RU2536779C1 - Method of determination of rate of corrosion of metal buildings and device for its implementation - Google Patents

Abstract

FIELD: measurement technology.

SUBSTANCE: device for determination of rate of corrosion consisting of the reference sample and two piezoelectric converters of separated combined and combined type, is placed in corrosion medium, sequentially, using the converter of each type the current thickness of the sample is determined by the time of acceptance of bottom echo signals. Then the rate is calculated, and the type of corrosion is determined by change of current values of the thickness of the reference sample with reference to initial one.

EFFECT: simplification of the method of determination of rate of corrosion for its use in the corrosion monitoring systems of trunk pipelines and creation of the device implementing the method using the standard ultrasonic inspection devices.

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Description

The invention relates to the field of assessing corrosion damage of underground structures and can be used in the oil and gas industry as part of systems for remote assessment of the corrosion rate and determining the type of corrosion (surface uniform, uneven, ulcers and pits) of underground pipelines.

Known methods for determining the corrosion rate, in particular gravimetric, which consists in assessing the change in mass of the sample susceptible to corrosion [Corrosion resistance of chemical equipment: Methods for protecting equipment from corrosion. Ref. ed. / Ed. A.M. Sukhotina. - L .: Chemistry, 1987. - P.6-12], a method for determining surface corrosion damage using a mechanical micrometer, which consists in measuring the depth of surface corrosion damage [Corrosion resistance of chemical equipment: Methods for protecting equipment from corrosion. Ref. ed. / Ed. A.M. Sukhotina. - L .: Chemistry, 1987. - S.22-23]. Also known is a method of determining the corrosion rate from polarization curves [Alexandrov Yu.V. Corrosion of gas pipelines. Electrochemical methods of protection / Yu.V. Alexandrov. - St. Petersburg: "Nedra", 2011. - P.70-85], which consists in conducting potentiostatic measurements using metal samples with the construction of polarization curves, the corrosion rate is estimated by the angle of inclination of the constructed curves. These methods are not applicable for remote monitoring, for the implementation of the methods requires access to the surface of the structure or sample, or they are implemented in laboratory conditions.

A known resistometric method for determining the corrosion rate, based on the assessment of changes in the electrical resistance of the conductor due to its corrosion [Akolzin P.A. Corrosion and metal protection of heat power equipment / P.A. Akolzin. - M .: Energoizdat, 1982. - P.251], which consists in the fact that a sensor consisting of a sensitive element (most often wire) is placed in a corrosive medium, the resistance of the conductor is measured, the corrosion rate is judged by the change in the resistance of the conductor over time. The method is suitable for remote monitoring, however, as a rule, there is a difference in the physicochemical properties of the sensitive elements of the sensors and the metal of the structure, which leads to an incorrect assessment of the corrosion rate, in addition, the dimensions of the sensitive elements (primarily the area of the corroding surface) do not completely simulate the corrosion processes occurring on the surface of structures, since electrochemical elements are formed on the surface of the structure, leading to uneven corrosion.

A known method of controlling the corrosion rate of metal structures, based on the assessment of the attenuation of an electromagnetic wave, which consists in installing a sensitive element near a structure located in a corrosive environment, exciting an electromagnetic wave with a shift of the magnetic field energy in the region between the sensitive element and the surface of the metal structure for excitation current in it, measure the change in deceleration of the excited electromagnetic wave, the corrosion rate of a metal object udyat this change in deceleration [Pat. No. 2110784. A method of controlling the corrosion rate of metal objects. Publ. 05/10/1998, IPC G01N 17/00]. The disadvantage of this method is the inability to determine the type of corrosion that occurs on the surface of the structure.

A device is known that makes it possible to estimate the corrosion rate by measuring the transit time of an ultrasonic wave through a test specimen that simulates a section of a pipeline that is not protected by an insulating coating [PM No. 123525. Corrosion rate sensor. Published on 12/27/2012. IPC G01N 17/02]. The device uses a combined type piezoelectric transducer that generates an ultrasonic pulse in the metal of the witness specimen and receives reflected bottom echo signals. The thickness of the sample is calculated by the time of arrival of the bottom echo signal, the corrosion rate is estimated by the change in thickness of the sample over time. To assess the corrosion rate of structures protected by electrochemical protection, an additional conductor creates contact with the structure. The disadvantage is that using a known device it is impossible to assess the rate of local corrosion (ulcers, pitting), it is also impossible to determine the type and differentially evaluate the rate of corrosion with a combination of different types of corrosion.

