| Field Signature Method
(FSM™): The FSM™ technique is non-intrusive and is used to
measure corrosion damage over a relatively large section of a structure. Sensing pins,
strategically positioned over the area of interest, are used to measure the voltage
response to an induced current. This type of measurement between two pins is closely
related to an electrical resistance measurement.
FSM™ technique principle, schematic.
Click on image to enlarge
The sensing pins are typically separated by a distance of 2-3 times wall thickness. It
is the change in the measured voltage distribution (the electrical field
"pattern") that is related to a change in wall thickness of the instrumented
structure. Essentially successive measurements are used for comparative purposes, to
detect a change in the degree of corrosion damage.
FSM™ technique applied to a buried pipeline - image courtesy of
CorrOcean.
Click image to enlarge.
| Smaller pin spacings are associated with increased
resolution in measuring wall thickness loss. Resolution levels ranging from better than
0.1% of wall thickness to 5% of wall thickness, depending on sensor pin and measurement
system configurations, have been reported by the commercial supplier of this technology. |
Published data on resolution and response time of a variety of
corrosion monitoring systems at different corrosion rates.
References/Literature:
M.W. Joosten, K.P. Fischer, R. Strommen, K.C. Lunden: "Internal
Corrosion Monitoring of Subsea Oil and Gas Production Equipment", Materials
Performance, April 1995, pp.44-48.
Links:
Miscellaneous publications by commercial supplier at:
http://www.corrocean.no/pdfs/ListOfPapers.htm
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