Magnetic Flux Leakage Technical Articles
Magnetic Flux Leakage Technology - JC Drury
Magnetic Flux Leakage (MFL) technology has been used in the monitoring of
Underfloor or Far Side (FS) corrosion for about 11 years. Silverwing (UK)
Ltd entered the field ten years ago, in 1991. As with all Non Destructive
Testing methods, MFL has both advantages and disadvantages, as well as
pitfalls for the unwary. This paper attempts to explain the underlying
principles of the method and highlights the advantages, disadvantages and
pitfalls.
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A comparison of the magnetic flux leakage & ultrasonic methods in the
detection & measurement of corrosion pitting in ferous plate & pipe - JC
Drury
Presented at the 15th World Conference in Rome 2000
Magnetic Flux Leakage (MFL) and manual Ultrasonics (UT) have been used
extensively for the detection and sizing of corrosion pits in ferrous
plates and pipes. Users and providers of these inspection services may have
different perceptions and expectations of the sensitivity and accuracy of
the methods. This paper discusses the underlying principles of the methods
and their effect on Probability of Detection (POD) and accuracy. It
addresses the limitation on accuracy of the ultrasonic method due to pit
shape and reflectivity, and also, for the first time, takes a quantitative
look at the effect of pit volume on MFL results.
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Corrosion pitting - How good is manual ultrasonics? - JC Drury
Presented at the ASNT Fall conference 2000 Indianapolis
During the last three years my interest in the use of ultrasonics for the
detection of corrosion and the measurement of remaining wall thickness has
been re-awakened. The method has been extensively used to verify and
quantify Magnetic Flux Leakage (MFL) results. Discrepancies between
ultrasonic and MFL results have usually been put down to "Another MFL false
- call." However, having watched many ultrasonic tests being carried out, I
have come to believe that the boot is often on the other foot and that we
place too much faith in the ultrasonic method for corrosion monitoring. The
techniques used by many practitioners give rise to serious shortcomings in
both probability of detection, and accuracy of remaining wall assessment.
These shortcomings are not confined to corrosion monitoring of flat plate,
but apply equally to pipe and vessel inspection. This paper looks at the
root causes of poor performance with ultrasonics and suggests some methods
to improve the situation.
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