Page 15 - Oil and Gas Simulations
P. 15


	 The corresponding signals Bx (tangential      FIGURE 1. Magnetic field components resulting from an ACFM measurement.
magnetic field) and Bz (normal magnetic
field) are shown in Figure 1. The uniform       performance, leading to its acceptance     Germanischer Lloyd. As all data is stored,
input current is disturbed by the presence      by major certification authorities around  irrespective of whether or not a default
of a surface-breaking defect, and the lines     the world including Det Norske Veritas     is found, the results are available for
of current are forced to flow around the        (DNV), the American Bureau of Shipping     audit or review by an independent expert
ends of the crack. The Bx signal shows a        (ABS), the Bureau Veritas Group, and OCB   without the need to revisit the site. v
peak where the lines of current are closely
concentrated, and a trough where they           ABOUT THE AUTHORS
are sparsely distributed. A clockwise flow
is translated into a positive Bz peak, and      Filip Van den Abeele holds an MS in Mechanical Engineering and a Ph.D. in
the counterclockwise flow is reflected in       Engineering Sciences from the Soete Lab at Ghent University, Belgium. He has
the negative Bz signal.                         recently completed his MS in Ocean and Offshore Technology at Cranfield
	 More complex ACFM probes are                  University, UK. Abeele is working as a simulation expert at OCAS NV, a joint
available containing multiple inspection        venture between ArcelorMittal and the Flemish Region. His main research
sensors. These are known as ACFM                focuses on offshore pipeline design and vortex induced vibrations, and he is
arrays and they allow larger areas to be        actively promoting the use of multiphysics modeling for the oil and gas industry.
inspected in a single scan. ACFM arrays         	 Patrick Goes studied physics and philosophy at Ghent University and holds
can also be fitted with position encoding       an MS in both disciplines. From 1985 on he has been involved in software
to allow a complete record of the distance      development, mathematical modeling, and the development of electron beam
traveled and the exact location of defects      texturing technology (EBT) at ArcelorMittal Gent. In 2005 he joined OCAS NV as
to be found. Examples of such systems           a senior research engineer, responsible for modeling and simulation, multiphysics
developed for the oil industry include          finite element analysis, and fatigue analysis.
the automated system that was built for
Statoil in Norway to inspect the company’s
titanium drilling risers.


Inspections of undersea risers using
conventional methods normally include
the cost of installing temporary access
platforms, paint removal, the inspection
itself, repainting, and finally removing
the temporary access. Depending on
the application, in some cases it is even
necessary to shut down the plant to reduce
temperatures before the inspection can
take place. If coating removal and the
construction of access platforms can be
avoided, very significant cost savings are
possible, not only in direct costs but also by
reducing the duration of interruption.
	 Time and cost savings of up to 60
percent have been reported in some
industries by the introduction of the
ACFM technique. For the past three years,
ACFM has been used by PETROBRAS for
the inspection of selected structural welds
on a fixed and floating (semisubmersible)
platform located in the Campos Basin.
Excellent results have been achieved
and the estimated savings compared
to conventional inspection methods
employing magnetic particle inspection
(MPI) is $1.5 million.
	 Of course, this new technique has
benefits beyond just saving money. It
is also important that quality not be
compromised. Trials of the technique have
been compared with MPI and show good

                                                                                           COMSOL NEWS                   15
   10   11   12   13   14   15   16   17   18   19   20