NDTsi 2001 Session: Advances in Non-Ultrasonic NDE Methods
Evaluation of Acoustic Emission Technology to Locate Flaws with Small Stress Intensity, and Determine their Type and Danger Level
R. Axelsson, L. Johansson, Oskarsham NPP, Sweden; J. Cwiefeld, AF Kontroll, Sweden; G. Muravin, B. Muravin, L. Lezvinsky, Margan Physical Diagnostics, Israel
ABSTRACT
Austenitic stainless steel pipes and bends with high carbon content have been removed from the piping system due to stress corrosion problems. Some of these pipes contain Intergranular stress corrosion cracks. The cracks were detected, located and sized by conventional NDE-methods. PT, RT and UT prior to acoustic emission (AE) investigations. J-integral values of flaws for operating conditions of piping were calculated. Five pipes with established and known cracks were selected for the AE-trial. Two identical crack-free bends were used as references. The nominal outer diameter varies from 168 to 219 mm. The nominal wall thickness varies between 12.5 to 16 mm. The pipes have one or two longitudinal welds. Two pipes, one with cracks and one flawless were reserved for calibration and open test. Five pipes were used for the "blind" trial of the AE specialists. The pipes were pressurised in steps between 50-135 bars at room temperature according to an established plan. Data collection was permitted to start 15 minutes after the testing pressure was stabilised. The power plant administration supervised the tests and evaluated the results. The results of the tests showed:
Pipes with cracks were separated from faultless pipes with an accuracy of 100% under 50% of the operational pressure.
Correct classification of the cracked pipes with respect to flaw size and its danger level.
Successful correlation between parameters of AE, pressure and flaws danger level (J-integral value).
Publication Source: 3nd International Conference on NDE in Relation to Structural Integrity for Nuclear and Pressurized Components, November 14-16, 2001, Seville Spain. Publisher: Tecnatom s.a. - [Homepage]
