Electrical spark-based tubing-casing external coating pinhole defect detection system

Abstract

The application discloses a tubing casing outer anticorrosion layer pinhole defect detection system based on electric spark, relates to the technical field of tubing casing anticorrosion layer quality detection, and aims at the technical defects of inner and outer detection separation of split type detection architecture, non-uniform positioning reference, and difficulty in identifying penetrating pinholes. A double-domain time-sharing common ground detection system is constructed, in which a common reference ground module is used as a unified electrical reference, and a central time sequence controller is used to realize time-sharing mutual exclusion excitation of an inner electrode detection domain and an outer electrode detection domain. In the process of one-time tubing axial movement, through the movement positioning module and the annular electrode array of the outer electrode assembly, a unified column coordinate system space position label is given to the inner and outer domain discharge events, and spatial correlation analysis is performed in the data fusion processing layer to automatically determine the penetrating pinhole defect. The scheme solves the problems that inner and outer defects cannot be aligned in the same coordinate and signal crosstalk, and simultaneously realizes reliable automatic identification of the high-risk penetrating pinhole defect.

Description

Technical Field

[0001] This invention relates to the field of oil pipe casing anti-corrosion coating quality inspection technology, specifically to an oil pipe casing external anti-corrosion coating pinhole defect detection system based on electrical discharge machining. Background Technology

[0002] Tubing and casing are core tubing components in oil and gas extraction, water injection, and downhole operations. Their working environment is consistently under harsh conditions of high pressure, corrosive media, and electrochemical corrosion. To prevent direct exposure of the tubing metal to this corrosive environment, both the inner and outer walls of the tubing and casing are coated with an anti-corrosion layer, forming an insulating barrier. However, during production, transportation, and use, the anti-corrosion layer is highly susceptible to developing tiny, penetrating pinhole-like defects due to coating process defects, mechanical impacts, and environmental stress cracking. Although these pinholes are small, they provide a direct channel for corrosive media to reach the metal substrate, potentially leading to pitting corrosion, perforation, or even tubing string breakage within a short period, seriously threatening the production safety of oil and gas wells.

[0003] Currently, the most effective non-destructive testing method for pinhole defects in anti-corrosion coatings is the high-voltage electric spark leak detection method. The principle is to apply a high-voltage DC or pulse voltage to the surface of the anti-corrosion coating. When the scanning electrode passes through the pinhole location, the electric field breaks down the air gap or the weak insulation at the defect, generating a spark discharge. The presence of the defect can be determined by detecting the discharge current.

[0004] Existing electrical spark testing equipment mostly adopts a split testing architecture, that is, the testing of the outer wall anti-corrosion layer and the testing of the inner wall anti-corrosion layer are completed by two separate sets of equipment and two separate processes. This split testing mode has the following prominent problems in practical applications: The low efficiency of the inspection means that a single tubing needs to be clamped twice and scanned twice along its full length. This makes the operation complex and doubles the time required. In addition, the internal wall inspection requires a special tube crawler or probe electrode. Equipment switching and debugging further prolong the inspection cycle, which seriously restricts the rapid sorting and evaluation of large batches of tubing during well workover operations.

[0005] The positioning references for internal and external inspections are not unified. The external wall inspection equipment and the internal wall inspection equipment each establish independent axial position coordinates. Due to factors such as positioning errors in two clamping operations, differences in the cumulative pulse equivalent of encoders from different equipment, and mechanical return clearance, the coordinate values ​​of pinholes at the same physical location in the external wall inspection record and the internal wall inspection record are deviated and cannot be directly aligned.

[0006] Penetrating pinholes cannot be automatically identified. When a penetrating pinhole exists in the anti-corrosion layer, extending from the inner wall to the outer wall, this physical defect will be recorded as a defect point in both the outer wall and inner wall inspections. However, due to the lack of uniformity in the coordinate systems mentioned above, the data fusion processing layer cannot reliably determine whether two defect points correspond to the same location. This makes it very easy for penetrating pinholes to be misjudged as two isolated single-sided pinholes, directly affecting the accurate assessment of the corrosion risk level and remaining life of the pipe.

[0007] Therefore, there is an urgent need for a detection system that can simultaneously perform electrical spark scanning of the inner and outer anti-corrosion layers during a single tubing journey and provide a unified spatial coordinate reference for internal and external defects, so as to fundamentally solve the efficiency and correlation analysis problems of split-type detection. Summary of the Invention

[0008] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a pinhole defect detection system for the outer anti-corrosion coating of tubing casing based on electrical discharge machining. Addressing the technical deficiencies of split-type detection architectures, such as separation of internal and external detection, inconsistent positioning benchmarks, and difficulty in identifying penetrating pinholes, this invention constructs a dual-domain time-division co-location detection system. This system uses a common reference ground module as a unified electrical benchmark and a central timing controller to achieve time-division mutually exclusive excitation between the internal and external electrode detection domains. During a single axial movement of the tubing, the system assigns a unified cylindrical coordinate spatial position label to the discharge events in both domains through the travel positioning module and the annular electrode array of the external electrode assembly. Spatial correlation analysis is then performed at the data fusion processing layer to automatically identify penetrating pinhole defects. This solution solves the problems of incoordinate alignment between internal and external defects and signal crosstalk, while also achieving reliable automatic identification of high-risk defects such as penetrating pinholes. This provides an efficient, accurate, and reliable technical means for evaluating the quality of tubing anti-corrosion coatings.

