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Tubing thread inspection by magnetic flux leakage
NDT&E International 39 (2006) 53–56 www.elsevier.com/locate/ndteint
Tubing thread inspection by magnetic flux leakage Ding Jinfeng*, Kang Yihua, Wu Xinjun Department of instrument science and technology, School of Mechanical Science and Engineering, HUST, Wuhan, Hubei 430074, People’s Republic of China Received 13 May 2005; revised 4 June 2005; accepted 6 June 2005 Available online 2 August 2005
Abstract The failure of the oil well tubing thread is a very serious problem which may result in accidents and repairs during well servicing. Routine inspections on the threads are thus necessary. This paper proposes a local magnetic flux leakage testing method to inspect the end of the pieces and introduces a certain kind of tubing thread testing equipment based on the magnetic flux leakage theory. The equipment consists of four key components—magnetizer, magnetic field inducer, linear scanner and synchronous sampling controller. The equipment can inspect and prevent tubing thread failures occurring in practice, such as rupture, thread abrasion, crack in the thread root, variations of the taper angle in the thread area, etc. It can meet the testing requirements of the tubing thread and has very wide application perspective. q 2005 Elsevier Ltd. All rights reserved. Keywords: Oil well tubing thread; Non-destructive testing (NDT); Magnetic flux leakage (MFL); Inspection
1. Introduction Oil well tubing is one of the most important components to extract oil in oil fields. Under the chronic and atrocious working environment, where components like the main body of the tubing has to work, the oil well tubing threads can fail by defects such as rupture, thread abrasion, crack in the thread root, variations of the taper angle in the thread area etc. These types of defects must be detected by periodic inspections to estimate the expected remaining (service) life of the tubing and to avoid accidents in oil fields. The most commonly used method today for inspecting the tubing thread is magnetic particles inspection [1]. However, a serious problem with this method is its low efficiency and reliability. MFL (Magnetic Flux Leakage) testing method is a magnetic NDT method derived from the Magnetic particles inspection, which uses sensing coils and probes substituting the fluorescent particles to detect the flux leakage of the flaw. MFL is an effective testing method to inspect ferromagnetic components like pipes. With the development of the MFL technology and the signal processing technology, the inspection precision and efficiency have been greatly * Corresponding author. Tel.: C86 13317108552; fax: C86 2787556942. E-mail address: [email protected] (D. Jinfeng).
0963-8695/$ - see front matter q 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.ndteint.2005.06.005
improved. However, the traditional MFL testing method has certain limitations such as the effect of uninspected pipe ends, testing velocity, magnetization method etc. These limitations make it difficult to test places like the thread area in the end of the oil well tubing. In this paper, a new MFL testing method which includes the magnetization, testing and signal processing, especially for the local inspection of pipes, is introduced,. An oil well tubing thread inspection equipment based on this approach is presented and its applicability and reliability are validated using experiments and Practical uses in the oil field.
2. Inspections of the thread area of oil well tubing The new local magnetization and inducing method we propose, based on the traditional MFL approach, can be used to avoid the effect of uninspected ends which is observed by the traditional MFL testing method. The new method involves fixing a magnetizing unit into the end area of the tubing and scanning the thread area with Hall components, which is shown below in Fig. 1. Magnetized to saturation by the magnetizing assembly, the area of the thread can hold no more magnetic flux and will begin to leak flux into the air if there is a crack or some other flaw in the thread foot [2]. In such cases, the magnetic flux leakage is enhanced because the magnetic flux can penetrate into the regions of the crest of the thread.
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D. Jinfeng et al. / NDT&E International 39 (2006) 53–56
Fig. 1. Thread Inspection Model Based on the MFL: 1 Soft Iron Yoke, 2 Magnetization Coil, 3 Oil Well Tubing Thread, 4 flaws, 5 Hall Components. The magnetizing unit composed of Soft Iron Yoke and Magnetization Coil is fixed in the end of the tubing and the Hall components scan the thread in axial direction, detecting the flaw signals.
The magnetic field and the leakage flux of the flaw produced by the magnetizing unit are shown in Fig. 2.
