CN110066997B - External corrosion AC/DC comprehensive detection method - Google Patents

External corrosion AC/DC comprehensive detection method Download PDF

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Publication number
CN110066997B
CN110066997B CN201910363048.1A CN201910363048A CN110066997B CN 110066997 B CN110066997 B CN 110066997B CN 201910363048 A CN201910363048 A CN 201910363048A CN 110066997 B CN110066997 B CN 110066997B
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alternating current
output
direct current
data
potential difference
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CN110066997A (en
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孙勤
王红军
卢少同
孔德生
高桂飞
李长安
张胜国
姜刚
李彦刚
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Qingdao Yahe Science & Tech Development Co ltd
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Qingdao Yahe Science & Tech Development Co ltd
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    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
    • C23F13/00—Inhibiting corrosion of metals by anodic or cathodic protection
    • C23F13/02—Inhibiting corrosion of metals by anodic or cathodic protection cathodic; Selection of conditions, parameters or procedures for cathodic protection, e.g. of electrical conditions
    • C23F13/06—Constructional parts, or assemblies of cathodic-protection apparatus
    • C23F13/08—Electrodes specially adapted for inhibiting corrosion by cathodic protection; Manufacture thereof; Conducting electric current thereto
    • C23F13/22—Monitoring arrangements therefor
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
    • C23F2213/00—Aspects of inhibiting corrosion of metals by anodic or cathodic protection
    • C23F2213/30—Anodic or cathodic protection specially adapted for a specific object
    • C23F2213/32—Pipes

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Investigating Or Analyzing Materials By The Use Of Electric Means (AREA)
  • Pipeline Systems (AREA)

Abstract

An external corrosion alternating current and direct current comprehensive detection method comprises the following steps: the constant potential rectifier inputs direct current to the pipeline through a first connecting cable, and a switch-on and switch-off device arranged on the first connecting cable is periodically and alternately switched on and off; the PCM transmitter inputs alternating current to the pipeline through a second connecting cable, and the PCM transmitter periodically and alternately outputs and interrupts the alternating current; the detection equipment acquires signals; the data acquisition terminal processes the alternating current data and the direct current data. The external corrosion alternating current and direct current comprehensive detection method eliminates mutual interference between alternating current detection and direct current detection by controlling the current output time, frequency and phase of a PCM transmitter and selecting and processing time periods and time points of data acquisition of an electromagnetic field, current, potential and potential difference, thereby realizing simultaneous detection of alternating current signals and direct current signals.

Description

External corrosion AC/DC comprehensive detection method
Technical Field
The invention belongs to the technical field of cathodic protection corrosion prevention, and particularly relates to an external corrosion alternating current-direct current comprehensive detection method.
Background
The mileage of in-service oil and gas pipelines is rapidly increased due to the rapid development of pipeline construction in China, and meanwhile, many existing-service buried pipelines in China are aged, the normal operation of the pipelines is seriously influenced due to the aging and corrosion of the pipelines, once an oil and gas conveying pipeline failure accident happens, the oil and gas conveying pipeline failure accident not only brings huge economic loss to production enterprises, but also can generate serious consequences to the society and the surrounding natural environment. Through the regular detection and evaluation of the pipeline anticorrosion protection system, the corrosion state of the oil and gas transmission pipeline can be timely and accurately mastered, and the method is important for ensuring the safe operation of the oil and gas pipeline.
The external corrosion direct Evaluation (ECDA) technology is a method for evaluating the influence of external corrosion on the integrity of a pipeline, and a technical standard is formed at present. The ECDA acquires the current situation information of the corrosion and corrosion prevention system outside the pipeline through an external detection means according to a standardized program, and systematically and comprehensively evaluates the corrosion prevention system outside the pipeline by combining excavation verification and analysis results of related data. Weak links, external corrosion conditions and related influence factors of the pipeline external corrosion prevention system can be judged through the ECDA.