[0009] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a pinhole defect detection system for the outer anti-corrosion layer of oil tubing casing based on electrical discharge machining, the system comprising: a high-voltage excitation source, a central timing controller, an external electrode detection domain, an internal electrode detection domain, a common reference ground module, a travel positioning module, and a data fusion processing layer; A high-voltage excitation source is used to generate the high-voltage voltage required for detection, and is connected to the first high-voltage switch of the outer electrode detection domain and the second high-voltage switch of the inner electrode detection domain, respectively. The central timing controller is used to generate a first excitation enable signal and a second excitation enable signal to control the opening and closing of the first high-voltage switch and the second high-voltage switch, so that the high-voltage excitation source alternately applies high voltage to the outer electrode detection domain and the inner electrode detection domain, and only one detection domain is subjected to high voltage at any given time. The external electrode detection domain includes a first high-voltage switch, an external electrode assembly, and an external discharge signal acquisition unit. The external electrode detection domain is used to perform electric spark scanning on the anti-corrosion layer of the outer wall of the oil pipe and pick up the external discharge signal. The inner electrode detection domain includes a second high-voltage switch, an inner electrode assembly, and an inner domain discharge signal acquisition unit. The inner electrode detection domain is used to perform electric spark scanning on the anti-corrosion layer of the inner wall of the oil pipe and pick up the inner domain discharge signal.

[0010] Furthermore, the system also includes: The common reference ground module provides a unified electrical reference ground for the outer domain discharge signal acquisition unit of the outer electrode detection domain and the inner domain discharge signal acquisition unit of the inner electrode detection domain; The travel positioning module is used to drive the outer electrode assembly and the inner electrode assembly to move axially relative to the oil pipe and output an axial encoded signal that represents the axial position in real time. The data fusion processing layer receives signals from the outer domain discharge signal acquisition unit, the inner domain discharge signal acquisition unit, and the travel positioning module, respectively. The data fusion processing layer is used to align the outer domain discharge events and the inner domain discharge events to a unified tube coordinate system, and to determine whether there is a penetrating pinhole defect based on the spatial proximity criterion.

[0011] Furthermore, the first excitation enable signal and the second excitation enable signal generated by the central timing controller are pulse signals with the same frequency and completely staggered phases, and a fixed dead time is set between the effective levels of adjacent first excitation enable signals and second excitation enable signals, so that the first high-voltage switch and the second high-voltage switch will not be turned on at the same time.

[0012] Furthermore, in the external electrode detection domain, the input terminal of the first high-voltage switch is connected to the output terminal of the high-voltage excitation source, and the output terminal of the first high-voltage switch is connected to the external electrode assembly; The external discharge signal acquisition unit is connected in series between the return ground circuit of the first high-voltage switch and the common reference ground module; When the first excitation enable signal is valid, the external electrode assembly is subjected to high voltage. When there is a pinhole in the anti-corrosion layer of the outer wall of the oil pipe, the discharge current flows back to the outer domain discharge signal acquisition unit through the external electrode assembly, the pinhole in the anti-corrosion layer of the outer wall of the oil pipe, the oil pipe body, and the common reference ground module, forming an outer domain discharge pulse signal.

[0013] Furthermore, in the internal electrode detection domain, the input terminal of the second high-voltage switch is connected to the output terminal of the high-voltage excitation source, and the output terminal of the second high-voltage switch is connected to the internal electrode assembly; The internal discharge signal acquisition unit is connected in series between the return ground circuit of the second high-voltage switch and the common reference ground module; When the second excitation enable signal is valid, the inner electrode assembly is subjected to high voltage. When there is a pinhole in the anti-corrosion layer of the inner wall of the oil pipe, the discharge current flows back to the inner domain discharge signal acquisition unit through the inner electrode assembly, the pinhole in the anti-corrosion layer of the inner wall of the oil pipe, the oil pipe body, and the common reference ground module, forming an inner domain discharge pulse signal.

[0014] Furthermore, the common reference ground module consists of multiple sets of elastic grounding copper brushes installed on the base of the travel positioning module. Under spring pressure, the elastic grounding copper brushes make close contact with the exposed metal at the end of the oil pipe or the grounding strip with the anti-corrosion layer removed, thereby defining the metal body of the oil pipe as the ground potential of the system.

[0015] A high-voltage excitation source is used to generate the high-voltage voltage required for detection, and is connected to the first high-voltage switch of the outer electrode detection domain and the second high-voltage switch of the inner electrode detection domain, respectively. The central timing controller is used to generate a first excitation enable signal and a second excitation enable signal to control the opening and closing of the first high-voltage switch and the second high-voltage switch, so that the high-voltage excitation source alternately applies high voltage to the outer electrode detection domain and the inner electrode detection domain, and only one detection domain is subjected to high voltage at any given time. The external electrode detection domain includes a first high-voltage switch, an external electrode assembly, and an external discharge signal acquisition unit. The external electrode detection domain is used to perform electric spark scanning on the anti-corrosion layer of the outer wall of the oil pipe and pick up the external discharge signal. The inner electrode detection domain includes a second high-voltage switch, an inner electrode assembly, and an inner domain discharge signal acquisition unit. The inner electrode detection domain is used to perform electric spark scanning on the anti-corrosion layer of the inner wall of the oil pipe and pick up the inner domain discharge signal.

