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• # <br />ing and ‘ <br />rnagcd in <br />. form. <br />. effect. <br />•einains <br />iunately > <br />variety <br />ne condi- <br />3xide <br />these <br />r effects <br />e properties <br />of good <br />seawater <br />Per Cent <br />ange in TS <br />; hull and <br />[stance and <br />t £A4./Acconcentration of other <br />onment . <br />:* :r:3 or cor.-.pcund;^ pr esent in the envir- <br />If this j;H ranp'-" is exc:jeiv? i, It.e cMidc: iiln diasolves. The <br />rate of dissolucVnn inc-r o:.*s the* acidity or basicity in- <br />creas*js. (Aluninctr. is s-ner'..V'y not used in such hi^;h3y <br />aTka?.ine or acidic environr.en t:'.) <br />« <br />Effect of Water Composition <br />Years of service experience huve aliusinuni alloys to be <br />coTipatible virith most natural v:ators and v/ith seawater. Usage <br />includes irrigation pipe, wa.ter storage tanks and covering for <br />wood piling in seawater. <br />The propensity for pitting corrosion increases with decreasing <br />electrical resistivity of the v/ater. This property is frequently <br />measured in at attempt to determine corrosiveness. Hov/ever, <br />additional analyses are necessary for a more quantitative estimate. <br />Certain ion species tend to increase pitting corrosion tendencies. <br />These include the chloride, sulfate, copper and iron ions. Dis­ <br />solved CO2 may ’nave an adverse effect in slightly acidic waters. <br />There are no simple formulas, hov/ever, that can be applied to <br />determine what concentration levels are excessive. <br />Effect of Soil <br />Soils vary v;idcly jn physical and chemical characteristics and <br />in their corrosivity towards metals. Analysis of data accumu­ <br />lated in extensive field tests of aluminum culvert shov/s good <br />perlormance over a v;ide /ariety of soils. With rare exception, <br />all soils of greater th^.n ^>00 ohm-cm minimum resistivity and <br />within the recommendec pH K to 9 range Viave proven to be com­ <br />patible. Further study is underway to more completely identify <br />the rare exception ;.oii. I’he non-draining clay-muck type with <br />pH and resistivity outside the established lirdts is suspect. <br />Galvanic Corrosion (Dissimilar N!etals^ <br />This is one of the most <br />roslon encountered v:ith <br />is bonded or coupled to <br />tJisn exposed to a corro <br />inum occurs because th- <br />protect the c'r CO’. <br />corrosion will aei-or./ <br />the relative areas of £•.- <br />common and destructive forms of cor- <br />rlu:=!inurn alloys. It occurs v;hen aluminum <br />m.LlJ .steel or to a copper baj'.ed alloy and <br />ive envlrcr :: jn t. Corrosion of the aluri- <br />a?urr:;!nu:n acts as a '’ificial anode to <br />e'’ alloy :'ru.-\ cojTOsicri. T;ic rate of <br />•n the 1;’ of th: envli-nnment and <br />eTri non-airaninuc. me cals nresent. <br />Corrosj-on of olumirru;.-. ty yal/cnic artaek cun be mininirced by <br />electrically sen ratin ' t:.e el r'in r'. and the dissimilar metal <br />by means of non-motallic ise of nine coav.lngs on the <br />steel provides an altern.'ite ini'^no i where st eel is involved.