Magnetic Particle Inspection

Magnetic Particle InspectionTeam 6

Allison LockCathlene Farnelli

Steve Kreeley

Objective●To detects voids in

ferrous materials●To identify a defect

by magnetic leakage in form of flux

●Allow defects to attract particles

●To reveal defects with UV light

Theory Behind Leakage

●Ferrous, flawless specimen:

●Ferrous, cracked specimen:

Method & Approach

●Magnetic field induced in material

●Apply coating of fluorescent magnetic particle solution

●Shine object with UV light

Method & Approach (cont.)●Direct Current or

Magnetic Flux Flow methods

●Digital Imaging and Filtering used

●Canny algorithm used to de-noise and detect edges

Method & Approach (cont.)●Similar to Dye Particle Inspection (DPI)●Used for Ferromagnetic Objects●Detects Surface or Near-Surface Flaws●Current must hit Long Dimension at Right Angle

Direct Current Method●Current sent

through Object ●Generates

Magnetic Field ●Identifies Defect.

Magnetic Flux Flow Method●Flux induced in object ●Done by Permanent

Magnet or Current from Coil or Conductor

Devices Used●Field Indicators●Hall Effect Meters●Two most common●Others include prods, portable coils, and conductive

cables

Field Indicators●Iron Vane rotates and

deflects with Magnetic Field ●Analogous to Weather

Vane with Wind●Iron Vane moves to rotate

a needle that turns a pointer

●Pointer indicates measurement

Hall Effect Meters●Also called Gauss or Tesla

Meters ●Provides Digital Output of

Magnetic Field Strength●Current Passes through

Conductor inside Probe●Probe placed in Magnetic Field●Magnetic Lines oriented at

Right Angle with Long Dimension

Real World Applications●Bridges●Underwater Utilities●Pressure Vessels●Boilers

● Surface defects● Welded joints ● Components of pressure systems

○ Boilers, pressure vessels, locomotives, tanks

Method Application

LEFT: Weld Inspection, CENTER: Drive Shaft with Cracking, RIGHT: Crack in Steam Drum Seam.

Laboratory Example (Crankshaft)●Crankshaft Rotates to get Complete View with UV

Light●CCD Camera Captures Images●PC Reads and Processes Images for Evaluation

Dry● Common, relatively cheap● Generally applied to

rougher surfaces● Particle types

○ Elongated - align well with magnetic fields

○ Rounded - move freely across a surface

Magnetic Particles

Wet● More expensive, accurate● Painted or sprayed onto

surfaces● Wet dye classifications

○ Light (UV or fluorescent)

○ Removal type (water, solvent, or emulsifier)

Sample Results

LEFT and CENTER: Image of pipe with and without magnetic particles showing cracks emanating from a hole. RIGHT: Magnetic particle wet fluorescent indication of a crack in a bearing.

Method AssessmentCons:Time consuming evaluation● Subjective based on user

experience and eyesight● Problems with area changes,

textures● Fluorescent lighting can be

damaging to the optic health of workers

● Magnetic coagulation of dyes

Pros:● Dry: common, relatively cheap● Wet: more expensive, accurate● Effective for detection, sizing

and location of surface and near-surface flaws

Depiction of Magnetic Field and Particle Coagulation Over a Crack with Parts of

Chain Both Inside and Outside of Magnetic Field

Two-dimensional median filter - filteringReduces the complexity, integrity is kept (assuming high

resolution)

Image Processing Example Procedure

Gradient operator and a grey-scale transform - enhancingGradient operator required for following step, grey-scale

transform amplifies/suppresses


Canny Operator (wavelet-based) for edge detection - segmentationWavelet-based: analyzes smaller windowRun through edge detection, then inverse in order to form

image with enhanced edges


Area filling - final imageAll areas considered to be part of crack are highlighted


Sample Results: Image Processing

Figure 6: Images of the Recorded Data Throughout Processing (1) Raw Data (2) Data After Median Filter (3) Data After Grey-Scale Transform (4) Data After

Wavelet-Based Canny Operator (5) Data After Filling (Final Image)

Pros:● Further processes data without

human inspector’s input● Less time and discrepancies● Increasing the readability of results● Can be done with original method or

as post-processing● May in the future be utilized as

a fully automatic process

Method AssessmentCons:

● More equipment required● Results may need to be done as post-

processing, not in field● More expensive, may require

inspection company to buy software

References"Examples of Visible Dry Magnetic Particle Indications." NDT Education Resource Center. Collaboration for Nondestructive Testing (Iowa State University), National Science Foundation, 2001. Web. 16 Nov. 2015. "Examples of Fluorescent Wet Magnetic Particle Indications." NDT Education Resource Center. Collaboration for Nondestructive Testing (Iowa State University), National Science Foundation, 2001. Web. 16 Nov. 2015. "GV-02 Crack Detection: Machine Vision Magnetic Particle Inspection."Sonic Diagnostic. Sonic Diagnostic, 2010. Web. 5 Dec. 2015.Luo, Jianlan, Zhewen Tian, and Jintao Yang. "Fluorescent Magnetic Particle Inspection Device Based on Digital Image Processing." Proceeding of the 11th World Congress on Intelligent Control and Automation (2014). Print.

"Manual for the Training Guidelines in Non-destructive Testing Techniques." Liquid Penetrant and Magnetic Particle Testing at Level 2, 11 (2000): 5-6. Print.

Shelikhov, G. S. "The Effect of Coagulation of Magnetic Particles on the Detectability of Flaws in Magnetic-Powder Inspection." Russian Journal of Nondestructive Testing. N.p., 6 Nov. 2004. Web. 26 Nov. 2015.

Worman, Jim. "Magnetic Particle Examination." The National Board of Boiler and Pressure Vessel Inspectors. N.p., 2015. Web. 17 Nov. 2015.

Documents

Magnetic Particle Inspection