Development of a Virtual Instrument for Immersion Type Ultrasonic Inspection with a Computer Controlled Multi-Axis Motion Controller
The Pulse Echo (PE) technique is a widely used ultrasonic non destructive testing technique to test materials by analyzing ultrasound echoes reflected from flaws and discontinuities. In conventional PE technique, called contact type PE, an ultrasonic transducer is in constant contact with a test piece, transmitting and receiving ultrasonic signals from the test specimen. The inherent shortcomings of PE are the need for; uniform couplant conditions, the ultrasonic transducer to remain in contact with the test object throughout the scan and a limitation to scan regular surfaced objects only. This paper provides for extending a system initially developed for contact type PE, to perform Immersion Testing (IT) which is a contactless pulse-echo inspection method with the probe and test piece separated by a predetermined volume of water of certain thickness. A computer controlled 3-axis transducer position manipulator (motion frame) is constructed for assistance in conducting automated tests. The efficacy of immersion testing relies on the precise control of the motion of transducer. The existing immersion type motion controllers along with dedicated data acquisition and analysis system are quite expensive and are beyond the affordability of smaller ultrasonic labs. Hence the proposed system including the motion frame and Data Acquisition Unit (DAQ) can serve as a competent, low-cost and reliable IT system benefitting several small scale industries and labs.
Immersion Ultrasonic Testing on EUROFER Welded Joints for Determination of the Minimum Detectable Flaw Size
The ferritic-martensitic steel EUROFER is intended for use as a structural material for blanket components of future fusion reactors. A blanket module consists of a multiplicity of diffusion-welded cooling plates, which are connected by TIG, EB or laser welding seams. For the quality assurance of these welding seams the ultrasonic non-destructive testing is currently examined. In the context of this work the ultrasonic immersion testing is considered for the examination of EUROFER parts including welding seams of different types (diffusion welding, electron-beam welding and TIG - welding). Differently arranged artificial flaws of varying sizes were introduced into the welding seams to determine their minimum detectable size. In essence, the artificially introduced flaws for immersion testing consisted of longitudinal holes and cross holes 0.2 mm to 1.0 mm in diameter as well as of tungsten wires whose diameter was in the range of 0.2 mm to 1.0 mm. Investigations were conducted using the KC 200 immersion testing facility developed by GE Inspection Technologies. Ultrasonic testing was performed intermitting straight- and angle beam examinations of longitudinal and transverse waves from sensors of different resolutions. The DAC (Distance Amplitude Correction) curves for flaws that are 0.2 mm and 0.1 mm in diameter were derived from the measuring results in addition.
Variations of sulphur dioxide at the cloud top of Venus’s dynamic atmosphere
A pulse of sulphur dioxide in Venus’s upper atmosphere was observed by the Pioneer Venus spacecraft in the 1970s and 1980s and attributed to volcanism. Recent sulphur dioxide measurements from Venus Express indicate decadal-scale fluctuations in sulphur dioxide above Venus’s cloud tops in an atmosphere that is more dynamic than expected. Sulphur dioxide is a million times more abundant in the atmosphere of Venus than that of Earth, possibly as a result of volcanism on Venus within the past billion years1,2. A tenfold decrease in sulphur dioxide column density above Venus’s clouds measured by the Pioneer Venus spacecraft during the 1970s and 1980s has been interpreted as decline following an episode of volcanogenic upwelling from the lower atmosphere3,4. Here we report that the sulphur dioxide column density above Venus’s clouds decreased by an order of magnitude between 2007 and 2012 using ultraviolet spectrometer data from the SPICAV instrument onboard the Venus Express spacecraft. This decline is similar to observations during the 1980s. We also report strong latitudinal and temporal variability in sulphur dioxide column density that is consistent with supply fluctuations from the lower atmosphere. We suggest that episodic sulphur dioxide injections to the cloud tops may be caused either by periods of increased buoyancy of volcanic plumes, or, in the absence of active volcanism, by long-period oscillations of the general atmospheric circulation. The 30-year observational record from Pioneer Venus and Venus Express confirms that episodic injections of sulphur dioxide above the clouds recur on decadal timescales, suggesting a more variable atmosphere than expected.