Quench cracks from hardening, laps and bursts from heading or forging, and seams from the bar all start at or near the surface, often at a thread root or the head-to-shank fillet where a bolt carries the most stress. Magnetic particle inspection finds them before the part goes into service. Because particles gather best where a flaw lies across the field, the part is magnetised in two directions.
ASTM A193 has a supplementary requirement for magnetic particle inspection of bar, and ASTM A962 one for 100% wet fluorescent inspection of the bolting to ASTM E1444, with set acceptance limits. It works only on ferromagnetic steels: austenitic stainless such as B8 and B8M, and most nickel alloys, are checked with liquid penetrant instead.
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model dataThe stud is drawn to scale: a 1-1/4 in. ASTM A193 B7 double-end stud, 10 in. long, threaded 8 per inch (8UN, the ASTM A962 default above 1 in.). The bench, coil and lamp are generic, and the seam and crack are illustrative. Wet fluorescent method to ASTM E1444 and E709; UV-A of at least 1000 µW/cm² at the part and ambient light of 2 foot-candles (20 lux) or less as cited from ASTM by a UV-A meter maker; flaws show best at 45–90° to the field (NASA preferred practice PT-TE-1425); inspection before demagnetising per ASTM E1444-21. The shots and the demagnetising reversals are slowed down.
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