[0016] Furthermore, the system also includes: The common reference ground module provides a unified electrical reference ground for the outer domain discharge signal acquisition unit of the outer electrode detection domain and the inner domain discharge signal acquisition unit of the inner electrode detection domain; The travel positioning module is used to drive the outer electrode assembly and the inner electrode assembly to move axially relative to the oil pipe and output an axial encoded signal that represents the axial position in real time. The data fusion processing layer receives signals from the outer domain discharge signal acquisition unit, the inner domain discharge signal acquisition unit, and the travel positioning module, respectively. The data fusion processing layer is used to align the outer domain discharge events and the inner domain discharge events to a unified tube coordinate system, and to determine whether there is a penetrating pinhole defect based on the spatial proximity criterion.

[0017] Furthermore, the first excitation enable signal and the second excitation enable signal generated by the central timing controller are pulse signals with the same frequency and completely staggered phases, and a fixed dead time is set between the effective levels of adjacent first excitation enable signals and second excitation enable signals, so that the first high-voltage switch and the second high-voltage switch will not be turned on at the same time.

[0018] Furthermore, in the external electrode detection domain, the input terminal of the first high-voltage switch is connected to the output terminal of the high-voltage excitation source, and the output terminal of the first high-voltage switch is connected to the external electrode assembly; The external discharge signal acquisition unit is connected in series between the return ground circuit of the first high-voltage switch and the common reference ground module; When the first excitation enable signal is valid, the external electrode assembly is subjected to high voltage. When there is a pinhole in the anti-corrosion layer of the outer wall of the oil pipe, the discharge current flows back to the outer domain discharge signal acquisition unit through the external electrode assembly, the pinhole in the anti-corrosion layer of the outer wall of the oil pipe, the oil pipe body, and the common reference ground module, forming an outer domain discharge pulse signal.

[0019] Furthermore, in the internal electrode detection domain, the input terminal of the second high-voltage switch is connected to the output terminal of the high-voltage excitation source, and the output terminal of the second high-voltage switch is connected to the internal electrode assembly; The internal discharge signal acquisition unit is connected in series between the return ground circuit of the second high-voltage switch and the common reference ground module; When the second excitation enable signal is valid, the inner electrode assembly is subjected to high voltage. When there is a pinhole in the anti-corrosion layer of the inner wall of the oil pipe, the discharge current flows back to the inner domain discharge signal acquisition unit through the inner electrode assembly, the pinhole in the anti-corrosion layer of the inner wall of the oil pipe, the oil pipe body, and the common reference ground module, forming an inner domain discharge pulse signal.

[0020] Furthermore, the common reference ground module consists of multiple sets of elastic grounding copper brushes installed on the base of the travel positioning module. Under spring pressure, the elastic grounding copper brushes make close contact with the exposed metal at the end of the oil pipe or the grounding strip with the anti-corrosion layer removed, thereby defining the metal body of the oil pipe as the ground potential of the system.

[0021] Furthermore, the external electrode assembly is composed of It consists of arc-shaped electrode plates evenly distributed along the circumference, and the arc-shaped electrode plates are numbered sequentially as follows: - ; The data fusion processing layer receives data from the first... When the outer domain discharge pulse signal of the arc-shaped electrode sheet is received, according to Calculate the circumferential angle of the outer domain discharge defect ,in, Indicates that the preset reference direction is Circumferential angle, The number of the arc-shaped electrode plate that detected the discharge; By utilizing the spatial distribution of the arc-shaped electrode sheets, the numbering of the arc-shaped electrode sheets is directly mapped to circumferential angular coordinates, providing a circumferential positioning reference for pinhole defects on the outer wall.

[0022] Furthermore, the data fusion processing layer also receives the axial encoded signal output by the travel positioning module, mapping each discharge event to cylindrical coordinate points. ,in The axial distance is calculated based on the cumulative number of pulses in the axial encoded signal. The data fusion processing layer performs spatial correlation analysis on the collected inner domain defect point set and outer domain defect point set. For any inner domain defect point... and any external defect point When both conditions are met and If the inner domain defect point and the outer domain defect point correspond to the same pinhole location, then a through-hole pinhole defect exists. The preset axial distance tolerance threshold, This is the preset circumferential angle tolerance threshold; If there is only an inner domain defect point and no corresponding outer domain defect point, it is determined to be an inner wall pinhole; if there is only an outer domain defect point and no corresponding inner domain defect point, it is determined to be an outer wall pinhole.

[0023] Compared with existing technologies, this spark-based oil pipe casing external anti-corrosion coating pinhole defect detection system has the following advantages: I. This invention constructs a dual-domain time-division common-ground detection system by building a shared common reference ground module for the outer and inner electrode detection domains and implementing time-division mutually exclusive excitation through a central timing controller. This system enables alternating and continuous spark scanning of the outer and inner anti-corrosion layers during a single axial movement of the tubing, integrating internal and external detection into a single process. This eliminates the auxiliary time for equipment switching and secondary clamping, significantly shortening the detection cycle of a single tubing. Furthermore, since both the inner and outer electrode assemblies are driven by the same travel positioning module, operators only need to start the operation once to obtain complete detection results, significantly reducing labor intensity and operational complexity. This provides an efficient tool for rapid sorting and repair decision-making for large batches of tubing in oilfields.

