NDT Knowledge
Discrimination of top and bottom discontinuities with MFL and the Surface
Topology Air-gap Reluctance System (STARS)
Published at the Australian Institute for Non Destructive Testing
Discontinuities due to corrosion can occur on the top and bottom surface of
above ground storage tank (AST) floors and can, if unknown increase the
likelihood of a leak as inadequate repair strategies may be applied. Although
surface discrimination can in some cases be achieved visually, low lighting
conditions and in particular ASTs with opaque coatings on the top surface of the
floor make the task of identifying top surface discontinuities dicult. This
paper presents a novel approach to the problem of discriminating top and bottom
discontinuities, an approach that has been incorporated into the next-generation
of Floormap MFL scanner (Floormap3D) developed and manufactured by Silverwing
(UK) Ltd...
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The influence of maintenance on the life cycle of above ground storage tanks
Published within INSIGHT magazine June 2012 edition
In supply chains such as those in the petrochemical industry, the above ground
storage tank (AST) plays an important role in ensuring a continuous flow of
product and these like other components must undergo regular maintenance. While
maintenance on the majority of surfaces of the typical AST can be conducted when
in its normal operational condition, the AST floor presents a particular
challenge because of its inaccessibility. As a consequence the tank has to be
periodically emptied and made out-of-service to conduct inspections and repair
work deemed necessary. This is a costly activity both in terms of loss of
earnings and the maintenance operation itself...
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Practical limits of MFL in steel plate inspection
Presented by Neil Pearson at the 18th World Conference for Non Destructive Test (18th WCNDT)
Magnetic flux leakage (MFL) is a widely used approach to detect corrosion in
applications where large areas are to be inspected in short time scales. A
particularly good example is in above ground storage tanks (ASTs) within the
petrochemical industry where tank floors are inspected periodically, calling for
the AST to be taken out-of-service and emptied. This makes maintenance times
that much more expensive and calls for techniques that are both reliable and
fast. MFL is widely used in the context because of its inherent speed. Magnetic
flux leakage (MFL) is a widely used and accepted technology for locating defects
on a tank floor. While MFL signals are often linked to the volume of a defect,
its depth is perhaps the most dicult to estimate and the most critical
dimension since it indicates the closeness of a potential leak and if
misinterpreted can lead to erroneous repair strategies with costly outcomes.
Therefore, accurately determining the geometry of defects is pivotal if an
optimum repair strategy is to be formulated...
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A study of MFL signals from a spectrum of defect geometries - Poster
Presented by Neil Pearson at the 18th World Conference for Non Destructive Test (18th WCNDT)
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The challenge to asset owners and operators is to use new systems to reduce out of service time during inspection and improve schedules increasing inspection activity
Published within Tank Storage Magazine Vol 8 Issue 2 March 2012
Storage tanks are an essential part of the distribution network and are vital in
buffering the varying demands of end users. They are most commonly built from
steel with thickness from 5-15 mm. Steel is a relatively cheap and strong
material that can easily fabricated on site but does have inherent problems of
corrosion over time...
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What preparation is required before a magnetic
flux leakage (MFL) tank inspection takes place?
General questions and answers tank preparation prior to an MFL inspection
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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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