6.4- NDT-Magnetic Particle Examination
-
Upload
katsaras-sotiris -
Category
Documents
-
view
40 -
download
2
description
Transcript of 6.4- NDT-Magnetic Particle Examination
FST 2002 – Welding &NDT No. 1
CONTENT PART 1
• Overview Test Methods
• Basis of test methods
• Execution of examinations
• Detectable type of faults
• Limits of application
FST 2002 – Welding &NDT No. 2
CONTENT PART 2
• Planning of NDT
• Content of test procedures
• Evaluation of results
• Recording of tests and results
• Applicable NDT Rules
FST 2002 – Welding &NDT No. 3
Magnetic Particle Testing (MT)
• Principle:
• Materials must be ferromagnetic• Stray flux of a magnetic field generates lines of
force, which emerge from the surface when passing a discontinuity
• Discontinuities will be visible by accumulation of ferromagnetic particles
FST 2002 – Welding &NDT No. 4
Generation of a Flux Indication
FST 2002 – Welding &NDT No. 5
Test Methods
FST 2002 – Welding &NDT No. 6
Contrast
Test Test surface and mag. particles together should provide high contrast.Appropriate particle colours should be chosen, e.g. black, red, grey.
With fluorescent particles, max. fluorescence brightness should be selected.
Remark: Thin surface coating (background paint “white”) together with black mag. Particles provide very good contrast.
poor contrastStrong background disturbance
FST 2002 – Welding &NDT No. 7
Distribution of Field Lines in the Material
FST 2002 – Welding &NDT No. 8
Magnetic Field Types
•Alternating Current:•Penetration depth 2-3 mm from surface•Small influence of surface shape•Required magnetic force is smaller (lower weight of equipment
•Scope of application:•Welds, gear-tooth
FST 2002 – Welding &NDT No. 9
Magnetic Field Types
•Direct current:•Deeper penetration•Insufficient magnetisation at
cross section changes, edges•Scope of application:
•Stationary equipment
FST 2002 – Welding &NDT No. 10
Depth Penetration of Magnetic Fields
Surface flaw Subsurface flaws
A.C magnetic field skin-effect, penetration small. Flaw depth max. 2-3 mm with f=50 hZ
D.C Magnetic field entire cross section magnetized, greater depth penetration. Flaw depth max.5-8 mm
FST 2002 – Welding &NDT No. 11
Standard Magnetic Particle TestingYoke Magnetization
FST 2002 – Welding &NDT No. 12
Yoke Magnetisation
a: Soft iron coreb: Magnetic field linesc: Magnetic coild: Flux indicatione: Stray fluxf: Defect
FST 2002 – Welding &NDT No. 13
Magnetisation Direction
FST 2002 – Welding &NDT No. 14
Standard Equipment
FST 2002 – Welding &NDT No. 15
Application of Cross Yoke Magnet
MT of a circumferential weld.
FST 2002 – Welding &NDT No. 16
Right – Hand - Rule
I = CurrentH = Magnetic Field Strength
(magnetic field lines)B = Magnetic Induction
The right hand rule define the relation between curent, magnetic induction and the direction of the magnetic field lines.
FST 2002 – Welding &NDT No. 17
Direct Fluxing
FST 2002 – Welding &NDT No. 18
Application of Direct Fluxing
Magnetisation by prods
FST 2002 – Welding &NDT No. 19
Application of Direct Fluxing
FST 2002 – Welding &NDT No. 20
Coil Magnetisation
FST 2002 – Welding &NDT No. 21
Application of Coil Magnetisation
FST 2002 – Welding &NDT No. 22
Threading Bar Technique
FST 2002 – Welding &NDT No. 23
Induction Fluxing
FST 2002 – Welding &NDT No. 24
Testing Accessories
• Indication capability of the testing fluid• Defect recognition• Suspension evaluation• After a setting time of 30 minutes the required concentration must be obtained.
FST 2002 – Welding &NDT No. 25
Test Block MTUC – No.3
• To check magnetic powder suspensions for theirefficiency
• Regular control
FST 2002 – Welding &NDT No. 26
Berthold Test Block
• For determination of the field direction• Minimum angle between field – and crack
direction 30o
FST 2002 – Welding &NDT No. 27
Field Strength Meter
• Determination of field strength• 20 to 65 A/cm or (2,0 to 6,5 kA/m)• Control of demagnetisation• Maximum allowable residual
field intensity• Max. 4A/cm (0,4 kA/m)
FST 2002 – Welding &NDT No. 28
Light Intensity Meter
UV Intensity Meter Luxmeter
FST 2002 – Welding &NDT No. 29
Detectable Flaw Sizes
FST 2002 – Welding &NDT No. 30
Defects IndicationSurface flaws Subsurface defects
FST 2002 – Welding &NDT No. 31
Irrelevant IndicationsDevelopment of stray-flux with strong magnetization
Cross-section changes, edges Irrelevant Indications
FST 2002 – Welding &NDT No. 32
Local Permeability Change
MT of 2,5% Ni-Steel, austenitic welded, rechecked by PT
FST 2002 – Welding &NDT No. 33
Evaluation of Discontinuities
Form of indication (linear,round)Size of indicationsQuantity of indicationsLocation, direction andOrientation of indications
FST 2002 – Welding &NDT No. 34
Magnetic Particle Standards
• Standards for performance of tests:• DIN EN 1290 “Magnetic Particle Examination of Welds”• ASME Sec. V, Subsection A, Article 7 “Magnetic Particle
Examination”• ASME E-709 “Standard Recommended Practice for
Magnetic Particle Examination”• DGZfP Richtline EMO “Performance of magnetic particle
examinations” (EN ISO 9934-1)
FST 2002 – Welding &NDT No. 35
Evaluation Standards
• AD-Merkblatt HP 5/3 Anlage 1 “Non Destructive testing of welded connections” (Pressure vessels)
• DIN-EN 1291 “Magnetic Particle Examination of Welds –Evaluation Criteria”
• Germanischer Lloyd II/3 Chapter 2 Sec.4 “Non Destructivetesting of welds”
FST 2002 – Welding &NDT No. 36
Acceptance Criteria
FST 2002 – Welding &NDT No. 37
Imperfections in Welded Joints in Steel according to EN 25817
FST 2002 – Welding &NDT No. 38
Recording of MT
• Details of test object:• Marking of test object• Material• Dimension• Welding proces• Area tp be tested• Specification
• Details of examination:
• Surface condition
• Type of magnetisation
• Tangential field strength
• Magnetic powder
• View conditions
• Demagnetisation