Flaw

In Section 13.2, it was suggested that opex is estimated at the development planning stage based upon a percentage of cumulafive capex (fixed opex) plus a cosf per barrel of hydrocarbon production (variable opex). This method has been widely applied, with the percentages and cost per barrel values based on previous experience in the area. One obvious flaw in this method is that as oil production declines, so does the estimate of opex, which is nof the common experience as equipment ages it requires more maintenance and breaks down more frequently. 

The main goal of ultrasonic grain noise suppression in material flaw detection is to improve the perceptual possibilities of the operator to observe defect echoes. The suppression is defined as perceptually ideal when a received signal (or image) which contains echoes buried in noise is filtered to yield nonzero values only at the positions of the defect echoes. 

The spectram acquired in this way can he used for characterization of the inspected object or detection of flaws in it. Since the spectram gathered by the modem instrument can consist... 

A number of real objects with artificially made disbonds were tested using the Fokker Bond Tester and spectra were stored in a PC for the classification. One of the objects, "Lower wing skin is shown in Figure 4. As can be seen, the positions and sizes of flaws are marked. The same marks were also drawn on the actual objects to facilitate measurements. 

Blind test data was classified 100% correctly between flawless and defect samples. Layer containing flaw was determined correctly in 97.2% of the cases (see Table 2 for details). 

The results obtained with NSC in different applications show that both flaw detection and localization can be performed automatically by the use of a neural network classifier. 

B. A. Auld, F. G. Muennemann and M. Riaziat, Quantitative modelling of flaw responses in eddy current testing. In R. S. Sharpe (ed.), Research techniques in nondestructive testing, Vol. 7. Academic, London, 1984. 

We present a novel method, called VIGRAL, to size and position the reflecting surface of a flaw. The method operates on standard B-scan recorded with traditional transducers, to extract Time-of-Flight (ToF) information which is then back-projected to reconstruct the reflecting surface of the flaw and characterize its radiation pattern. The VIGRAL method locates and sizes flaws to within k/2, and differentiates between flat and volumetric defects. 

Figure 3 Virtual source distribution for a rounded flaw.

The upi-SO screen display ( Figure 7 ) shows the A-scan signal (top) and the resulting B-scan image (bottom) for the tandem arrangement of Figure 6. The flaw reflection is seen on the left. 

To evaluate the VIGRAL method, we scanned steel blocks with simulated flaws using a Flexilrak and a upi-50 instrument. This system allows for rapid and accurate acquisition of the desired data, including the A-scan, B-scan, and C-scan data, and serves to evaluate, offline, the V-scan image (Figure 8). 

This step is dedicated to the extraction of various flaw parameters (topological, geometrical and functional), such as texture, size or shape, which ate essential for the pattern recognition module. 

An invariant pattern recognition method, based on the Hartley transform, and applied to radiographic images, containing different types of weld defects, is presented. Practical results show that this method is capable to describe weld flaws into a small feature vectors, allowing their recognition automatically by the inspection system we are realizing. 

New Flaw Visualization NDE Tools as a Basis for Modem Strength Maintenance. 

Insurance in pressure boundary integrity of NPP unit is strongly influenced by technical capabilities and efficiency of metal examination system. Ordinary ultrasonic examination tools and procedures have limitations in flaw sizing and positioning. The problems arise for welds and repair zones of welds made by filler materials of austenitic type. 

Up-to-day reliability requirements as applied to NPP strength maintenance govern development of new generation of computerized systems for in-service inspection. These systems in parallel with capabilities of ordinary ultrasonic techniques allow to reconstruct high resolution image of inner flaw and increase available amount of information. 

The main purpose of AUGUR4.2 expert ISI is the application to zones where some flaws (indications) had been revealed by scheduled manual ultrasonic inspections. Information provided by AUGUR 4.2 is used for decision-making further surveillance of these zones or corrective measures. The procedure of AUGUR 4.2 examination is included into the approved general scheme of ISI [1]... 

Real position, type and sizes of these flaws have been discovered. On the basis of this information it was possible to characterize flaw as independent or take into account their interaction in strength assessments. 

AUQUR 4.2 revealed a number of small-size defects with the height of about 2 mm did not detected by manual inspection. These flaws were located near the boundaries of cut-off zone of repaired welds and likely had originated after near-boundary passes of repair welding [3]. 

Anumber of defects with manual inspection indications clarified by AUGUR 4.2 records have been accepted for further operation in 1996 with prescription of next year AUGUR 4 2 inspection. Based on two consecutive inspections (1996-97 years) comparative analysis of AUGUR 4.2 data was executed. It was shown that the flaw configurations, reproduced by AUGUR 4.2 are stable and the small differences are conditioned only by system thresholds of linear coordinate and signal amplitude as well as variations in local conditions of in-site inspection. 

The results of the comparative analysis in terms of changes in flaw length and maximum height are shown in Fig. 3. As can be seen the flaw parameters are stable, and the height maximum increase (2 mm) correlates with the AUGUR4.2 precision of linear measurements. 

Information supplied by flaw visualization systems has decisive influence on fracture assessment of the defect. Results of expert ultrasonic examination show that in order to take advantage of AUGUR4.2 potentialities in full measure advanced methods of defect assessment should be applied using computer modelling, in-site data of material mechanical properties and load monitoring [4]. 

Using flaw visuahzation system data the strength and fracture mechanics estimations are carried out in accordance with defect assessment regulatory procedure M-02-91 [5]. Recently, the additions had been included in the procedure, concerning interpretation of expert flaw visualization sysf em data, computer modelling, residual stresses, in-site properties of metal, methods of fracture analysis. 

AUGUR-family expert NDE tools, developed in Russia, showed good capabilities of flaw sizing and characterization during on-site inspections at numerous Russian NPPs. 

The benefits of flaw visualization tools applications are supported by strength maintenance software, based on computer modelling and realizing assessment procedure. 

Arzhaev A T, Bougaenko S E., Denisov I N., Aladinsky V V, Makhanev V.O. Technical basis and software development for flaw assessments in NPP pipeline welds. In Ageing of Materials andMethods for the Assessment of Lifetimes of Engineering Plant, R.K. Penny (Ed ), 1997, pp. 63-68. 

RDIPE, VNIIAES. Procedure for Allowable Flaw Sizes Evaluation in Metal of Equipment and Piping during NPP Operation, M-02-91, (in Russian). 

Fig. 2. Images of the flaws detected by Augur 4.2 in the primary circuit welds...

Fig. 3. Changes in flaw dimensions detected by Augur4.2 during 1996 and 1997 years inspections.

It must be admitted that eddy currents are a little unmanageable, they tend to flow where they want as soon as the magnetic field leaves the probe, so we may not know for certain what a flaw is really like. 

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