Vol 52, No 10 (2016)

Passive ultrasonic tomography is described. Results of developing, modeling, and testing some key techniques in passive ultrasonic tomography are provided. The techniques include an algorithm for determining arrival times of noisy acoustic signals with sloping leading edge; a method for determining the source coordinates and onset times of acoustic signals and estimating the accuracy of those; and regularizing procedures for tomographic reconstruction of nonuniform distributions of propagation speed of acoustic signals. The results of modeling the effect of measurement noises on the accuracy of source location and the mutual influence of the source location accuracy and the soughtfor nonuniform distribution of propagation speed of acoustic signals are described. Results of experimental testing of the developed techniques are also provided.

Ultrasonic Time of Flight Diffraction (TOFD) is now a well established NDE technique finding wide applications in the industry for inspection during manufacture, pre-service and also inservice. While conventionally interpretations of UT images are done by the inspector, a need has always been felt for automated evaluation and interpretation especially when large inspection volumes are involved. Apart from enhancing the speed of inspection, automated evaluation and interpretation provides better reliability of inspection. A number of approaches based on signal analysis coupled with artificial neural networks (ANN) are being tried internationally and limited success has also been obtained. This paper focuses on the development of a semi automatic toolbox for reliable and fast flaw classification in TOFD images using ANN. TOFD images are first acquired and statistical parameters such as mean, standard deviation, energy, skewness and kurtosis are calculated for the region of interest in the images. The classification of the flawed region like Crack, Lack of Fusion, Lack of Penetration, Porosity and Slag Inclusion was materialized using different ANN approaches which made use of these statistical parameters as their input. The process of optimization of a network involves comparison of classification accuracy and the sensitivity of the selected networks. The Cascade Feed Forward Back Propagation (CFBP) network with log sigmoidal activation function proved to be the optimized network model for the data set considered in this study.

A review is provided of techniques for digital processing of noisy X-ray computed tomography and introscopy data that are represented by halftone images. The most hazardous crack flaws placed against a background with a wide range of brightness have been studied. Difference median and slit filters are proposed for processing such images.

Some results are presented that are concerned with the use of magnetic methods and tools for nondestructive testing of articles made of OAO Izhstal’ austenitic chrome-nickel steels. It is shown that modern magnetic-testing techniques help significantly in optimizing the industrial process while improving the technical specs of the produce.

Results of using powerful LED matrices to inspect metal articles for hidden corrosion by active thermal-wave method are described. The effect of the color of paint-and-lacquer coating on the efficiency of heating with LED and halogen emitters is analyzed. The possibility of using powerful LED panels as thermal stimulation sources in portable flaw detectors is described.

A radiowave method of detecting and positioning hydrate blocks in pipelines is considered. The method consists in probing a pipeline with a high-frequency nanosecond-duration radio pulse with subsequent measurement of its travel time to the hydrate block and back. Results of a natural experiment and flow charts of a device for determining the position of a hydrate block imitator (ice) in a stub pipe with a diameter of 273 mm. A Gunn diode is used as a generator of microwave pulses with a duration of 10 ns and a basic frequency of 10 GHz. The decay of microwave pulses in the pipe and the potential of the radiowave method are estimated.

Possibilities, application domains, advantages, and limitations are considered for currently used physical methods of nondestructive testing of additive manufactured parts. The methods are classified according to the physical principle of operation.