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WorksheetsCATHODIC PROTECTION
Total questions: 29
Worksheet time: 15mins
4 things that must be present for corrosion to occur
anode,cathode, metallic pathway, electrolyte.
all
?
electrons flow from anode to cathode through metallic pathway. the ions flow from anode to cathode through the electrolyte and that wastage of metal, corrosion, occurs at the
anode
metallic pathway
cathode
electrolyte
cathodic protection 1 amp for 1 yr removes 23.5lbs of
iron
coating
solvents
none
cathodic protection is used to protect structures, which are ? we will call the environment from which the structure is being protected the electrolyte.(so water is electrolyte)
buried
submerged in water
used contain liquids, (primarily water based or contain some water)
all
cathodic makes use of a flow of electric current through whatever the structure is
buried in
submerged in
or what ever structure contains.
all
one reason for applying coatings to structure, to provide electrical insulation between the structure and electrolyte.
true
false
cathodic protection definition
is the reduction or elimnation of the corrosion by making the structure to be protected a cathode by means of an impressed current or attached to a galvanic anode(magnesium, aluminum, or zinc)
none
how cathodic protection works
cathode is the electrode, prior to applying cathodic protection,(steel has cathodic and anode areas) if the anodic areas of steel are converted to cathode, then entire steel would be a cathode, corrosion will be satisfactorily controlled.
yes
how cathodic protection works according to nace 2 book
direct current electricity to a corroding metal, cause structure to become cathodic.
D.C Power + to anode, - to pipe(cathode), direct current is flowing from the anodic areas into the soil, through the soil and onto the cathodic areas, and back through the pipe itself to complete the circuit.
driving voltage(galvanic potential between anode & cathode) amount of current is limited by resistivity of the enviroment(ohm-centimeters)& degree of polarization at anodic & cathodic areas.
corrosion results at the current discharge from metal to electrolyte(soil) at anodic areas. will current flows from enviroment to pipe(cathodic areas) no corrosion
all
cathodic protection current flows into the environment from a special ground connection called
ground bed
soil connection gel
sol connection
grounded soil
cathodic protection systems can be monitored by measuring the electrical potential (voltage) of the protected structure with a reference cell ,can be,(?) and a special voltmeter.
copper, copper sulfate, silver, silver chloride, mercury,
base upon a specially refined high-purity zinc
both
two types of cathodic protection systems
galvanic
impressed current
both
galvanic systems
(dissimilar metals in contact) more active is anode
sacrificial anode can be described as a metal that will have a voltage difference with respect to the corroding structure and will discharge current which will flow through the environment to the structure.
galvanic anodes, corrode preferentially ot the protected structure, providing protection to the structure.
materials suitable for use as galvanic anodes include(aluminmum,magnesium, zinc.)
all
anodes are cast in numerous weights and shapes to meet (
cathodic protection design requirments
?
Impressed current systems
ground bed anodes are not the source of electrical power, instead, an external source of direct current power is connected (impressed) between the structure to be protected and the ground bed.
all
the positive terminal of the power source always must be connected to the
ground bed
pipe
both
impressed current systems anodes
ground bed anodes forced to discharge current will corrode
important to use a anode materials that consumed relatively low rates
permit designing ground beds that discharge large amounts of current and still have long service life.
all
types of materials used to make impressed current (anode)
scrap steel, graphite, iron oxide
high silicon chromium-bearing cast iron
platinized niobium & titanium
all
impressed current power sources
rectified commercial power
solar cells,generators,fuel cells,
wind powered cells, thermoelectric cells
all
? is a device which uses power from electric utility lines to convert the alternating current to a lower voltage direct current by means of step down trasformer
rectifier
converter
both
factors of cathodic protection system
regulatory requirements, economics, metal to be protected, service requirements, total current requirments, variations in environment
protective coatings, electrical shielding, maintenance, stray current effect, temperature, wire and cable, anode backfill
all
problem areas when using cathodic protection system
resistance/throw
cathodic disbondment
inspection criteria
all
? is a minimum requirement for protection
-.85v
1amp
1v
all
in order to protect structure to be maintained at this voltage, some areas will see a increase in ? voltage(potential)
more negatie
more positive
none
due to size, design, placement of the anodes, type and resistance of the electrolyte, this increased negative potential can result in a phenomenon known as
cathodic disbondment
reduction heating
oscillation
resistance and throw aka caused increase in negative voltage causing
cathodic disbondment
none
stable cathodic impress current at -negative .85v
will usually have no effect on coating
will cause cathodic disbondment
when voltage goes above negative -0.85v the increase in the negative voltage will cause
hydroxyl(OH) FORMATION
CATHODIC DISBONDMENT
BOTH
NONE
AS VOLTAGE INCREASES PASS -.85V EVEN MORE THE NEGATIVE INCREASE VOLTAGE WILL CAUSE CATHODIC DIS-BONDMENT BY
HYDROGEN (H)
HYDROXL OH
BOTH
