Advanced NDT
ACFM inspection (alternating current field measurement)
Alternating current field measurement detects and sizes surface-breaking cracks in metal, and it does so through paint and coatings. That makes it the method of choice for fatigue-crack surveys on coated structures, offshore nodes and weld toes, where blasting the coating off for magnetic particle testing would be slow, costly and would leave a repair to make good.
How ACFM works
The probe induces a uniform alternating current in a thin layer at the surface. Where a crack is present, the current flows around the ends and under the crack, and the magnetic field above the surface changes in two components: Bx, which reduces over the crack and relates to its depth, and Bz, which shows positive and negative peaks at the crack ends and gives its length. Because the field is uniform, length and depth can be estimated from mathematical models without calibrating on a crack of each size.
Probes are run along weld toes in a set pattern, with the data recorded and position-referenced, so the survey can be audited and repeated at the next inspection.
Typical applications
- Fatigue-crack surveys on offshore structure nodes and splash-zone welds.
- Crane, lifting-equipment and rotating-equipment welds that cannot be taken out of service for long.
- Coated process vessels and tanks where coating removal is not acceptable.
- Sizing of cracks for an engineering critical assessment to BS 7910 or API 579-1.
Limits to know
- ACFM finds surface-breaking cracks; it does not find embedded flaws (use UT for those).
- Very thick or conductive coatings, and complex geometry, reduce sensitivity; the procedure states the coating thickness range covered.
How we deliver it
ACFM crack detection is carried out to a written procedure approved for the scope, naming the code and edition, the equipment and calibration, the coverage and the acceptance criteria. The procedure and each technician’s certification are submitted for the client’s review before mobilisation.
Work is planned and supervised by ASNT Level III personnel; our founder holds ASNT NDT Level III in UT, RT, MT, PT and VT. Reports state the coverage achieved and any limitations, so the engineer reading them knows what was examined and what was not, and any reportable finding is raised the same day.
Governing codes and standards
- ASTM E2261 (examination of welds using ACFM)
- BS 7910 and API 579-1/ASME FFS-1 (assessment of crack-like flaws)
- ASME Section V (general NDE requirements adopted by referencing codes)
What you receive
- Weld-by-weld scan record with Bx/Bz traces
- Crack location, length and estimated depth
- Recommendations for confirmation or repair
Industries served
- Offshore and marine structures
- Oil and gas production
- Power generation
- Heavy lifting and cranes
Frequently asked questions
Does ACFM need coating removal?
No. ACFM works through non-conductive coatings within the thickness range stated in the procedure, which is its main advantage over magnetic particle testing on coated welds.
Talk to an inspection engineer
Send the equipment list or drawings, the inspection you need and your timing. Quotes are prepared for each scope and region.
Request a QuoteRequest an inspection quote (RFQ)
Tell us the asset, the method, where it is, the governing code, your dates, the size of the job and the report you need. We reply with questions or a quote. Affordable, accessible, fully customizable — no published pricing.
Or email the same details to info@atlantisndt.com. Mobilisation: North America; confirm your location in your RFQ.
Speak to an ASNT NDT Level III
Atlantis NDT provides ASNT Level III consulting, NDT training to ASNT SNT-TC-1A, inspection management software and independent report validation. Request a free consultation and we will return a tailored quote — affordable, accessible and fully customizable to your programme.