The current ECDA technical standard comprises four detection methods: 1. densometer potential measurement (CIPS); 2. direct current potential gradient method (DCVG); 3. alternating current attenuation (PCM); 4. alternating potential gradient method (ACVG). The device performing the DCVG/CIPS detection function is also commonly referred to as DCVG at present, the device performing the PCM/ACVG detection function is commonly referred to as PCM, and DCVG and PCM are the main detection devices for the corrosion detection outside the pipeline at present.
When two kinds of detection equipment of DCVG and PCM work at present, there are main problems in that: when ECDA detection is performed, PCM and DCVG interfere with each other and cannot be used simultaneously. When PCM is detected, the signal output by the transmitter contains alternating current components with various frequencies, and the accuracy of DCVG potential detection is influenced. In order to ensure the quality of engineering detection, the common method in engineering is to separately detect the PCM and the DCVG, so that the detection work of the same pipeline must be performed twice, the cost is high, and the efficiency is low.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides an external corrosion alternating current-direct current comprehensive detection method which can enable PCM and DCVG to be used simultaneously.
In order to achieve the purpose, the invention adopts the technical scheme that:
an external corrosion alternating current and direct current comprehensive detection method comprises the following steps:
the constant potential rectifier inputs direct current to the pipeline through a first connecting cable, and an on-off device mounted on the first connecting cable periodicallyAlternately switching on and off, and switching on and off once in one on-off period of the on-off device for a switching-on duration of T1Off duration of T2；
The PCM transmitter inputs alternating current to the pipeline through a second connecting cable, the PCM transmitter periodically and alternately outputs and interrupts, one output and one interruption are performed in one working period of the PCM transmitter, and the output duration is T3Interruption duration of T4；
The on-off of the on-off device and the output of the PCM transmitter are started simultaneously, the phase of the output current when the output of the PCM transmitter is interrupted is the same as that when the output of the PCM transmitter is started, the on-off period of the on-off device is the same as the working period duration of the PCM transmitter, and the on-off duration T is1Greater than the output duration T3；
The detection equipment carries out signal acquisition:
the alternating current signal detection equipment detects an electromagnetic field signal generated on a pipeline, and the detected electromagnetic field signal is sent to the data acquisition terminal; the direct current signal detection equipment detects the pipe ground potential difference between a pipeline connected with the direct current signal detection equipment through a conducting wire and the ground, and the detected pipe ground potential difference is sent to the data acquisition terminal;
the data acquisition terminal processes the alternating current data and the direct current data:
the data acquisition terminal continuously records the received electromagnetic field signal data, removes the electromagnetic field signal of the PCM transmitter in the output interruption time period, and stores the spliced rest electromagnetic field signals as electromagnetic field data into a memory arranged in the data acquisition terminal; and the data acquisition terminal stores the tube ground potential difference when the on-off device is switched on and off in the output interruption period of the PCM transmitter into the memory as power-on potential detection data and power-off potential detection data respectively.
Preferably, when the detection device performs signal acquisition:
the method comprises the following steps that an alternating current signal detection device detects alternating current potential difference between two points spaced on the earth surface above a pipeline, the detected alternating current potential difference is sent to a data acquisition terminal, a direct current signal detection device detects direct current potential difference between the two points spaced on the earth surface above the pipeline, and the detected direct current potential difference is sent to the data acquisition terminal;
when the data acquisition terminal processes the alternating current data and the direct current data:
the data acquisition terminal continuously records the received alternating current potential difference, removes the alternating current potential difference of the PCM transmitter in the output interruption time period, and stores the residual alternating current potential difference data as alternating current potential difference data into a memory arranged in the data acquisition terminal after splicing; and the data acquisition terminal stores the direct current potential difference when the on-off device is switched on and off in the output interruption period of the PCM transmitter into the memory as the power-on direct current potential difference data and the power-off direct current potential difference data respectively.
Preferably, the phase of the output current when the output of the PCM transmitter is interrupted and the phase of the output current when the output of the PCM transmitter is started are both located at a phase zero point.
