FIELD STRENGTH & DIRECTION

VERIFICATION of field:• ASTM Pie gauge is positioned on the

examination surface with brazed pie-sections toward the examination surface.

• A clearly defined line or lines when particles are applied simultaneously with magnetizing force indicates adequate strength.

MEASURING FIELD STRENGTH:• Hall-effect tangential probe positioned on

the surface • The peak-value of tangential field is

measured when magnetizing force is applied

• Value of 30 to 60 Gauss (2.4 k to 4.8 k Amps /meter) indicates adequacy of field

MAGNETISING DIRECTION

• The direction of magnetization is verified using ASTM pie-gauge

• Pie gauge is positioned so that• brazed pie-sections toward the

examination surface • Cu plate away form surface.

• A clearly defined line or lines in the desired direction when particles reapplied simultaneously with magnetizing force

• fulfills the requirement of field direction

 

DRY CONTINUOUS

APPLICATION OF DRY PARTICLES :• Flow of magnetizing current

initiated• Cloud of Dry particles floated with

low velocity upto the surface • Application of current terminated

after the application of powder has been completed and any excess has been blown-off.

• Build-up of indication observed as the particles are being applied used for examination.

YOKE TECHNIQUE

• To detect discontinuities open to surface • Yokes have TWO adjustable legs • Adjustable legs permit changing the

contact space in between the legs and improved contact area with surface

• Legs of yoke are positioned similar to prods & pressed against surface

• The discontinuities anticipated should be centrally located in the area between pole pieces

• The effective inspection area • space in between the legs is the area of

examination • Lateral area of 38 mm on each side of

the center-line of yoke legs• Depends on part geometry and

qualified using Hall-effect gauss meter

ELECTRO-MAGNETIC YOKES

• A single leg used in areas of tight access• Flux lines for single leg yoke flow

radially producing radial magnetization • ELECTRO-MAGNETIC YOKES:• DC yoke has greater penetration while

AC yoke concentrates the field on the surface of weld providing greater sensitivity

• At maximum pole spacing used for examination the minimum Lifting power of AC yokes shall be:4.5 kg; DC yokes:18.1 kg.

• The yoke techniques produce LONGITUDINAL magnetic field on the surface in between the pole-pieces

PERMANENT YOKES

• Permanent yokes used where no electric power is available or where arcing is not permitted

• The strength of any yokes is determined by its lifting power

• At maximum pole spacing used for examination he minimum Lifting power of Permanent yoke shall be:18.1 kg