Magnetic flux leakage
Analysts interpret the chart recording of the leakage field to identify damaged areas and to estimate the depth of metal loss.
Utilizing the information from an MFL ILI inspection is not only cost effective but can also prove to be an extremely valuable building block of a Pipeline Integrity Management Program.
Originally designed for detecting areas of metal loss, the modern High Resolution MFL tool is proving to be able to accurately assess the severity of corrosion features, define dents, wrinkles, buckles, and cracks.
In some countries, a pig is known as a "Diablo", literally translated to mean "the Devil" relating to the shuddering sound the tool would make as it passed beneath people's feet.
An MFL tool is known as an "intelligent" or "smart" inspection pig because it contains electronics and collects data real-time while traveling through the pipeline.
Sophisticated electronics on board allow this tool to accurately detect anomalies as small as 1 mm2, which can include dimensions of a pipeline wall as well as its depth and thickness.
Other designs of smart pigs can address other directional data readings or have completely different functions than that of a standard MFL tool.
Oftentimes an operator will run a series of inspection tools to help verify or confirm MFL readings and vice versa.
This section can be split into a number of bodies depending on the size of the tool, and contains the electronics required for the PIG to function.
The remaining flux leaks out of the pipewall and strategically placed tri-axial Hall effect sensor heads can accurately measure the three-dimensional vector of the leakage field.
To more accurately predict the dimensions (length, width and depth) of a corrosion feature, extensive testing is performed before the tool enters an operational pipeline.
The algorithms and neural nets designed for calculating the dimensions of a corrosion feature are complicated and often they are closely guarded trade secrets.
In this way, the effective area of metal loss can be calculated and used in acknowledged formulas to predict the estimated burst pressure of the pipe due to the detected anomaly.
Open lines of communication usually exist between the inspection companies and the pipeline operators as to what was reported and what was actually visually observed in an excavation.
The three components of the MFL vector field are viewed independently and collectively to identify and classify corrosion features.
where large non-axial oriented cracks have been found in a pipeline that was inspected by a magnetic flux leakage tool.
To an experienced MFL data analyst, a dent is easily recognizable by trademark "horseshoe" signal in the radial component of the vector field.
