b'Corrosion Test Results:Doctors Laboratories, that the acidic conditions dissolve the iron oxideadivisionoftheRoyalMilitaryCollegeof as it forms leaving the iron in direct contact withCanadaexposedirontoaeratedwateratroom the water.temperature and determined the corrosion rate as ZincGalvanizingforCorrosionProtection:a function of the pH of the water. In Frank Porters Corrosion Resistance of ZincAs the water became highly acidic (pH less than and Zinc Alloys, he determined that dissolved4), the steel corroded more quickly than the steel chloride content in water is highly corrosive todid in a highly alkaline environment (pH greater zinc.When zinc is subjected to hard (alkaline)than 10).It is also interesting to note that zinc water,theinsolublesaltsinthewaterformausedforgalvanizationprovidesthebest scale of calcium carbonate and zinc carbonate onprotectiontosteelsubjectedtothese thesurfaceofthezinccoatingthatprovidesaenvironments.Zinc provides the most effective protectivebarrieragainstattackfromfreeprotection through a range of 5.5 pH 12.5. chloride anions.In the absence of air, a zinc oxide film does not Frank Porter attributes this insoluble scale for theformonthezincgalvanizedsurfaceand significantlyincreasedcorrosionfreelifeofcorrosioncanbemorerapidwhenmoistureis galvanizedpilesinsoilswherepHrangespresent. between5.5and12.5.Roathali,CoxandThe corrosion rate of steel in soil can range from Littreal,theauthorsof MetalsandAlloys,less than 0.79 mils per year (0.0008 in/yr) under 1963; presented data showing the corrosion ratefavorable conditions to more than 7.87 mils per of zinc is a function of pH.Excerpts from theiryear(0.0079in/yr)inveryaggressivesoils. data are presented in Graph 2.Therearesimilaritiesinthecorrosionratesofgalvanizedcoatings. Underfavorable The Effect of pH onconditions, the zinc may corrode at less than 0.20 Corrosion of Zincmils per year under mild conditions to more than 1.20.98 mils in unfavorable soil conditions.Loss Rate (Mils per year)The results of the testing are shown in Graph 1. 1.0The data suggests that in the range of 4 pH 0.810 the corrosion rate of iron is independent of theacidity or alkalinity (pH) of the environment.In 0.6acidicconditions(pH4)thecorrosionrate 0.4dramatically increases.The scientists concluded0.2The Effect of pH on 0Corrosion of Iron80 2 4 6 8 10 12 1470 pHLoss Rate (Mils per year)Graph 2.6050 OxygenAvailability:Inadditiontosoil40 moisture,freeoxygenmustbeavailabletocompletethecorrosionprocess.Oxygen30 combineswiththemetalionstoformoxides,20 hydroxides and metal salts.10 Corrosion rates will drop significantly when the0 steelstructureisbelowagroundwatertable0 2 4 6 8 10 12 14 (GWT), and the water is relatively stagnant (lowpH to no flow velocity) since available free oxygenis much reduced under these conditions.Graph 1.ECP Technical Design Manual Corrosion Life2021 Earth Contact Products, L.L.C.2021-09 Chapter 8 - Page 149 All rights reserved'