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Continued from The
Blog, p. 13.
The following items relate to cathodic & anodic protection.
Please be advised that the items are
not peer-reviewed, and opinions and suggestions are entirely those of the in- quirers and respondents. NACE Interna- tional does not guarantee the accuracy of the technical solutions discussed.
welcomes additional responses to these items. They may be edited for clarity.
Aluminum anodes
standard stipulating the water resistivity values? For example, NACE standards state that zinc with gypsum and bentonite JIKSÅTT IZM ][ML QV [WQT[ PI^QVO ZMTI\Q^MTa TW_ ZM[Q[\Q^Q\a $
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amount of chlorides to operate the anodes will have a low resistivity, but resistivity Q[ VW\ \PM SMa NIK\WZ ?M KW]TL PI^M I medium with low resistivity, but if there are no chlorides, the anodes will not _WZS )KKWZLQVO \W ; 6 ;UQ\P M\ IT MP
A NACE International, Vol. 51, No. 3 ¤ KU
Normally aluminum anodes are used only in seawater, which has I ZM[Q[\Q^Q\a f ¤ KU -^MV then they have a small amount
WN ITTWaQVO \W XZM^MV\ XI[[Q^I\QWV )T] minum anodes generally require chloride ions in the electrolyte to function prop MZTa )[ \PM Y]IV\Q\a WN KPTWZQLM QWV[ decreases below normal seawater con KMV\ZI\QWV[
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current capacity of the anode decreases, and the anode potential becomes more VWJTM :MNMZ \W \PM NACE Corrosion Engineer's Reference Book, Third Edition, in the chapter "Design Criteria for Off shore Cathodic Protection Systems" X
Aluminum alloy anodes require the presence of chloride ions to XZM^MV\ XI[[Q^I\QWV 7J^QW][Ta IV MV^QZWVUMV\ _Q\P I []NÅKQMV\
Could you tell me in what resistivities alu- minum anodes work efficiently? Is there any
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quired chloride concentration in waters Q[ f \W
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1V ;Q IVWLM[ QV JZIKSQ[P _I\MZ[ & seawater strength exhibit current capaci \QM[ ) P SO MY]IT \W \PW[M WJ[MZ^ML QV N]TT [\ZMVO\P [MI_I\MZ )\ [ITQVM [\ZMVO\P $ [M^MZM KIXIKQ\a [KI\\MZ _I[ WJ [MZ^ML )VWLM XW\MV\QIT[ [PW_ IKKMX\IJTM ^IT]M[ WN · \W · > ^[ [QT^MZ [QT^MZ KPTWZQLM C)O )O+TE \PZW]OP [\ZMVO\P [MI_I\MZ )\ f [MI_I\MZ strength and less, noticeable potential ^IZQIVKM _QTT WKK]Z
Cathodic protection for tank bottom
high-density polyethylene Q IT\MZVI\Q^M[
\IVS JW\\WU \W ÆM` IVL [MXIZI\M NZWU \PM Continued on page 38
A A
March 2012 MATERIALS PERFORMANCE 37
I have never heard those con cerns, but I also realize that the \IVS[ IZM VW\ IT_Ia[ N]TT -UX\a QVO IVL ÅTTQVO \PM \IVS KI][M[ \PM
(HDPE) liner present? The sys tem will be installed between the HDPE TQVMZ IVL \IVS JW\\WU ;PW]TL _M ][M UQ`ML UM\IT W`QLM 557 [\ZQX[ WZ _QZM in a grid or polymer anodes? 7]Z M`XMZQMVKM [PW_[ \PI\ 557
strip anodes in a grid is the best system JI[ML WV \PM XI[\ MQOP\ aMIZ[ WN ][M ?QTT gases be generated at the anode surface due to anodic reactions? How will these be dissipated? Or will they get entrapped under the steel tank bottom?
In your case, I would prefer the +8 OZQL [a[\MU _Q\P 557 [\ZQX IVWLM[ IVL KWVL]K\WZ JIZ[ You can also consider other
What is the best sys- tem for protecting a coated tank bottom on the soil side with a
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