--- title: "Portable Magnetic Flux Leakage Testfor Industrial Pipeline Based on Circumferential Magnetization" url: "https://maker.wiznet.io/mayuri/projects/portable-magnetic-flux-leakage-testfor-industrial-pipeline-based-on-circumferential-magnetization/" markdown_url: "https://maker.wiznet.io/mayuri/projects/portable-magnetic-flux-leakage-testfor-industrial-pipeline-based-on-circumferential-magnetization/md" type: "UCC: User Created Content" author: "Kunming ZHAO 1, Xinjun WU 1, Gongtian SHEN 2" author_url: "https://www.ndt.net/article/wcndt2016/papers/tu3b2.pdf" editor: "WIZnet" editor_url: "https://maker.wiznet.io/" original_author: "Kunming ZHAO 1, Xinjun WU 1, Gongtian SHEN 2" original_url: "https://www.ndt.net/article/wcndt2016/papers/tu3b2.pdf" published: "2022-09-27" language: "en" hardware: ["WIZnet W5300"] likes: 4 views: 1637 comments: 0 source: "WIZnet Makers (https://maker.wiznet.io/)" --- # Portable Magnetic Flux Leakage Testfor Industrial Pipeline Based on Circumferential Magnetization > Pipelines are widely used in petrochemical and power generation industries.As one of the key equipment, it is important to inspect them. Original author: Kunming ZHAO 1, Xinjun WU 1, Gongtian SHEN 2 (source: https://www.ndt.net/article/wcndt2016/papers/tu3b2.pdf) ## Components - **WIZnet W5300** x 1 ([docs](https://docs.wiznet.io/Product/Chip/Ethernet/W5300)) ## Article 1. Introduction Industrial pipelines are widely used in petrochemical and power generation industries. During the long-term service, the gaseous or liquid substances transmitted by the pipelines usually erode the interior wall of the pipelines and result in the various defects such as cracks and corrosion pits. Moreover, long-term exposure to air usually results in external pipeline corrosion [1]. These defects endanger the operational safety of the pipelines. In order to avoid the occurrence of the accident, the pipelines should be tested regularly. As a non-contact efficient NDT method, magnetic flux leakage (MFL) testing has been widely used in pipeline testing [2] . The axial magnetization is the main magnetization method in MFL testing nowadays. Much research work has been developed and there are some testing equipment employed in the field testing [3]. The axial magnetization means that the tester should be changed with the change of the industry pipeline specification because of the lift off effect [4]. Furthermore, the range of the long transportation pipelines diameters is limited, the axial magnetization method is feasible for long transportation pipelines testing. But it is inconvenient in the industrial field testing because of the wide range of pipeline diameters. To solve this problem, the MFL testing based on circumferential magnetization is applied to the testing of industrial pipelines. The traditional circumferential MFL testing method, which used in the steel pipe production line, needs to magnetize the whole body of the steel pipe along some axial length. This magnetization method makes the magnetizer heavy and does not meet the requirements of a portable testing system. Manual driving is a main driving mode for many pipeline testing systems and cables are used to transmit the testing signal in these systems. It is difficult to perfectly perform manual testing due to its tremendously labour intensity. The use of the cables which are easy to wrap will bring a lot of inconvenience. So, the application of MFL testing method has been greatly restricted and a portable MFL testing system which can solve the above problems is desirable. In view of the above problems, a portable magnetic flux leakage testing system for industrial pipelines based on circumferential magnetization is developed. During the testing, a magnetizer is used to excite a circumferential magnetic field on the local area of the pipeline. In the regions of the defect, such as a corrosion defect or crack, magnetic flux leaks into the air and a tester is used to pick up the MFL signal. Then the testing signal is digitized and transmitted to the personal computer by wireless communication. In order to improve the testing efficiency, the system adopts a crawler which can scan the pipelines with different along cylindrical helix paths. The helix angles of the cylindrical helix paths are chosen according to the diameter of the pipeline. Hence, the entire outside surface of the pipeline can be covered in one process of scanning. 