Alternating Current Field Measurement (ACFM)

ACFM stands for Alternating Current Field Measurement. It is a non-destructive testing (NDT) technique that is primarily used for the inspection of ferrous materials, such as steel, to detect and size surface-breaking cracks and other defects. key features and aspects of Alternating Current Field Measurement (ACFM)

Eddy Currents

When the alternating magnetic field encounters a surface-breaking crack or defect, eddy currents are induced in the material. The presence of the crack disrupts the flow of eddy currents, creating a measurable change in the magnetic field.


ACFM is commonly used in industries such as oil and gas, maritime, and aerospace for inspecting structures, pipelines, and other components where the detection and sizing of surface cracks are critical for safety and integrity.

Portable Systems

ACFM systems are often portable, allowing for on-site inspections. This portability is valuable for inspecting components in their operational environment without the need for extensive disassembly.

Detection and Measurement

A receiver in the ACFM system detects the changes in the magnetic field caused by the presence of defects. By analysing these changes, the system can identify the location and size of the defects.


ACFM has several advantages, including the ability to inspect surfaces with coatings, the provision of quantitative data on defect size, and the capacity to detect defects in various orientations.

• Quantitative Analysis.
One of the advantages of ACFM is its ability to provide quantitative data about the size of surface cracks. This quantitative analysis makes it a valuable tool for assessing the severity of defects and determining whether they meet acceptable standards.

• Surface Inspection.
ACFM is particularly useful for inspecting surfaces that may be coated or covered with paint, rust, or other materials. It can effectively detect and size defects even when they are not visible to the naked eye.

Complement to Other NDT Techniques

ACFM is often used in conjunction with other NDT techniques, such as ultrasonic testing or magnetic particle inspection, to provide a more comprehensive assessment of the material’s condition.
ACFM is a valuable NDT technique for the detection and sizing of surface-breaking cracks and defects in ferrous materials. Its ability to provide quantitative data and its suitability for inspecting coated surfaces make it a versatile tool in various industries.