RU2532141C1 - Method of non-destructive test of long-term operated metal of operated elements of heat power equipment - Google Patents

Abstract

FIELD: test equipment.

SUBSTANCE: invention is used for the non-destructive test of long-term operated metal of operated devices of heat power equipment. The essence of the invention consists in that the delay time of surface ultrasonic waves is determined, and electronic-microscopic examinations of long-term working built-up and basic metal are performed, meanwhile the acoustic criteria of assessment of resource of long-term working basic and built-up metal contains the coefficient which takes into account an anisotropy of acoustic characteristics, and also the coefficient which takes into account the change of value of local fields of internal stresses in the studied metal.

EFFECT: possibility during assessment of level of metal damages to take into account quantitatively a degree of change of structural - phase state of built-up and basic metal during long-term operation.

Description

The invention relates to methods for studying and analyzing the nanostructured state of a long-term deposited and base metal of operated elements of heat power equipment using methods of physical metallurgy, in particular electron microscopic studies of the nanostructure (local fields of internal stresses, dislocations), as well as acoustic non-destructive testing methods.

During the long-term operation of the elements of heat-power equipment at high temperatures and pressures, the long-running deposited and base metal undergo complex physicochemical processes, caused primarily by the decomposition of the pearlite component of the microstructure, coagulation and spheroidization of carbides, and the formation and accumulation of microdamage.

Of great danger from the point of view of safe operation are the zones of elements of thermal power equipment subjected to high pressure and temperature. In such zones micro-discontinuities develop, which in the early stages are not detected by existing non-destructive testing methods.

In the power system, the acoustic emission control method is used to control the metal quality of equipment elements (see Gosgortekhnadzor of Russia, State Unitary Enterprise and Scientific and Technical Center "Industrial Safety". Collection of documents. Series 28. Issue 2001).

The basis of the method of acoustic emission control is, in particular, work on the assessment of the health of welded joints (see Ivanov V.I., Belov V.M. Acoustic emission control of welding and welded joints. M: Mechanical Engineering, 1981, 184 s. .).

The method of acoustic emission control is based on the emission of elastic waves by the material caused by dynamic local restructuring of its structure. The performance assessment of a long-running deposited and base metal is carried out by recording and analysis excited by developing defects in acoustic vibrations.

The disadvantages of this method of non-destructive testing of metal elements of heat power equipment include:

- the complexity and high cost of equipment;

- low noise immunity of the equipment;

- not an explicit relationship between the parameters of the microstructure in the zone of micro-discontinuity formation and the acoustic emission characteristics.

Closest to the invention should include a method for identifying pre-fracture zones in welded joints of heat-resistant steels (Patent for invention No. 2457478, registered in the State register of inventions of the Russian Federation on July 27, 2012), which includes measuring the delay time of surface acoustic waves in an idle welded joint with the initial state , in an operated welded joint in the weld metal and near-weld zones in two mutually perpendicular directions, further based on the measurement of local long-distance stvuyuschih internal stress fields and the delay time of the surface acoustic waves determined acoustic criterion resource welds evaluation:

, $$K=\frac{R_{01}\cdot R_{02}}{R_{t01}\cdot R_{t02}}$$

,

where R ₀₁ is the average delay time of a surface acoustic wave polarized along the idle weld in the initial state, ns;

R _t01 is the average delay time of a surface acoustic wave polarized along an operated weld, ns;

R ₀₂ - the average delay time of a surface acoustic wave polarized across the idle weld in the initial state, ns;

R _t02 - the average delay time of a surface acoustic wave polarized across the operated weld, ns,

moreover, when the value of the acoustic criterion for evaluating the resource of the welded joint is less than or equal to 0.98, the operated element is replaced.

The disadvantages of the method for identifying pre-fracture zones in welded joints of heat-resistant steels include the fact that when determining the degree of damage to metals, the degree of change in the structural-phase state of the deposited and base metal during long-term operation is not quantitatively taken into account.

