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I N N O V AT I O N S • V O L . V I I , N O. 4 • 2 0 1 5
A TECHNICAL NOTE ON THE STATE OF NDE
Good pipeline integrity management practices are critical to ensure safe
operation. Current practice for condition assessment is to combine data from one
or more inline inspection (ILI) sensor technologies – such as magnetic flux leakage
(MFL) – and one or more ultrasonic measurement modalities with some sampling
of in-ditch, indenter-based hardness testing, and, potentially, a limited number of
cutout and destructive tests.
Ideally, we would like to have a map of local strength parameters at all points
along a pipeline, similar to those for wall thickness, but with values for yield strength,
tensile strength, transition temperature, and fracture toughness. Currently, there is no
technology that can be added to the ILI tool set to provide such data. For decades, the non-destructive measurement
of mechanical properties has been called one of the “holy grails” of non-destructive testing (NDT). Now there is hope
that some technologies may be able (at least partially) to fill this characterization gap and provide material state to
complement defect maps.
Several groups have reported that when current ILI tool data is reviewed, say for an MFL inspection, distinctive
differences in response (as seen in background color or noise level) are seen between sections of pipe with different
mechanical properties. There remain questions regarding the significance and quantification of these differences and
how these indications – together with the future, appropriately optimized sensor packages – could potentially provide
data that can relate to and estimate pipe properties, such as yield strength.
Research is ongoing to identify the
microstructural features of pipeline steels
that are most relevant in determining the
mechanical properties of interest, and
to identify or develop non-destructive
evaluation (NDE) measurement techniques
for characterizing these features, which
can form the basis for in-ditch material
state assessment. Various ultrasonic
and electromagnetic methods are being
evaluated.
For additional information or to offer to
provide samples of characterized pipeline
steel, please contact the Center for NDE,
Iowa State University –
bondlj@iastate.edu.
Leonard J. Bond,
F.AAAS., F.Inst.P.
DIRECTOR – CENTER FOR NONDESTRUCTIVE EVALUATION,
IOWA STATE UNIVERSITY
Industry Commentary from Around the World
NDE DATA SAMPLES
Yield Strength Data – Stress Strain Curve
Actual Wall Thickness (AWT) Data
Phased Array
Yield Strength Data – Load vs. Depth