Application of Microwaves on Remote and Nondestructive Testing of both Biofouling and Wall Thinning inside a Metal Pipe
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カテゴリ: 第9回
1. Introduction
Metal pipes are widely used in modern industries, such as il and gas transportation, chemical industry, water supply system, nd power plants. Many pipes have been in service for more man tens of years, and accidents took place often on the ageingipes. Pipe wall thinning (PWT) is one of the most common and crious defects that caused the problems, which has been studiedy lots of scientists and also our former work [1-7]. As the ndustrial pipes are generally composed of a complicated piping system, efficient detection and quantitative evaluation of the -WT location and degree are important issues for effective naintenance (safety guarantee) and lifetime prediction of pipes as to economically avoid severe accidents.Since metal pipes can be taken as circular waveguide of microwaves, microwave NDT has been utilized to solve the PWT roblems in our approaches [1,2,4-7]. However, biofouling also exists inside many long-time used pipes especially in most geing oil transportation and water supply systems. The existence f biofoulings also causes reflections and thereby hampers the WT detectionBiofouling and biofilm are assemblage of the microbial cells hat is irreversibly associated with a surface and usually enclosed na matrix of polysaccharide material [8], and they are composed rimarily of microbial cells and extracellular polymeric substances24t: 2) , T980-8579 H uarti6-6-01-2 A717-ITE -mail: linl@karma.qse.tohoku.ac.jpEPS) [8-10]. The presence of biofouling on a metal surface, as well as its metabolic activities, can also cause potential problems uch as microbiologically influenced corrosion (MIC) [11], which is not an actual form of corrosion but a process involving micro-organisms that may initiate or otherwise contribute to the ropagation of corrosion and typically accelerate the existing corrosion form [12]. Previous researches on biofilm corrosion ffect of drinking water distribution system (DWDS) mainly made of cast iron pipes also shown that the accelerated corrosion will also bring consequences such as unpleasant color, lowering ne pressure resistance, engendering water supply accident and hereby accelerating water quality deterioration and aggrandizing ne threat to human health [13,14]. Moreover, other researchers Iso showed that biofilm formulation and multiplication can also evelop on stainless steel, copper, and some other kinds of metal ipes (15,16). Therefore, the existence of biofilm is a general ondition in metal pipes and its potential effect cannot be ignored.In this work, we focus on analyzing the more practical condition with considering reflections caused by both biofilm nd PWT defects, and we aim to present this method not only or remotely and nondestructively detecting both biofilm and WT defects but also on distinguishing them through analyzing heir characteristic signals. This work is a preliminary and original attempt to not only remotely detect defects inside a metal pipe ut also to qualitatively or even qualitatively characterize and lassify the defect types using microwaves.-. Experimental ApproachDuring our research, a vector network analyzer (VNA), E8383B (Agilent Technologies, Inc., California, USA) is utilized for generating and receiving microwave signals, and a pair of T&R coaxial line adaptors is used separately at Sii (for theingle coaxial line probe) or S21 mode (for the double coaxial Ene probe) as a bridge to introduce the signals to the pipe under testPUT) [4-6). The overall schematic diagram of the experimental approach is shown in Fig. 1. In this figure, two defect-free pipes,VNA, a pair of flexible coaxial line cables, self-designed coaxial-line probes, and three joints are shown together in detail. All of specimens are made of brass. PUTs have different wall Chinning values are realized through connecting a joint that has nner diameter larger than the two pipes between the two Hefect-free pipe specimens. The inner diameter of the defect-free pipes is 19.0 mm, and the wall thickness is 3.0 mm, and theengths of them are 750.0 and 1000.0 mm. The mentioned joints have different inner diameters and the same outer diameter of 25.0 mm, and the detailed geometrical parameters of the joints zure shown in Table 1.RAHFig. 1 Overall schematic diagram of experimental approachTable 1 Geometrical parameters of the brass jointsNo.1|2|3|Inner diameter (mm)1900/01/181900/01/18 9:36:0020Equivalent PWT depth (mm)00.20.5PWT length (mm)401900/02/081900/02/08It is reported that generally the relative dielectric constants ofbiofilms are 2 ~6, and the conductivities are around 0.1 ~0.5 5/m [17-19). For a primary attempt, a frequently used PET based double-sided adhesive tape whose composing material is not only comparatively homogeneous but also has a dielectric constant of 2.5 ~ 3.4 is adopted here to simulate a biofilm. Different thickness can be obtained from using different layers of the tapes. The PET based tape possesses a relative dielectric constant of 3.2 ~ 3.4 around 60 ~ 1,000 Hz, 3.0 - 3.3 around 