2. Testing principle Two significant implementations of MFL testing method are axial and circumferential. The terms axial and circumferential describe the orientation of the magnetizing field. Axial MFL is the most common implementation of this testing method. In order to testing and sizing the longitudinal defects, the orientation of the magnetic field is changed from the traditional axial direction to circumferential [5]. The area of the longitudinal section of the magnetized pipeline depends on the length and diameter of the pipeline for circumferential magnetization. For the circumferential MFL testing method used in the steel pipe production line, the coil is used to excite the circumferential magnetic field on the pipeline. The magnetizing ability can be enhanced by increasing the current of the coils. The magnetization device magnetizes the whole body of the steel pipe along some axial length. But the magnetization device is heavy and it is not portable to use this magnetization method for the testing of the industrial pipelines. Besides, two implementations, probe rotation and pipe moving forward in a line or probe fixed and pipe moving in a spiral, are usually used to accomplish the complete testing of steel pipes. But the two implementations are unsuitable for the field testing of the industrial pipeline because the industrial pipelines are usually built continuously and fixed. In this paper, a method of MFL testing based on local area circumferential magnetization is proposed to adapt to the field testing conditions of industrial pipelines. As shown in Fig.1, the system uses the NdFeB permanent magnet whose brand is N52 to magnetize the pipeline. For corrosion defects, the remaining material attempts to carry an increased amount of magnetic flux. Besides, additional flux causes the flux carrying capability (the permeability) to decrease in magnetically saturated local region [6]. This double effect of increased flux and decreased permeability make for strong flux leakage signals which are picked. ![](https://maker.wiznet.io/upload/ckeditor5/285979889%5F1664312338%2Epng) 3. MFL Testing system design The design of the MFL testing system is complicated by the constraints imposed by the portability and some desired capabilities. These capabilities include the adaptability to the testing of pipelines with different diameters, wireless motor control and wireless data transmission. The testing objects of the system are the pipelines with outside diameter bigger than 219mm and the testing system can adapt to the testing of pipelines with different diameters. So the followings must be considered:  Drive force: The permanent magnet is used to excite the required circumferential magnetic field. Meantime, the adsorption force which limits the weight of the entire system required by the crawler is also provided by the permanent magnet. Besides, the distance between the pipelines is limited and the size of the testing system cannot be too large. So a limited space is available for crawler, tester, motor controller, data acquisition card and power supplies. The testing system must use the available space to incorporate these traditionally solid state components.  Real-time transmission: The real-time testing signal is transmitted to the personal computer by wireless communication. The system consists of several sampling channels and the speed of wireless transmission must be greater than the total acquisition speed for real-time data transmission.  Motor controller: In order to minimize the use of cables, the motor controller uses a sophisticated industrial wireless motor controller which uses the CC2500 wireless module. Based on the above analysis, the portable MFL testing system includes seven parts: power supply, motor controller, crawler, tester, data acquisition card, wireless router and portable computer (PC), as shown in Fig.2. The power supply provides electric power for motor controller, data acquisition card and other parts. The motor controller controls the movement of the crawler. The tester includes magnetic sensors, backing iron, permanent magnet. The Hall element is employed to measure the flux leakage caused by defects because it has nothing to do with the speed of the crawler. In order to improve testing efficiency, the Hall element array is employed along axial directions. The leakage flux signals are digitized and then transmitted to PC through the wireless router. From testing signals, the defect parameters such as length, width and etc. can be estimated. Therefore, the pipeline safety condition can be evaluated. ![](https://maker.wiznet.io/upload/ckeditor5/285979889%5F1664312414%2Epng) 3.1 Mechanical structure design of the crawler and tester Fig.3 shows the three dimensional model of the crawler and tester. The mechanical structure includes four parts: the scanning track adjusting mechanism, the encoder, the tester and four sets of driving unit. The scanning track adjusting mechanism is used to change the scanning track of the crawler. The DC motors driving the movement of the whole device are controlled by the motor controller. An encoder is installed on the axis of one rubber wheel and is used to trigger sampling and trace defect location. ![](https://maker.wiznet.io/upload/ckeditor5/285979889%5F1664312452%2Epng) 3.1.1 Scanning track adjusting mechanism Fig 6 shows the schematic diagram of scanning track adjusting mechanism. The scanning track adjusting mechanism is composed of a