The technical result of the invention is to prevent damage to a long-running deposited and base metal elements of heat power equipment.

The specified technical result is achieved by the fact that the acoustic criterion for assessing the resource of a long-term working base and deposited metal contains a coefficient taking into account the anisotropy of acoustic characteristics, as well as a coefficient taking into account a change in the structural-phase state (the value of local fields of internal stresses) in the metal under study

, $$F_c=\gamma \cdot K_C^{-\mathrm{one}}$$

,

where K _C - coefficient taking into account the anisotropy of acoustic characteristics and is expressed as

, $$K_C=\frac{\Delta R_{\mathrm{one}}}{\Delta R_2}$$

,

γ is a coefficient that takes into account the change in the value of local fields of internal stresses in the studied metal and is expressed by the formula:

, $$\gamma =\frac{{\tau }_{\mathrm{at}n}^0-{\tau }_{\mathrm{at}n}}{{\tau }_{\mathrm{at}n}}$$

,

- величина локальных полей внутренних напряжений в исследуемом длительно работающем металле,Where $${\tau }_{\mathrm{at}n}^0$$

- the value of the local fields of internal stresses in the studied long-running metal,

τ _int - the value of the local fields of internal stresses in the investigated deposited metal,

ΔR ₁ and ΔR ₂ are the anisotropy of the delay time of surface acoustic waves in the deposited metal and in the long-running metal, respectively. These values are calculated as

, $$\Delta R_2=\left|{\overline{R}}_2^{nepn}-{\overline{R}}_2^{nap}\right|$$

, $$\Delta R_{\mathrm{one}}=|\; |\; |{\overline{R}}_{\mathrm{one}}^{nepn}-{\overline{R}}_{\mathrm{one}}^{nap}|\; |\; |$$

, $$\Delta R_2=|\; |\; |{\overline{R}}_2^{nepn}-{\overline{R}}_2^{nap}|\; |\; |$$

,

- среднестатистическое время задержки поверхностной акустической волны, поляризованной вдоль исследуемого образца наплавленного металла, нс;Where $${\overline{R}}_{\mathrm{one}}^{nap}$$

- the average delay time of a surface acoustic wave polarized along the investigated sample of the deposited metal, ns;

- среднестатистическое время задержки поверхностной акустической волны, поляризованной перпендикулярно исследуемому образцу наплавленного металла, нс; $${\overline{R}}_{\mathrm{one}}^{nepn}$$

- the average delay time of a surface acoustic wave polarized perpendicular to the sample of the deposited metal, ns;

- среднестатистическое время задержки поверхностной акустической волны, поляризованной вдоль исследуемого образца длительно работающего металла, нс; $${\overline{R}}_2^{nap}$$

- the average delay time of a surface acoustic wave polarized along the studied sample of a long-working metal, ns;

- среднестатистическое время задержки поверхностной акустической волны, поляризованной перпендикулярно исследуемому образцу длительно работающего металла, нс; $${\overline{R}}_2^{nepn}$$

- the average delay time of a surface acoustic wave polarized perpendicular to the studied sample of a long-working metal, ns;

moreover, with the magnitude of the acoustic criterion for assessing the resource of a long-term working base and deposited metal of elements of thermal power equipment of more than 0.22, the operated element is replaced.

The claimed method is as follows. For non-destructive testing of the long-working metal of the operated elements of the heat-power equipment, the delay time of a surface wave polarized along and across the zones of the deposited metal in the initial state and in the long-working metal of the operated elements of the heat-power equipment is measured. Measurements are taken at no less than twelve points in each area. Then, samples (sections) are made from these sections with a measured delay time of surface acoustic waves, which are examined by electron microscopy at the points of measurement of the delay time of surface acoustic waves. At these points, the nanostructure is studied: the magnitude of the local fields of internal stresses and the density of dislocations are determined, and the presence of micro discontinuities is detected. The reliability of the results is confirmed by the use of statistical methods for processing the results.

The nanostructure studies are carried out using electron microscopy methods on an EM-125K microscope at an accelerating voltage of 125 kV using a goniometer.

