MR87-1_REDUCED.pdf

timeand has been the subject of many studies to determinewhy it fails and to t ry to predict life expectancy indifferen t environments . Zinc-coated steel is affected bywater , low pH ,anaerobi c bacteria ,low electrical resistivity of soils,abrasive material, chlorides, sulfates ,and many other factors .Predictions of life expectancy aregenerally based on only part of the environmental factorsand therefore the predictive procedures should be consideredlocal i n nature. For i nstance , California uses pH andelectrical resistivity to predict life expectancy .Thismethod of trying to predict e xpected life has been thesubject of several States ' research and at least inthereports revi ewed ,the States have not been able to make theCalifornia method correlate \",ith actual experience .The pHandelectrical resistivity are important factors in settingthe stage for corrosion but are not the only factors andinsome cases are not considered significant .Wisconsin foundbacteria to be a contributing factor in corrosion in 31percent of the study sites .Maine and Ohio found little , ifany , correlation between electric resistivity and actualcondition . Utah found that approximately 14 pH tests werenecessary in the field to obtain the true pH value within ±1/2 unit . They also found the Department of Agriculture isomaps to not be accurate enough to use .They recommended pHbe a lab test , not a field test . Neither California orWisconsin gave weight to abrasion which is considered a- 30 -