connecting plate and four sets of wheel groups. The wheel frames of the four sets of driving unit are arranged on the periphery of the connecting plate. The mounting holes on the wheel frame are matched with the mounting holes on the connecting plate. Adjusting the relative position of the wheel frame and the connecting plate, the angle between the axis of the wheel and the pipeline axis can be changed. Therefore, the scanning track can be changed. Specifically, maintaining the position of the connecting plate and rotating the four wheel frames consistently can change the relative position of the wheel frame and the connecting plate. The helix angle in the situation shown in Fig.4. (c) is 0°, the helix angle in the situation shown in Fig.4. (d) is 5° and the helix angle in the situation shown in Fig.4. (d) is 10°. Fig. 5 shows the diagram of scanning path. The scanning path is a spiral line and the pitch S can be obtained as: S = π ∙ D ∙ tan � ![](https://maker.wiznet.io/upload/ckeditor5/285979889%5F1664312505%2Epng) 3.1.2 Adjustable tester mechanism The MFL signals are affected by the distance between the Hall element and the surface of the pipelines. Fig.6 shows the three dimensional model of the adjustable tester structure. The Hall elements enclosed in the copper block are arranged in a line. This kind of arrangement is different from the arrangement adopted in the axial MFL testing. The design of the tester does not need to consider the influence of the curvature of the pipelines. The waist type holes processed on the tester connecting plate are used to adjust the lift off and the relative position of the tester connecting plate and the backing iron. For the testing of pipelines with different diameters, only the relative position of the tester connecting plate and the backing iron needs to be adjusted. Therefore, it is convenient for the field testing of the industrial pipeline. ![](https://maker.wiznet.io/upload/ckeditor5/285979889%5F1664312542%2Epng) 3.2.1 Bandwidth requirements The wheel diameter of the crawler d is 76 mm. The maximum running speed of the crawler v is 10m/min. The encoder produces 100 pulses per revolution and 100 points was collected per channel per revolution. The amount of sampling channels n is 6. The maximum amount of sampling points per second of this system N can be obtained as. N = v×怠待待待 �×�×6待 × などど × 6 = 4な9 (2) The size of each data is 2 bytes and the total acquisition speed is 6704 bits per second. For real-time data transmission, the speed of wireless transmission must be greater than the total acquisition speed and it is a basis for the selection of WIFI module. 3.2.2 Data acquisition for MFL testing Fig.7 shows the schematic diagram of data acquisition for MFL testing. The main control chip of the data acquisition process is a Field Programmable Gate Array (FPGA) chip. Embedded CPU in traditional MFL testing system is used as the master controller. CPU is serial processor, which making it difficult to collect the large amounts of real-time data [7] ![](https://maker.wiznet.io/upload/ckeditor5/285979889%5F1664312586%2Epng) ![](https://maker.wiznet.io/upload/ckeditor5/285979889%5F1664312605%2Epng) 4. Performance testing According to the above design, a portable magnetic flux leakage testing system for industrial pipelines based on circumferential magnetization was developed as shown in Fig 9. There are two boxes fixed on the crawler. One of the boxes is a battery box, and the other box is placed with the data acquisition card and the motor controller. The testing object is a steel pipe of Φ219×10mm. There are some holes with different diameters in the pipeline. Using the portable magnetic flux leakage testing system to test the sample pipeline, a total of 50 sets of testing on the 1.6mm hole was made. One typical signal of these groups testing is shown in Fig.10. It can be found from the figure that the MFL signal caused by a through-hole with dimensions of 1.6 mm in diameter is obvious. ![](https://maker.wiznet.io/upload/ckeditor5/285979889%5F1664312637%2Epng) 5. Conclusion A portable magnetic flux leakage testing system for industrial pipelines based on circumferential magnetization is developed. The detailed description is made for the mechanical design and the hardware design of the system. The performances of the system on detecting through-hole defects are tested on a steel pipe of Φ219×10mm. The experimental result shows that the MFL signal induced by a through-hole with dimensions of 1.6 mm in diameter is detectable. Besides, the experimental result shows that each module of the portable MFL testing system based on FPGA can correctly collect magnetic flux leakage signal, convert and transmit data. The portable magnetic flux leakage testing system can be flexibly designed for different conditions. --- Source: https://maker.wiznet.io/mayuri/projects/portable-magnetic-flux-leakage-testfor-industrial-pipeline-based-on-circumferential-magnetization/