Next, the critical level of local fields of internal stresses is determined for a long-term deposited and base metal, which leads to the occurrence of micro-discontinuities and destruction.

Reference curves are constructed between the magnitude of the local fields of internal stresses and the delay time of surface acoustic waves for a long-term deposited and base metal.

For acoustic research, the ASTRON multifunctional automated spectral-acoustic system is used. The basis of the operation of the hardware of the system is a method for detailed registration of the entire series of reflected acoustic pulses for its subsequent processing by the software of the system.

After that, the limiting value of the acoustic criterion is determined, which characterizes the formation of micro-discontinuities in the long-term deposited and base metal elements of the heat and power equipment, leading to the appearance of cracks and fracture.

The acoustic criterion for assessing the resource of a long-term working base and deposited metal of elements of heat power equipment is determined by the formula:

, $$F_c=\gamma \cdot K_C^{-\mathrm{one}}$$

,

where K _C - coefficient taking into account the anisotropy of acoustic characteristics and is expressed as

, $$K_C=\frac{\Delta R_{\mathrm{one}}}{\Delta R_2}$$

,

γ is a coefficient that takes into account the change in the value of local fields of internal stresses in the studied metal and is expressed by the formula

, $$\gamma =\frac{{\tau }_{\mathrm{at}n}^0-{\tau }_{\mathrm{at}n}}{{\tau }_{\mathrm{at}n}}$$

,

- величина локальных полей внутренних напряжений в исследуемом длительно работающем металле,Where $${\tau }_{\mathrm{at}n}^0$$

- the value of the local fields of internal stresses in the studied long-running metal,

τ _int - the value of the local fields of internal stresses in the investigated deposited metal,

ΔR ₁ and ΔR ₂ are the anisotropy of the delay time of surface acoustic waves in the deposited metal and in the long-running metal, respectively.

These values are calculated as

, $$\Delta R_2=\left|{\overline{R}}_2^{nepn}-{\overline{R}}_2^{nap}\right|$$

, $$\Delta R_{\mathrm{one}}=|\; |\; |{\overline{R}}_{\mathrm{one}}^{nepn}-{\overline{R}}_{\mathrm{one}}^{nap}|\; |\; |$$

, $$\Delta R_2=|\; |\; |{\overline{R}}_2^{nepn}-{\overline{R}}_2^{nap}|\; |\; |$$

,

- среднестатистическое время задержки поверхностной акустической волны, поляризованной вдоль исследуемого образца наплавленного металла, нс;Where $${\overline{R}}_{\mathrm{one}}^{nap}$$

- the average delay time of a surface acoustic wave polarized along the investigated sample of the deposited metal, ns;

- среднестатистическое время задержки поверхностной акустической волны, поляризованной перпендикулярно исследуемому образцу наплавленного металла, нс; $${\overline{R}}_{\mathrm{one}}^{nepn}$$

- the average delay time of a surface acoustic wave polarized perpendicular to the sample of the deposited metal, ns;

- среднестатистическое время задержки поверхностной акустической волны, поляризованной вдоль исследуемого образца длительно работающего металла, нс; $${\overline{R}}_2^{nap}$$

- the average delay time of a surface acoustic wave polarized along the studied sample of a long-working metal, ns;

- среднестатистическое время задержки поверхностной акустической волны, поляризованной перпендикулярно исследуемому образцу длительно работающего металла, нс; $${\overline{R}}_2^{nepn}$$

- the average delay time of a surface acoustic wave polarized perpendicular to the studied sample of a long-working metal, ns;

moreover, when the value of the acoustic criterion for assessing the resource of a long-term working base and deposited metal of elements of thermal power equipment is more than 0.22 (if the coefficient taking into account the change in the value of the local fields of internal stresses in the studied metal is more than 0.13, and the coefficient taking into account the anisotropy of acoustic characteristics is in ranging from 0.64 to 1), then replace the operated element.

