Zinc
Ribbon Anodes - AC Mitigation
AC
Mitigation | Cathodic Protection
| Above Ground Storage Tanks
Grounding Rods | Grounding
Mats
Technical Practices Document
1- Connection Practices
Technical Practices Document
2- Connection Practices - Crimps
The
long-term trend in the United States and many other
countries is shared land use for pipelines and other
utilities. This movement has increased the number of
overhead high voltage transmission lines parallel to
and sharing a corridor with an underground pipeline.
This combination has increased the need for grounding
of the pipeline to dissipate interference.
In these systems, A.C. voltages are transmitted 1°
the pipeline by conductive or inductive interference.
Magnetic induction acts along the pipeline or pipeline
segment that is approximately parallel to the power
line and can cause significant pipeline potentials even
at relatively large separation distances.
Consideration must be given to safety of personnel and
the public who may come into contact with above ground
portions of the pipeline such as valves and test stations.
These exposed structures can be a potential shock hazard
when touched while the soil is at a significantly different
potential.
Advances
in interference control have resulted in the gradient
control wire method. This method consists of one or
more bare zinc conductors buried parallel to and near
the pipeline and regularly connected to it. Plattline™
zinc ribbon anode used in this way is very effective
in mitigating excessive pipeline potentials due to both
inductive and conductive interference. (See Figures
] & 2.) Plattline evens out pipeline and soil potential
differences. Additionally, Plattline can provide cathodic
protection to the pipeline.
It
is important to review the use and design of a gradient
control wire system with an engineer experienced with
this system, as its performance will depend on the multilayered
structure of the earth.
For inductive interference, gradient control wires provide
additional grounding for the pipeline and decrease the
induced pipe potential rise. At the same time, they
raise local ground potentials, thus sharply reducing
touch potentials and coating stress voltages.
For conductive interference, gradient control wires
dampen the soil potential rise close to the pipe while
raising pipe potentials, thus providing reduced touch
voltages and decreasing coating stress voltages.
Life expectancy of Plattline in this application would
be quite long and would generally be determined by Plattline
as a projected cathodic protection system. The most
common sizes of Plattline for AC mitigation are plus
and standard.
 Plattline
can provide a significant means to mitigate potential
gradients along the length of a pipeline. Importance
must also be placed on reducing the potentials at valve
sites, metering stations, pig launchers and receivers
and other accessible installations for worker safety.
Gradient control grids or grounding mats raise local
ground potentials in the same way gradient control wires
do. These grounding mats can be made in several forms.
Spiral and rectangular designs are generally standard
for grounding mats. These are shown in Figures 3, 4
and 5. The most common size of Plattline for grounding
mats is standard.
Reference should be made to NACE Standard RP0177 (Latest
Revision) - Recommended Practice on Mitigation of Alternating
Current & Lightning Effects on Metallic Structure
and Corrosion Control Systems. Also, ANSI/IEEE Standard
80 specifies safety design criteria for determining
maximum acceptable touch and step voltages during fault
conditions.
Finally, during fault conditions on the power line,
the system must ensure that pipeline coating stress
voltages remain within acceptable limits to prevent
coating damage and damage to the pipeline steel. Coating
damage can occur in the range of 1000 - 2000 volts for
bitumen based coatings and in the range of 3000 - 5000
volts for polyethylene or fusion-bonded epoxy coated
pipelines.
Zinc
Ribbon Anodes Continued>
E-mail:
plattline@plattbros.com
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