Preferably, the PCM transmitter, the on-off device and the data acquisition terminal are all connected with a satellite synchronous clock.
Preferably, the alternating current of the input pipeline of the PCM transmitter comprises 1 alternating current component with a reference frequency and 1 or more alternating current components with frequencies of different integral multiples of the reference frequency, and all the alternating current components are simultaneously output from the phase zero point when the output of the PCM transmitter is started.
Compared with the prior art, the invention has the advantages and positive effects that:
1. the external corrosion alternating current and direct current comprehensive detection method eliminates mutual interference between alternating current detection and direct current detection by controlling the current output time, frequency and phase of a PCM transmitter and selecting and processing time periods and time points of data acquisition of an electromagnetic field, current, potential and potential difference, thereby realizing simultaneous detection of alternating current signals and direct current signals.
2. By removing the alternating current signal detection data measured in the interruption time period output by the PCM transmitter and retaining and splicing the alternating current signal detection data detected in the continuous time period output by the PCM transmitter, the finally spliced alternating current detection data can reflect the alternating current signal on the pipeline when the PCM transmitter is continuously and uninterruptedly output, so that the obtained alternating current detection data is more accurate, and the interference of the discontinuous output mode of the PCM transmitter on the alternating current detection data is eliminated.
3. The power-on potential and the power-off potential are collected when the output of the PCM transmitter is interrupted, so that the interference of the alternating voltage applied to the pipeline by the PCM transmitter on the direct current potential detection is eliminated, the removal processing of the alternating voltage interference is not needed, the accurate direct current potential can be quickly measured, the detection efficiency is improved, and the alternating current signal detection and the direct current signal detection can be simultaneously carried out.
4. The alternating current transmitted by the PCM transmitter comprises 1 reference frequency alternating current component and 1 or more alternating current components with frequencies being different integral multiples of the reference frequency, all the alternating current components are simultaneously output from a phase zero point when the output of the PCM transmitter is started, so that the output interruption and the output starting of the PCM transmitter can be positioned at the phase zero point, the condition that the output current is increased to a higher set point when the PCM transmitter is started is avoided, the output power when the output of the PCM transmitter is started is reduced, the impact of equipment operation is reduced, the time error caused by the fact that the output current needs to be increased to the set point from zero is eliminated, and the detection precision is increased.
5. The PCM transmitter, the on-off device and the data acquisition terminal adopt satellite synchronous clocks, the output of the PCM transmitter and the on-off device can be synchronously started, the data acquisition terminal can determine the time period when the output of the PCM transmitter is in an interruption state and the time period when the on-off device is switched on and off in the time period, so that the acquisition moments of the power-on potential, the power-off potential, the power-on direct current potential difference and the power-off direct current potential difference are selected, the acquired power-on potential, the power-off potential, the power-on direct current potential difference and the power-off direct current potential difference are ensured to be measured when no alternating voltage interference exists, and the detection accuracy is ensured.
Drawings
FIG. 1 is a system diagram of the apparatus used in the method for comprehensive detection of external corrosion by AC/DC;
in the above figures: 1. a pipeline; 2. testing the pile; 31. a PCM transmitter; 32. an alternating current signal detection device; 33. a-shaped frame; 34. a probe; 41. a direct current signal detection device; 42. a reference electrode; 5. a potentiostat; 6. an on-off device; 7. and a data acquisition terminal.
Detailed Description
The invention is described in detail below by way of exemplary embodiments. It should be understood, however, that elements, structures and features of one embodiment may be beneficially incorporated in other embodiments without further recitation.
In the description of the present invention, it should be noted that the terms "inside", "outside", "upper", "lower", "front", "rear", and the like indicate orientations or positional relationships based on positional relationships shown in the drawings, and are only for convenience in describing the present invention and simplifying the description, but do not indicate or imply that the device or element referred to must have a specific orientation, be constructed in a specific orientation, and be operated, and thus, should not be construed as limiting the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.
