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The Ultrasonic Testing System application at the Russian NPP with the Coerent Data Treatment 'AUGUR' V.G. Badalyan, A. K. Vopilkine Scientific and production center "Echo+", Russia, 123183, Kurchatov-place, 1. Tel. (095) 196-7119, Fax (095) 9357390. E-mail : echo.ndt@g23.relcom.ru. Web : www.echoplus.ru. Contact

I. Introduction

The manual ultrasonic testing methods are the wide-spread ones for NPP equipment testing. But these nondestructive methods have a number of the essential imperfections, the main ones of them are:
1. The impossibility to measure the real dimensions of defects (not the conditional or equivalent ones, as it is usually done). That's why the ungrounded strict standards are appeared and as a result the considerable volume of repair of welds is needed for the unhazardous defects.
2. The absence during the manual testing of the objective document with its results decreases the testing reliability.
3. The operator could receive great doses of the radiation at the manual testing.

The automatic ultrasonic testing methods are free from the mass of these imperfections (2 and 3). The use of these methods is allowed to apply the different data treatment methods, including the coherent ones and then to weaken the effect of the first imperfection. Really, the information parameters at manual ultrasonic testing methods are:
• The presence of discontinuity (defect),
• The conditional length of defect,
• The defect coordinates,
• The reflected signal amplitude, characterized the equivalent defect area.
The information parameters for coherent data treatment methods are:
• The presence of defect,
• The length of defect,
• The height and profile of defect,
• The defect coordinates.
The strength experts are needed the data about the real length of defects, their height, profile and coordinates for analysis. Namely these data are the result of the testing with the use of the coherent treatment methods.
The scientific and production center "Echo+" together with the experts from ENTEK and Russian scientific center "Kurchatov's Institute" has proposed and realized a new approach to the weld quality analysis with the use of the number of the "Augur" systems, developed in our center. The coherent signal treatment is used in these systems.

II. The idea of the weld quality analysis

The use of the coherent data treatment in the computer systems of the "Augur" series is allowed to apply a new approach to the weld quality analysis by means of the analysis of the influence of the defects on the weld strength.
The algorithm of this idea is shown on Fig.1. The crux of the problem is the next. The conventional ultrasonic testing is produced firstly according to the standards and methods applied in nuclear engineering. It could be the manual testing, but the use of the "Augur" system in the round-up (searching) regime is preferable. In this case there is a possibility to have the objective document with results of testing and the operator could not receive great doses of the radiation. If the defects with the higher then the searching or control levels were found, the expert testing is provided by the "Augur" system. The field of each defect is registered in details in this regime with the step of the order 0.3 mm. Then these data are treated and analyzed by the expert in the laboratory in the easy and comfortable conditions. The information about the defect parameters is transferred to the strength experts.

Fig 1: The algorithm of the complex analysis of the weld strength.


It is necessary to point out that there is the considerable experience in the strength calculation and resource determination. The calculation methods are produced and sertificated [1]. The absence of the specific defect dimensions only does not allow to use them widely. The decision on the weld repair advisability is taken on the base of the strength calculation.

III. The apparatus realization of the proposed idea.

The ideology of the developed series of systems is based upon the next essential claims:
• The automatic "Augur" system series should be suitable for the testing of the maximally wide lot of the pipeline diameters and thickness without the essential alteration of the system itself (the scanner and the acoustical block should be adapted to the specific product).
• An optimal set of the system is necessary to ensure during the testing of the specific product of the maximum mobility and the comfort of use. The transportation of the system and
• The system should allow to accomplish the remote automatic control.
• The system should ensure the discontinuity searching regime along the full length of the weld (the fast searching regime).
• The system should ensure the detail data registration regime (the expert regime) for the discontinuity analysis and determination of their real (not conditional ones) parameters, such as coordinates, length, height, type.
• The system should ensure the documentation and the testing result storage for enough long period of time.

