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In Soil

Another common exposure for hot-dip galvanized steel is partially or fully buried in soil. Withmore than 200 different types of soil identified in North America, hot-dip galvanizings

performance in soil is varied and hard to predict. !ven in very close proximity, soil conditionscan have significant variations.

"he main factors that dictate the corrosivity of the soil are moisture content, p# level, and

chlorides. "hese soil conditions are affected by additional characteristics such as aeration,

temperature, resistivity, and texture or particle size. A general rule of thumb is galvanizingperforms $ell in bro$n sandy soils, and not as $ell in gray, clay-li%e soils. "his is because soil

$ith larger particles $ic% moisture a$ay from the surface more &uic%ly so the galvanized piece

has less exposure to moisture.

"he first step to estimating the performance of hot-dip galvanized steel in soil is to classify it."he corrosion rate of steel in soil can range from less than 20 microns per year in favorable

conditions, to 200 microns per year or more in very aggressive soils. "hus, highly corrosive

soils $ill dictate the need for a reliable corrosion protection system, such as hot-dip galvanizing,to ensure long-term protection.

As soil changes even over a short area, and the corrosivity of the soil can vary greatly,

misclassifying the soil can lead to unpredicted performance. "he A'A has developed a chart for

estimating #('s performance in soil based on real $orld corrosion data. )n this case, servicelife is defined as total consumption of the coating plus 2*+, and is an indication of $hen the

structure should be replaced.

"here are four different sub charts based on the classification of the soil. sing the chart

belo$, the first classification is by chloride content / harts 1 and 2 top ro$ are used forsoils $ith high chlorides 20 334 and harts 5 and 6 bottom ro$ are used for soils $ith lo$

chlorides 720 334. 8nce you have identified the chloride content, there is a second

classification to determine the correct chart to use. 9or soils $ith high chlorides, the seconddetermination $ould be moisture content. :oils $ith lo$ moisture 71;.*+ fall on hart 1,

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$hile soils $ith high moisture 1;.*+ fall on hart 2. 9or lo$ chlorides, the second

determination is the p# level. :oils $ith high p# levels ;.0 fall on hart 5, $hile soils $ith

lo$ p# 7;.0 fall on hart 6.

"he blue line on all four charts represents the average for soils surveyed in that characteristic

group. "he green line represents the best soil in the category sampled, and the red line representsthe $orst soil in the category from the study. "he shaded areas sho$ ho$ the changes in p# and

moisture content affect the estimated service life. Assuming 5.* mils as a minimum thic%ness for

#(' buried in soil, the chart sho$s the average life in the harshest soils uncommon $ould beapproximately *0 years and in the best soils exceed 120 years.

"he ne$ soil chart is based on data from t$o ma