Corrosion Rate (MPY) =0.84+1.0 (0 2 ) + 0.014 (T) 



(avg of carbon and 

 low alloy steels) 



Corrosion Rate (MPY) = 0.19 + 1.1 (O2) +0.1 (T) 



(AISI 1010) 



The corrosion rates are in mils per year (MPY) , the oxygen content of 

 seawater in milliliters per liter (ml/1) and temperature in degrees 

 Centigrade (°C) . 



These derived formulae illustrate two important points: 



(1) The concentration of oxygen in seawater is a major vari- 

 able and its effect on the corrosion rate of steel in seawater is 

 linear. 



(2) The temperature of the seawater has less effect on the 

 corrosion of steel in seawater than the oxygen content and its effect 

 is also linear. 



These formulae, however, cannot be used to predict the corrosion 

 rates of steels in seawater at other locations due to the influences of 

 other variables such as time, currents, sediment effects, etc. For 

 example, the above formulae are not satisfactory for predicting cor- 

 rosion rates for steels in the Tongue-of-the-Ocean, Atlantic Ocean. 

 Since they are not applicable, it is obvious that other variables in 

 that location are different from those in the Pacific Ocean off the 

 Channel Islands. 



The effect of time of exposure in surface seawater on the average 

 corrosion rates of steels is shown in Figure 22. The corrosion rates 

 decrease parabolically with increasing time of exposure. 



All the steels except AISI Type 502, in general, corroded uniformly 

 except for some pitting in surface seawater which was caused by fouling. 

 AISI Type 502, because it contained about 5 percent chromium, was pit- 

 ted. 



CAST IRONS 



The chemical compositions of the cast irons are given in Table 10 

 and their corrosion rates and types of corrosion in Table 11. The 

 effects of depth, concentration of oxygen in seawater and time are shown 

 graphically in Figures 23 to 25. 



The effect of depth on the corrosion rates of the cast irons is 

 shown in Figure 23. The shape of the corrosion rate curve for the alloy 