[0024] Second, this invention provides axial encoded signals from the same incremental photoelectric encoder to the outer and inner domain discharge signal acquisition units through a positioning module. Combined with the channel number mapping of the outer electrode assembly's ring electrode array to the circumferential angular coordinates, each outer and inner domain discharge event is assigned a position label in a unified pipe cylindrical coordinate system. Based on this, the data fusion processing layer performs spatial correlation analysis, determining the tolerance of the axial distance and circumferential angular deviation between the inner and outer domain defect point sets. It automatically identifies penetrating pinhole defects where inner and outer discharge signals occur simultaneously in the same spatial location. This mechanism solves the problem of misalignment of inner and outer defect coordinates caused by inconsistent positioning benchmarks in split-type detection, eliminating the risk of penetrating pinholes being misjudged as isolated single-sided pinholes. This provides a reliable basis for accurate classification of pipe corrosion and assessment of remaining pipe strength.

[0025] Other advantages, objectives and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination or study, or may be learned from the practice of the invention. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0027] Figure 1 This is a system data flow diagram of the oil pipe casing external anti-corrosion layer pinhole defect detection system based on electrical discharge machining in an embodiment of the present invention; Figure 2 This is a schematic diagram of the outer wall discharge current detection circuit in an embodiment of the present invention; Figure 3 This is a schematic diagram of the inner wall discharge current detection circuit in an embodiment of the present invention; Figure 4 This is a flowchart illustrating the overall system workflow in an embodiment of the present invention. Detailed Implementation

[0028] To better understand the above technical solutions, a detailed description of the solutions will be provided below in conjunction with the accompanying drawings and specific embodiments. Obviously, the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0029] This embodiment provides a pinhole defect detection system for the external anti-corrosion layer of oil tubing casing based on electrical discharge machining (EDM). It aims to solve the problems of low detection efficiency, inconsistent internal and external positioning benchmarks, and difficulty in automatically identifying penetrating pinholes in existing split-type detection systems. The system described in this embodiment, as follows... Figure 1 As shown, its components include: a high-voltage excitation source, a central timing controller, an external electrode detection domain, an internal electrode detection domain, a common reference ground module, a travel positioning module, and a data fusion processing layer. These components work together to construct a dual-domain time-sharing and common-ground detection system.

[0030] The high-voltage excitation source is a programmable high-voltage pulse generator used to generate a stable high-voltage electrical signal required for detection. In a specific example, the output voltage range of the high-voltage excitation source is 5kV-30kV, and the output frequency is adjustable. Its output is divided into two paths: the first path is connected to the input terminal of the first high-voltage switch in the external electrode detection domain via a first high-voltage cable; the second path is connected to the input terminal of the second high-voltage switch in the internal electrode detection domain via a second high-voltage cable. The high-voltage excitation source internally includes a step-up transformer, a rectifier and filter circuit, and a pulse forming circuit, which can output a high-voltage pulse with stable amplitude and steep edges according to preset parameters.

[0031] like Figure 2 and Figure 3 As shown, the central timing controller generates two control signals that are completely isolated in timing, namely the first excitation enable signal EN1 and the second excitation enable signal EN2. The EN1 signal precisely controls the conduction and cutoff of the first high-voltage switch through the first control cable, and the EN2 signal precisely controls the conduction and cutoff of the second high-voltage switch through the second control cable. The central timing controller generates the EN1 and EN2 waveforms through its internal logic circuit.

[0032] The external electrode detection domain is a unit specifically designed for detecting pinhole defects in the anti-corrosion coating of the outer wall of the oil pipe. It consists of three parts: a first high-voltage switch, an external electrode assembly, and an external discharge signal acquisition unit.

[0033] First high-voltage switch: This switch is a high-voltage solid-state relay or a high-voltage gas discharge tube. Its input terminal is connected to the output terminal of the high-voltage excitation source, and its output terminal is connected to the external electrode assembly. Its control terminal receives the first excitation enable signal EN1 sent by the central timing controller.

[0034] External electrode assembly: This assembly is a mechanical scanning device used to perform physical contact or maintain a small gap scanning on the outer wall surface of the oil pipe. In one specific embodiment, the external electrode assembly is designed as a ring electrode array that can be completely sleeved on the outside of the oil pipe to be tested. The ring electrode array consists of multiple arc-shaped electrode plates evenly distributed along the circumference. Each arc-shaped electrode plate is electrically connected to the output terminal of the first high-voltage switch through an independent wire.

[0035] External Discharge Signal Acquisition Unit: This unit is a high-sensitivity current-to-voltage conversion and pulse detection circuit. Its input terminal is connected in series between the return ground circuit of the first high-voltage switch and the common reference ground module. Specifically, the return ground terminal of the first high-voltage switch is connected to the input terminal of the external discharge signal acquisition unit, and the output terminal of the external discharge signal acquisition unit is connected to the common reference ground module. The external discharge signal acquisition unit contains a high-speed transimpedance amplifier and a voltage comparator, which can convert the discharge current pulse into a standard TTL level pulse signal with an amplitude of 5V.

