TABLE 2 - MAJOR FACTORS AFFECTING CORROSION 

 IN SEAWATER ENVIRONMENT* 



Chemical 



(1) 



Dissolved Gases 

 Oxygen 

 Carbon Dioxide 



Chemical Equilibrium'^^ 

 Salinity 

 PH 

 Carbonate Solubility 



Physical 



Velocity^^^ 

 Air Bubbles 

 Suspended Silt 



Temperature 



(4) 



Biological 



Biofouling'-^-' 



Hard Shell Types 

 Types without Hard 



Shells 

 Mobile and Semimobile 



Types 



Plant Life 



Oxygen Generation 

 Carbon Dioxide 

 Consumption 



Animal Life 



Oxygen Consumption 

 Carbon Dioxide 

 Generation 



*Using iron as reference, the following trends are typical; 



(1) Oxygen is a major factor in promoting corrosion. 



(2) The tendency to form protective scale (carbonate- 

 type) increases with higher pH. 



(3) Increasing velocity tends to promote corrosion, 

 especially if entrained matter is also present. 



(4) Temperature increase tends to accelerate attack. 



(5) Biofouling can reduce attack or promote local 

 corrosion cells. 



Uniform corrosion is the wasting or thinning of a metal surface 

 exposed to a corrodant. Attach occurs evenly over the exposed surfaces. 

 The rate of uniform attach (a measure of metal loss or penetration) is 

 usually reported as mils (0.001 in.) per year (mpy) and is represented by 

 time-averaged values. Because the initial rate of attack is often greater 

 than the final rate, exposure time has to be considered in evaluating data. 

 Pitting is localized attack where the corrosion is greater in some areas 

 than in others. During immersion, factors leading to pitting are: 

 (1) relatively stagnant environment, (2) higher dissolved oxygen content, 

 and (3) local deposits of foreign matter. Galvanic corrosion results from 

 the electrical interconnection of metals with differing potentials, with 

 subsequent dissolution of the least noble metal. 



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