ASTM-A578/A578M:17 pdf free download – Standard Specification for Straight-Beam Ultrasonic Examination of Rolled Steel Plates for Special Applications.
6.6.3 When a discontinuity condition is observed during general scanning adjust the instrument to produce a first reflection from the opposite side of a sound area of the plate of 75 ± 5 % of full scale. Maintain this instrument setting during evaluation of the discontinuity condition.
7. Recording
7.1 Record all discontinuities causing complete loss of back reflection.
7.2 For plates ¾ in. 120 mml thick and over, record all indications with amplitudes equal to or greater than 50 % of the initial back reflection and accompanied by a 50 ‘k loss of back reflection,
Noii I—Indications occurring midway between the initial pulse and the lirst back reflection may cause a second reflection at the location of the first back reflection. When this condition is observed it shall he investigated additionally by use of multiple hack reflections.
7.3 Where grid scanning is performed and recordable conditions as in 7.1 and 7.2 are detected along a given grid line, the entire surface area of the squares adjacent to this indication shall be scanned. Where parallel path scanning is performed and recordable conditions as in 7.1 and 7.2 are detected, the entire surface area of a 9 by 9-in. 1225 by 225-mmj square centered on this indication shall be scanned. Tbe true boundaries where these conditions exist shall be established in either method by the following technique: Move the transducer away from the center of the discontinuity until the height of the back reflection and discontinuity indications are equal. Mark the plate at a point equivalent to the center of the transducer. Repeat the operation to establish the boundary.
8. Acceptance Standard—Level A
8.1 Any area where one or more discontinuities produce a continuous total loss of back reflection acconipanied by continuous indications on the same plane (within 5 c of plate thickness) that cannot be encompassed within a circle whose diameter is.. in. 175 mml or ½of the plate thickness. whichever is greater. is unacceptable.
9. Acceptance Standards—Level B
9.1 Any area where one or more discontinuities produce a continuous total loss of back reflection accompanied by continuous indications on the same plane (within 5 % of plate thickness that cannot be encompassed within a circle whose diameter is 3 in. 175 mml or ½ of the plate thickness, whichever is greater. is unacceptable.
9.2 In addition, two or more discontinuities smaller than described in 9.1 shall be unacceptable unless separated by a minimum distance equal to the greatest diameter of the larger discontinuity or unless they may be collectively encompassed by the circle described in 9.1.
10. Acceptance Standard—I .c el C
10.1 Any area where one or more discontinuities produce a continuous total loss of back reflection accompanied by continuous indications on the same plane that cannot be encompassed within a 1-in. [25-mm] diameter circle is unacceptable.