[0036] The inner electrode detection domain is a unit used to detect pinhole defects in the anti-corrosion layer of the inner wall of the oil pipe. Its structure is symmetrical with that of the outer electrode detection domain, and it consists of a second high-voltage switch, an inner electrode assembly, and an inner domain discharge signal acquisition unit.

[0037] The second high-voltage switch has the same electrical characteristics and control method as the first high-voltage switch. Its input terminal is connected to the output terminal of the high-voltage excitation source, and its output terminal is connected to the internal electrode assembly. Its control terminal receives the second excitation enable signal EN2 sent by the central timing controller.

[0038] Internal electrode assembly: This assembly is an in-scanning device containing a retractable insulated support rod and a spiral or cylindrical metal electrode fixed to its end. The internal electrode assembly is inserted into the oil pipe via a cable. Driven by the travel positioning module, its metal electrode maintains a constant small gap with the inner wall of the oil pipe. The metal electrode is connected to the output terminal of the second high-voltage switch via a high-voltage wire.

[0039] Inner domain discharge signal acquisition unit: Its circuit structure and function are exactly the same as those of the outer domain discharge signal acquisition unit. The input terminal is connected in series between the return ground circuit of the second high voltage switch and the common reference ground module, which is used to convert the inner wall discharge current pulse into a standard TTL level pulse signal.

[0040] The common reference ground module provides a unified, low-impedance electrical ground potential for the entire detection system. In this embodiment, the module is implemented as follows: a metal busbar installed on the base of the travel positioning module, and multiple sets of elastic grounding copper brushes electrically connected to the busbar. Before the detection begins, these elastic grounding copper brushes, under the pressure of springs, contact the exposed metal ring strip pre-polished at the end of the oil pipe or a specially set grounding terminal, thereby clearly defining the metal body of the oil pipe (i.e. the metal substrate of the pipe being detected) as the ground potential (zero potential reference point) of the entire system. The output terminals of the outer domain discharge signal acquisition unit and the inner domain discharge signal acquisition unit are both connected to the metal busbar through shielded wires.

[0041] The aforementioned positioning module is used to implement both driving and positioning functions.

[0042] Drive function: Includes a servo drive roller assembly, which consists of a servo motor, a reducer and a drive roller. It clamps and drives the oil pipe or drives the entire detection head to move in a uniform linear motion along the oil pipe axis through friction.

[0043] Positioning function: Includes an incremental photoelectric encoder, whose shaft is coaxially mounted with a driven roller or servo-driven roller. When the oil pipe and the detection component move axially relative to each other, the encoder rotates accordingly and outputs quadrature encoded pulses (phase A and phase B). This pulse signal is the axial encoded signal. The phase difference between phase A and phase B is 90 degrees, used to determine the direction of movement. By counting the pulses of any phase, the axial displacement at the current moment can be obtained.

[0044] The data interface of the data fusion processing layer includes: Multiple digital input ports are used to receive TTL level pulse signals output by the outer domain discharge signal acquisition unit and the inner domain discharge signal acquisition unit, and to mark them with timestamps.

[0045] An orthogonal encoder interface is used to receive axial encoded signals (A-phase and B-phase pulses) sent by the travel positioning module, and to perform phase detection and counting of the pulses to calculate the axial coordinate z of the current detection position in real time.

[0046] Multiple general-purpose input / output ports are used to receive channel selection signals from each arc-shaped electrode in the external electrode assembly to determine the circumferential position where the discharge occurs.

[0047] In a preferred embodiment, the central timing controller starts working after power-on, generating a first excitation enable signal EN1 and a second excitation enable signal EN2 with the same frequency but completely staggered phases. For example, the signal frequency is set to 500Hz and the period is 2ms. The high level duration of the EN1 signal in one period is 0.9ms and the low level duration is 1.1ms. The EN2 signal is the opposite, with a high level duration of 0.9ms, but the starting phase is delayed by 1.1ms relative to EN1. A fixed dead time, such as 0.1ms, is set between the falling edge of the EN1 signal (from high level to low level) and the rising edge of the EN2 signal (from low level to high level). Similarly, an equal dead time is set between the falling edge of EN2 and the next rising edge of EN1. The dead time ensures that the first high-voltage switch and the second high-voltage switch will not be turned on at the same time, thereby avoiding crosstalk or overload of the high-voltage excitation source caused by the simultaneous application of high voltage to the external electrode assembly and the internal electrode assembly.

[0048] During the effective period when EN1 is high (excluding dead time), the first high-voltage switch is turned on and the second high-voltage switch remains off. The high-voltage electrical signal generated by the high-voltage excitation source is applied to all the arc-shaped electrode plates of the outer electrode assembly through the first high-voltage switch. A high-voltage electric field is formed between the outer electrode assembly and the anti-corrosion layer of the outer wall of the oil pipe. The travel positioning module drives the system to move along the axial direction of the oil pipe, and the outer electrode assembly continuously scans the outer wall.

[0049] If the anti-corrosion layer on the outer wall of the oil pipe is intact at the current scanning location, its insulation impedance is extremely high, no discharge current is formed, no current flows through the input terminal of the external discharge signal acquisition unit, and its output terminal remains at a low level.

