T9074-AS-GIB-010/271 Rev 1
4.3.3 Dry Powder Method.
4.3.3.1 General Requirements for Magnetic Particles. The magnetic particles used for obtaining patterns of discontinuities shall be of a nontoxic, finely divided ferromagnetic material of high permeability and low retentivity, free from deleterious rust, grease, paint, dirt, or other material that might interfere with their proper functioning. Particles shall be of such size, shape and color as to provide adequate sensitivity and contrast for the intended use. All particles shall meet the requirements of SAE AMS 3040. 4.3.3.2 Application and Removal of Particles. Dry magnetic particles shall be applied in such a manner that a light, uniform, dust-like coating settles upon the surface under test. 4.3.3.2.1 Removal of Excess Particles. Excess dry particles shall be removed by means of a dry air current of sufficient force to remove excess particles without removing relevant indications formed during powder application. Removal of excess particles shall comply with the procedure of 4.3.1.2 and must be accomplished while the magnetic field is applied to the item under test. 4.3.3.2.2 Automated Equipment. Automatic powder blowers or any other form of forced air other than from a hand-held bulb shall not be used for the application or removal of dry magnetic particles unless specifically approved by NAVSEA.
4.3.3.3 Magnetizing Procedures.
4.3.3.3.1 Circular Magnetization. The method of magnetization and the magnetizing current shall be as specified in 4.3.2.5.3, 4.3.2.5.4, and 4.3.2.5.5, as applicable. 4.3.3.3.2 Longitudinal Magnetization. The method of magnetization and the magnetizing current shall be as specified in 4.3.2.5.6 and 4.3.2.5.7. 4.3.3.3.3 Yoke Magnetization. Yoke spacing of greater than 8 inches or less than 2 inches is not recommended. However, if yoke spacing of greater than 8 inches or less than 2 inches must be employed, the procedure must be qualified with the exact yoke spacing that is to be used. In complex or restrictive configurations, where the placement of yoke legs may be impractical, AC or DC prods may be used in place of an AC yoke provided that the prod procedure has been properly qualified. 4.3.3.3.4 Magnetizing Current (Prod Methods). For prods, the magnetizing current, direct or rectified, shall be computed on the basis of 100 to 125 amperes per inch of prod spacing. Prod spacing of greater than 8 inches or less than 2 inches is not recommended. However, if prod spacing of greater than 8 inches or less than 2 inches must be employed, the procedure must be qualified with the exact prod spacing that is to be used.
4.3.3.4 Magnetizing Technique (Yoke and Prod).
4.3.3.4.1 Weld Inspection. The magnetic field shall be induced with the prods or yoke legs placed diagonally, 30 to 45 degrees, to the longitudinal axis of the weld, and repeating this test along the opposite diagonal of the weld. During inspection of adjacent areas of the weld, the prods or yoke legs shall overlap the previous placement by a minimum of 1 inch. As an alternative, the magnetic fields may be induced by placing the prods or yoke legs parallel to the longitudinal axis of the weld, overlapping the previous placement by a minimum of l inch. Subsequent to the longitudinal placement, the weld shall be inspected by placing the prods or yoke legs perpendicular to the weld. When this alternative is used, the area to be inspected shall be limited to one-fourth of the prod or yoke leg spacing on either side of a line joining the prods or yoke legs. 4.3.3.4.2 Base Metal. Base metal shall be inspected using the prod and yoke leg placement requirements of 4.3.3.4.1 to establish a grid pattern that ensures two-directional coverage of inspection areas. 4.3.3.4.3 Continuous Magnetization. During inspection, the magnetizing current shall remain on during the period the magnetic particles are being applied and while excess particles are being removed. For cases where the magnetic particles
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