Corrosion tests seawater

Vanadium is resistant to attack by hydrochloric or dilute sulfuric acid and to alkali solutions. It is also quite resistant to corrosion by seawater but is reactive toward nitric, hydrofluoric, or concentrated sulfuric acids. Galvanic corrosion tests mn in simulated seawater indicate that vanadium is anodic with respect to stainless steel and copper but cathodic to aluminum and magnesium. Vanadium exhibits corrosion resistance to Hquid metals, eg, bismuth and low oxygen sodium. 

Saponification Paints are most commonly used to protect steel from corrosion by seawater in marine applications and soil in the case of buried structures. Additional protection is often supplied by the application of cathodic protection to the steel. Any paint coating used in conjunction with cathodic protection must be resistant to the alkali which is produced on the steel at defect sites in the coating. The amount of alkali generated depends on the potential to which the steel is polarized. Some paint binders such as alkyds and vinyl ester are very susceptible to saponification, and should not be used on cathodically protected structures. Cathodic disbondment testing should be undertaken if the relevant information is not available. 

Guide for crevice corrosion testing of iron base and nickel base stainless steels in seawater and other chloride-containing aqueous environments... 

The impetus for further developments was the recognition of the economic significance of corrosion phenomenon during the 19th century that led the British Association for the Advancement of Science to sponsor corrosion testing projects such as the corrosion of cast and wrought iron in river and seawater atmospheres in 1837. Early academic interest in corrosion phenomenon (up to the First World War) was followed by industrial interest due to the occurrence of equipment failures. An example of this is the corrosion-related failure of condenser tubes as reported by the Institute of Metals and the British Non-ferrous Metals Research Association in 1911. This initiative led to the development of new corrosion-resistant alloys, and the corrosion related failure of condenser tubes in the Second World War was an insignificant problem. 

Guide for Crevice Corrosion Testing of Iron-Base and Nickel-Base Stainless Alloys in Seawater and Other Chloride-Containing Aqueous Environments, G 78, Annual Book of ASTMStandards, ASTM, 1992, p 463-470... 

Titanium does not undergo crevice corrosion in seawater at room temperature, but instances have been recorded in hot seawater, such as under an asbestos gasket at 95-120°C (200-250°F) [25]. Attack of this kind, it is reported, does not occur at temperatures below about 95°C (200°F) also, such attack is more commonly observed in acid and neutral rather than in alkaline chloride solutions. In laboratory tests, Griess [26] showed that titanium undergoes crevice attack in IM NaCl containing dissolved oxygen at 150°C (300°F). For this type of corrosion, CT was not necessary crevice attack was also observed in hot solutions of T, Br , and 801 . Susceptibility was related to acid anodic corrosion products... 

The number of replicate test specimens depends upon the desired reliability of the results of the test. ASTM G 16 gives guidance for establishing the required number of replicate specimens. In general, as recommended in ASTM G 52, triplicate specimens for each exposure period are sufficient for many seawater corrosion tests. 

TABLE 3— Results of crevice corrosion tests in natural seawater from the LaQue Center for Coirosion Technology, circa 1993 [77]. 

Kain, R. M., Crevice Corrosion Testing in Natural Seawater Significance and Use of Multiple Crevice Assemblies, Journal ofTestingandEvaluation, Vol. 18, No. 5,1990, pp. 309-318. 

OO] Dmgli, J. M. and Johnsen, R., Corrosion Testing of Stainless Steel Weldments in Seawater, NaCl- and FeCl3 Solutions, Paper 410, NACE CORROSION/88, St. Louis, MO, 1988. 

FIG. 1—Sequence of events (left to right) in a stress corrosion test on an iniUatty smooth specimen. For low-alloy steels In seawater, the rale of growth of SCC is faster than it is for pitting by a factor of about 106, and fast fracture propagates at about 1010 times faster than SCC [0]. 

Seawater is a unique environment. A recent worldwide test program was recently completed by ASTM Task Group Gl.09.02.03 to evaluate the corrosivity of seawater at a number of sites [/5]. Though these results indicated the uniqueness of natural seawater, corrosivity was site-specific and influenced by numerous factors. Seawater can vary widely in terms of chemical composition, dissolved oxygen content, temperature, salinity, pH, carbonate levels, flow, degree of fouling, biological activity, and pollution [16. ... 

Temperature variations due to seasonal changes may also affect corrosion rates in seawater. For many copper and iron alloys, the corrosion rates increase during the warmer months of the year. The start of the corrosion test, therefore, may be affected by the time that a corrosion test is initiated, and there is a tendency for corrosion rates to slow down with increased times of exposure to the natural seawater environment, depending on the actual environmental zone. 

In-service testing provides the advantage of examining the corrosion behavior of a metal in the actual service environment. The advantages and disadvantages of some of these tests are briefly described below. More detail can be found in the article titled In-Service Monitoring in Ref 69. Section III—Types of Tests—Seawater, describes further details on seawater testing. 

PhuU, B. S., Pikul, S. J., and Kain, R. M., "Seawater Corrosivity Around the World Results from Five Years of Testing, Corrosion Testing in Natural Waters Second Volume, ASTM STP 1300, R. M. Kain and W. T. Young, Eds., ASTM International, West Conshohocken, PA, 1997, pp. 34-73. 

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