Finite Eleent Model based Optiization of Pulsed Eddy Current Excitation Rise Tie N. N. Bharadwaj, V. Arjun, B. Purnachandra Rao Indira Gandhi Centre for Atoic Research, Kalpakka, India
Eddy Current Testing Sinusoidal excitation Single frequency content Liited depth of investigation For deep penetration High excitation current Low frequency Excitation coil Eddy current Priary agnetic field Eddy current field J x = J 0 e x/δ Jx - eddy current density at depth x J 0 - eddy current density at surface δ - skin depth = 1/(πμσf) 1/2 Conductive specien Pulsed excitation Rich in frequency content Wide depth of investigation short duration high aplitude Reduced heating
Optiisation of pulsed eddy current probe for detection of sub-surface defects in stainless steel plates V. Arjun, B. Sasi, B. Purna Chandra Rao, C.K. Mukhopadhyay, T. Jayakuar Current (A) Highlights For effective detection of deeper defects, probe design plays a ajor role. FEM based approach for optiizing probe configuration and diensions. Send-receive type ferrite cored probe of 19 outer diaeter shows better detection sensitivity. Experiental study also confirs its detection sensitivity for sub-surface defects. For defect detection, Excitation characteristics of the probe also play a crucial role. Rise tie Pulse aplitude Pulse width Tie (s)
Current (A) Objective I: FEM of PEC Optiization of rise tie for enhanceent in detection of defects in a SS plate of 5,8,10 and 12 thickness. II: Analysis using Frequency spectru. III: Study of different conductivity speciens. Rise tie Specien thickness Defect depth below surface Pulse aplitude Pulse width Tie (s) Defect detection Exciter Signal
Modelling Study Geoetry Height() Width() Ferrite-1 Receiver Ferrite-2 Ferrite-1 20 1 Receiver 10 3 Ferrite-2 20 3 Exciter DEFECT Exciter 15 3 Specien Variable(5,8,10,12) 50 PROBE Defect Variable(1-11) 5 Lift-off 0.1 - Material μ r ε r Ferrite 1500 1 100 Copper 1 1 6e7 Stainless steel 1 1 1.34e6 SPECIMEN Air 1 1 5 h
Typical Model Nuber of eshes: 32489 Axi syetry Magnetic insulation COMSOL Software Magnetic Field doain Transient tie solving tool Maxwell s Equation: 2 A A t V J s
Current (A) Induced Voltage (V) Siulation Results Exciter signal Receiver signal Rise tie Pulse aplitude Peak aplitude Pulse width Tie to peak Tie (s) Tie (s)
Induced Voltage,V 1 1 2 3 4 5 6 7 d e f e c t f r e e h h h h h h 3.5x10-6 3.0x10-6 2.5x10-6 2.0x10-6 1.5x10-6 1.0x10-6 5.0x10-7 0.0-5.0x10-7 3.46E-006 3.44E-006 3.42E-006 0.00040 0.00042 0.00044 0.00046 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 tie,s A 1 2 3 4 5 6 7 defectfree Detection Paraeters 1. Peak aplitude(pa) 2. Tie to peak(ttp) Paraeter to be optiised Rise tie Receiver Signal Exciter Signal As defect depth increases, peak aplitude decreases, tie to peak increases and the difference (in pa & ttp) between successive defects also decreases. So, the effect of rise tie on the difference(in pa & ttp) is studied for enhanced defect detection.
Rise Tie Study SS plate (2.23 % IACS) In this study, pulse aplitude is fixed at 0.5 A. Pulse width is fixed at 150 % of rise tie. Rise tie is varied to exaine the sensitivity paraeters. Rise ties considered: 5 plate: 100 μs, 200 μs, 400 μs, 800 μs, 900 μs. 8 plate: 200 μs, 400 μs, 800 μs, 900 μs, 1000 μs. 10 plate: 800 μs, 900 μs, 1000 μs, 1200 μs, 1500 μs. 12 plate: 1250 μs, 1500 μs, 1750 μs, 2000 μs, 2250 μs.
