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CL BLOG Continued from page 41
product selection and application are important too. We have found that the best way to
get the coating system applied correctly is \W ][M I 6)+- KMZ\QÅML +WI\QVO 1V[XMK- tor for oversight of the coatings phases of the project, including inspecting the work in the shop. This works well if you PI^M \PM XTIV[ IVL [XMKQÅKI\QWV[ NWZ \PM job prepared by (or at least reviewed by) a NACE inspector and an engineer who is very familiar with storage tank design and construction. Plan on full-time coatings oversight
JW\P QV \PM [PWX IVL ÅMTL ,WV¼\ J]a into anything less than that, no matter how much someone tries to convince you about "critical phase" coating inspection. 1\¼[ ITT KZQ\QKIT
+8 ZMK\QÅMZ [PW]TL PI^M XW\MV\QIT KWV\ZWT with a current and voltage limit set to prevent overprotection. We typically shoot for –0.900 to –0.950 V vs. copper/ copper sulfate (Cu/CuSO4
A
interdependent on the others for struc- tural integrity—it is important that they are carefully inspected during construc- tion. Watch for proper wire (or cable) spacing and be absolutely certain that the outer mortar cover is adequate. The manufacturers of prestressed
A
tanks are very willing to give your or- ganization a presentation. We recently had a whole spectrum of tank builders come through and show off their stuff.
NACE International, Vol. 51, No. 3 March 2012 MATERIALS PERFORMANCE 43 ) "instant off"
XW\MV\QIT 1N \PM ^WT\IOM IVL K]ZZMV\ _MZM limited so greater than –1.050 V vs. Cu/ CuSO4
could not exist, you should have
no problem with the coating manufac- turer over disbonding issues. An anode system that is distributed vertically will keep the maximum potentials when volt- age limit occurs level independent.
Prestressed tanks of that dimen- sion are certainly possible. With tanks of that construction—a composite of materials with each
The CP design and installation should be approved by the coat- ing inspector, manufacturer, and installer. The impressed current
There are many prestressed con- crete tanks in use in the United ;\I\M[ J]\ 1 LWV¼\ SVW_ WN IVa that are as high as 85 ft.
many years and remain in service in seismically active areas.
A Continued on page 45
1 PI^M [MMV I V]UJMZ WN XZM- stressed concrete tanks in North- ern California, but not at 85-ft tall. They have been in service for