An example of a specific application of the proposed method.

, $${\overline{R}}_1^{nepn}$$

, $${\overline{R}}_2^{nap}$$

, $${\overline{R}}_2^{nepn}$$

равны 5805, 5790, 5882 и 5860 нс соответственно, а вычисленный коэффициент, учитывающий анизотропию акустических характеристик K_C=0,681, $${\tau }_{вн}^0=1100МПа$$

, τ_вн=520 МПа, тогда коэффициент, учитывающий изменение величины локальных полей внутренних напряжений γ=0,47, а акустический критерий оценки ресурса длительно работающего основного и наплавленного металла барабанов котлов высокого давления равен F_C=0,7, что свидетельствует о том, что на участках между водоопускными отверстиями возникли значительные локальные поля внутренних напряжений и образовались микронесплошности, приводящие к появлению трещин и разрушению. Следовательно, дальнейшая эксплуатация барабана котла высокого давления может привести к разрушению технического устройства и возникновению аварийной ситуации.For the investigated long-term deposited and base metal of the drum of a high-pressure boiler made of special molybdenum steel after 320 thousand hours of operation at a temperature of 316 ° C and a pressure of 11.0 MPa $${\overline{R}}_{\mathrm{one}}^{nap}$$

, $${\overline{R}}_{\mathrm{one}}^{nepn}$$

, $${\overline{R}}_2^{nap}$$

, $${\overline{R}}_2^{nepn}$$

equal to 5805, 5790, 5882 and 5860 ns, respectively, and the calculated coefficient taking into account the anisotropy of the acoustic characteristics K _C = 0,681, $${\tau }_{\mathrm{at}n}^0=1100MP\mathrm{but}$$

, τ _int = 520 MPa, then the coefficient taking into account the change in the value of local fields of internal stresses γ = 0.47, and the acoustic criterion for assessing the resource of a long-term working base and deposited metal of the drums of high-pressure boilers is F _C = 0.7, which indicates that in the areas between the water openings significant local fields of internal stresses arose and micro-discontinuities formed, leading to the appearance of cracks and destruction. Therefore, further operation of the drum of the high-pressure boiler can lead to the destruction of the technical device and the emergence of an emergency.

Thus, the proposed method for the first time allows you to identify areas of micro-discontinuity formation in the operated elements of power equipment by the acoustic criterion, which takes into account both the anisotropy of the acoustic characteristics and the change in the structural-phase state (the value of local fields of internal stresses) in the metal under study.

Claims (1)

Method of non-destructive testing of long-working metal of exploited elements of heat-power equipment, including determining the delay time of surface acoustic waves and electron microscopic studies of a long-running deposited and base metal, characterized in that the acoustic criterion for evaluating the resource of a long-working base and deposited metal contains a coefficient that takes into account the anisotropy of acoustic characteristics, as well as a coefficient taking into account the change in Ichin local internal stress fields in the test metal

,
where K _C - coefficient taking into account the anisotropy of acoustic characteristics and is expressed as

,
γ is a coefficient that takes into account the change in the value of local fields of internal stresses in the studied metal and is expressed as

,
Where

- the value of the local fields of internal stresses in the studied long-running metal,
τ _int - the value of the local fields of internal stresses in the investigated deposited metal,
ΔR ₁ and ΔR ₂ are the anisotropy of the delay time of surface acoustic waves in the deposited metal and in the long-working metal, respectively, which are calculated as

,

,
Where

- the average delay time of a surface acoustic wave polarized along the investigated sample of the deposited metal, ns;

- the average delay time of a surface acoustic wave polarized perpendicular to the sample of the deposited metal, ns;

- the average delay time of a surface acoustic wave polarized along the studied sample of a long-working metal, ns;

- the average delay time of a surface acoustic wave polarized perpendicular to the studied sample of a long-working metal, ns;
moreover, with the magnitude of the acoustic criterion for assessing the resource of a long-term working base and deposited metal of elements of thermal power equipment of more than 0.22, the operated element is replaced.