Distributed circle method for guided wave based corrosion detection in plate-like structures

Patent metadata

Field	Value
Publication number	US-2017191966-A1
Application number	US-201614987179-A
Country	US
Kind code	A1
Filing date	Jan 4, 2016
Priority date	Jan 4, 2016
Publication date	Jul 6, 2017
Grant date	—

Abstract

A system and methods for defect detection and characterization in plate-like structures, more particularly to detect corrosion in complex plate-like structures that result in a deviation in thickness in at least a patch of the structure. The system comprises a plurality of transducers configured to be adjacent to at least a portion of a plate-like structure. A controller is coupled to the plurality of transducers. The method includes propagation of guided waves through the plate-like structure and capture of data to detect the presence of at least one defect using at least a pair of transmitting/receiving transducers based on a change in the velocity of wave transmission as compared to the velocity predicted for a pristine structure. The method also includes estimated localization, and estimation in size and change in thickness of one or more patches using at least four discrete wave transmission paths that traverse the defect by using optimization of a proposed error function to estimate based on distributed circles using a derivative free optimization based algorithm.

First claim

1 . A method for characterizing a thickness deviation in at least a portion of a plate-like structure, the method comprising:
deploying adjacent to at least a portion of a plate-like structure a sensor network comprising a plurality of transducers, the at least a portion of the plate-like structure having a presumed substantially uniform pristine thickness and formed of an presumed substantially homogenous material and characterized by a known dispersion curvatures that depend on the plate thickness and material properties; propagating guided waves through the at least a portion of the plate-like structure within the sensor network, wherein the sensor network provides at least four discrete wave transmission paths that traverse the at least a portion of the plate-like structure; determining the velocity of the guided waves along each discrete wave transmission path based on a predetermined distance between sensors that define the path and the time of flight of the transmitted waves along the wave transmission path; detecting within the at least a portion of the plate-like structure the presence of any deviation in thickness from the presumed pristine thickness, wherein a deviation in thickness is present when the determined velocity along at least one of the wave transmission paths deviates from an expected pristine guided wave velocity provided by the known wave mode velocities that depend on the relationship between wavelength and plate thickness; and estimating the location and approximate area of any deviation in the thickness within the at least a portion of the plate-like structure, wherein a deviation in thickness is present when at least four wave transmission paths traverse the deviation as evidenced by a detected deviation of velocity from expected pristine guided wave velocities along at least four wave transmission paths, and whereby the location and size of a patch of thickness deviation is estimated as a circle based on the determined velocities and predetermined distances for each of the transmission paths, and the expected pristine guided wave velocity provided by the known wave mode velocities that depend on the relationship between wavelength and plate thickness.

2 . The method for characterizing a thickness deviation in at least a portion of a plate-like structure according to claim 1 ;
wherein the known wave mode velocities that depend on the relationship between wavelength and plate thickness are provided by guided ultrasound (Lamb) wave group dispersion curves, and wherein the sensor network is deployed adjacent to the surface of the plate-like structure and the guided ultrasound waves are propagated between pairs of transducers in the sensor network, wherein each transducer is paired with another transducer to provide sets of paired transducers comprising a transmitting and a receiving transducer, wherein the sets of paired transducers provides at least four discrete wave transmission paths, each wave transmission path defined between two paired transducers; and wherein the velocities of guided waves between the transducers are detected in A 0 and S 0 modes, and wherein deviation comprising a decrease in the thickness will result in a detected reduction in wave velocity, included but not limited to the wave modes including the A 0 mode and the S 0 mode, wherein in the A 0 mode and a detected increase in wave velocity in the S 0 mode.

3 . The method for characterizing a thickness deviation in at least a portion of a plate-like structure according to claim 2 , wherein the algorithm for estimating the size and location of a thickness deviation patch comprises solving for the coordinates for the center and the radius of a circle that estimates the deviation patch, shown by the relationship Γ(x, y)≈C(x c , y c , r), wherein F is the deviation patch, C is the estimated circle, x c , y c describe the center point of the estimated circle, and r describes its radius, and wherein the distance of the portion of a transducer pair's transmission path through the deviation patch can be approximated and theoretically calculated as distributed circles for each transducer pair, and wherein the circle C variables are determined using a least square optimization problem given as

min




J


(

x
c

,

y
c

,
r
,

V
_

)

=

∑

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=
1

N



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(

T
_

k

-

T
_

k

)

2

,

N
≥
4

where N is the number of transducer pairs whose transmission paths go through the deviation patch, T k is the total and T k is the actual time of flight of the transmission of a wave along a transducer pair path associated with the k-th transducers pair, and V is the determined wave velocity.

4 . The method for characterizing a thickness deviation in at least a portion of a plate-like structure according to claim 3 , wherein the actual time of flight is determined by one of threshold crossing, cross correlation, and wavelet analysis.

5 . The method for characterizing a thickness deviation in at least a portion of a plate-like structure according to claim 3 , wherein the least square optimization problem is solved by an algorithm selected from a derivative free optimization based Genetic Algorithm, Particle Swarm Optimization, Mesh Grid Optimization, and coordinate search.

6 . The method for characterizing a thickness deviation in at least a portion of a plate-like structure according to claim 3 , wherein the deviation is a reduction in thickness caused by corrosion.

7 . A method for identifying corrosion in at least a portion of a plate-like structure, comprising:
arranging a plurality of transducers along a boundary of a corrosion detection area of the planar structure, the transducers paired to transmit and receive between them along a rectilinear communication path along the planar structure; actuating the transducers to propagate guide

Assignees

• Gen Electric

Inventors

• Niri Ehsan Dehghan
• Falsetti Robert Vincent
• Rose Curtis Wayne

Classifications

• G01N17/00

  Investigating resistance of materials to the weather, to corrosion, or to light · CPC title

• G01N2291/0427

  Flexural waves, plate waves, e.g. Lamb waves, tuning fork, cantilever · CPC title

• G01N2291/011

  Velocity or travel time · CPC title

• G01N2291/106

  one or more transducer arrays · CPC title

• G01N29/07 Primary

  by measuring propagation velocity or propagation time of acoustic waves · CPC title