New Sensor Could Help Avert
10/3/2008 - National Institute of Standards and Technology (NIST)
Researchers at the National Institute of Standards and Technology (NIST)
and Colorado School of Mines (CSM) have developed a prototype sensor
that quickly detects very small amounts of hydrogen accumulation in
coated pipeline steel.
The new sensor could provide
early warning of pipes that have accumulated excessive amounts of
hydrogen—a notorious source of embrittlement—and avert potentially
disastrous failures of pipelines carrying hydrogen fuel.
Hydrogen is attractive as a fuel because it burns cleanly without
carbon emissions and can be derived from domestic sources.
However one long-recognized
challenge is that hydrogen can cause gradual embrittlement in
conventional pipelines by slowly diffusing into the metal.
The NIST/CSM sensor, described
today at the 7th International Pipeline Conference,* could monitor
for hydrogen buildup before a pipeline actually fails in service, or
during testing or production.
The nondestructive, non-contact hydrogen sensor is approximately 4
square inches and is designed to be a portable sensor to make
measurements on excavated or unexcavated pipeline steels.
The sensor sends a current
through the pipe and measures changes in impedance (resistance with
a function of depth) as an indicator of hydrogen content within the
steel and the overall steel pipe integrity.
The hydrogen sensor is based on
electromagnetic concepts to generate alternating currents into the
pipeline steel, which in turn induces an opposing magnetic field.
Any change in the hydrogen content in the steel modifies the
current, resistivity, and thus the impedance.
NIST laboratory and field test results show that a pipe's impedance,
and thus resistivity, increases with increasing hydrogen content.
The measurement sensitivity is
exceptional: the sensor can measure hydrogen content levels in
pipeline steel well below 1 part per million (ppm).
High strength pipeline steels
can tolerate only a few parts per million of hydrogen before
significant problems arise.
By contrast, conventional
analytical techniques do not have sensitivity or accuracy below 1
The new hydrogen sensor also
acts as a forewarning or preventative monitoring system to detect
the agents that actually cause the flaws, cracks and defects before
Most traditional nondestructive
tools used in the pipeline industry (such as ultrasonics and
magnetic flux leakage) are used for determination of cracks,
corrosion or other flaws that have already occurred.
The sensor development was supported in part by the Minerals
Management Service and Department of Transportation.
* A. Lasseigne, K. Koenig, J. Jackson, D. Olson, B. Mishra, T.A.
Siewert and J.D. McColskey.
hydrogen sensors to prevent material degradation from hydrogen
damage. Paper presented Oct. 1 at IPC2008, 7th International
Pipeline Conference, Sept. 29 " Oct. 3, 2008, Calgary, Alberta,