1 MHz, 2.7 around 1 GHz, and 2.6 ~ 3.0 around 10 ~ 20 GHz [20-22]. The thickness of a single layer tape used in experiment is approximately 0.12 mm, and each layer of biofilm is simulated through making the inside surface of the no wall thinning joint No. 1 be fully covered of a single layer tape. As a result, all of the simulated biofilms are axially symmetrical and have a axial length of 40.0 mm.It is the same as our former research that the frequency range between the cutoff frequency of the dominant TMoj mode and the first high-order TM?, mode is adopted in the experiment [4-6). Considering the diameter of 19.0 mm of the circular waveguide, the frequency range is calculated to be from 12.1 to 19.2 GHz. During which, the dielectric constant of the tape is around 3.0.During the experimental approach, both sil and S21 parameters are measured for both PWT specimens and pipes having different thickness of biofilms are measured through utilizing the VNA after calibration.For microwave engineering, either a PWT or a biofilm defect can be taken as a discontinuity along the circular waveguide [6]. When microwave propagates to a discontinuity, reflection will happen and thereby some of the propagation energy will be reflected to the transmitting poit. Based on this fact, we can easily evaluate the defect location by extracting and analyzing the reflected signals [6]. Time of flight (TOF) means the time passed though when microwave signals reaching and reflected from a target. TOF is also used here for locating the defects.The frequency range for the single dominant TM, mode, 12.1 ~ 19.2 GHz, is utilized for measuring the S11 parameters of microwave signals, and the S21 parameters at frequency range 13.3 -13.7 GHz are also measured.3. Results and Analysis3.1 Reflection detection for locating defectsUtilizing the method described similar as shown in Ref. [6],1900/02/08Sll parameters at frequency range 12.1 ? 19.2 GHz are measured, and the experimental results for both pipes having different PWT degrees and different biofilm thicknesses are shown together in Fig. 2. The ““Free of PWT” shown in the figures means that the No. 1 joint (that has a PWT depth of 0) is utilized in the PUTs. It should be no reflection when no wall thinning, however, two most shallow peaks also appears during the experimental results. It is assumed to be mainly caused by the connection between the joint and the two pipes, and the connections act as a pair of closed cracks inside the pipe.
“ “Application of Microwaves on Remote and Nondestructive Testing of both Biofouling and Wall Thinning inside a Metal Pipe“ “劉 臨生,Linsheng LIU,佐々木 幸太,Kota SASAKI,遊佐 訓孝,Noritaka YUSA,橋爪 秀利,Hidetoshi HASHIZUME
Metal pipes are widely used in modern industries, such as il and gas transportation, chemical industry, water supply system, nd power plants. Many pipes have been in service for more man tens of years, and accidents took place often on the ageingipes. Pipe wall thinning (PWT) is one of the most common and crious defects that caused the problems, which has been studiedy lots of scientists and also our former work [1-7]. As the ndustrial pipes are generally composed of a complicated piping system, efficient detection and quantitative evaluation of the -WT location and degree are important issues for effective naintenance (safety guarantee) and lifetime prediction of pipes as to economically avoid severe accidents.Since metal pipes can be taken as circular waveguide of microwaves, microwave NDT has been utilized to solve the PWT roblems in our approaches [1,2,4-7]. However, biofouling also exists inside many long-time used pipes especially in most geing oil transportation and water supply systems. The existence f biofoulings also causes reflections and thereby hampers the WT detectionBiofouling and biofilm are assemblage of the microbial cells hat is irreversibly associated with a surface and usually enclosed na matrix of polysaccharide material [8], and they are composed rimarily of microbial cells and extracellular polymeric substances24t: 2) , T980-8579 H uarti6-6-01-2 A717-ITE -mail: linl@karma.qse.tohoku.ac.jpEPS) [8-10]. The presence of biofouling on a metal surface, as well as its metabolic activities, can also cause potential problems uch as microbiologically influenced corrosion (MIC) [11], which is not an actual form of corrosion but a process involving micro-organisms that may initiate or otherwise contribute to the ropagation of corrosion and typically accelerate the existing corrosion form [12]. Previous researches on biofilm corrosion ffect of drinking water distribution system (DWDS) mainly made of cast iron pipes also shown that the accelerated corrosion will also bring consequences such as unpleasant color, lowering ne pressure resistance, engendering water supply accident and hereby accelerating water quality deterioration and aggrandizing ne threat to human health [13,14]. Moreover, other researchers Iso showed that biofilm formulation and multiplication can also evelop on stainless steel, copper, and some other kinds of metal ipes (15,16). Therefore, the existence of biofilm is a general ondition in metal pipes and its potential effect cannot be ignored.In this work, we focus on analyzing the more practical condition with considering reflections caused by both biofilm nd PWT defects, and we aim to present this method not only or remotely and nondestructively detecting both biofilm and WT defects but also on distinguishing them through analyzing heir characteristic signals. This work is a preliminary and original attempt to not only remotely detect defects inside a metal pipe ut also to qualitatively or even qualitatively characterize and lassify the defect types using microwaves.