A known method of assessing the corrosion rate and a device for its implementation using the ultrasonic method for the study of substances selected as a prototype [US Patent 6,490,927. Publ. 12/10/2002. IPC G01N 29/10]. A test specimen made of a metal identical to the metal of the building under control with a transducer mounted on it is placed in a corrosive environment, capable of exciting ultrasonic vibrations and receiving echo signals. Using a converter, a pulse is generated in the sample, echoes reflected from the surface damaged by corrosion are received, and the data obtained is analyzed. The corrosion rate and size of the defect are estimated by the time of arrival of the echo signals, which are the result of reflection of the ultrasonic wave from the surface of the defects and recorded between the probe pulse and the bottom echo signal.

The disadvantages include the need to use precision equipment and the need to create certain control conditions (the measurement result depends on the position of the transducer relative to the defect), for example, using standard ultrasonic testing tools in pipe steels, it is impossible to register the echoes of reflection of ultrasonic waves from defects that occur in the method between the probe pulse and the bottom echo signal, which complicates the application of the method as part of remote tsenki corrosion rate and determining the type of corrosion.

The objective of the invention is to simplify the method of assessing the corrosion rate for use as part of corrosion monitoring systems of pipelines and to create a device that implements the method using standard ultrasonic testing tools.

In terms of the device, the problem is solved in that in the device for assessing the corrosion rate, consisting of a witness specimen made of metal identical to the metal of the structure under control, and a transducer mounted on it, capable of generating ultrasonic vibrations and receiving echo signals to excite ultrasonic vibrations and receiving echo signals, a set of two standard piezoelectric transducers of a different type is used: combined and separately combined, mounted on its surface. The design of the device is illustrated by a sketch (figure 1).

A combined 3 and separately-combined 4 piezoelectric transducers are installed on the test specimen 1 through the contact layer 2, conductors 6 are used to transmit electrical signals to the transducers, and the structure is isolated from the external environment by a protective coating 5.

In terms of the method, the problem is solved in that in the method for determining the corrosion rate of underground structures, including the placement of a device for assessing the corrosion rate in a corrosive environment, the excitation of ultrasonic vibrations in the witness specimen, the reception of echoes reflected from the corrosion-damaged surface of the witness specimen, echo analysis -signals, calculating the thickness of the sample by the time of arrival of the echo signals, determining the speed and type of corrosion by changing the values of the current thickness of the witness sample relative to the initial one, for excitation To receive and receive echo signals, two different types of piezoelectric transducers are used: separately-combined and combined. The measurements are carried out sequentially by each transducer and analyze the results in the following order (figure 2): evaluate the current thickness of the sample according to the results of measurements by a separately-combined transducer, in the absence of changes in the thickness of the witness sample compared to the original, conclude that there is no corrosion, in in the case of a change in thickness, the transducer is combined type. If changes in the thickness of the witness specimen are not revealed by the results of measuring with a combined transducer, then this indicates the presence of only local defects (ulcers or pitting), if the changes are fixed, then the thickness values determined by the measurement results of each of the transducers are compared. If the thickness values measured by different piezoelectric transducers are equal, they conclude that there is uniform surface corrosion, their difference indicates the development of local corrosion against a uniform background.

Corrosion rate V _cor. , mm / year, is determined by the ratio of the decrease in the thickness of the test specimen Δh, mm, which is the difference between the values of the initial h _n , mm and the current measured thickness h _{n + 1} , mm, to the time between two measurements τ, years:

$$$$

$$V_{\mathrm{to}\mathrm{about}R.}=\frac{h_n-h_{n+\mathrm{one}}}{\tau }.(\mathrm{one})$$

The thickness of the test specimen h, mm, is defined as the product of the propagation velocity of longitudinal ultrasonic waves in the metal of the test specimen, υ, m / s, and half the time of the return of the bottom echo signal, t, s:

$$h=\frac{\upsilon \cdot t}{2}.(2)$$

и $$h_n{}^{PC}$$

соответственно.Since the thickness of the test specimen is determined using combined and separately combined piezoelectric transducers, and the measured values may differ, these values are divided by $$h_n{}^C$$

and $$h_n{}^{PC}$$

respectively.

