RU2229121C1 - Procedure establishing distance between converter and source of acoustic emission - Google Patents

Abstract

FIELD: diagnostics of equipment and various articles on basis of acoustic-emission method of nondestructive test. SUBSTANCE: procedure establishing distance between converter and source of acoustic emission consists in placement of one converter on one end of tested article, in loading of article and in reception of signals of acoustic emission generated by developing effect. Time difference ΔT between start of signal and maximum of this signal or maximum of its envelope passed to acoustic emission converter and distance to source is found by formula L = K•ΔT, where K is proportionality factor which value is determined by positioning of acoustic emission converter on outer surface of tested article, imitation of signals of acoustic emission at distances specified beforehand, measurement of corresponding time differences between start of signals and maxima of these signals or maxima of their envelopes, construction of dependence between specified distances and corresponding time differences of signals coming to acoustic emission converter and approximation of given dependence. EFFECT: establishment of distance to source of acoustic emission by means of single acoustic emission converter and increased authenticity of results of nondestructive test for lengthy structures with limited, unidirectional or inconvenient access to surface. 2 dwg

Description

The invention relates to the diagnosis of equipment and products of the chemical, petrochemical, energy, metallurgical industries, vehicles during their operation and tests based on the use of the acoustic emission (AE) method of non-destructive testing and can be used to determine the distance between the acoustic emission transducer (PAE) and the source AE, which is a developing defect.

The known method [1] of determining the coordinates of the source of AE signals when monitoring extended objects, which consists in the fact that two PAEs are installed on the test product at a distance X from each other. The time difference ΔT of the arrival of AE signals to the converters is determined and the source coordinates are determined from this difference and a given propagation speed V of AE signals by the formula

The disadvantage of this method is the need to use two PAEs (and the AE source must be between the PAEs), as well as the need for preliminary justification of the set propagation speed V of the AE signal.

Closest to the invention is a method [2] for measuring the distance from a single PAE to the AE source, where the difference in the arrival time ΔT on the PAE of two different types of waves or frequency components of the same type of wave generated by one AE event is measured. The velocities V ₁ and V _{2 of} two different types of waves or frequency components of the same type of wave must be known or measured in advance. The calculation of the distance is carried out according to the formula

The disadvantage of this method is the need to know the propagation velocities of V ₁ and V ₂ waves, as well as to recognize the time of arrival of the first and second type of waves or frequency components of the same wave type on the PAE to determine ΔТ. The invention aims to determine the distance to the AE source using one PAE , increasing the reliability of the results of non-destructive testing through the use of an additional diagnostic parameter - the distance and accuracy of determining the coordinates of AE sources for extended structures with a limited, one-sided, or difficult access to the surface, as well as the rise in productivity and reliability of diagnosis.

The method for determining the distance between the converter and the AE source is that one PAE is installed at one end of the controlled product, the product is loaded, AE signals generated by a developing defect are received, characterized in that the time difference ΔT between the signal beginning and the maximum of this signal is measured or the maximum of its envelope, which came to the PAE (figure 1), and the distance to the source is determined by the formula

ΔT,L = K

ΔT,

where K is the coefficient of proportionality, the value of which is determined experimentally.

Figure 1 is a typical AE waveform with a designation of the measured time interval ΔT between the beginning of the AE signal and the time corresponding to the maximum of the AE signal, where 1 is the envelope of the AE signal.

Figure 2 - a typical dependence (obtained experimentally) between the distance from the converter to the AE source and the time difference ΔT between the beginning of the AE signal and the time corresponding to the maximum of the AE signal.

The experimental determination of the coefficient K was carried out in laboratory and factory conditions. The experiments in laboratory conditions were carried out on a steel pipe ⌀32 × 4 mm, in the factory - on existing steel seamless pipelines of gaseous ammonia ⌀70 × 4 mm and 219 × 8 mm, as well as on a pipeline of liquid ammonia ⌀70 × 4 mm. One PAE was installed on the outer surface of the pipeline, AE signals were simulated at a known distance L (for example, using the Hsu-Nielsen simulator), the time difference ΔT was measured, and then the relationship between the distance L and the time difference ΔT was built. The approximation of the results was carried out using polynomials of degrees 1–4, while the standard deviation for the pipelines of gaseous ammonia was 0.98–0.99, for liquid ammonia — 0.82–93.

The experimental results showed that the proposed method for determining the coordinates of the AE source provides accuracy that is high enough for practical use and is simple to implement.

The technical result of this method is to determine the distance to the AE source using one PAE, increase the reliability of the diagnostic results by using a parameter that is valuable in the diagnostic sense - the distance to the AE source, and also increase the productivity and reliability of diagnosis by reducing the minimum required number of PAEs, in particular, when monitoring extended objects.

The advantages of this method are the low complexity of its hardware implementation, the reduction in the cost of preparatory work necessary for conducting AE control associated with the excavation of pits, opening of insulation, surface cleaning, as well as an increase in the accuracy of determining the coordinates of AE sources in comparison with the commonly used zone control method in the diagnosis of long and large objects. It is also an advantage that for the first time a method for determining the distance is proposed, which does not require any preliminary measurements of the propagation velocity of the waves or the allocation of various frequency components of one type of wave.

Sources of information

1. Patent of the Russian Federation No. 1730917, cl. G 01 N 29/04, 1994.

2. Copyright certificate of the USSR No. 1536304, cl. G 01 N 29/04, 1990.

Claims (1)

A method for determining the distance between the transducer and the acoustic emission source, which consists in installing one acoustic emission transducer (PAE) at one end of the monitored product, loading the product, receiving acoustic emission signals generated by a developing defect, characterized in that the time difference ΔT is measured between the beginning of the signal and the maximum of this signal or the maximum of its envelope, which arrived at the PAE, and the distance to the source is determined by the formula L = K · ΔT, where K is the proportionality coefficient, the value of which is determined by installing on the outer surface of the controlled product PAE, simulating acoustic emission signals at previously known distances, measuring the corresponding time differences between the beginning of the signals and, accordingly, the maxima of these signals or the maxima of their envelopes, building the relationship between the given distances and the corresponding differences in the arrival times of the signals at the PAE and the approximation of this dependence.

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