Peak aplitude,v tie to peak,s 5 thick plate Peak aplitude and tie to peak variation with defect depth at different rise ties 2.2x10-5 2.0x10-5 1.8x10-5 1.6x10-5 1.4x10-5 1.2x10-5 1.0x10-5 8.0x10-6 5.0x10-4 4.0x10-4 3.0x10-4 2.0x10-4 6.0x10-6 4.0x10-6 1.0x10-4 2.0x10-6 1 2 3 4 defectfree depth below surface, 1 2 3 4 defectfree depth below surface, Peak aplitude reduces with increase in rise tie. Tie to peak increases with increase in rise tie.
Difference,V Difference,s Difference variation with rise tie (Defect at 4 and defect-free plate) 4.0x10-7 3.5x10-7 3.0x10-7 2.5x10-7 defect=4 & defectfree 4 1.0x10-6 9.0x10-7 8.0x10-7 2.0x10-7 1.5x10-7 1.0x10-7 5.0x10-8 0.0 7.0x10-7 6.0x10-7 5.0x10-7 4.0x10-7 defect=4 & defectfree risetie,s Defect-free risetie,s Good difference is obtained in peak aplitude and tie to peak at rise tie of 400 μs.
Difference,V Difference,s 8 thick plate Difference variation with rise tie (Defect at 7 and defect-free plate) 4.0x10-8 3.5x10-8 3.0x10-8 2.5x10-8 2.0x10-8 1.5x10-8 1.0x10-8 5.0x10-9 0.0 defect=7 & defectfree 7 4.0x10-7 3.0x10-7 2.0x10-7 1.0x10-7 0.0 defect=7 & defectfree risetie,s Defect-free rise tie,s Good difference is obtained in peak aplitude and tie to peak at rise tie of 800 μs.
Difference,V Difference,s 10 thick plate Difference variation with rise tie (Defect at 9 and defect-free plate) 3.0x10-10 2.0x10-7 2.5x10-10 2.0x10-10 defect=9 & defectfree 9 1.8x10-7 1.6x10-7 1.5x10-10 1.4x10-7 1.0x10-10 1.2x10-7 defect=9 & defectfree 5.0x10-11 1.0x10-7 Defect-free risetie,s risetie,s Good difference is obtained in peak aplitude and tie to peak at rise tie of 1200 μs.
Difference,V Difference,s 12 thick plate Difference variation with rise tie (Defect at 11 and defect-free plate) 2.0x10-11 1.0x10-7 1.8x10-11 1.6x10-11 1.4x10-11 defect=11 & defectfree 11 9.5x10-8 9.0x10-8 defect=11 & defectfree 1.2x10-11 8.5x10-8 1.0x10-11 8.0x10-8 risetie,s Defect-free risetie,s Good difference is obtained in peak aplitude and tie to peak at rise tie of 2000 μs.
Optiised risetie, s Optiised Risetie variation with specien thickness 2000 1600 1200 800 400 5 6 7 8 9 10 11 12 Specien thickness, As specien thickness increases, optiised risetie also increases.
Fax,Hz Eax,J Tax, s Tie Frequency Analysis Rise tie(µs) Fax(Hz) Eax(J) Tax(µs) Used to find doinant frequency, tie of occurrence of doinant frequency and its energy. 100 3906.3 2.5130e-4 74.6 200 2256.3 2.0891e-4 129.2 400 1302.1 1.6182e-4 232.8 5 4000 3500 3000 Fax 2.6x10-4 2.4x10-4 2.2x10-4 Eax 500 400 Tax 800 680.8 1.1896e-4 435.4 900 611.25 1.1255e-4 485.6 Rise tie(µs) Fax(Hz) Eax(J) Tax(µs) 200 2170.1 1.9795e-4 131.4 400 1223.1 1.5694e-4 `237.2 800 673.85 1.1732e-4 441.8 8 2500 2000 1500 1000 500 0 200 400 600 800 1000 rise tie, s 2.0x10-4 1.8x10-4 1.6x10-4 1.4x10-4 1.2x10-4 1.0x10-4 0 200 400 600 800 1000 rise tie, s 300 200 100 0 0 200 400 600 800 1000 rise tie, s Energ y 900 599.2 1.1123e-4 492.4 1000 543.24 1.0599e-4 542.8 Rise tie(µs) Fax(Hz) Eax(J) Tax(µs) 800 662.77 5.8227e-5 443.75 900 592.48 5.5261e-5 495.4 1000 538.09 5.2695e-5 545.2 1200 454.66 4.8463e-5 646 1500 365.44 4.3629e-5 797 10 400 µs 800 µs 1200 µs 12:-2000 µs-279.01hz,2.4002e- 4J,.0011s.
