems. This paper describes the results obtained to date and proposed methods of evaluating inspection reliability. A method has been developed for evaluating inspection reliability based on the measured variability of the inspection process. Estimates of the current level of inspection reliability have been made. Efforts are currently in progress to verify the results of these predictions and the effectiveness of the predictive model.</p

Digital Repository @ Iowa State University (ISU)

INTEGRATION OF NONDESTRUCTIVE EXAMINATION RELIABILITY AND FRACTURE MECHANICS L. Becker and S. Doctor Battelle Pacific Northwest Laboratories Richland, Washington ABSTRACT In evaluating the integrity of a system using fracture mechanics analysis, it is necessary to know the maximum size of flaws which are likely to be present. The effectiveness in reliability of non-destructive examination techniques are used to establish the probability of detection curves for different types of flaws and for different flaw characteristics, 1.e., size, shape, orientation, tightness, roughness and location. This information on flaws must be known in order to ensure the systems integrity. The U.S. Nuclear Regulatory Commission has instituted a research program to establish the effectiveness and reliability of ultrasonic in-service inspections performed on light water reactor primary. typing systems. This paper describes the results- obtained to date and proposed methods of evaluating inspection reliability. A method has been developed for evaluating inspection r~liability based on the measured variability of the inspection process. Estimates of the current level of inspection reliability have been made. Efforts are currently in progress to verify the results of these predictions and the effectiveness of the predictive model. 21 SUMMARY DISCUSSION Bruce Thompson (Rockwell Science Center [now Ames Laboratory]): I have two questions. The first one: it seems to me that the data you showed and what you're going to get out of the round robin is sort ·of the same thing. Was it the initial experiment you did that helped to structure the round robin the most optimally? Steven Doctor (Battelle Northwest): That is right. Number one, you have to be able to grow cracks in a known fashion because statistical design says that I want to measure a given size of crack. You don't want cracks scattered all throughout the different sizes because then you don't have a good measure at a particular crack size. There are number of things like that that influence why we did all this preliminary work. Number two, we wanted to come up with some kind of a beforehand estimate as to the range of variations. So this also impacted the statistical design. Bruce Thompson: The second question is: it would seem that ultimately, at least as pertains to the crack orientation parameters, roughness, and so forth, you would like to be able to use some sort of a theoretical basis to predict those variations, particularly as you come into new geometries and so forth and so on; and I guess that's one of the things that's being addressed in this program. Do you have any comments, guidance, or whatever in if you think that would be a useful thing? And, if so, how you see things being vectored to reach that purpose? Steven Doctor: I think it is useful in the sense that right now we're trying to find improved procedures. The better we understand the scattering form for flaws that are not vertical but are off at some misoriented angle, the better we can come up with an improved procedure that has some defense. Right now, the existing code doesn't really have any defense. It is a bunch of work that people have done, but it has not been thorough enough and has not been understood well enough. That is the reason we have an inadequate code section 11 right now. So, yes, I am all for that; and I think its important. If it can be done in a timely fashion to support this, more power to it. I would like to see that kind of effort integrated in. The sooner it can happen, the better off we're going to be because with this kind of lack of credibility as far as I.S.I. is concerned, the sooner we can turn that around, the better the acceptance of the American public to nuclear reactors. Since we haven't been able to find manykinds of flaws with I.S.I., we can't really justify a program to detect and prevent failures as they're happening, on the basis that we are go·ing in to try to figure out how to detect them. Dick Berry (Lockheed): Who are the participants going to be on this round robin? Secondly, wasn't there a previous round robin that EPRI sponsored a while back? Steven Doctor: The question in regard to the previous round robin, I don't know. I know there are some engineering evaluations of advanced techniques that have been going on, but I don't know of an evaluation of ASME code procedure requirements. Unidentified Speaker: Only RP-605. That was part of the round robin. Steven Doctor: You're right. That was a plate that originally started out with Babcock and Wilcox. They put in a number of different defects that were welded in place, and this plate was sent around then to a number of researchers within the u.s. and also over in ~rope. However, a final report on that effort has not been published. There are actually seven groups. They are: NES (Nuclear Energy Services), Southwest Research Institute, Peabody, General Electric, Westinghouse, Lambert, McGill, and Thomas. There is one other one. Otto Buck: (Rockwell Science Center [now Ames Laboratory]): Can you say something if you look at cracks -does mode two- are you balled for difference in crack geometries like mode two cracks, mode one cracks, branched cracks. Did you take those things into consideration in your work? Steven Doctor: I'm not sure what you mean by mode one and mode two. Otto Buck: A shear mode kind of crack, crystallogrphic crack, for instance, which is one that is perpendicular to the tri-axis, more roughness and more opening than in a shear mode. Steven Doctor: Well, in regard to the data base, the bending fatigue cracks are quite smooth and quite open. The thermal fatigue cracks, we don't have as much control over those. They tend not to all lie in a plane, and they tend to be very rough; and sometimes you do get some end effects and discontinuities and things like this, so they are somewhat of a collage, if you will, of all the bad things. They don't tend to splinter up like an IGSCC does, however. They don't give you large amount of branching. 22 G.J. Posakony (Battelle Northwest): One of the important things to recall on the slides that were shown -we often talk of probability of protection. Steve was talking of probability of recording level. It may well have been detected, but in accordance with the code requirement, it was not reportable. Consequently, the statistic says it's a zero instead of a positive, and it really affects the curves. It affects our ability to get data that we can then translate to other people saying what our reliability of detection is, or reliability of inspection. Very dramatic influence, though, on what the code says we're going to do versus that which is really seen from the instrumentation. Mike Buckley, Chairman (DARPA): Thanks very much, Steve. 23 

Integration of Nondestructive Examination Reliability and Fracture Mechanics

Becker, L

Doctor, S

Iowa State University Computer Science Technical Reports

https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1004&amp;context=cnde_yellowjackets_1981

Integration of Nondestructive Examination Reliability and Fracture Mechanics

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Digital Repository @ Iowa State University (ISU)

Iowa State University Computer Science Technical Reports