Example 1. A test specimen, steel grade 17G1S, and an initial thickness of 10 mm were made from a pipe fragment of the main gas pipeline. To measure the corrosion rate by the proposed method, corrosion damage was created artificially in the laboratory. On the outside of the test specimen during corrosion tests in accordance with GOST 9.308-85 for 120 days by uniform immersion in an electrolyte (sodium chloride concentration of 30 ± 3 g / dm ³ ), uniform corrosion was created with a metal loss of 0.8 mm. After this, local corrosion defects were artificially simulated: three damage with a diameter of 2, 3 and 4 mm were made by drilling, with a depth of 3.2, 2.2 and 1.2 mm relative to the corroded surface, respectively. Two piezoelectric transducers (PECs) are installed on the inner surface of the witness specimen: a separately-combined Panametrics D799 probes with an operating frequency of 5 MHz and a combined A551S probes with an operating frequency of 5 MHz. The Panametrics EPOCH LT ultrasonic flaw detector was used to measure the return time of the bottom echo. According to the reference information, it is accepted that the propagation velocity of longitudinal ultrasonic waves in the metal of the test specimen is 5990 m / s.

равна измеренной начальной толщине $$h_n{}^C$$

и соответствуют фактической толщине образца-свидетеля:Before the creation of artificial corrosion damage, measurements were made by each transducer, the time of arrival of the bottom echo signal t was 3.33 μs, therefore, the measured initial thickness of the sample $$h^{PC}{}_n$$

equal to the measured initial thickness $$h_n{}^C$$

and correspond to the actual thickness of the witness specimen:

$$h=\frac{\upsilon \cdot t}{2}=\frac{5990\cdot 3,33\cdot {10}^{-6}}{2}=10,00mm$$

образца-свидетеля 6 мм, зафиксирована убыль металла Δh=4, что соответствует наиболее глубокому (самому опасному) искусственно созданному локальному дефекту. Поскольку толщина не соответствует первоначальной $$h^{PC}{}_n$$

, проводят измерения совмещенным преобразователем. Время прихода эхо-сигнала, зафиксированное совмещенным преобразователем, составляет 3,07 мкс, что соответствует толщине 9,2 мм. Толщина образца $$h^C{}_{n+1}$$

, определенная по результатам измерения совмещенным преобразователем, не соответствует первоначальной $$h^C{}_n$$

и толщине $$h^{PC}{}_{n+1}$$

, определенной с помощью раздельно-совмещенного преобразователя. Таким образом выявлена локальная коррозия с убылью толщины образца-свидетеля Δh=4 мм на фоне поверхностной коррозии с глубиной повреждения в 0,8 мм.Next, measurements were made by a separately combined transducer; the time of arrival of the bottom echo signal was 2.00 μs, which corresponds to the current thickness $$h^{PC}{}_{n+\mathrm{one}}$$

of the test specimen 6 mm, metal loss Δh = 4 was recorded, which corresponds to the deepest (most dangerous) artificially created local defect. Since the thickness does not match the original $$h^{PC}{}_n$$

, carry out measurements by the combined converter. The arrival time of the echo signal recorded by the combined transducer is 3.07 μs, which corresponds to a thickness of 9.2 mm. Sample Thickness $$h^C{}_{n+\mathrm{one}}$$

determined by the results of measurements with a combined transducer does not correspond to the original $$h^C{}_n$$

 and thickness $$h^{PC}{}_{n+\mathrm{one}}$$

determined using a separately-combined transducer. Thus, local corrosion with a decrease in the thickness of the witness specimen Δh = 4 mm against the background of surface corrosion with a damage depth of 0.8 mm was revealed.

