Dacon Inspection Services recently held an “8” MFL pipeline inspection” demonstration to show its latest in-line inspection technology to representatives of the Bureau of Natural Gas Business Safety and the Department of Energy Business (DOEB), Ministry of Energy. The objective is to explain how the Magnetic Flux Leakage (MFL) pipeline inspection tools work and how it is different from Ultrasonic (UT) pipeline inspection.
Dacon has over 15 years of experience with Pipeline Inspections however we have always been primarily focused on the use of Ultrasonic technology which is preferred for its absolute measurement of corrosion and wall loss in pipelines. Dacon firstly introduced MFL as one of pipeline solution to Thailand and worldwide market. In this event, Dacon got very good feedback and attention from the DOEB representatives.
Magnetic Flux Leakage (MFL) tools identify and measure metal loss through the use of an axially oriented applied magnetic field. An axial MFL tool induces a magnetic field in the pipe by using powerful magnets to magnetize the pipe wall to saturation. When corrosion or other degradation of the wall occurs, the pipe wall thickness is reduced. At areas of corrosion (reduced wall thickness) the amount of magnetic flux carried is less than that with full wall thickness. This means that there is leakage of magnetic flux at these areas. The reduction in the wall thickness at both outer and inner walls of the pipe can cause the same effect. The tool locates and records magnetic flux anomalies in the pipe and the recorded magnetic flux data is converted to provide an indication of metal loss in the pipe.
The measured flux leakage is dependent on the material characteristics of the pipe, wall thickness, stresses in pipelines, and dimensions of the flaw. Apart from the reduction of wall thickness, a crack in the pipe wall can also cause flux leakage, however, axial MFL employs flux lines that are parallel to the axis of the pipe and can therefore not detect axial stress corrosion cracks or seam weld cracks.
MFL Pipeline Inspection technology gives a quantitative assessment of the amount of corrosion or metal loss in a pipeline. Whilst MFL data cannot be used for the same degree of assessment as Ultrasonic data it is very widely used for 3 main reasons. Firstly, it can be used in gas pipelines whereas Ultrasonic tools can only be used in a pipeline filled with a liquid. Secondly, the tool can gather data whilst travelling at higher speeds than ultrasonic tools thus minimizing pipeline downtime. Thirdly, it is very mature and well proven technology that has consequently led to its price being much lower than that of the more advanced ultrasonic inspection tools.