[0050] If a pinhole defect (i.e., a tiny hole penetrating the outer coating) exists in the anti-corrosion layer of the tubing at the current scanning location, the insulation capability of the anti-corrosion layer is compromised. In this case, the high voltage applied to the external electrode assembly will break down the air gap at the pinhole, generating a spark discharge. The discharge current path is as follows: it flows from the positive terminal of the high-voltage excitation source, through the first high-voltage switch, the external electrode assembly, the spark discharge channel, and the exposed metal substrate at the pinhole on the tubing's outer wall, before flowing into the tubing body metal. Since the common reference ground module has defined the tubing metal body as ground potential, this discharge current will continue from the tubing body metal, through the elastic grounding copper brush of the common reference ground module, and the metal busbar, ultimately flowing back to the input terminal of the external discharge signal acquisition unit and from its output terminal back to the negative terminal of the high-voltage excitation source, forming a complete circuit.

[0051] This instantaneous discharge current pulse is captured by the external discharge signal acquisition unit connected in series in the loop. Its internal transimpedance amplifier converts the current pulse into a voltage pulse, which is then shaped into a standard TTL level pulse by a voltage comparator. This TTL pulse signal is sent to the data fusion processing layer, indicating that a pinhole defect has been detected in an external wall scan.

[0052] During the effective time period when EN1 is low and EN2 is high (after the dead time), the second high-voltage switch is turned on and the first high-voltage switch is turned off. The high-voltage electrical signal from the high-voltage excitation source is then applied to the inner electrode assembly. A high-voltage electric field is formed between the inner electrode assembly and the anti-corrosion layer of the inner wall of the oil pipe. Its detection principle is completely symmetrical with that of the outer wall detection.

[0053] When pinhole defects exist in the anti-corrosion layer of the inner wall of the tubing, spark discharge will also occur. The discharge current path is as follows: high-voltage excitation source, second high-voltage switch, inner electrode assembly, inner wall pinhole discharge channel, tubing body metal, common reference ground module, inner domain discharge signal acquisition unit, and negative electrode of high-voltage excitation source. The inner domain discharge signal acquisition unit also converts the captured current pulses into TTL level pulse signals and sends them to the data fusion processing layer.

[0054] In a preferred embodiment, the incremental photoelectric encoder in the positioning module continuously outputs orthogonal encoded pulses as the system moves. The data fusion processing layer has a built-in high-precision counter that performs quadrature frequency multiplication and counting on the pulse signal. During system initialization, the encoder counter is cleared to zero and a physical reference zero point is defined. Each encoder pulse corresponds to a fixed axial displacement. The data fusion processing layer calculates the axial coordinate z of the current discharge event in real time.

[0055] The external electrode assembly is a ring electrode array, consisting of N arc-shaped electrode plates evenly distributed along the circumference. Each electrode plate is assigned a unique hardware number 1-N in clockwise or counterclockwise order. The signal channels of these electrode plates are independently and in parallel connected to the data fusion processing layer.

[0056] When a discharge event occurs at a certain angular position, only the signal channel corresponding to the arc-shaped electrode plate covered at that position will be triggered. After receiving the pulse signal from the i-th arc-shaped electrode plate, the data fusion processing layer calculates the circumferential angle. : For example, if Each electrode sheet covers The circumferential range. When (Electrode plate numbered 1 is preset as the reference direction) If a discharge is detected, then ,when At that time, In this way, the system assigns precise circumferential angular coordinates to each outer wall discharge defect; The data fusion processing layer combines each received discharge event with the simultaneously acquired axial encoded signal and channel number information to generate a data record with precise timestamps and spatial coordinates. This record is then used by the detection system to collect a series of internal defect point sets. and external domain defect point set Each point can be represented in cylindrical coordinates. To automatically identify penetrating pinholes (i.e., holes that extend from the inner wall to the outer wall), the data fusion processing layer executes the following spatial correlation analysis algorithm: For any point in the set of defect points in the inner domain and any point in the outer domain defect point set Calculate the axial distance deviation between the two respectively. and circumferential angle deviation The system has two preset empirical thresholds: an axial distance tolerance threshold. and circumferential angle tolerance threshold , It can be set to 5mm to compensate for axial movement of the mechanical system and cumulative encoder error. It can be set to cover half the angle of a single arc-shaped electrode, for example, the electrode covers... hour, Can be set to It is used to compensate for discretization errors and centering errors in circumferential positioning.

[0057] Penetrating pinhole: If and If the system determines that the two discharge events originated from the same physical location, that is, there is a through-hole defect connecting the inner and outer walls at that location.

[0058] For pinholes on the inner wall: If in Around the point (i.e., axial distance) Circumferential angle No matching criteria were found within the neighborhood of [the specified location]. The point will then be It was determined to be an isolated internal wall pinhole defect.

[0059] Pinholes on the outer wall: If in No matching criteria were found around the point. The point will then be It was determined to be an isolated pinhole defect on the outer wall.

