Measurement of Acoustic Emission Signals: Influence of the Couplant

The acoustic emission (AE) technique, whose modern roots are found in the early 50’s, analyses the elastic waves generated into solid materials in a frequency range usually well above the human ears limit. AE are sound waves emitted when abrupt variations occur in the local distribution of strain in a medium. These variations are generally associated with, for example, the growth of fractures, phase transformations and corrosion under various loading conditions. This is why the AE technique can be applied as a non destructive and passive tool in condition monitoring of structures, a typical application being the pressure vessels and piping field. In this paper, after a short summary on wave propagation, the AE is simulated by a pulse generator, acting on a bar and a plate. The aim is to highlight the effects of the sensors positioning on some of the parameters frequently adopted to describe the AE activity, e.g. its amplitude and strength.

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INFORMATION AND KINETIC APPROACH TO THE EVALUATION OF STRESS STATE OF VESSELS OPERATING UNDER PRESSURE IN HYDROGEN ENVIRONMENTS

Kontrol Diagnostika ◽

10.14489/td.2021.06.pp.030-045 ◽

2021 ◽

pp. 30-45

Author(s):

V. V. Nosov ◽

A. R. Yamilova

Keyword(s):

Acoustic Emission ◽

Pressure Vessels ◽

Maximum Activity ◽

The State ◽

Material Structure ◽

Diagnostic Efficiency ◽

Active Volume ◽

And Control ◽

Non Destructive ◽

Altitude Level

Separation of the influence of various factors on the strength of the material and control parameters is the basis for increasing the diagnostic efficiency. The article describes methods for assessing the state of pressure vessels, features of their damage under conditions of hydrogen absorption, presents data from acoustic emission and ultrasonic testing, compares them, sets out an approach to non-destructive assessment of the strength state of technical objects, based on a multilevel model of time dependences of acoustic emission parameters (AE), the kinetic concept of strength, micromechanics of fracture of discrete media, their relationship with the resource, parameters of fatigue curves and characteristics of the material structure, the problems of the influence of strength and metrological heterogeneity on the information content of control, the sequence of assessing the indicators of the strength state and resource of vessels, the model of strength and metrological heterogeneity of the AE are presented control, explaining the maximum activity of AE during tests in the first periods of operation, a methodology for assessing the strength state of pressure vessels is presented. Demonstration of the effectiveness of the technique is shown as an example of AE testing of an absorber for purifying hydrogen sulfide with a monoethanolamine solution by predicting the resource of its components and comparing the prediction results with the coordinate-altitude level of the adsorber belt, which correlates with the average internal hydrostatic stresses. Approbation of the approach has shown its versatility on the example of effective application for objects with defects of both fatigue and chemical origin under conditions of hydrogenation. Using the example of assessing the state of the most damaged lower belt, it is shown that an increase in the AE activity during hydrogenation of the material occurs mainly due to the growth of the acoustically active volume of the controlled zone, which is not unambiguously associated with the resource, and therefore the activity and energy intensity of the AE should not be considered sufficient a sign of the danger of a defect formed under the influence of hydrogen-containing media.

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