-. Experimental ApproachDuring our research, a vector network analyzer (VNA), E8383B (Agilent Technologies, Inc., California, USA) is utilized for generating and receiving microwave signals, and a pair of T&R coaxial line adaptors is used separately at Sii (for theingle coaxial line probe) or S21 mode (for the double coaxial Ene probe) as a bridge to introduce the signals to the pipe under testPUT) [4-6). The overall schematic diagram of the experimental approach is shown in Fig. 1. In this figure, two defect-free pipes,VNA, a pair of flexible coaxial line cables, self-designed coaxial-line probes, and three joints are shown together in detail. All of specimens are made of brass. PUTs have different wall Chinning values are realized through connecting a joint that has nner diameter larger than the two pipes between the two Hefect-free pipe specimens. The inner diameter of the defect-free pipes is 19.0 mm, and the wall thickness is 3.0 mm, and theengths of them are 750.0 and 1000.0 mm. The mentioned joints have different inner diameters and the same outer diameter of 25.0 mm, and the detailed geometrical parameters of the joints zure shown in Table 1.RAHFig. 1 Overall schematic diagram of experimental approachTable 1 Geometrical parameters of the brass jointsNo.1|2|3|Inner diameter (mm)1900/01/181900/01/18 9:36:0020Equivalent PWT depth (mm)00.20.5PWT length (mm)401900/02/081900/02/08It is reported that generally the relative dielectric constants ofbiofilms are 2 ~6, and the conductivities are around 0.1 ~0.5 5/m [17-19). For a primary attempt, a frequently used PET based double-sided adhesive tape whose composing material is not only comparatively homogeneous but also has a dielectric constant of 2.5 ~ 3.4 is adopted here to simulate a biofilm. Different thickness can be obtained from using different layers of the tapes. The PET based tape possesses a relative dielectric constant of 3.2 ~ 3.4 around 60 ~ 1,000 Hz, 3.0 - 3.3 around 1 MHz, 2.7 around 1 GHz, and 2.6 ~ 3.0 around 10 ~ 20 GHz [20-22]. The thickness of a single layer tape used in experiment is approximately 0.12 mm, and each layer of biofilm is simulated through making the inside surface of the no wall thinning joint No. 1 be fully covered of a single layer tape. As a result, all of the simulated biofilms are axially symmetrical and have a axial length of 40.0 mm.It is the same as our former research that the frequency range between the cutoff frequency of the dominant TMoj mode and the first high-order TM?, mode is adopted in the experiment [4-6). Considering the diameter of 19.0 mm of the circular waveguide, the frequency range is calculated to be from 12.1 to 19.2 GHz. During which, the dielectric constant of the tape is around 3.0.During the experimental approach, both sil and S21 parameters are measured for both PWT specimens and pipes having different thickness of biofilms are measured through utilizing the VNA after calibration.For microwave engineering, either a PWT or a biofilm defect can be taken as a discontinuity along the circular waveguide [6]. When microwave propagates to a discontinuity, reflection will happen and thereby some of the propagation energy will be reflected to the transmitting poit. Based on this fact, we can easily evaluate the defect location by extracting and analyzing the reflected signals [6]. Time of flight (TOF) means the time passed though when microwave signals reaching and reflected from a target. TOF is also used here for locating the defects.The frequency range for the single dominant TM, mode, 12.1 ~ 19.2 GHz, is utilized for measuring the S11 parameters of microwave signals, and the S21 parameters at frequency range 13.3 -13.7 GHz are also measured.3. Results and Analysis3.1 Reflection detection for locating defectsUtilizing the method described similar as shown in Ref. [6],1900/02/08Sll parameters at frequency range 12.1 ? 19.2 GHz are measured, and the experimental results for both pipes having different PWT degrees and different biofilm thicknesses are shown together in Fig. 2. The ““Free of PWT” shown in the figures means that the No. 1 joint (that has a PWT depth of 0) is utilized in the PUTs. It should be no reflection when no wall thinning, however, two most shallow peaks also appears during the experimental results. It is assumed to be mainly caused by the connection between the joint and the two pipes, and the connections act as a pair of closed cracks inside the pipe.
“ “Application of Microwaves on Remote and Nondestructive Testing of both Biofouling and Wall Thinning inside a Metal Pipe“ “劉 臨生,Linsheng LIU,佐々木 幸太,Kota SASAKI,遊佐 訓孝,Noritaka YUSA,橋爪 秀利,Hidetoshi HASHIZUME