Define the rate of artificially reproduced corrosion for the conditions of Example 1:

; $$V_{l\mathrm{about}\mathrm{to}.\mathrm{to}\mathrm{about}R.}=\frac{h_n^{PC}-h_{n+\mathrm{one}}^{PC}}{\tau }=\frac{10-\mathrm{four}}{120}=0,05mm/\mathrm{from}\mathrm{at}t=\mathrm{eighteen},25mm/g\mathrm{about}d$$

;

. $$V_{R\mathrm{but}\mathrm{at}n.\mathrm{to}\mathrm{about}R.}=\frac{h_n^C-h_{n+\mathrm{one}}^C}{\tau }=\frac{10-9,2}{120}=0,0067mm/\mathrm{from}\mathrm{at}t=2,43mm/g\mathrm{about}d$$

.

Example 2. It is necessary to evaluate the effectiveness of the electrochemical protection system of an underground gas pipeline by determining the corrosion rate, the pipes of which are made of steel grade 09G2S. For the manufacture of the device, a test specimen is used from steel grade 09G2S with a thickness of 10 mm, made from an emergency reserve pipe, a separately combined D1762 transducer with an operating frequency of 5 MHz and a combined S3567 transducer with an operating frequency of 2.5 MHz, the register block is made on the basis of an ultrasonic thickness gauge A1210. The surface area of the witness specimen in contact with the corrosive medium is 2 cm ² . Operating experience of gas pipelines shows that the most common local insulation damage is of comparable size. A device for assessing the corrosion rate is placed in the near-pipe space of the gas pipeline, the conductor creates an electrical contact between the witness sample and the gas pipeline.

. Текущая толщина образца $$h^{PC}{}_{n+1}$$

отличается от начальной, поэтому далее проводят измерение совмещенным преобразователем, время прихода донного эхо-сигнала составило 3,32 мкс, что соответствует толщине 9,94 мм. Значения толщины образца-свидетеля $$h^{PC}{}_{n+1}$$

и $$h^C{}_{n+1}$$

, определенные по результатам двух измерений, равны, таким образом делают вывод о том, что выявлена поверхностная равномерная коррозия.Six months after the device was placed in the ground, measurements were taken. The time of arrival of the bottom echo signal from a separately combined transducer was 3.32 μs, which corresponds to the thickness $$h^{PC}{}_{n+\mathrm{one}}=9,94mm$$

. Current sample thickness $$h^{PC}{}_{n+\mathrm{one}}$$

differs from the initial one, therefore, a combined transducer is then measured, the time of arrival of the bottom echo signal is 3.32 μs, which corresponds to a thickness of 9.94 mm. Thicknesses of the witness specimen $$h^{PC}{}_{n+\mathrm{one}}$$

and $$h^C{}_{n+\mathrm{one}}$$

determined by the results of two measurements are equal, thus conclude that revealed surface uniform corrosion.

Determine the corrosion rate for the conditions of Example 2:

. $$V_{R\mathrm{but}\mathrm{at}n.\mathrm{to}\mathrm{about}R.}=\frac{h_n^C-h_{n+\mathrm{one}}^C}{\tau }=\frac{10-9,94}{0,5}=0,12mm/g\mathrm{about}d$$

.

According to STO Gazprom 9.0-001-2009 “Protection against corrosion. Basic Provisions ”, the corrosion rate in the surveyed area corresponds to an interval of 0.1-0.3 mm / year, which indicates increased corrosion hazard, it is recommended that the operating modes of the electrochemical protection system be adjusted.

Claims (2)

1. A method for determining the corrosion rate of underground structures, including the placement of a device for assessing the corrosion rate in a corrosive environment, the excitation of ultrasonic vibrations in a witness specimen, the reception of echoes reflected from the surface of a corrupted corrosion specimen, the analysis of echo signals, and the calculation of the thickness of the sample from the time of arrival of the echo signals, determining the speed and type of corrosion by changing the values of the current thickness of the witness specimen relative to the initial one, characterized in that ultrasonic vibrations and receive echo signals from a corroded surface by two types of transducers: separately-combined and combined, calculate the initial and current thickness of the witness sample according to the results of measuring the time of arrival of an echo from a separately-combined and combined piezoelectric transducer, compare the initial and current values the thickness of the witness specimen, calculated for the measurement results by the transducer of each type, determines the corrosion rate and judges the type of corrosion. 2. A device for implementing the method according to claim 1, comprising a witness specimen of a metal identical to the metal of an underground structure, a piezoelectric transducer of a combined type, a piezoelectric transducer of a separately combined type, connecting conductors, an external protective coating.

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