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.
Definition
Central-conductor technique inspects ring-shaped parts, tubular components, and threaded couplings. The bar must be sized so current density at the part is adequate without overheating, and the part is rotated through multiple positions to inspect the full circumference.
What it is
A conductor threaded through a hollow part's bore carrying magnetizing current — inducing a circular field in the part without any contact, so inner and outer surfaces are examined with zero arc-burn risk.
Correct use
The technique of choice for rings, nuts, hollow shafts and tubular parts: field strength falls with radius, so amperage is set for the outer diameter, and off-centre conductors bias the field — multiple shots with the conductor repositioned (or centring) restore uniformity on larger bores.
Governing standards
ASME Section V Article 7 and ASTM E1444 give amperage guidance and coverage rules for central conductor technique.
The usual mistake
One off-centre shot on a large-bore ring: the near side saturates while the far side sits under-magnetised — verified coverage means field indicators at the weakest position, not the strongest.
Where Central Conductor fits in an inspection programme
A term is only useful when it connects to a decision. Central Conductor 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
- 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.
- 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.
- 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.
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.