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

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CONTENT PART 2

• Planning of NDT

• Content of test procedures

• Evaluation of results

• Recording of tests and results

• Applicable NDT Rules

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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

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Generation of a Flux Indication

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Test Methods

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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

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Distribution of Field Lines in the Material

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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

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Magnetic Field Types

•Direct current:•Deeper penetration•Insufficient magnetisation at

cross section changes, edges•Scope of application:

•Stationary equipment

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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

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Standard Magnetic Particle TestingYoke Magnetization

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Yoke Magnetisation

a: Soft iron coreb: Magnetic field linesc: Magnetic coild: Flux indicatione: Stray fluxf: Defect

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Magnetisation Direction

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Standard Equipment

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Application of Cross Yoke Magnet

MT of a circumferential weld.

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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.

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Direct Fluxing

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Application of Direct Fluxing

Magnetisation by prods

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Application of Direct Fluxing

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Coil Magnetisation

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Application of Coil Magnetisation

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Threading Bar Technique

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Induction Fluxing

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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.

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Test Block MTUC – No.3

• To check magnetic powder suspensions for theirefficiency

• Regular control

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Berthold Test Block

• For determination of the field direction• Minimum angle between field – and crack

direction 30o

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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)

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Light Intensity Meter

UV Intensity Meter Luxmeter

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Detectable Flaw Sizes

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Defects IndicationSurface flaws Subsurface defects

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Irrelevant IndicationsDevelopment of stray-flux with strong magnetization

Cross-section changes, edges Irrelevant Indications

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Local Permeability Change

MT of 2,5% Ni-Steel, austenitic welded, rechecked by PT

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Evaluation of Discontinuities

Form of indication (linear,round)Size of indicationsQuantity of indicationsLocation, direction andOrientation of indications

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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)

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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”

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Acceptance Criteria

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Imperfections in Welded Joints in Steel according to EN 25817

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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