As shown in FIG. 1, the device adopted by the external corrosion AC/DC comprehensive detection method comprises a PCM detection unit and a DCVG detection unit.
The PCM detection unit comprises a PCM transmitter 31, an ac signal detection device 32 and an a-frame 33 to which the ac signal detection device 32 is connected.
The PCM transmitter 31 is connected to the pipe 1 directly by a cable or by connecting the test pile 2 connected to the pipe 1 such that the PCM transmitter 31 is connected to the pipe 1, and the PCM transmitter 31 can input an alternating current to the pipe 1.
The ac signal detection device 32 is capable of detecting that an ac current forms an electromagnetic field on the pipeline 1 and sending the detected electromagnetic field signal to the data acquisition terminal 7 for storage.
The a-frame 33 detects the surface alternating current potential difference between the probes 34 through the pair of probes 34 installed, so as to obtain the alternating current electric field signal generated on the surface by the alternating current flowing out from the pipeline anticorrosive coating damage point, and sends the measured alternating current potential difference to the data acquisition terminal 7 for storage.
The DCVG detection unit includes a direct current signal detection device 41. The direct current signal detection device 41 is provided with two electrodes, one electrode is connected with the pipeline 1, and the other electrode is connected with the reference electrode 42 for grounding, so that the direct current signal detection device 41 performs direct current potential detection on the pipeline 1, thereby detecting the voltage difference between the pipe grounds, and sending the detected pipe ground potential difference to the data acquisition terminal 7 for storage.
The reference electrodes 42 in the DCVG detection unit are two and are respectively fixed on two probing bars, the two reference electrodes 42 are connected to two positions spaced on the ground, the direct current potential between the two reference electrodes 42 is detected while the potential difference between the tube and the ground is detected, so that the direct current potential difference between two points spaced on the ground surface above the pipeline 1 is obtained, and the detected direct current potential difference is sent to the data acquisition terminal 7 for storage.
The data acquisition terminal 7 analyzes and processes the acquired data, so as to obtain detection results of DCVG, CIPS, PCM and ACVG.
The data acquisition terminal 7 analyzes and processes the received electromagnetic field signal, so that the size and the direction of the alternating current on the pipeline 1 and the depth and the position of the pipeline 1 can be obtained, and the PCM detection function is realized.
The data acquisition terminal 7 analyzes and processes the received alternating current potential difference, so that the position and the size of the damage point of the anti-corrosion layer on the pipeline 1 can be obtained, and the ACVG detection function is realized.
The data acquisition terminal 7 analyzes and processes the received pipe ground potential difference, so that the current cathodic protection state of the pipeline 1 can be obtained, and the CIPS detection function is realized.
The data acquisition terminal 7 analyzes and processes the received direct current potential difference, so that the position of the anticorrosive coating damage point of the pipeline 1 and the current direction flowing through the anticorrosive coating damage point under the on-off state of the constant potential rectifier can be obtained, the severity of the anticorrosive coating damage point of the pipeline 1 is obtained, and the DCVG detection function is realized.
The potentiostat 5 is connected with the pipeline 1 through a first connecting cable, and inputs direct current to the pipeline 1 to form cathode protection on the pipeline 1. And an on-off device 6 is arranged on the first connecting cable, and can control the on-off between the potentiostat 5 and the pipeline 1.
When the on-off device 6 is switched on, the constant potential rectifier 5 is connected and conducted with the pipeline 1, the constant potential rectifier 5 conducts electricity to the pipeline 1, and the detected voltage difference between the pipeline and the ground is an electrified potential; when the on-off device 6 is turned off, the constant potential rectifier 5 is disconnected from the pipeline 1, the constant potential rectifier 5 stops electrifying the pipeline 1, and the detected voltage difference between the pipeline and the ground is the power-off potential.
