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CP BLOG Continued from page 37
soil surface. This phenomenon might also help release any gas trapped in the inter- face due to the anodic reaction. One way to prove that this situation is not happening is to measure the circuit resistance after the system is working. If gases are generated during the anodic reaction and cannot by released, it is most likely that the circuit resistance
will increase. I do not remember seeing this change in the circuit resistance in regular aboveground tank CP systems. Of course, you have to be sure that you are taking the measurements with all other conditions remaining the same; for example, measure the tank liquid level every time you are inspecting the tank CP system.
good design with other systems might work as well or in some cases even better depending on the conditions and work- manship. You can design with MMO using a spiral or several concentric circles.
A
Alternating current corrosion of buried pipelines
on buried steel pipelines is related to overhead AC power
Q
that most of the high-voltage power ca- bles have some kind of metal armor that provides some degree of shielding of the UIOVM\QK ÅMTL 0W_M^MZ QVL]KML )+ voltages depend on many factors: ground- ing design, separation, parallelism, cable type, load conditions, soil conditions, etc. Every case should be addressed sepa- ZI\MTa 1 _W]TL LMÅVQ\MTa \ISM I KTW[MZ look.
A 38 MATERIALS PERFORMANCE March 2012
transmission lines. If, however, there is an underground
high-voltage (14.4 kV) AC duct bank near a steel pipeline, does it have the same effect as overhead AC power lines? In other words, does it matter whether the AC lines are overhead or underground when determining if they might cause AC corrosion on the steel pipe?
In general, the induced AC volt- age is lower from underground cables than overhead power lines. The main reason for this is
Most of the literature that I have read re- garding alternating current (AC) corrosion
I prefer the MMO grid system, mostly because I believe the re- sistance will be quite low and the installation is really fast. Any
NACE International, Vol. 51, No. 3