3. Structure of the inspection equipment MFL inspection equipment typically has five components: a drive system, magnetizing assembly, sensor
array, data acquisition and recording module Fig. 3 shows the structure of the whole oil well tubing thread inspection equipment. In 8 channels, the MFL signals from the probe are amplified by an amplifier and filtered by a high pass filter that filters out the low-frequency signal components produced by the background magnetic field outside the thread. Fig. 4 shows the signal with the low-frequency signal component and the signal after the high-pass Filter (Fig. 4 compares several signals and shows certain effect of something. I think you should rewrite this sentence..) In the entire inspection equipment, the probe, which is responsible for the acquisition of the flaw signal and affects the inspection accuracy and signal-to-noise ratio, is the most important component. Hence the design of an effective MFL inducing probe is a critical step. Fig. 5 illustrates the sketches of the probe design. The magnetizing exciter, including 1 (the soft iron yoke) and 2 (Magnetization Coil), magnetizes the tubing thread area to the saturation. Eight pieces of Hall sensors are fit in 3 (the underlay) and are pressed by 4 (the spring), ensuring the Hall sensor to be close to the inspected surface of the thread and reducing the impact of the lift off to
Fig. 2. The magnetic field and the leakage flux of the flaw produced by the magnetizing unit is shown: 1 Leakage Flux, 2 Tubing Thread, 3 Crack in the thread. The acreage of section A is much larger than that in section B. The magnetic flux penetrates into the crest region, so when there are failures near section B, the magnetic field leakage will be enhanced.
MFL Signals from the probes
Amplifier
High-pass Filter
8 Bit A/D converter
EPP interface of Computer
DSP System
Display
Fault diagnoses and Classification
Output Testing Report
Fig. 3. Diagram of the whole structure of the thread inspection equipment.
D. Jinfeng et al. / NDT&E International 39 (2006) 53–56
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Fig. 4. The effect of the background magnetic flux to the thread magnetic flux.
the signal [3]. The eight pieces of Hall sensors are evenly distributed around the thread and pulled by the linear motor from position A to position B along the axial direction, detecting the radial component of the magnetic flux.
4. Experiments and results In order to document the practicability and reliability of the tubing thread inspection equipment explained above, we created some artificial flaws simulating the real flaws in practice such as rupture, thread abrasion, crack in the thread root, etc.in the laboratory,. These flaws were then inspected by the probe designed according to the structure in Fig. 5. The signals were acquired by the corresponding hardware and transmitted to the computer and afterwards were processed by a software program (designed by our lab) named ‘signal processing system of MFL inspection’. The signal waveform is displayed by the program and the failure of the tubing thread is classified and evaluated. The oil well
tubing thread with flaws and their inspection signal waveform are shown in the following pictures (Fig. 6). From the above signal waveform, we can see that the thread with no flaw has a regular signal as in (a), and different deep cracks are indicated with different peak values. The deeper the crack is, the higher is the peak value as shown in (c). The flaw type like thread abrasion and corrosion pitting have relative larger wave-form-width than the cracklike flaws and have greater influence on the magnetic flux in the vicinity of the flaw as shown in (b) and (d). In other words, different kinds of defects and different defect sizes have different characteristics and can be clearly identified by evaluating the inspection signal.
5. Conclusion The new MFL inspection method, which magnetizes the end area of the tubing and pipe from the inside and scans the surface of the work piece outside, can be successfully applied to the testing of oil well tubing thread and can also
Fig. 5. The structure of the tubing thread inspecting equipment. 1 Soft iron yoke, 2 Magnetization coil, 3 Underlay of inducer, 4 springs, 5 Hall components, 6 Oil well tubing thread, 7 Connection flange, 8 Linear motor.
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Fig. 6. The oil well tubing with different flaws and their inspection waveform.
be used in other inspection tasks such as the inspection of uninspected end regions of steel tubes. The thread inspection equipments based on the magnetic flux leakage principles has been validated by a large number of laboratory experiments and field applications. the practicability and reliability of the equipment has also been demonstrated. Additional work has to be done in the next future on signal processing in order to enhance a reliable detection and to develop the ability in sizing the flaws.
References [1] Francisco Valentine. Effect of pipeline debris on MFL tool data. Pipes& Pipelines international, March-April 2000. [2] Weihua Mao, Lynann Clapham, David L.Atherton. Effects of alignment of nearby corrosion pits on MFL. NDT&E International 36(2003)111-116. [3] Gwan Soo Park and Eun Sik Park. Improvement of the sensor system in magnetic flux Leakage-Type Non-destructive Testing. IEEE transactions on magnetics, Vol.38, NO.2, March 2002.