The set of the "Augur" series system.
The systems of the "Augur" series are consisted from:

1. The base electronic block with note-book computer, equipped by the talking duplex device. All system control is accomplished by the keyboard or note-book mouse.
2. The remote electronic block.
3. The set of scanners for the automatic travel of the ultrasonic transducers.
   The changing guides are mounted on the scanners to allow to travel the ultrasonic transducers along of pipeline up to 150 mm. The choice of the guiding length is determined by the optimal testing method for the specific pipeline with the thickness from 7 up to 75 mm. It is possible to mount on the scanners of 2, 4 and 6 ultrasonic transducers, which allowed the simultaneous testing of the both weld sides.
4. The set of ultrasonic transducers.
   The set of ultrasonic transducers is determined by the tested products, by their thickness, by the weld type, by the material of product.
5. The set of connecting cables.
   The set of connecting cables, the same for all testing variants, is allowed to ensure the remote control up to 90 m between the scanner and the base electronic block.
6. The software.
The software is allowed to ensure the testing in the searching and expert regime. The software is allowed to analyse the received data as during the registration and mainly after the end of registration.

The main characteristics of the "Augur" series systems


1. The searching regime:

   the pipeline diameter range, mm the weld thickness range, mm the number of ultrasonic transducers, piece the minimal discovered defect, equiv. diameter the mean time for the system mounting and dismounting on the weld, min. the mean testing time for a weld of 1 meter long, min the possibility testing of the austenite welds

   100 - 200 5 - 70 1 - 6 1 3 7 there is

2. The expert regime

   the measured discontinuity characteristics length, height, type (plane or volume) the defect size measurement accuracy, mm the mean time of the expert testing of one defect place, min the increase of the signal-noise ratio at the austenite weld testing, db (it is depended from the weld structure and the applied method)

   ± 1.0 10 6-15

IV. The practical realization of the proposed idea.

The mass expert and searching testing was provided of the most crucible welds of the equipment of the first contours of the Leningrad, Smolensk, Kursk, Balakovo and abuilding Rostov NPP. The generalized testing results are shown in Table 1. The welds were tested, which were rejected according to the in-service manual testing results.

The pipeline diameter, mm	325x16	870x35	980x65	1344x72	Amount
The number of welds, rejected by the manual testing and transferred for the expert testing, pieces	490	220	48	16	774
The number of welds, assayed to repeat expert testing, pieces	170 (110 from them - three times)	84 (54 from them - three times)	5	8	267 (164 from them - three times
The number of welds, allowed to the exploitation according to the expert testing, pieces	425	202	48	16	691
The number of welds, repaired after the expert testing, pieces	65	18	-	-	83
The number of welds, in which the defects are found by the expert testing, pieces	77	15	10	5	105
Table 1: The generalized results for the pipeline welds at the NPP.

All of the defected welds should be repaired according to the existed technology. The welds with the 300 mm stainless steel pipeline diameter were demanded the biggest volume of testing. 490 welds were tested, 425 welds were allowed to the exploitation without the repair after the testing and the strength analysis of and only 65 welds were transferred for the repair. The expert testing showed that there is as the over-rejection at the manual testing (about 7% of the rejected welds did not have defects) and the under-rejection of results up to 30% (the omission of the defects, including the dangerous ones). There is an analogous situation for other types of pipelines.
It is necessary to point that the use of the coherent data treatment is giving a possibility to accomplish the monitoring of the weld state. This monitoring was, in particular, accomplished in Leningrad, Smolensk, Kursk and Balakovo NPP.

V. Conclusions

1. The new approach to the determination of the important weld quality by the complex investigation including the strength calculation was described and used very widely at the Russian NPP. It allowed to reduce considerably the weld repair volume and raise of their exploitation security because the grounded knowledge of the measure of their danger.
2. The Augur-systems, realized this idea, were approved, legitimated at the NPP and used very widely in the repair work periods.
3. The Augur-system use is allowed to minimize the imperfections, inherent in manual testing, to ensure 100% testing volume, to document the results, to reduce considerably (in 10 times) the doses of the radiation for the staff.
4. The Augur-system use is allowed too to accomplish the monitoring, i.e. to look for the defect development during the exploitation and to prepare the weld repair according to the plan.

References

1. Badalyan V.G., Vopilkin A. Kh. The computer systems for the ultrasonic nondestructive testing. Soviet J. of Nondestructive testing, No 3, 7-13, 1993.
2. The method of calculation of the permissible metallic defects in the pipelines during the nuclear power plant exploitation. M-02-91, ENTEK, 1991.

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