The on-off device 6 operates according to a fixed on-off cycle, alternately turning on and off. The on-off period of the on-off device 6 is one-time on and one-time off, and the on duration is T1Off duration of T2。
The PCM transmitter 31 feeds ac current to the pipe 1 via a second connection cable, according to a fixed duty cycle. The output of the PCM transmitter 31 is operated intermittently, i.e., output operation and output interruption are alternated. An output and an interruption are performed during a duty cycle of the PCM transmitter 31, the output duration being T3Interruption duration of T4。
The on of the on-off switch 6 and the output of the PCM transmitter 31 start at the same time, i.e., the on-off period of the on-off switch 6 starts at the same time as the duty cycle of the PCM transmitter 31.
The phase of the output current when the output of the PCM transmitter 31 is interrupted is the same as the phase of the output current when the output of the PCM transmitter 31 is started, that is: when the output of the PCM transmitter 31 is interrupted in one duty cycle and the output of the PCM transmitter 31 is started in the next duty cycle, the phase magnitude and the phase direction of the output current are the same, and the waveforms of the output current of each output period of the PCM transmitter 31 are spliced end to end continuously to obtain the same waveform diagram as that of the PCM transmitter 31 when the output current is continuously interrupted.
The on-off period of the on-off device 6 is the same as the working period duration of the PCM transmitter 31, that is, the on-off period of the on-off device 6 and the working period of the PCM transmitter 31 are simultaneously finished, so that the on-off device 6 and the output of the PCM transmitter 31 are always simultaneously started.
On-time T1Greater than the output duration T3In the output of PCM transmitter 31When the current is cut off, the potentiostat 5 and the pipeline are still in the on state for a duration of Δ T, where Δ T is equal to T1-T3。
An alternating current signal detection device 32 in the PCM detection unit detects an electromagnetic field signal on the pipeline 1, and the detected electromagnetic field signal is transmitted to the data acquisition terminal 7.
The a sub-frame 33 of the PCM detection unit detects an ac potential difference between two points spaced above the ground surface of the pipeline by a pair of probes 34 installed, and the detected ac potential difference is transmitted to the data acquisition terminal 7.
The direct current signal detection device 41 detects the tube ground potential difference between the pipeline 1 connected with the direct current signal detection device 41 through a lead and the ground and the direct current potential difference between the reference electrodes 42 through the reference electrodes 42 on the two sounding poles, and the detected tube ground potential difference and the detected direct current potential difference are sent to the data acquisition terminal 7.
The dc potential difference between the reference electrodes 42 is the dc potential difference between two points spaced above the earth's surface above the pipe.
The data acquisition terminal 7 can be an electronic device capable of recording and processing data, such as a mobile phone and a computer which are held by a tester.
The data acquisition terminal 7 processes the alternating current data:
the alternating current data comprises electromagnetic field signals and alternating current potential difference, a data processing unit arranged on the data acquisition terminal 7 continuously records the received electromagnetic field signals and the alternating current potential difference, removes the electromagnetic field signals and the alternating current potential difference in a time period when the PCM transmitter 31 is in an output interruption state, splices the rest electromagnetic field signals and the alternating current potential difference and stores the spliced electromagnetic field signals and the spliced alternating current potential difference as electromagnetic field data and alternating current potential difference data into a memory arranged on the data acquisition terminal 7.
And the data acquisition terminal 7 analyzes and processes the electromagnetic field data and the alternating current potential difference data stored in the memory to realize PCM/ACVG detection.
The data acquisition terminal 7 processes the direct flow data:
the data acquisition terminal 7 stores the tube ground potential difference acquired by the direct current signal detection device 41 at the time X when the PCM transmitter 31 is in the output interruption period and the on-off device 6 is in the on period, as the energization potential data, into the memory.
The data acquisition terminal 7 stores the tube ground potential difference acquired by the direct current signal detection device 41 at the Y time in the output interruption period of the PCM transmitter 31 and the turn-off period of the on-off switch 6 into the memory as the power-off potential data.
The data acquisition terminal 7 stores the dc potential difference acquired by the dc signal detection device 41 at the X time in which the PCM transmitter 31 is in the output interruption period and the on-off device 6 is in the on period, as the energization dc potential difference detection data, into the memory.