Tubing thread inspection by magnetic flux leakage Ding Jinfeng*, Kang Yihua, Wu Xinjun Department of instrument science and technology, School of Mechanical Science and Engineering, HUST, Wuhan, Hubei 430074, People’s Republic of China Received 13 May 2005; revised 4 June 2005; accepted 6 June 2005 Available online 2 August 2005
Abstract The failure of the oil well tubing thread is a very serious problem which may result in accidents and repairs during well servicing. Routine inspections on the threads are thus necessary. This paper proposes a local magnetic flux leakage testing method to inspect the end of the pieces and introduces a certain kind of tubing thread testing equipment based on the magnetic flux leakage theory. The equipment consists of four key components—magnetizer, magnetic field inducer, linear scanner and synchronous sampling controller. The equipment can inspect and prevent tubing thread failures occurring in practice, such as rupture, thread abrasion, crack in the thread root, variations of the taper angle in the thread area, etc. It can meet the testing requirements of the tubing thread and has very wide application perspective. q 2005 Elsevier Ltd. All rights reserved. Keywords: Oil well tubing thread; Non-destructive testing (NDT); Magnetic flux leakage (MFL); Inspection
1. Introduction Oil well tubing is one of the most important components to extract oil in oil fields. Under the chronic and atrocious working environment, where components like the main body of the tubing has to work, the oil well tubing threads can fail by defects such as rupture, thread abrasion, crack in the thread root, variations of the taper angle in the thread area etc. These types of defects must be detected by periodic inspections to estimate the expected remaining (service) life of the tubing and to avoid accidents in oil fields. The most commonly used method today for inspecting the tubing thread is magnetic particles inspection [1]. However, a serious problem with this method is its low efficiency and reliability. MFL (Magnetic Flux Leakage) testing method is a magnetic NDT method derived from the Magnetic particles inspection, which uses sensing coils and probes substituting the fluorescent particles to detect the flux leakage of the flaw. MFL is an effective testing method to inspect ferromagnetic components like pipes. With the development of the MFL technology and the signal processing technology, the inspection precision and efficiency have been greatly * Corresponding author. Tel.: C86 13317108552; fax: C86 2787556942. E-mail address: [email protected] (D. Jinfeng).
0963-8695/$ - see front matter q 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.ndteint.2005.06.005
improved. However, the traditional MFL testing method has certain limitations such as the effect of uninspected pipe ends, testing velocity, magnetization method etc. These limitations make it difficult to test places like the thread area in the end of the oil well tubing. In this paper, a new MFL testing method which includes the magnetization, testing and signal processing, especially for the local inspection of pipes, is introduced,. An oil well tubing thread inspection equipment based on this approach is presented and its applicability and reliability are validated using experiments and Practical uses in the oil field.
2. Inspections of the thread area of oil well tubing The new local magnetization and inducing method we propose, based on the traditional MFL approach, can be used to avoid the effect of uninspected ends which is observed by the traditional MFL testing method. The new method involves fixing a magnetizing unit into the end area of the tubing and scanning the thread area with Hall components, which is shown below in Fig. 1. Magnetized to saturation by the magnetizing assembly, the area of the thread can hold no more magnetic flux and will begin to leak flux into the air if there is a crack or some other flaw in the thread foot [2]. In such cases, the magnetic flux leakage is enhanced because the magnetic flux can penetrate into the regions of the crest of the thread.
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D. Jinfeng et al. / NDT&E International 39 (2006) 53–56
Fig. 1. Thread Inspection Model Based on the MFL: 1 Soft Iron Yoke, 2 Magnetization Coil, 3 Oil Well Tubing Thread, 4 flaws, 5 Hall Components. The magnetizing unit composed of Soft Iron Yoke and Magnetization Coil is fixed in the end of the tubing and the Hall components scan the thread in axial direction, detecting the flaw signals.
The magnetic field and the leakage flux of the flaw produced by the magnetizing unit are shown in Fig. 2.
