Method for precise testing of off-potential in impressed current cathodic protection

Abstract

The application provides a method for accurately testing off power potential in forced current cathodic protection, determining a real potential reading time of the cathodic protection, judging that a surge effect disappears according to a surge potential characteristic, connecting a potential test piece and a cathodic protection cathode through a relay based on a polarization probe or a reference tube, and making an internal reference electrode close to the potential test piece, so that a test potential between the internal reference electrode and the potential test piece is a power-on potential; after a preset program is started, a CPU disconnects the relay, and simultaneously starts recording a potential between the potential test piece and the internal reference electrode at each time. The CPU analyzes and calculates the test recorded data according to a calculation scheme, so that a test terminal or an upper computer can accurately determine a real potential of the cathodic protection. The application has the advantages that the read test piece potential is more accurate and more accurate compared with a traditional method, and the difficulties and pain points of the accurate evaluation and intelligent management of the cathodic protection of the current cathodic protection intelligent test terminal are solved.

Description

Technical Field

[0001] This invention relates to the field of true potential testing for cathodic protection, and particularly to a method for accurately testing the de-energization potential in forced current cathodic protection. Background Technology

[0002] Research on cathodic protection technology began as early as 1823, when scientist David studied how two metals with different properties corroded rapidly when placed in an electrolyte solution, while the other corroded slowly. In 1824, cathodic protection technology was first implemented on a British Royal Navy warship. In the early 20th century, with oil becoming the world's primary energy source, the construction of oil and gas pipelines began to develop, and corrosion of long-distance pipelines became a serious problem. In the 1930s, cathodic protection technology was widely used in long-distance pipelines in the United States. In 1962, my country applied cathodic protection technology to the Karamay-Dushanzi long-distance pipeline in the Xinjiang oilfield, establishing its first cathodic protection station. With the development of science and technology, oil and gas pipelines built in recent years have generally adopted a control method combining anti-corrosion coatings and cathodic protection devices, gradually improving and enhancing cathodic protection technology.

[0003] The current development trend of cathodic protection focuses on improving reliability, ensuring the implementation of impressed current cathodic protection, reducing equipment maintenance frequency, and extending equipment uptime. It emphasizes the importance of considering the pipeline environment, taking into account various factors affecting corrosion rates, obtaining corresponding given potentials based on different environments, and utilizing advanced cathodic protection devices to improve the precise control of the cathodic protection potential. Simultaneously, it combines this with a cathodic protection potential acquisition system to measure the potential, avoiding overly positive or negative potentials at critical points and reducing the risk of cathodic protection failure. Therefore, intelligent monitoring and remote control technologies for cathodic protection are rapidly developing. These technologies enable the measurement of all necessary data in the central control room, data analysis, remote adjustment of the polarized DC power supply output parameters, and even autonomous adjustment of the output potential based on power failure potential. In the event of overcurrent, overvoltage, or high temperature in the DC power supply, the system can diagnose and autonomously handle the situation. Cathodic protection technicians can intuitively observe the data displayed on the host computer, browse the generated charts, and enjoy a simple and efficient process. Historical data can also be quickly retrieved, providing guidance for cathodic protection work. Therefore, accurate measurement of the pipeline's cathodic protection potential is the core of the intelligent pipeline control system.

[0004] In a cathodic protection system, the cathodic protection potential of the pipeline is the sole parameter for evaluating its protection effectiveness. The cathodic protection potential under energized conditions, known as the energized potential Von, is obtained by measuring the potential difference between the pipeline and the reference electrode in the soil near the pipeline. However, due to the presence of external currents, including cathodic protection current and stray currents, the measured energized potential generally has a large systematic error; Von is not equal to the true polarization potential Vt of the pipeline. This error caused by external currents is collectively referred to as the IR drop. The IR drop is caused by the cathodic protection current between the reference electrode and the pipeline potential measurement point, soil resistance, and the resistance of the pipeline surface film or insulation layer. It is a DC ohmic voltage drop, a pure ohmic voltage drop caused by the cathodic protection current, which disappears immediately upon interruption of the cathodic protection current. The error V0, which cannot be eliminated by the power-off method, is caused by the ground potential gradient resulting from various stray currents and secondary currents. It is an ohmic voltage drop caused by non-cathodic protection currents, known as the non-ohmic voltage drop. Stray currents are currents flowing in non-designated circuits. Secondary current is the IR drop generated on the electrolyte (i.e., soil) between the reference electrode and the sample at the location of polarization difference caused by the different polarization degrees of the protected metal. When using a surface reference electrode to measure the off-voltage potential of the sample, a closer distance between the reference electrode and the sample reduces the influence of stray current to some extent. Currently, domestic and international techniques for measuring IR drop-free samples mainly use polarization probes or reference tubes to reduce the IR drop by decreasing the distance between the reference electrode and the sample.

