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Alternating Current Field Measurement - ACFM - Electromagnetic NDT

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Alternating current field measurement
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Alternating current field measurement (ACFM) is an electromagnetic inspection technique used to size and detect surface breaking cracks in metals and welds. As a non-destructive testing technique, it combines the advantages of the alternating current potential drop (ACPD) technique and Eddy Current Testing (ECT) in terms of defect sizing without calibration and the ability to work without electrical contact respectively.

The ACFM probe introduces an electric current locally into the part and measures the associated electromagnetic fields close to the surface. The presence of a defect disturbs the associated fields and the information is graphically presented to the system operator. The ends of a defect are easily identified to provide information on defect size and location. Through wall extent of the flaw plays an important role in determining structural integrity and the same is calculated using mathematical computation, thus allowing an immediate evaluation of the implication of the indication. The ACFM technique can be performed through paint and coatings, hence it is considered to be a faster and more economic technique than many others (e.g. magnetic particle inspection (MPI)).

Insights

Find out more about alternating current field measurement testing at TWI:

Research 1

ACFM Testing on Train Bogie

TWI conducted a project to determine the feasibility of using ACFM testing to inspect train bogies without removing the surface coating.

Learn more
Research 2

ACFM Storage Tank Weld Inspection

TWI conducted a project aimed to determine the feasibility of using ACFM to inspect the floor of a storage tank without removing the surface coating.

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Research 3

A Novel NDT Technique for Inspecting Offshore Structures

The use of a remote operated vehicle to conduct ACFM testing for the sub-sea inspection of offshore structure welds.

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Core Research Programme (CRP) and Joint Industry Projects (JIP)

Core Research

Each year the TWI Core Research Programme (CRP) addresses challenges on behalf of our Industrial Members as well as developing specific technologies and processes. Each of the projects under the CRP is focussed on engineering, materials or manufacturing technologies.

Find out more here

Joint Industry Projects

TWI also conducts Joint Industry Projects (JIPs) that bring together groups of Industrial Members to share the cost of research activities in areas of mutual industrial interest, gaining exclusive access to the outcomes. These projects cover a broad range of topics.

Find out more here

Alternating Current Field Measurement at TWI

Our experts provide ACFM testing and support with our state-of-the-art Amigo ACFM system supplied by Technical Software Consultants (TSC), which is accompanied by special probes. The induction coil typically operates at 5 kHz with standard probes and 50 KHz with special high-frequency probes. The 50 kHz high-frequency probes are typically used to obtain higher test sensitivity for nonmagnetic conductive materials.

Example Applications

  • Detection and sizing of fatigue cracks and hydrogen cracking
  • Fillet weld inspection in mobile offshore drilling units
  • Inspection of fillet welds in highway bridge
  • Inspection of rail components
  • Inspection of gear box, gear teeth, crank shafts, cylinder heads, turbines, etc. in aerospace industries
  • Detection and sizing of surface breaking cracks and corrosion in vessels, storage tanks, and piping in the oil and gas and the power generation industries
  • Inspection of drilling tools
  • Inspection of various components in the automotive industry

Benefits

ACFM offers a number of benefits, including:

  • Applicable for base material or welds, ferritic or non-ferritic conductive metals
  • Can be used on hot surfaces, underwater, or in irradiated environments
  • Provides both depth and length information
  • Accurate sizing of defects up to 25mm in depth
  • Requires minimal surface preparation and can be applied over paint and other coatings
  • Applicable for under water inspection as well as normal inspection
  • Inspection data can be stored and analysed offline
  • Inspection can be encoded

Because we operate as an independent and impartial organisation, our experts will provide the most suitable testing technique to meet your needs. For more information about TWI's NDT techniques and services, including ACFM, please email contactus@twi.co.uk.

For more information please email:


contactus@twi.co.uk