[0060] In a preferred embodiment, the common reference ground module is described as multiple sets of flexible grounding copper brushes including: an annular copper slip ring surrounding the end of the oil pipe, and a carbon brush assembly cooperating with the slip ring. Before detection, the end of the oil pipe is machined into a 20mm wide exposed metal strip using a lathe. The annular slip ring is tightly fitted onto this exposed metal strip by a compression spring, achieving a reliable 360° electrical connection without dead angles. The carbon brushes are fixed to the base of the detection system and slide in contact with the rotating slip ring. A low-impedance, low-noise electrical connection is maintained between the oil pipe metal body and the common reference ground module, thereby improving the signal-to-noise ratio and system stability of the discharge signal acquisition. In a preferred embodiment, the outer domain discharge signal acquisition unit and the inner domain discharge signal acquisition unit are preamplifiers composed of high-speed junction field-effect transistors or insulated-gate bipolar transistors, followed by a shaping circuit composed of a high-speed comparator. The specific connection method is as follows: Preamplifier stage: It adopts a common source or common emitter amplification structure. Its input terminal is directly connected in series in the return ground circuit of the high voltage switch. It can quickly and linearly convert the discharge current pulse into a negative or positive voltage pulse. The amplitude of the voltage pulse is proportional to the peak value of the discharge current.

[0061] Noise suppression and filtering: The output of the preamplifier is connected to a low-pass filter to filter out high-frequency noise interference. The cutoff frequency of the filter is set according to the effective spectrum of the discharge pulse.

[0062] Pulse Shaping Stage: The filtered voltage signal is input to the non-inverting input of a high-speed voltage comparator, and the inverting input is connected to an adjustable reference voltage source. When the amplitude of the input voltage pulse exceeds the preset reference voltage, the comparator output flips rapidly, generating a digital pulse signal with steep edges (rise / fall time <10ns) and level standards compatible with the input port of the data fusion processing layer (e.g., 3.3VTTL).

[0063] Output protection: A current-limiting resistor is connected in series with the output of the comparator, and a transient voltage suppression diode is connected to ground to prevent electrostatic discharge or external surges from damaging the data fusion processing layer interface of the subsequent stage.

[0064] In a preferred embodiment, such as Figure 4 As shown, the specific operation process of the above system is as follows: S100. Place the oil pipe to be tested on the transfer roller, ensuring that the annular array of the outer electrode assembly surrounds the outer wall of the oil pipe and the inner electrode assembly has been inserted into the inner wall of the oil pipe.

[0065] S200: Make the flexible grounding copper brush or slip ring-carbon brush assembly of the common reference ground module into close contact with the exposed metal strip at the end of the tubing to complete the common ground connection between the system and the tubing body, start the high-voltage excitation source and the central timing controller, and the system enters the standby state.

[0066] S300: Through the human-machine interface (connected to the data fusion processing layer), the detection parameters can be set, including: the output voltage of the high-voltage excitation source, the operating frequency of the central timing controller, the traveling speed of the traveling positioning module, the axial distance tolerance threshold, and the circumferential angle tolerance threshold.

[0067] S400: Start the servo motor of the positioning module to drive the system to move at a constant speed from one end of the oil pipe to the other. The central timing controller starts to output EN1 and EN2 signals, and the system performs alternating scanning.

[0068] S500: Throughout the entire process, the data fusion processing layer receives pulses from the outer / inner domain discharge signal acquisition unit, encoder pulses from the travel positioning module, and channel numbers from the electrode array in real time. It processes the data in real time, converts each discharge event into a data point with coordinates and source (inner / outer), and performs spatial correlation analysis.

[0069] S600: When the system reaches the other end of the oil pipe, the detection is completed, and the data fusion processing layer generates a complete detection report.

[0070] In summary, the spark-based oil pipe casing external anti-corrosion layer pinhole defect detection system provided by this invention, with its dual-domain time-sharing and co-location detection system, combined with a unified coordinate benchmark and spatial correlation analysis, not only merges the detection of inner and outer walls, greatly improving detection efficiency, but also reliably identifies penetrating pinhole defects that pose the greatest threat to pipe safety, providing technical support for the quality assessment and life prediction of oil pipe casing.