Correlation of rise tie with specien thickness Thickness Rise tie Doinant frequency Skin depth 1/(πμσf) 1/2 5 400 µs 1302.1 Hz 11.97 2.39*thickness 8 800 µs 673 Hz 16.64 2.08*thickness 10 1200 µs 454.6 Hz 20.25 2.03*thickness 12 2000 µs 279 Hz 25.85 2.15*thickness For any specien thickness, the optiised rise tie has doinant frequency that has skin depth at twice the specien thickness.
Difference,s Difference,s Difference,s Hastelloy Plate (1.5 % IACS) Difference variation with rise tie 5 8 10 6.0x10-7 2.0x10-7 1.2x10-7 5.5x10-7 1.9x10-7 1.1x10-7 5.0x10-7 defect=4 & defectfree 1.8x10-7 defect=7 & defectfree 1.0x10-7 defect=9 & defectfree 4.5x10-7 1.7x10-7 9.0x10-8 4.0x10-7 1.6x10-7 8.0x10-8 risetie,s risetie,s risetie,s Optiu rise ties obtained are 200 µs, 500 µs and 1000 µs for 5, 8 and 10 plates respectively.
Difference,s Difference,s Difference,s Aluiniu plate (30 % IACS) Difference variation with rise tie 5 8 10 1.4x10-5 4.0x10-6 2.0x10-6 1.3x10-5 3.8x10-6 1.9x10-6 1.2x10-5 defect=4 & defectfree 3.6x10-6 3.4x10-6 defect=7 & defectfree 1.8x10-6 1.7x10-6 defect=9 & defectfree 1.1x10-5 3.2x10-6 1.6x10-6 1.0x10-5 3.0x10-6 1.5x10-6 4 6 7 10 15 8 10 11 12 25 12 13 14 15 30 risetie,s risetie,s risetie,s Optiu rise ties obtained are 7 s, 10 s and 13 s for 5, 8 and 10 plates respectively.
Epirical Relation Optiu rise tie = p 00 + p 10 * T + p 01 * C + p 20 * T 2 +p 11 *T*C + p 02 *C 2 (T Thickness; C Conductivity) p 00 = -971.3; p 10 = 202.3; p 01 = 29.47; p 20 = -7.778; p 11 = 37.44; p 02 = 0.8302. Specien Conductivity(% IACS) Hastelloy 1.5 Stainless Steel 2.23 Aluiniu 30 Thickness () Actual Rise tie (µs) Epirical Rise tie(µs) Error(%) 5 200 172.623 13.69 8 500 644.661-28.93 10 1000 881.573 11.84 5 400 333.053 16.74 8 800 887.084-10.89 10 1200 1178.659 1.78 5 7000 7093.03 1.33 8 11000 10766.19 2.13 10 13000 13137.18-1.06
Suary Pulsed eddy current rise tie has been optiized for enhanced sub-surface defect detection in SS plate, Hastelloy plate and Aluiniu plate of thickness 5, 8, 10 and 12. An epirical relation is given for optiu pulse rise tie as a function of specien thickness and conductivity. Further, tie-frequency analysis of the excitation signals revealed that the optiized rise tie has doinant frequency that has skin depth at twice the specien thickness.
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