Yoke lift test and ASME coil shot

Formula

• Lift: AC 10 lb (4.5 kg); DC 30 lb at 2–4 in. or 50 lb at 4–6 in. leg spacing (E1444, E709); DC or permanent magnet 40 lb (18 kg) (ASME V, ABS)
• ASME V coil, L/D ≥ 4: NI = 35,000 / (L/D + 2)
• ASME V coil, 2 ≤ L/D < 4: NI = 45,000 / (L/D); L/D < 2: no coil shot
• I = NI / N (within 10 %); L ≤ 18 in. (450 mm) per section; hollow: D(eff) = √(OD² − ID²)

Units. Lengths in mm or in. L/D is a ratio, so the coil formula is the same in both; only the 18 in. / 450 mm section length uses the figure ASME prints for each system. Leg spacings in mm are read against the 50/100/150 mm the documents print beside 2/4/6 in. Lift in lb and kg as printed, and newtons.

Assumptions and limits

• The lift figures are minimums at the leg spacing you will use, with contact like the examination's. ASME V checks before use each day; ABS at the start and end of each inspection day; E1444 every six months (Table 1); E709 suggests six months.
• E709 Table 3 lists the AC figure only under the 2–4 in. spacing, and E1444 and E709 give no figure for permanent magnets. Where a document gives no figure, this says so rather than borrowing another's.
• E709 prints 50 lb as 23.0 kg (225 N); E1444 prints it as 22.5 kg. Each is shown as its own document prints it; newtons elsewhere are converted from pounds (1 lbf = 4.448222 N).
• The coil formulas apply to direct or rectified current. Field adequacy is still shown with shims or a field indicator where ASME V asks for it (T-753.2(d), (e); T-764). With a Hall-effect probe on other techniques, ASME V T-764.2(c) looks for 30–60 G (2.4–4.8 kA/m) and E1444 §6.3.1.2 for at least 30 G.

Sources

1. ASME Boiler and Pressure Vessel Code, Section V (2025), Article 7 — T-753.2(a)–(f) and its 10 in. × 2 in. example; T-753.3 and its 5-turn example; T-762 lifting power of yokes; T-764.2(c) tangential field.
2. ASTM E1444/E1444M-26, Standard Practice for Magnetic Particle Testing — §7.4.4 dead weight check; Table 1 (every 6 months); §6.3.1.2 and A4.2 tangential field.
3. ASTM E709-21, Standard Guide for Magnetic Particle Testing — §20.3.7 and Table 3 minimum yoke lifting force; Table 2 check interval.
4. ABS Requirements for Nondestructive Testing (January 2025), Section 7 Magnetic Particle Testing — 5.7.2 magnetic field strength (test bar weights, daily checks).
5. NIST Special Publication 811, Guide for the Use of the International System of Units, Appendix B conversion factors (lbf to N).

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