The data acquisition terminal 7 stores the dc potential difference acquired by the dc signal detection device 41 at the Y time when the PCM transmitter 31 is in the output interruption period and the on-off device 6 is in the off period, as power-off dc potential difference detection data, into the memory.
The data acquisition terminal 7 sends the electrified potential data, the power-off potential data, the electrified direct current potential difference data and the power-off direct current potential difference data stored in the memory to the analysis equipment for analysis and processing, so that the DCVG/CIPS detection is realized.
The power-on potential data, the power-off potential data, the power-on direct current potential difference data and the power-off direct current potential difference data are collected when the output of the PCM transmitter 31 is interrupted, no alternating current exists on the pipeline 1, and the interference of alternating current detection on direct current detection is eliminated. In addition, the electromagnetic field data and the alternating current potential difference data obtained through removal and splicing are data results acquired when alternating current and direct current exist on the pipeline 1 at the same time, namely the electromagnetic field data and the alternating current potential difference data are both measured when the potentiostat 5 is electrified with the pipeline and are alternating current data on the pipeline 1 when the pipeline is in a cathode protection state, so that the obtained alternating current data are more accurate, and the interference of the direct current on alternating current detection data is eliminated.
By the mode, mutual interference between alternating current detection and direct current detection is eliminated, and simultaneous PCM detection and DCVG detection are realized.
In order to make the data acquisition terminal 7 know the operation states of the PCM transmitter 31 and the switch 6, the PCM transmitter 31, the switch 6 and the data acquisition terminal 7 are all connected with a satellite synchronous clock.
By the satellite synchronous clock, the PCM transmitter 31, the on-off switch 6 and the data acquisition terminal 7 all operate at the same clock time, and since the on-off switch 6 and the output of the PCM transmitter 31 are simultaneously started, the on-off period of the on-off switch 6 is the same as the working period duration of the PCM transmitter 31. Therefore, inputting the output start time of the PCM transmitter 31 and the time length of the operating cycle of the PCM transmitter 31 into the data acquisition terminal 7 enables the data acquisition terminal 7 to know the on start time of the on/off switch 6 and the time length of the on/off cycle of the on/off switch 6, the data acquisition terminal 7 to know the time length of the PCM transmitter 31 in the output interruption state and the on/off switch 6 in the on state, and the time length of the PCM transmitter 31 in the output interruption state and the on/off switch 6 in the off state, and further to determine the X time and the Y time, so as to obtain the power-on potential data, the power-off potential data, the power-on direct current potential difference data, and the power-off direct current potential difference data.
In order to keep the output current of the PCM transmitter 31 in phase continuity and simultaneously realize the start of the PCM transmitter 31 by means of soft start, the phase of the output current when the output of the PCM transmitter 31 is interrupted and the phase of the output current when the output of the PCM transmitter 31 is started are both located at the phase zero point.
Since the output current of the PCM transmitter 31 starts from the phase zero point, when the PCM transmitter 31 starts a working cycle, the PCM transmitter 31 starts, and the output power gradually increases from zero at the start, thereby avoiding the output current of the PCM transmitter 31 starting from a higher phase set point, preventing the PCM transmitter 31 from starting, i.e., operating at a higher output power, reducing the load of the device, and improving the service life of the device.
If the output current of the PCM transmitter 31 starts from a higher phase set point, the output current needs to rapidly rise from the phase zero to the phase set point, consuming a certain time and forming a delay. Therefore, the output current of the PCM transmitter 31 is started from the phase zero point, and compared with the phase set point which is higher, the time delay can be eliminated, and the accuracy of the phase state of the output current of the PCM transmitter 31 can be ensured, so that the accuracy of PCM/ACVG detection can be ensured.