[0005] The theoretical test curve of the de-energized potential of the test piece is shown in the figure. Figure 1 As shown, at the instant the test piece is disconnected, the IR drop generated by the external current acting on the test piece and the circuit resistance, which is the system error, suddenly drops to 0 due to the disconnection of the test piece, and the IR drop also reaches 0. At this time, the depolarization reaction on the test piece has not yet started. Therefore, the potential of the test piece at this moment is the true potential after eliminating the IR drop, which is the true potential of the tested structure. It truly reflects the true protection potential of the tested structure or the potential in a state without stray current, and is also a key parameter for accurately evaluating the cathodic protection effectiveness of the tested structure. However, in actual measurement circuits, due to the influence of hardware structures such as system test time, sampling frequency, and relay (switch) action time, both types of system errors cannot be avoided when measuring the true potential. Figure 2This is the potential test curve of the test piece after power-off under actual test conditions. The surge potential generated when the relay disconnects the test piece, i.e., during the short period of time the relay operates, the potential of the test piece experiences a potential backlash. On the one hand, the true IR drop potential is masked by the backlash potential; on the other hand, due to different hardware and test circuits, the duration of this surge phenomenon varies significantly, greatly affecting the actual potential value obtained in the test. Since there may be a brief surge phase after the test piece is powered off, a specific time for reading the power-off potential needs to be determined to obtain an accurate power-off potential. NACE™ 0497-2002 considers that after a power-off time exceeding 3000ms, the polarization decay region is entered, and within 500ms, the voltage surge region is in effect.

[0006] Marec JC proposed 2000ms as the reading time for the power-off potential. Weng Yongji adopted this conclusion, determining the power-off potential value by measuring 1000-2000ms after power failure. Huang Tengfei, through experimental research, used 50ms as the reading time for the power-off potential. Peng Rong et al., through experimental research, believed that in testing, recording the power-off potential value as the instantaneous potential value measured 100ms after power failure can approximate the true potential of the pipeline to a considerable extent. Qin Ying, through experimental research, believed that the power-off potential collected within a micro-segment of about 500ms after power failure is relatively accurate. In summary, there is no unified understanding on the reading time of the power-off potential, and further research is needed. No unified opinion has been reached domestically or internationally. In-depth research has not been conducted on aspects such as the polarization time of the test piece and the reading time of the power-off potential. The application and promotion of the test piece power-off method in China still lacks theoretical support and experimental basis. Currently, this situation may lead to significant errors in different scenarios when using different reading times for the power-off potential, resulting in misjudgments of cathodic protection effectiveness and operation and maintenance, and even serious safety accidents. Summary of the Invention

[0007] The de-energized potential of a test piece plays a crucial role in the assessment and maintenance of cathodic protection. The de-energized potential reading time is a significant factor affecting the de-energized potential (the true potential after removing IR drop). Currently, there is no unified understanding on this in academia and engineering. Therefore, the purpose of this invention is to develop a method and testing equipment for measuring the true potential of a test piece after de-energization, based on research into the potential change of the test piece after de-energization.

[0008] like Figure 2 As shown, the surge (reverse) potential generated in the actual circuit at the moment of power failure is a systematic error affecting the accurate reading of the true potential. This error causes random fluctuations in the potential of the test piece after power failure. Observing this surge potential, it can be found that after the surge effect disappears, the potential of the test piece returns to the true cathodic protection potential. Therefore, mathematical methods can be used to determine the time when the surge potential disappears, that is, the accurate reading time of the true potential can be determined.

[0009] Surge potential has the following characteristics: the potential fluctuates up and down, then continues to decrease; after the surge disappears, the potential drops sharply. Based on these two characteristics, the present invention provides a method for accurately testing the de-energization potential in forced current cathodic protection, and determining the moment for reading the true cathodic protection potential: i>1 Where: V Ti Let i be the potential of the test piece at test time i; V Ti-1 The potential of the test piece at test time i-1; V T The potential difference of the test piece at two test times; Based on the characteristics of surge potential, the surge effect can be judged to have disappeared when VT has the following two characteristics: 1. When two or more consecutive VT>0; 2. Max(VT); Therefore, the moment when both conditions are met simultaneously is the actual cathodic protection potential reading moment, see... Figure 3 As shown.

[0010] like Figure 4 As shown, the test hardware includes a CPU (which acts as a central controller, controlling the acquisition timing, issuing commands, and performing data calculations), a high-speed potential acquisition unit, and a calculation program.

[0011] Based on a polarization probe or reference tube, the potential test piece is connected to the cathode of the cathodic protection via a relay, and the internal reference electrode is close to the potential test piece. At this time, the test potential between the internal reference electrode and the potential test piece is the on-state potential. When it is necessary to accurately set the time for reading the power-off potential of the polarization probe or reference tube, a command is issued by the host computer, or a preset program command is executed to start the preset program. At this time, the CPU of the test hardware controls the timing, recording time, and potential curve after power-off. After the preset program is started, the CPU disconnects the relay and simultaneously begins recording the potential between the potential test piece and the internal reference electrode at each moment. Figure 2 The technical time is no less than 300 seconds. After the test, the CPU connects to the relay to complete the hardware test program. The CPU analyzes and calculates the test record data according to the calculation scheme to determine the power-off potential reading time of the polarization probe or reference tube, and saves it in the test hardware, or sends it to the host computer for setting, so that the test terminal or host computer can accurately measure the true potential of the cathodic protection.

