RU2777695C1 - Method for assessing the resistance of steels and alloys to corrosion - Google Patents

Abstract

FIELD: corrosion protection.

SUBSTANCE: invention relates to a method for non-destructive magnetic control of local zones of increased corrosion activity. A method for monitoring zones of excessive corrosion activity of steel metal structures consists in the local determination of the magnetization reversal curve: the magnetic hysteresis loop, while magnetic hysteresis loops are represented as a time-varying signal, analyzed by Fourier spectral functions, the magnitude of harmonic components or their combinations determine the corrosion rate at the measurement site and find areas with excessive corrosion activity for each specific aggressive environment.

EFFECT: reduction in the complexity of determining the values of corrosion characteristics, an increase in the efficiency and resolution of sorting ferromagnetic materials and equipment by local corrosion activity and corrosion compatibility of the connected elements at the stages of manufacture, construction, installation, repair, reconstruction, operation and technical diagnostics.

1 cl, 3 dwg

Description

The invention relates to non-destructive testing methods and is intended for monitoring local areas of increased corrosivity of ferromagnetic materials, products, equipment and structures at the stage of manufacturing, construction, installation, repair, reconstruction, operation and technical diagnostics using a set of magnetic parameters.

A known method for determining the corrosion rate of underground structures, including the placement of a device for estimating the corrosion rate in a corrosive environment. The method is based on the excitation of ultrasonic vibrations in the witness sample, the reception of echo signals reflected from the surface of the witness sample damaged by corrosion, the analysis of echo signals, the calculation of the sample thickness from the time of arrival of echo signals, the determination of the rate and type of corrosion by changing the values of the current thickness of the sample -witness regarding the initial [RU2536779C1, IPC G01N17/02, publ. 12/27/2014. A method for determining the corrosion rate of metal structures and a device for its implementation].

The disadvantages of this method are:

− - significant time spent on control;

− - the presence of contact surfaces subject to intense wear;

− - high demands on the quality of contact of sensors with the surface;

Known gravimetric method for determining the corrosion rate, which consists in assessing the change in the mass of the sample subject to corrosion [Corrosion resistance of chemical production equipment: Methods for protecting equipment from corrosion. Ref. ed. / Ed. A.M. Sukhotin. - L.: Chemistry, 1987. - S.6-12]. Also known is a method for determining the corrosion rate by polarization curves [Aleksandrov Yu.V. Corrosion of gas and oil pipelines. Electrochemical protection methods / Yu.V. Alexandrov. - SPb.: "Nedra", 2011. - P.70-85], which consists in carrying out potentiostatic measurements using metal samples with the construction of polarization curves, the corrosion rate is estimated from the slope of the constructed curves. These methods have a significant limitation on the place of application and are implemented only in laboratory conditions.

A known method for determining the resistance of pipes made of ferromagnetic steel to inside boiler corrosion [SU 571658 A1, MPK6 F22B 37/10, F28F 19/00, G01N 17/00, publ. 09/05/1977], which consists in measuring the coercive force of the material, the value of which, under certain conditions, depends on the thickness of the metal, which changes during the corrosion destruction of steel.

The disadvantage of the known method should be attributed to the significant methodological complexity of the procedure for selecting the size of the poles to ensure the necessary dependence of the coercive force on the thickness for a particular material.

The closest in technical essence, taken as a prototype, is a method for controlling excessive corrosion of steel by the magnitude of the residual magnetization field [RU (11) 2 570 704(13) C1, IPC G01N 17/00, publ. 12/10/2015].

The disadvantage of this method is the influence of the stress-strain state on the magnitude of the magnetic field created by the residual magnetization and the need for demagnetization of the tested ferromagnet.

The task to be solved by the claimed invention is the development of a method for determining local zones of increased corrosion activity through the use of a complex parameter based on the spectral components obtained from the magnetic hysteresis loops (magnetization reversal curve) of a ferromagnet, which allows testing both in laboratory and in the field while maintaining high efficiency and speed of monitoring corrosion characteristics.

The result of using this type of control is to increase the efficiency and accuracy of corrosion control of ferromagnetic materials, products, equipment and structures.

The distinguishing features of the method are that the obtained harmonics of the Fourier spectrum actually carry information about all points of the magnetic hysteresis loop, and, consequently, the structural components of the material and its properties, in contrast to standard methods, where only some of these points are used for the purposes of non-destructive testing: coercive force, magnetic permeability, relaxation coercive force, differential magnetic permeability, etc.

