Corrosion testing continued natural waters

A comprehensive table of corrosion rates in sea water has been compiled by LaQue . This appears to show no obvious dependence of corrosion rates on the geographical location of the testing site, and few of the rates depart widely from an average of 0-11 mm/y. It is suggested that a figure of 0-13 mm/y may be taken as a reasonable estimate of the expected rate of corrosion of steel or iron continuously immersed in sea water under natural conditions, in any part of the world. 

Protective films on metals also can be destroyed and corrosion accelerated by the impingement of a high-velocity stream of sea water onto the metallic surface. The inlet ends of condenser tubes, are frequently attacked (Figure 3,a). Jet tests have been devised for ranking the susceptibility of metals to such impingement attack. A corrosion cell is formed between the bare surface directly under the jet (anode) and the adjacent filmed surface (cathode). These jet tests give more dependable information, if natural sea water is continuously supplied to the equipment. 

The higher inherent corrosion resistance of aluminum alloys in saltwater, as compared to steel, has led to the use of a wet/dry saltwater immersion-type test being used at the Alcoa Laboratories instead of the ASTM B 117 procedure. In fact, the continuous immersion of aluminum bonded joints in 3.5% sodium chloride solution or even natural seawater may not deteriorate such joints as much as distilled or deionized water exposure. The amount of... 

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