In order to facilitate the determination of the position of the phase zero point and ensure the detection of the anticorrosive layer, the determination of the current direction and the positioning of the position of the pipeline 1 during the PCM/ACVG detection, the alternating current input to the pipeline 1 by the PCM transmitter 31 is alternating current mixed with various frequencies. Each alternating current component in the alternating current comprises 1 reference frequency alternating current component and 1 or more alternating current components with the frequencies being different integral multiples of the reference frequency, and all the alternating current components are simultaneously output from a phase zero point when the output of the PCM transmitter is started, so that all the alternating current components can be at the phase zero point at a certain same moment.

Claims (5)

1. An external corrosion alternating current and direct current comprehensive detection method is characterized by comprising the following steps:
the constant potential rectifier inputs direct current to the pipeline through a first connecting cable, a switch mounted on the first connecting cable is periodically and alternately switched on and off, one switching-on and one switching-off are carried out in one switching-on period of the switch, and the switching-on duration is T1Off duration of T2；
The PCM transmitter inputs alternating current to the pipeline through a second connecting cable, the PCM transmitter periodically and alternately outputs and interrupts, one output and one interruption are performed in one working period of the PCM transmitter, and the output duration is T3Interruption duration of T4；
The on-off of the on-off device and the output of the PCM transmitter are started simultaneously, the phase of the output current when the output of the PCM transmitter is interrupted is the same as that when the output of the PCM transmitter is started, the on-off period of the on-off device is the same as the working period duration of the PCM transmitter, and the on-off duration T is1Greater than the output duration T3；
The detection equipment carries out signal acquisition:
the alternating current signal detection equipment detects an electromagnetic field signal generated on a pipeline, and the detected electromagnetic field signal is sent to the data acquisition terminal; the direct current signal detection equipment detects the pipe ground potential difference between a pipeline connected with the direct current signal detection equipment through a conducting wire and the ground, and the detected pipe ground potential difference is sent to the data acquisition terminal;
the data acquisition terminal processes the alternating current data and the direct current data:
the data acquisition terminal continuously records the received electromagnetic field signal data, removes the electromagnetic field signal of the PCM transmitter in the output interruption time period, and stores the spliced rest electromagnetic field signals as electromagnetic field data into a memory arranged in the data acquisition terminal; and the data acquisition terminal stores the tube ground potential difference when the on-off device is switched on and off in the output interruption period of the PCM transmitter into the memory as power-on potential detection data and power-off potential detection data respectively.
2. The external corrosion alternating current-direct current comprehensive detection method according to claim 1, characterized in that when the detection equipment carries out signal acquisition:
the method comprises the following steps that an alternating current signal detection device detects alternating current potential difference between two points spaced on the earth surface above a pipeline, the detected alternating current potential difference is sent to a data acquisition terminal, a direct current signal detection device detects direct current potential difference between the two points spaced on the earth surface above the pipeline, and the detected direct current potential difference is sent to the data acquisition terminal;
when the data acquisition terminal processes the alternating current data and the direct current data:
the data acquisition terminal continuously records the received alternating current potential difference, removes the alternating current potential difference of the PCM transmitter in the output interruption time period, and stores the residual alternating current potential difference data as alternating current potential difference data into a memory arranged in the data acquisition terminal after splicing; and the data acquisition terminal stores the direct current potential difference when the on-off device is switched on and off in the output interruption period of the PCM transmitter into the memory as the power-on direct current potential difference data and the power-off direct current potential difference data respectively.
3. The external corrosion alternating current-direct current comprehensive detection method according to claim 1, wherein the phase of the output current when the output of the PCM transmitter is interrupted and the phase of the output current when the output of the PCM transmitter is started are both located at a phase zero point.
4. The comprehensive external corrosion alternating current and direct current detection method according to claim 1, wherein the PCM transmitter, the on-off device and the data acquisition terminal are all connected with a satellite synchronous clock.
5. The method according to claim 1, wherein the alternating current of the input pipeline of the PCM transmitter comprises a plurality of alternating current components with different integral multiples of the reference frequency, wherein the frequency of one alternating current component is the reference frequency, and all the alternating current components are simultaneously output from the phase zero point when the output of the PCM transmitter is started.
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