The method consists in recording dynamic or quasi-static magnetic hysteresis loops (magnetization reversal curves) on a controlled steel product using a magnetic structuroscope or other device or system. In order to prevent the occurrence of interference that distorts the results obtained, the following should be taken into account: the anisotropy of the properties of a ferromagnetic material; the presence of eddy currents that limit the depth of magnetization and distort the amplitude and phase of the output signal; restrictions on the depth of magnetization of the product associated with the design features of the device.

For processing, both partial and complete magnetic hysteresis loops (magnetization reversal curve) can be used. To remove the magnetic hysteresis loops (magnetization reversal curve), the magnetization and demagnetization current generated on the device can be described by some sawtooth or sinusoidal function. Given the direct proportionality between the time-varying current value and the magnetic field strength, it becomes possible to make a replacement by representing the magnetic field strength as a “pseudo-temporal” value according to formula 1:

(1)

(one)

– время, с;where

– time, s;

– напряженность магнитного поля, А/м;

– magnetic field strength, A/m;

– коэффициент перевода.

is the conversion factor.

. Таким образом, получается представление петли гистерезиса в виде функции

(фиг.1). Для такой функции может быть выполнено преобразование Фурье. By symmetrically displaying the descending (upper) or descending (lower) branch of the loop relative to the vertical line passing through the point

. Thus, we get the representation of the hysteresis loop as a function

(figure 1). For such a function, a Fourier transform can be performed.

For discrete data, it is necessary to process, taking into account the possibility of having a different discretization step between adjacent values in the array of processed data. To do this, you can use the numerical integration method or other mathematical methods designed to find intermediate values. For example, the formulas for calculating the coefficients of the Fourier series, taking into account the numerical integration method, will take the following form:

(2)

(2)

(3)

(3)

– период функции;where

is the period of the function;

– начальное значение аргумента;

– initial value of the argument;

– значение аргумента в анализируемой точке;

is the value of the argument at the analyzed point;

– число анализируемых точек;

is the number of analyzed points;

– шаг дискретизации по аргументу.

is the discretization step with respect to the argument.

Harmonic amplitudes are determined according to formula 4.

(4)

(four)

– коэффициент ряда Фурье, характеризующий косинусоидальные составляющие;where

is the coefficient of the Fourier series, which characterizes the cosine components;

– коэффициент ряда Фурье, характеризующий синусоидальные составляющие.

is the coefficient of the Fourier series characterizing the sinusoidal components.

A complex parameter can be represented as a sum, difference, product or ratio of the amplitude components or a combination of these procedures on the amplitudes of the harmonics. For example, the complex parameter P1 can be defined as:

(5)

(5)

– амплитуда первой гармоники;where

is the amplitude of the first harmonic;

– амплитуда третьей гармоники;

is the amplitude of the third harmonic;

– амплитуда пятой гармоники.

is the amplitude of the fifth harmonic.

According to the harmonic components obtained as a result of spectral analysis or their various combinations, the corrosion rate is determined according to the regression equations obtained from previously determined dependencies (Fig. 2, 3) of the change in the amplitudes of the harmonic spectrum on the corrosion rate in a certain aggressive environment. In FIG. 2a shows the dependence of the amplitude of the third harmonic on the corrosion rate for heat-treated samples of steel 45Kh in a 5% hydrochloric acid solution; 2b dependence of the amplitude of the fifth harmonic on the corrosion rate for heat-treated samples of steel 45Kh in 5% sulfuric acid solution. The dependences of the complex parameter P1 on the corrosion rate of steel 09G2S in a 3% hydrochloric acid solution are shown in Fig. 3a. Fig. 3b - dependence of the complex parameter P1 on the corrosion rate of steels of various grades in sea water. Fig. 3c - dependence of the complex parameter P1 on the corrosion rate of steels of various grades in a 5% sulfuric acid solution

Regression equations can serve as calibration curves, which can be used to determine how well a material will resist corrosion by first determining the harmonic spectrum. According to the calculated value of the corrosion rate, the presence of zones of increased activity of changing the structure of the material, which causes increased corrosion of the product in this zone, is judged.

Claims (1)

A method for controlling zones of excessive corrosion activity of steel structures, which consists in locally determining the magnetization reversal curve (magnetic hysteresis loop), characterized in that the magnetic hysteresis loops are represented as a time-varying signal, are analyzed by Fourier spectral functions, and are determined by the magnitude of harmonic components or their combinations the corrosion rate at the measurement site and find areas with excessive corrosive activity for each specific aggressive environment.

Images