An AC Magnetic Flux Leakage (MFL) survey is a method used in the pipeline industry to inspect pipelines for corrosion and metal loss.

It involves the use of specialized tools, such as magnetic field sensors, which are placed around the pipeline. An alternating current (AC) signal is then passed through the pipeline, causing a magnetic field to be generated. The magnetic field sensors detect changes in the magnetic field, which are caused by the leakage of magnetic flux from the pipeline wall. The location and size of these changes are used to identify areas of the pipeline that may be experiencing corrosion or metal loss.

The advantage of AC MFL surveys over other methods, such as ultrasonic testing, is that they can be performed without the need to physically access the inside of the pipeline. Additionally, they can be performed while the pipeline is in service, making them a convenient and efficient option for pipeline operators.

It is important to note that while AC MFL surveys are a useful tool for detecting corrosion and metal loss, they are not capable of detecting all forms of corrosion. In cases where corrosion is present on the inside of the pipeline, other inspection methods, such as internal pigs, may be required to properly assess the condition of the pipeline.