[0071] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A system for detecting pinhole defects in the external anti-corrosion coating of oil tubing casing based on electrical discharge machining, characterized in that, The system includes: A high-voltage excitation source is used to generate the high-voltage voltage required for detection, and is connected to the first high-voltage switch of the outer electrode detection domain and the second high-voltage switch of the inner electrode detection domain, respectively. The central timing controller is used to generate a first excitation enable signal and a second excitation enable signal to control the opening and closing of the first high-voltage switch and the second high-voltage switch, so that the high-voltage excitation source alternately applies high voltage to the outer electrode detection domain and the inner electrode detection domain, and only one detection domain is subjected to high voltage at any given time. The external electrode detection domain includes a first high-voltage switch, an external electrode assembly, and an external discharge signal acquisition unit. The external electrode detection domain is used to perform electric spark scanning on the anti-corrosion layer of the outer wall of the oil pipe and pick up the external discharge signal. The inner electrode detection domain includes a second high-voltage switch, an inner electrode assembly, and an inner domain discharge signal acquisition unit. The inner electrode detection domain is used to perform electric spark scanning on the anti-corrosion layer of the inner wall of the oil pipe and pick up the inner domain discharge signal. The common reference ground module provides a unified electrical reference ground for the outer domain discharge signal acquisition unit of the outer electrode detection domain and the inner domain discharge signal acquisition unit of the inner electrode detection domain; The travel positioning module is used to drive the outer electrode assembly and the inner electrode assembly to move axially relative to the oil pipe and output an axial encoded signal that represents the axial position in real time. The data fusion processing layer receives signals from the outer domain discharge signal acquisition unit, the inner domain discharge signal acquisition unit, and the travel positioning module, respectively. The data fusion processing layer is used to align the outer domain discharge events and the inner domain discharge events to a unified tube coordinate system, and to determine whether there is a penetrating pinhole defect based on the spatial proximity criterion. In the external electrode detection domain, the input terminal of the first high-voltage switch is connected to the output terminal of the high-voltage excitation source, and the output terminal of the first high-voltage switch is connected to the external electrode assembly. The external discharge signal acquisition unit is connected in series between the return ground circuit of the first high-voltage switch and the common reference ground module; When the first excitation enable signal is valid, the external electrode assembly is subjected to high voltage. When there is a pinhole in the anti-corrosion layer of the outer wall of the oil pipe, the discharge current flows back to the outer domain discharge signal acquisition unit through the external electrode assembly, the pinhole in the anti-corrosion layer of the outer wall of the oil pipe, the oil pipe body, and the common reference ground module, forming an outer domain discharge pulse signal. In the internal electrode detection domain, the input terminal of the second high-voltage switch is connected to the output terminal of the high-voltage excitation source, and the output terminal of the second high-voltage switch is connected to the internal electrode assembly. The internal discharge signal acquisition unit is connected in series between the return ground circuit of the second high-voltage switch and the common reference ground module; When the second excitation enable signal is valid, the inner electrode assembly is subjected to high voltage. When there is a pinhole in the anti-corrosion layer of the inner wall of the oil pipe, the discharge current flows back to the inner domain discharge signal acquisition unit through the inner electrode assembly, the pinhole in the anti-corrosion layer of the inner wall of the oil pipe, the oil pipe body, and the common reference ground module, forming an inner domain discharge pulse signal.

2. The oil pipe casing external anti-corrosion layer pinhole defect detection system based on electrical discharge machining according to claim 1, characterized in that, The first and second excitation enable signals generated by the central timing controller are pulse signals with the same frequency and completely staggered phases. A fixed dead time is set between the effective levels of adjacent first and second excitation enable signals to ensure that the first and second high-voltage switches do not conduct simultaneously.

3. The oil pipe casing external anti-corrosion layer pinhole defect detection system based on electrical discharge machining as described in claim 1, characterized in that, The common reference ground module consists of multiple sets of elastic grounding copper brushes installed on the base of the travel positioning module. Under spring pressure, the elastic grounding copper brushes make close contact with the exposed metal at the end of the oil pipe or the grounding strip with the anti-corrosion layer removed, thereby defining the metal body of the oil pipe as the ground potential of the system.

4. The oil pipe casing external anti-corrosion layer pinhole defect detection system based on electrical discharge machining according to claim 1, characterized in that, The positioning module includes a servo-driven roller assembly and an incremental photoelectric encoder. The servo-driven roller assembly drives the entire detection head to move along the oil pipe axis, and the incremental photoelectric encoder outputs orthogonal encoded pulses as the axial encoded signal as the rollers rotate. The external electrode assembly is a ring electrode array, consisting of multiple arc-shaped electrode pieces evenly distributed along the circumference, each arc-shaped electrode piece having a unique electrode number. When a discharge occurs in any area covered by an arc-shaped electrode, the signal channel corresponding to the arc-shaped electrode that is discharging is triggered, and the data fusion processing layer obtains the circumferential phase information of the discharge defect based on the triggered signal channel.

5. The oil pipe casing external anti-corrosion layer pinhole defect detection system based on electrical discharge machining according to claim 4, characterized in that, The external electrode assembly is composed of It consists of arc-shaped electrode plates evenly distributed along the circumference, and the arc-shaped electrode plates are numbered sequentially as follows: ; The data fusion processing layer receives data from the first... When the outer domain discharge pulse signal of the arc-shaped electrode sheet is received, according to Calculate the circumferential angle of the outer domain discharge defect ,in, Indicates that the preset reference direction is Circumferential angle, The number of the arc-shaped electrode plate that detected the discharge; By utilizing the spatial distribution of the arc-shaped electrode sheets, the numbering of the arc-shaped electrode sheets is directly mapped to circumferential angular coordinates, providing a circumferential positioning reference for pinhole defects on the outer wall.

6. The oil pipe casing external anti-corrosion layer pinhole defect detection system based on electrical discharge machining according to claim 4, characterized in that, The data fusion processing layer also receives the axial encoding signal output by the traveling positioning module, mapping each discharge event to cylindrical coordinate points. ,in The axial distance is calculated based on the cumulative number of pulses in the axial encoded signal. The data fusion processing layer performs spatial correlation analysis on the collected inner domain defect point set and outer domain defect point set. For any inner domain defect point... and any external defect point When both conditions are met and If the inner domain defect point and the outer domain defect point correspond to the same pinhole location, then a through-hole pinhole defect exists. The preset axial distance tolerance threshold, This is the preset circumferential angle tolerance threshold; If there is only an inner domain defect point and no corresponding outer domain defect point, it is determined to be an inner wall pinhole; if there is only an outer domain defect point and no corresponding inner domain defect point, it is determined to be an outer wall pinhole.

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