[0012] Compared with the prior art, the advantages of this invention are: The method of this invention can automatically obtain the reading time of the true cathodic protection potential by calculating the power-off potential data collected at different times by a prefabricated high-speed potential acquisition instrument (sampling frequency <5Hz). The reading of the test piece potential is more accurate and precise than that of traditional methods, solving the difficulties and pain points of accurate cathodic protection assessment and intelligent management in current intelligent cathodic protection testing terminals. Attached Figure Description

[0013] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments: Figure 1 This is the potential curve of the test piece under ideal conditions of de-energized potential. Figure 2 This is the potential curve of the test piece under the actual de-energized potential; Figure 3 This is the actual time to read the cathodic protection potential; Figure 4 This is a hardware block diagram for high-speed potential acquisition and calculation based on CPU control. Figure 5 The flowchart shows the procedure for determining the timing of data acquisition, calculation, judgment, and reading after the test piece is powered off. Detailed Implementation

[0014] The present invention will be further explained below with reference to specific implementation schemes, but it is not limited to the present invention. The structures, proportions, sizes, etc. shown in the accompanying drawings are only used to complement the content disclosed in the specification, so as to enable those skilled in the art to understand and read, and are not intended to limit the conditions under which the present invention can be implemented. Therefore, they have no substantial technical significance. Any modification of the structure, change of the proportion relationship or adjustment of the size, without affecting the effect and purpose that the present invention can produce, should still fall within the scope of the technical content disclosed in the present invention.

[0015] This invention provides a method for accurately testing the de-energization potential in forced current cathodic protection, and for determining the true potential reading time of the cathodic protection: i>1 Where: V Ti Let i be the potential of the test piece at test time i; V Ti-1 The potential of the test piece at test time i-1; V T The potential difference of the test piece at two test times; Based on the characteristics of surge potential, the surge effect can be judged to have disappeared when VT has the following two characteristics: 1. When two or more consecutive VT>0; 2. Max(VT); Therefore, the moment when both conditions are met simultaneously is the actual cathodic protection potential reading moment, see... Figure 3 As shown.

[0016] like Figure 4 As shown, the test hardware includes a CPU (which acts as a central controller, controlling the acquisition timing, issuing commands, and performing data calculations), a high-speed potential acquisition unit, and a calculation program.

[0017] Based on a polarization probe or reference tube, the potential test piece is connected to the cathode of the cathodic protection via a relay, and the internal reference electrode is close to the potential test piece. At this time, the test potential between the internal reference electrode and the potential test piece is the on-state potential. When it is necessary to accurately set the time for reading the power-off potential of the polarization probe or reference tube, a command is issued by the host computer, or a preset program command is executed to start the preset program. At this time, the CPU of the test hardware controls the timing, recording time, and potential curve after power-off. After the preset program is started, the CPU disconnects the relay and simultaneously begins recording the potential between the potential test piece and the internal reference electrode at each moment. Figure 2 The technical time is no less than 300 seconds. After the test, the CPU connects to the relay to complete the hardware test program. The CPU analyzes and calculates the test record data according to the calculation scheme to determine the power-off potential reading time of the polarization probe or reference tube, and saves it in the test hardware, or sends it to the host computer for setting, so that the test terminal or host computer can accurately measure the true potential of the cathodic protection.

[0018] Matters not covered in this invention are common knowledge.

[0019] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for accurately testing the disconnection potential in forced current cathodic protection, characterized in that: Determine the exact moment to read the true cathodic protection potential: i>1 Where: V Ti Let i be the potential of the test piece at test time i; V Ti-1 The potential of the test piece at test time i-1; V T The potential difference of the test piece at two test times; Based on the characteristics of surge potential, the surge effect can be judged to have disappeared when VT has the following two characteristics:

1. When two or more consecutive VT>0; 2. Max(VT); The moment when both of these conditions are met is the moment when the true cathodic protection potential is read.

2. The method for accurately testing the disconnection potential in forced current cathodic protection according to claim 1, characterized in that: The test includes a CPU, a high-speed potential acquisition unit, and a calculation program; based on a polarization probe or reference tube, the potential test piece is connected to the cathode protection cathode via a relay, and the internal reference electrode is close to the potential test piece. At this time, the test potential between the internal reference electrode and the potential test piece is the energized potential. When it is necessary to accurately set the reading time of the polarization probe or reference tube power-off potential, the host computer issues a command or the program presets the command to start the preset program. The timing, recording time, and potential curve after power failure are controlled by the CPU of the test hardware; after the preset program starts, the CPU disconnects the relay and starts recording the potential between the potential test piece and the internal reference electrode at each moment, with a technical time of not less than 300 seconds. After the test, the CPU connects to the relay to complete the hardware test program; the CPU analyzes and calculates the test record data according to the calculation scheme to determine the power-off potential reading time of the polarization probe or reference tube, and saves it in the test hardware, or sends it to the host computer for setting, so that the test terminal or host computer can accurately measure the true potential of the cathodic protection.

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