3. Structure of the inspection equipment MFL inspection equipment typically has five components: a drive system, magnetizing assembly, sensor
array, data acquisition and recording module Fig. 3 shows the structure of the whole oil well tubing thread inspection equipment. In 8 channels, the MFL signals from the probe are amplified by an amplifier and filtered by a high pass filter that filters out the low-frequency signal components produced by the background magnetic field outside the thread. Fig. 4 shows the signal with the low-frequency signal component and the signal after the high-pass Filter (Fig. 4 compares several signals and shows certain effect of something. I think you should rewrite this sentence..) In the entire inspection equipment, the probe, which is responsible for the acquisition of the flaw signal and affects the inspection accuracy and signal-to-noise ratio, is the most important component. Hence the design of an effective MFL inducing probe is a critical step. Fig. 5 illustrates the sketches of the probe design. The magnetizing exciter, including 1 (the soft iron yoke) and 2 (Magnetization Coil), magnetizes the tubing thread area to the saturation. Eight pieces of Hall sensors are fit in 3 (the underlay) and are pressed by 4 (the spring), ensuring the Hall sensor to be close to the inspected surface of the thread and reducing the impact of the lift off to
Fig. 2. The magnetic field and the leakage flux of the flaw produced by the magnetizing unit is shown: 1 Leakage Flux, 2 Tubing Thread, 3 Crack in the thread. The acreage of section A is much larger than that in section B. The magnetic flux penetrates into the crest region, so when there are failures near section B, the magnetic field leakage will be enhanced.
MFL Signals from the probes
Amplifier
High-pass Filter
8 Bit A/D converter
EPP interface of Computer
DSP System
Display
Fault diagnoses and Classification
Output Testing Report
Fig. 3. Diagram of the whole structure of the thread inspection equipment.
D. Jinfeng et al. / NDT&E International 39 (2006) 53–56
55
Fig. 4. The effect of the background magnetic flux to the thread magnetic flux.
the signal [3]. The eight pieces of Hall sensors are evenly distributed around the thread and pulled by the linear motor from position A to position B along the axial direction, detecting the radial component of the magnetic flux.
4. Experiments and results In order to document the practicability and reliability of the tubing thread inspection equipment explained above, we created some artificial flaws simulating the real flaws in practice such as rupture, thread abrasion, crack in the thread root, etc.in the laboratory,. These flaws were then inspected by the probe designed according to the structure in Fig. 5. The signals were acquired by the corresponding hardware and transmitted to the computer and afterwards were processed by a software program (designed by our lab) named ‘signal processing system of MFL inspection’. The signal waveform is displayed by the program and the failure of the tubing thread is classified and evaluated. The oil well
tubing thread with flaws and their inspection signal waveform are shown in the following pictures (Fig. 6). From the above signal waveform, we can see that the thread with no flaw has a regular signal as in (a), and different deep cracks are indicated with different peak values. The deeper the crack is, the higher is the peak value as shown in (c). The flaw type like thread abrasion and corrosion pitting have relative larger wave-form-width than the cracklike flaws and have greater influence on the magnetic flux in the vicinity of the flaw as shown in (b) and (d). In other words, different kinds of defects and different defect sizes have different characteristics and can be clearly identified by evaluating the inspection signal.
5. Conclusion The new MFL inspection method, which magnetizes the end area of the tubing and pipe from the inside and scans the surface of the work piece outside, can be successfully applied to the testing of oil well tubing thread and can also
Fig. 5. The structure of the tubing thread inspecting equipment. 1 Soft iron yoke, 2 Magnetization coil, 3 Underlay of inducer, 4 springs, 5 Hall components, 6 Oil well tubing thread, 7 Connection flange, 8 Linear motor.
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Fig. 6. The oil well tubing with different flaws and their inspection waveform.
be used in other inspection tasks such as the inspection of uninspected end regions of steel tubes. The thread inspection equipments based on the magnetic flux leakage principles has been validated by a large number of laboratory experiments and field applications. the practicability and reliability of the equipment has also been demonstrated. Additional work has to be done in the next future on signal processing in order to enhance a reliable detection and to develop the ability in sizing the flaws.
References [1] Francisco Valentine. Effect of pipeline debris on MFL tool data. Pipes& Pipelines international, March-April 2000. [2] Weihua Mao, Lynann Clapham, David L.Atherton. Effects of alignment of nearby corrosion pits on MFL. NDT&E International 36(2003)111-116. [3] Gwan Soo Park and Eun Sik Park. Improvement of the sensor system in magnetic flux Leakage-Type Non-destructive Testing. IEEE transactions on magnetics, Vol.38, NO.2, March 2002.