GALVANIC CORROSIONGALVANIC CORROSION Corrosion as a result of
the electrical contact of different met Corrosion as a result of
the electrical contact of different metals. als. Galvanic series:
understand and use it properly! Galvanic series: understand and use
it properly! Insulate anode from cathode if possible. Insulate
anode from cathode if possible. Area ratio of anode and cathode is
important. Area ratio of anode and cathode is important.Avoid
unfavorable ratio of small anode to large cathode. Avoid
unfavorable ratio of small anode to large cathode.Weld metal, bolts
& nuts, rivets should be more noble than the s Weld metal,
bolts & nuts, rivets should be more noble than the substrate
ubstrate UnderstandUnderstand noble metal coating noble metal
coating concept. concept.Never just specify coat the anode only.
Never just specify coat the anode only. Careful in using copper
tube, Hg Careful in using copper tube, Hg- -containing manometers.
containing manometers.Galvanic corrosion Galvanic corrosionGalvanic
corrosionGalvanic corrosionSTS/carbon steel STS/carbon steel STS
STS- -Cu CuCORROSION of Al LAMELLAECORROSION of Al LAMELLAEAl Al-
-Cu CuAl Al- -STS STSGALVANIC SERIESGALVANIC SERIESChange in
environment?Change in environment?A new series should be
established.A new series should be
established.--ComplexingComplexingions, pH, temperature, velocity
ions, pH, temperature, velocity ....--Potential (SCE) of
highPotential (SCE) of high--alloy STS in sea water alloy STS in
sea water (SW)(SW)Deaerated SW:Deaerated SW:- -450 mV 450 mVSW with
200 ppb O SW with 200 ppb O2 2: : - -100 mV 100 mVHot SW: Hot SW:
100 mV 100 mVNatural, aerated SW: Natural, aerated SW: 300 mV 300
mVChlorinated SW: Chlorinated SW: 600 mV 600 mVCh i l l i hGalvanic
Corrosion by Potential ReversalGalvanic Corrosion by Potential
Reversalbicarbonate, nitrate bicarbonate, nitratesulfate
sulfatephosphate phosphateGalvanic Corrosion by Copper
DepositionGalvanic Corrosion by Copper DepositionCooling water
systems: corrosion of steel after deposition of co Cooling water
systems: corrosion of steel after deposition of copper.pper. FORMS
OF GALVANIC CORROSIONFORMS OF GALVANIC CORROSION Contact corrosion
Contact corrosion Deposition corrosion Deposition corrosionCathodic
contamination of anode via deposition of more nobleCathodic
contamination of anode via deposition of more noble metals or metal
oxides metals or metal oxides Reversal of potential Reversal of
potential Thermogalvanic corrosion Thermogalvanic
corrosionPreferential attack at the hot area when metal is
subjected to a Preferential attack at the hot area when metal is
subjected to athermal gradient. thermal gradient.GALVANIC CORROSION
CELLGALVANIC CORROSION CELLTypical conductivity values: Typical
conductivity values:Fresh distilled waterFresh distilled water0.5
0.5- -22 S/cm S/cmStored distilled water Stored distilled water 2
2- -44 S/cm S/cmSupply water Supply water 50 50- -15001500 S/cm
S/cmSea water Sea water 40,00040,000 S/cm S/cmSat.Sat. NaCl NaCl
solution solution 250,000250,000 S/cm S/cmSulfuric acid Sulfuric
acid