6_231128_Eargle_ ISO5817 MT Training Material.pptx

Click to insert Picture Magnetic Testing Training Material     Sidney Eargle CWI KION NA - Summerville, SC DEC 04, 2023 Black lights • Best results when light produced has a wavelength of • 3.6Sx10-4 mm • Intensity should not be less than 800 µW/cm2 when measured 380mm from face of light le...

Click to insert Picture Magnetic Testing Training Material     Sidney Eargle CWI KION NA - Summerville, SC DEC 04, 2023 Black lights • Best results when light produced has a wavelength of • 3.6Sx10-4 mm • Intensity should not be less than 800 µW/cm2 when measured 380mm from face of light lens filter • Light should be allowed to warm up a minimum of 10 minutes prior to use • Examination should occur in a darkened area where the ambient light level does not exceed 32 lux (3 fc) − Operator should allow his eyes to adjust to the light level for at least 5 minutes prior to interpretation of indications 2 MT Training Material Selection of technique • Basic technique variables − Type of current − Type of particles and method of application − Sequence of steps − Direction of field − Sensitivity level − Equipment 3 MT Training Material Type of current to be used • Direct current − Deeper penetration − Ability to detect subsurface defects − Reduced particle mobility − Not preferred for rough surfaces • Alternating current − More sensitive to surface defects − Excellent particle mobility, even on rough surfaces • Half wave rectified AC − Sensitive to surface and subsurface defects − Excellent particle mobility 4 MT Training Material Type of particles to be used • Primary choice between dry and wet types − Dry more sensitive to subsurface defects − Wet more sensitive to very fine surface defects 5 MT Training Material Sequence • Residual method − Parts are magnetized, then the magnetic particles are applied − May only be used on materials having sufficient retentivity, such as those with high hardness − May require higher magnetizing current levels − Generally only reliable for detection of surface defects • Continuous method − Magnetic particles are applied while the magnetizing current is flowing − More sensitive than the residual method 6 MT Training Material Direction of magnetic field • Decision based on shape and orientation of defect in relation to shape and principal axes of the part • May require circular magnetization for some locations and longitudinal for others • When feasible, circular magnetization is preferred because there is less tendency for creation of irrelevant indications 7 MT Training Material Sensitivity level required • Sensitivity dependent upon numerous factors − Type of magnetic particles − Dry or wet − Visible or fluorescent − Type of magnetizing current − Circular − Longitudinal − Sequence − Residual − Continuous − Amount of current required 8 MT Training Material Equipment • Depends on size, shape, number and variety of parts to be tested − Bench type units preferred for production testing of numerous parts which are relatively small, but not necessarily identical in shape − For large parts, portable units such as prods or yokes are preferred − Customized, automatic or semi-automatic units may be justified for production testing of identical or closely similar parts 9 MT Training Material Application of MT • Preparation of test surface • Application of magnetic field • Application of magnetic particles • Interpretation of indications • Demagnetization 10 MT Training Material Preparation of test surface • All dirt, rust, loose scale, and oil or grease shall be removed from test area • Where surface irregularities exist, additional surface treatment may be required 11 MT Training Material Application of magnetic field • Prior to testing production parts, the performance of the system (apparatus, magnetic particles and suspension as well as the strength and direction of the magnetic field on the surface of the test object) should be verified by one or more of the following techniques − Testing of production test parts with discontinuities − Testing of fabricated test parts with discontinuities − Testing of magnetic field indicators 12 MT Training Material Use of magnetic field Indicator • Magnetic field indicator (or "pie gage") consists of eight segments of steel separated by nonmagnetic material and with a copper backing 13 MT Training Material Use of magnetic field indicator • Place magnetic field indicator on surface of test object with copper side exposed • Apply magnetic field and magnetic particles • Observe the indications that are revealed • This is not a quantitative measurement of field strength or distribution • It only indicates field strength and direction at the surface in the area of the part under test • A suitable field is indicated when a clearly defined line of magnetic particles forms when the continuous method of magnetization is applied 14 MT Training Material Applying magnetic field • During production testing, the magnetic field must be applied to the part in directions that will reveal all possible flaws, no matter what their orientation − For complete coverage, the magnetic field must be applied in 2 directions, approximately 90° apart − The magnetic field must be applied so that there is at least a 10% overlap of each test area 15 MT Training Material Effective area of coverage 16 MT Training Material Overlap of effective areas 17 MT Training Material Yoke placement for weld examination 18 MT Training Material Applying magnetic particles • Continuous method is to be used − Magnetic particles shall be applied to the test area during the time when the magnetic field is present 19 MT Training Material Interpretation of indications • Once the magnetic field and magnetic particles have been applied, the test area shall be examined for indications • When using the fluorescent method, this examination must take place in a darkened enclosure where the ambient light level is no greater than 32 lux (3 fc) 20 MT Training Material Interpretation of indications • Indications must be interpreted to assure that they do not such as: − Magnetic writing − Abrupt sectional variation indication − Electric current indication − Electrode indication − Magnetic pole indication − Surface roughness indication − Material junction indication 21 MT Training Material result from false indications, Demagnetization • When the presence of residual magnetism may affect the subsequent processing or use of the part, it shall be demagnetized • A number of different methods may be applied • Two common methods include: − Passing the part through an energized AC coil − Application of an AC yoke, followed by its withdrawal while the field is still being applied 22 MT Training Material Demagnetizing methods 23 MT Training Material Discontinuity detection • In order to be revealed, discontinuities must cause a sufficient disturbance of the applied magnetic field to produce a visible indication of particle accumulation • There are a number of characteristics of discontinuities that will affect this 24 MT Training Material Discontinuity characteristics • Discontinuities Open to the Surface 25 MT Training Material Discontinuities open to the surface • Depth, D • Length, L • Width, W • Shape - sharpness at the bottom - V or U • Angle of penetration with respect to the surface • Orientation • Frequency - number per unit of surface area • Interrelationship - grouping, alignment, etc. • Relationship of all characteristics to service stresses and critical stress locations • Stress concentration effects 26 MT Training Material Subsurface indications 27 MT Training Material Subsurface indication characteristics • Detection will depend upon − Depth below surface — more than 1/16” below will be difficult to detect with normal techniques − Orientation will also affect detectability − Powder buildup will be less defined, making interpretation more difficult 28 MT Training Material Typical weld cracking locations 29 MT Training Material Typical dry powder indications 30 MT Training Material Typical dry powder indications 31 MT Training Material Dry powder indications — slot welds in armor steel 32 MT Training Material Typical dry powder indications 33 MT Training Material Typical fluorescent indications 34 MT Training Material Typical fluorescent indications 35 MT Training Material False/ nonrelevant indications • Two terms sometimes used interchangeably, but are defined by ASTM E709 as: − Nonrelevant: Indications resulting from leakage fields created by conditions that required no evaluation (such as the natural weld profile at weld toes) − False: Indications that are not the result of magnetic forces but where powder is held mechanically or by gravity ln shallow depressions or at scale on the surface 36 MT Training Material Examples False indications with wet fluorescent MT False indication from weld scale 37 MT Training Material Same location as above with dry powder MT, showing absence of any valid indications Nonrelevant HAZ indication 38 MT Training Material 39 MT Training Material