Corrosion effects of stray currents on underground steel pipelines

Report
Stray currents corrosion
of underground steel pipelines
Groza Stefana
Madalina
ISBE, 2nd year
ELECTROMAGNETIC POLLUTION
Earth’s molten
iron-nickel core
Charged gases of
the ionosphere
Resonances
Biological time clocks
DISORIENTATION
DISCOMFORT
MAN
ANIMAL
PLANT
DEATH
ALL TYPES OF BACKGROUND RADIATION
HAVE INCREASED SO DRASTICALLY AND SO
QUICKLY IN THE LAST FIFTY YEARS THAT WE
CAN NO LONGER HOPE TO COPE WITH THEM.
STRAY CURRENT CORROSION
ELECTROMAGNETIC FIELDS
THERMAL
SIDE EFFECT
ELECTRIC AND
MAGNETIC
COMPONENTS
NATURAL PROCESSES
TECHNOLOGICAL
AND INDUSTRIAL
DEVELOPMENT
PRODUCTION AND
CONSUMPTION OF
ELECTRICITY
ELECTROMAGNETIC
POLLUTION
THE CORROSION OF THE UNDERGROUND STEEL PIPELINES
The first mobile
laboratory specialized in
investigating and
determining the
dispersion in DC currents
(Los Angeles, 1910)
Stray currents may originate from
• cathodic protection system
• electrical welding machines
• grounded dc electric sources
• street railway systems, etc
DC traction system
Stray current
corrosion
In this case rails act as primary current return path and the surrounding ground acts
as a conductor that can carry stray currents. There is a fundamental tendency for the
return current in the rails to flow from the train to the substation. Because the tack is
not perfectly insulated from the ground, there is a tendency for the current to flow in
the ground in the same direction. Here the stray current will be picked up by the
pipeline near the train and discharge near the substation.
The corrosion resulting
from stray currents
(external sources) is similar
to that from galvanic cells
(which generate their own
current) due to the fact
that the corroding metal is
again considered to be the
anode from which current
leaves to flow to the
cathode.
Soil and water characteristics affect the corrosion rate in the same manner
as with galvanic-type corrosion.
Despite the apparent similarity, stray current strengths may be
much higher than those produced by galvanic cells and thus corrosion may
be much more rapid. Moreover, seeking the path of least resistance, the
stray current from a foreign installation may travel long distances along a
pipeline causing severe corrosion where it leaves the line.
Accentuated
degradation of the
fastened elements in
the Budapest’s
subway
The corrosion of the
gas pipes due to the
stray DC currents
which originate in
Bucharest’s tram and
subway
Damages of the
pipeline in Cluj-Napoca
Stray current corrosion prevention
Eliminate or reduce stray current
Acting on the source instead on the consequences
Increasing the global circuit resistance
• sacrificial anodes
CATHODIC • impressed
PROTECTION
current/voltage
anodes
• varying the
boosting DC
voltage
CURRENT
DRAINAGERS • changing the
resistance of the
direct connection
• bringing the galvanic
potential of the metal to a
level where the anodic
reactions are impossible for
the given circumstances
• an external current that
reduces or inverses the
anodic current.
• possible when the
sources of the stray
currents are accessible
• the connection is made
unidirectional, such that
current can only flow
from the buried
structure to the negative
pole of the DC source,
thus rounding the
electrolyte (the soil)
Bibliography
www.radioamator.ro
www.corrosion-doctors.org
www.enotalone.com
www.google.com

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