·Table of Contents
·Workshop - Reliability
Systematics of NDE Reliability: A Practical Point of ViewGregory Ya. Dymkin, Vera N. Konshina
(NDT Center of RIBNT, St.Petersburg RUSSIA)
An "ideal" way ensure complete and precise evaluation but it is not reproducible and could not be realized because of difficulties to select the representative collection of a test pieces with nature flaws and their destructive examination.
The proposed "practical" way is based on using the test pieces with an artificial reflectors. The only requirement is to make an adequate artificial reflector in the object under NDE and to proof that their are covering the same range of reflection properties that an nature flaws are.
If a manual NDE techniques are validating we must to take into account the effects of AP and HF. That is why practical assessment have to be made
|Stage||"Ideal" procedure||"Practical" procedure|
|Selection of the Reliability Indexes||Justification and choosing of the Reliability Indexes from the list of recommended ones|
|1. Selection of the test pieces||The representative collection of a test pieces with the real flaws||The number of a test pieces with an artificial reflectors of adequate reflection properties|
|2. Practical assessment||Blind Trial using technique under validation and appropriate qualified personnel|
|3. Description of the defective conditions (defect state)||Open trial with an expert technique and Destructive examination||-|
|4. Statistical assessment||Signal interpretation and calculation of the Reliability Indexes|
|5. Evaluation of the result||Comparing of the Reliability Indexes to requirements or other NDE technique, that have been already validated|
|Table 1 : Essential Steps and Features of NDE Technique Validation Procedures|
|No||Terms of the Reliability Indexes||Name||Method|
|1.||Probability of truth detection||P11||POD|
|2.||Probability of false call||P01|
|3.||Indicative size of the defect under given Probability of truth detection||X(P11*)|
|4.||Probability of truth detection under given Indicative size of the defect||P11(X*)|
|5.||Probability of truth detection under given Probability of false call||P11(P01*)||ROC|
|6.||Probability of false call under given Probability of truth detection||P01(P11*)|
|7.||"Reliability function"||D =1 - (P01 + P10)|
|8.||Square under ROC-curve|
|10.||Average "Truth rate"||(P11/ P01)av|
|Table 2 : Statistical Reliability Indexes|
The statistical indexes (Table 2) are based on the probability of true detection and false calls resulting from use of an NDE system. They are derived and constructed using POD and ROC methods.
|Fig 1: Investigation of the stastical reliability indexes|
The test pieces contains the segment reflectors of different size. Reflection properties of segment reflectors extremely depends on the direction of insonification.. The experiment made it possible to verify the following:
In order to check the above mentioned "practical" validation procedure we have compared the techniques of manual (M) and automated (A) ultrasonic testing of welds. The test pieces contain an artificial reflectors such as vertical cylinders and segments. To proof the adequate reflection properties of artificial reflectors the experiment (fig. 2a, b) have been done.
Practical assessment carried out by personnel of UT level II (EN473) qualification.
Statistical assessment has been carried out in agree with procedure described in . The results are:
P11A > P11M ; P11A(dL*) > P11M(dL*); P01A > P01M; DA ~ DM.
The evaluation of the results of validation is based on the values of reliability indexes and depends on practical requirements for the techniques.
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