oxidation - ANSWERSloss of electrons, positive charge atoms (anode)
reduction - ANSWERSgain of electrons, negative charged atoms (cathode)
forms of corrosion - ANSWERSuniform, crevice, galvanic (dissimilar metals) if two metals have to be couple then best to couple metals close together in t...
oxidation - ANSWERSloss of electrons, positive charge atoms (anode)
reduction - ANSWERSgain of electrons, negative charged atoms (cathode)
forms of corrosion - ANSWERSuniform, crevice, galvanic (dissimilar metals) if two metals have to be
couple then best to couple metals close together in the galvanic series, pitting, intergranular, selective
leaching (dezincification, graphitization), velocity phenomena, environmental cracking (corrosion
fatigue, hydrogen embrittlement, SCC (Carbonates/bicarbonates)
High PH - ANSWERSLow hydrogen, alkaline, easy polarization
Low PH - ANSWERShigh hydrogen, acidic, harder to polarize
High oxygen/High Hydrogen concentration - ANSWERSharder to polarize, work at the cathode only,
called cathodic depolarizers.
B. concentration cells (oxygen, temp, etc.) In an oxygen concentration cell, what is the anode? (i.e. the
area with more or less oxygen?) In a metal ion cell, which area is the anode (i.e. the area with the
greater of lower concentration)?
C. Anaerobic bacteria (MIC) Absence of oxygen, depolarizer
polarization - ANSWERSa. corrosion current reduces with polarization
b. polarization increases with CP current applied
c. Occurs at surface of both anode and cathode.
,shielding - ANSWERSa. shorted casings
b. proximity of other structures
c. reinforced concrete
amphoteric materials - ANSWERScorrode at low and high pH
on potential - ANSWERSnative + polarization + IR drop
,test stations - ANSWERSallow electrical connection to structure for potential measurements and bonds.
Spans allow current and direction (IR drop).
inistall during construction
pH - ANSWERSmeasure of acidity(hydrogen ion concentration)
high pH is alkaline
low pH is acid
pH is a log function therefore each increase in pH is a factor of 10.
RECTIFIER - ANSWERS- positive to anode
-negative to structure
- AC suppy
-AC circuit breaker
-Transformer (increase or decrease voltage)
-AC fuse
-rectifier bridge - diodes change AC to DC
-Voltmeter and Ammeter
-Surge Protection
-Filters
Esecondary = (Eprimary x Secondary turns) / primary turns
Reference electrode location - ANSWERSthe reference electrode should be placed as close to the
structure as practical. (underground piping or tanks- over the center of the structure, multiple readings
along the structure as required)
internal surfaces of storage tanks, waterfront and offshore structures (as close to the wall as possible)
impressed current vs sacrificial - ANSWERSimpressed current- higher current, better control
, sacrificial- no power required, less maintenance, easy to install, less land
AC considerations - ANSWERScapacitance, inductance, and resistance
hazardous AC potential - 15 Vac
Safe method of connecting ground0 cable to ground then to pipe
arcing hazards
corrosion rates from AC (current density)
switching or pulse rectifiers
Reference cells - ANSWERSCuCuSO4- most common, (soil, fresh water)
AgAgCL - seawater
Calomel- lab
Hydrogen - standard (lab)
zinc- stationary
Cathodic Protection - ANSWERSprotect the cathode
attempts to bring the cathode potential as negative as the anode potential
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