Yoke
A yoke is a handheld electromagnet with two articulated legs used in magnetic particle testing to induce a longitudinal magnetic field between the leg tips for detecting transverse surface defects.
Definition
Yokes are convenient field MT tools. AC yokes give the best surface-defect sensitivity; DC and permanent-magnet yokes give better near-surface sensitivity. A lifting-power check (typically 4.5 kg for AC, 18 kg for DC) verifies adequate field strength.
What it is
A portable electromagnet whose poles induce a longitudinal field in the part between them — the field-work staple of MT because it needs no electrical contact and cannot arc-burn the part.
Correct use
Detects discontinuities oriented across the line between the poles, so every area is examined twice at right angles. Capability is verified by dead-weight lift test — a defined weight lifted per ASTM E709/E1444 practice — at intervals, not assumed from the nameplate.
Governing standards
ASME Section V Article 7 and ASTM E1444 cover yoke technique, lift verification and coverage overlap.
The usual mistake
Coverage discipline. A yoke examines a small patch per placement; on a large weld the examination is a mosaic of overlapping placements in two orientations, and the finding rate of a rushed mosaic drops invisibly — nothing looks wrong, things simply are not found.
Where Yoke fits in an inspection programme
A term is only useful when it connects to a decision. Yoke appears in written procedures, in technique sheets, and in the records an owner or accreditation body reviews afterwards — which means the way it is defined in your documentation has to match the way it is applied on site. Where the two drift apart, audits find it. Atlantis writes and reviews procedures against the governing codes, trains inspection personnel to apply them, and builds the record-keeping that makes the evidence retrievable years later. Procedure development and code consulting · NDT training and certification · Ask us about your programme.
Related terms
- Prods — Prods are a pair of handheld copper or copper-aluminum electrodes that pass high current through a localized area of a ferromagnetic part to induce a circular magnetic field for magnetic particle testing.
- Central Conductor — A central conductor is a current-carrying copper bar passed through the bore of a hollow ferromagnetic part during magnetic particle testing to induce a circular magnetic field around the inner and outer surfaces.
- Multi-Directional Magnetization — Multi-directional magnetization applies two or more magnetic fields in different directions simultaneously or in rapid sequence so that defects of any orientation can be detected in a single inspection shot.
- Magnetic Particle Testing (MT) — Magnetic Particle Testing (MT) is a surface and near-surface NDT method for ferromagnetic materials that detects discontinuities by applying a magnetic field and observing the leakage flux attract magnetic particles to the flaw indication.
Further reading
magnetic particle inspection procedure interpretation
More equipment terms
Calibration Block · Transducer · Dual-Element Probe · Angle-Beam Probe · Normal-Beam Probe · Couplant · Reference Reflector · Side-Drilled Hole · Flat-Bottom Hole · Notch Reference
Where this comes up in practice
Terms like this one appear in three places that matter commercially: the written practice that governs how your personnel are qualified, the procedures and technique sheets that define how an examination is actually performed, and the evidence an auditor or client asks for when they want to know why an inspection was accepted. Getting the terminology right is the easy part; being able to produce the qualification record, the calibration traceability and the procedure revision that applied on the day of the inspection is the part that decides audits.
Atlantis NDT provides NDT training and certification against ASNT SNT-TC-1A and ISO 9712, ASNT Level III consulting for written practices and procedure approval, inspection management software that holds qualification, calibration and procedure-revision evidence in recoverable form, and an asset integrity platform that binds inspection results to the asset they describe. Browse the full NDT glossary or ask a Level III directly.