Table of Contents ECNDT '98 Session: Ultrasonic

MAPPscan - Acoustic Positioning System for Manual Ultrasonic testing of Pipes and Componets. P-H Svahn SAQ Kontroll AB Corresponding Author Contact: Alexander Blomquist SAQ Kontroll AB, SE-431 53 MOLNDAL - Sweden, Tel: +46-31-866000, Fax: +46-31-866162 Email: alexander.blomquist@saq.se

TABLE OF CONTENTS

Abstract The UT Acqusition System The Evaluation System Performed Tests Conclusion References

Abstract

MAPPscan is a manual ultrasonic testing system connected to an acoustic positioning system.. The system is developed as a consequence of the increased radiation doses in nuclear plants . The system has the same flexibility as manual scanning with the same accuracy and the possibilties to collect, store and evaluate the UT data as with mechanised Ultrasonic systems. The positioning system is based on spatial acoustic triangulation and have an accuracy of better than 1.0 mm within its recommended range.
Advantages of the MAPPscan system compared to a manual system:


• Ensures a high quality and reliability of the testing.
• Great reproduceability in reinspection
• Superior data evaluation features
• Complete documentation (Printouts of all images)
• Potential to reduce radiation doses for a small and specially trained group of UT evaluation experts.
Another advantage with the system is that the quality of the scanning, in terms of the angle towards the weld and track partition is increased compared to manual ultrasonic testing due to the fact that the scanning technician is able to concentrate on the object rather than on the oscilloscope while scanning.
The positioning system is connected to a computer where the UT-signals are stored and presented together with parameters for positioning and UT-setup. In the evaluation post processing software the stored UT-data can be presented as A-,B- and C-scans . The C-scan can be presented with Top-, End- and Side views.

Fig 1: The positioning system

THE POSITIONING SYSTEM is acoustic using spatial acoustic triangulation to measure the physical position of the ultrasonic probe. It consists basically of a transmitter sending signals to microphones mounted on a collar attached to the tested object. The signals are then measured and calculated by a calculation computer which transforms the signals into X-and Y co-ordinates which are then transferred to the acquisition unit together with the ultrasonic data.The system is tuned and filtered so that noise from the surroundings is prevented to interfear with or disturbe the positioning signals.
The system also consists of a LCD-screen located nere the object to be scanned. This screen is a slave to the one on the acqusition computer and consequently shows the same image. The purpose of this screen is to help the scanner technician to acheive a full coverage of the area to be scanned.
The screen shows the predefined area to be scanned and filled to ensure maximum coverage. The transmitter operates with a frequency of 40 kHz and with a pulse repetition frequency of 200 Hz. This gives the system an accuracy in positioning of better than 1 mm.
The maximum distance between transmitter and receiver is 350 mm. The transmitter on the probe can be rotated making it possible to perform a sequence of scans on a perticular weld and on neighbouring welds without moving the microphone collar. The Calibration of the positioning system is carried out using a bar with a given distance which is placed between the referenspoint on the microphone collar and the probe. The distance is then entered into the acquisition software together with informations of the air temperature close to the tested object, pipe dimension, type of UT-probe (probe height) and scanning direction.

The UT Acquisition System

The UT-Acquisition system hardware consists of a 1 channel ultrasonic board, for puls/echo, one or two crystal probes. It operates within a frequency range of 0,5 - 15 Mhz and with variable sampling frequencies in steps of 20,40 or 80 MHz.
The software contains features such as TCG- compensation, information on probe rotation, compensations for object geometry and can provide a choice of A- , B- and C-scan images while scanning.
The software also hosts a maximum amplitude function which ensures that the signal with the largest amplitude is stored for each point. This function also guarantees that such a signal is not written over by a following scan producing a lower amplitude signal at the same point. It can also provide a full documentation of data set parameters.

Fig 2: The MAPPscan SYSTEM Layout

The Evaluation System

The Evaluation system is a Windows based open system through DLL, Dynamic Link Library, which provides great flexibility in evaluation and presentation of data. It also makes it possible to customise evaluation and images for special applications. The time gates can be set after testing and there is a 256 colour range for amplitude. The software include FFT -facilities which enables measurements on used probes for parameters such as center frequenzy and bandwidth.
Another feature is a repositioning program (Repos.exe) which is used for the purpose of correcting positioning data collected when scanning on a pipe elbow or when scanning is performed with the microphone collar mounted on the elbow itself.
This type of scanning produces positioning data which is false in both x- and y-direction caused by the fact that acqusition software operates assuming that the shape of the test object is cylindrical. The acqusition file has then to be processed by the repositioning program before processing of the UT-data together with the positioning data for evalutation can be performed.

Performed Tests

The system has been in full use during the shutdown periods of 1996 and 97 in the nuclear industry in Sweden. Performed tests have produced excellent results under sometimes difficult conditions.
The system has been qualified under the new regulations for ISI in Swedish nuclear plants, SKIFS, during the spring of 98.

Conclusions

The system has proven to be a powerful tool for inspections in the Nuclear industry with the potential of reducing the radiation doses for a highly qualified group of personnel and at the same time ensure a high quality and reproducibility of testing.

References

1. P.Mas, P. Delmotte, P. Sas , Proc. of IEEE Instrumentation and Measurement Technology Conference; Brussels, June 4-6, 1996.
2. A.Shimokobe, S. Ma, Proc. of the 11^th IMEKO World congress, Houston, Vol B, pp.441-447, October 1988.
3. ASME XI Boiler and Pressure Vessel code. Appendix III "Ultrasonic examination of piping systems"
4. Dr. H. Wirdelius, Private Communication (1997)