Exposure to Seawater

PDMS has been widely used in antifouling coatings where it receives extensive exposures to seawater. The nature and extent to which the PDMS surface was modified can be determined in a variety of ways, including scanning electron microscopy and x-ray photoelectron spectroscopy.  

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Halmyrolysis The processes that alter the chemical composition of terrestrial clay minerals during their first few months of exposure to seawater. 

Exposure to seawater results in decrease in critical stress intensity factor and the susceptibility to SCC68 0.2% Fe improves the resistance to SCC presence of >5 wt percent of A1 increases the velocity of cracking Sn in the alloy decreases SCC resistance chloride bromide and iodide induce or accelerate SCC69 Occurs by trangranular cleavage of a-phase in which a-phase controls the crack propagation rate Intergranular corrosion due to formation of titanium methoxide... 

Galvanic corrosion rates (mils) of some couples after 16 yr exposure to seawater and fresh water are given in Table 7.23. In the cae of carbon steel/aluminum the data show that in fresh water carbon steel corrodes to a greater extent than aluminum which provides further evidence for polarity reversal of the steel/Al couple in fresh water. 

Palmer C. A., Finkelman R. B., and Luttrell G. H. (2002) Coal from a mid-Atlantic Ocean shipwreck the source of the coal in the Titanic and effects of exposure to seawater. Nineteenth Annual International Pittsburgh Coal Conference, CD-ROM. 

More information about the ubiquitous presence in seawater of natural organic surfactants has been obtained by the use of seawater/solid interfaces than from studies of the interface between seawater and air. For practical reasons, it is usually very much simpler to study the adsorption of organic matter from solution onto solid surfaces, where a variety of powerful techniques such as electrocapillarity, electrical double-layer capacitance measurements, electrophoresis and ellipsometry can be used to study the progress of adsorption and the nature of the adsorbed layer. Neihof and Loeb (1972, 1974) and Loeb and Neihof (1975, 1977) have demonstrated by electrophoresis and ellipsometry that a wide variety of solid surfaces become covered by a strongly adsorbed film of polymeric acids upon exposure to seawater. Hunter (1977) found the same type of effect and has shown by electrophoretic studies at different pH and metal ion concentrations that phenolic and carboxylic groups are probably responsible. This adsorbed organic material seems hkely to represent an important part of the natural surfactants in seawater and, as such, will adsorb at the air/sea interface as well. 

Figure 3.13 Corrosion profile of steel piling after 5-year exposure to seawater (7).

An amoimt up to 5% chromium (0.08% C) was reported to decrease weight losses in seawater at the Panama Canal [53] at the end of one year. A sharp increase in rates was observed between 2 and 4 years after 16 years, the chromium steels lost 22-45% more weight than did 0.24% C steel. Depth of pitting was less for the chromium steels after one year, but comparable to pit depth in carbon steel after 16 years. Hence, for long exposures to seawater, low-chronaium steels apparently offer no advantage over carbon steel. By comparison, however, low-alloy chromium steels (<5% Cr) have improved resistance to corrosion fatigue in oil-well brines free of hydrogen sulfide. 

Arce, F. T. Avd, R. Beech, I. B. Cooksey, K. E. Cooksey, B. W., Modification of Surface Properties of Poly(dimethylsiloxane)-Based Elastomer, RTVll, upon Exposure to Seawater. Langmuir 2006,22, 7217-7225. 

A further complication is that these variations may not affect the deterioration of materials in a simple manner. In many cases, metal corrosion is dependent upon surface 61ms that form upon exposure to seawater. Variations of irutial exposure conditions can affect the protective nature of these 61ms, which can affect the further corrosion behavior of the material. Thus, a sample 6rst exposed under conditions conducive to the formation of a protective 61m may perform very differently than the same material exposed for an identical period, but was ffrst exposed to conditions that resulted in the formation of a 61m that was less protective. In other cases, short-term variations in environment may be sufficient to initiate attack that would not occur during typical conditions and that, once initiated, can continue over extended exposures. 

However, no significant changes in material properties nor any reliable weight loss of differently modified PE and PP could be observed by Gonsalves and co-workers [9, 10] upon exposure to seawater (1-9 m depth, temperatures of 13-30 °C) for 5-12 weeks. The primary (chemical) degradation depends on the exposure temperature and the normal temperatures (maximum and minimum) found in seawater, the reaction rate is probably too slow to observe any changes in the materials within the duration employed. 

Ferritic stainless steels offer useful resistance to mild atmospheric corrosion and most freshwaters. They will corrode with exposure to seawater atmospheres. These alloys are also useful in high-temperature situations, with 446... 

Concrete may deteriorate if adequate precautions are not exercised to protect it from adverse effects that could result from exposure to natural or artificial conditions. Several physical, chemical, and electrochemical processes are known to induce cracking of concrete. Concrete can have durability problems as a consequence of its exposure to seawater, sulfates, chlorides, freeze-thaw action, carbon dioxide, etc., or when it is attacked by artificially induced processes such as exposure to acids and salts in chemical plants or to fire. In recent years, a new type of durability problem was encountered that involved use of steam cured concrete products. The distress was caused by the formation of delayed ettringite. If the raw materials in concrete are not carefully controlled, there may be an eventual failure of concrete elements, eg., the presence of excess alkali in concrete that promotes alkali-aggregate expansion reaction, harmful impurities in the aggregates, or the presence of excess amounts of dead-burnt MgO. Thermal techniques in combination with others have been employed with success to examine the raw materials as well as the failed concrete. The knowledge gained from such work has been applied to produce more durable concrete. 

The first successful major use of stainless steel for seawater systems was in the Gullfaks oilfield in the Norwegian offshore sector where Avesta 254SMO (21% Cr, 18% Ni, 6% Mo, 0.2% N) was adopted. The reason for this selection was the need for a material resistant to alternate exposure to seawater and sulfide-containing oil in the storage/ballast spaces in concrete platforms. Several thousand tonnes of superaustenitic stainless steel are now in service, mainly on offshore platforms. ... 

The long-term-exposure tests indicated that the rolled surfaces of the 8090-T851 sheet were more resistant to corrosion than those of the conventional 2024-T3 sheet. Except for some pits that developed at an air/water interface, these surfaces suffered only minor corrosion. The same tests indicated that the rolled surfaces of the 2090-T8 sheet suffered at least as much corrosion damage as their counterparts on the 7075-T6 sheet. Some fairly deep pits occurred on the rolled surfaces of the 2090, even during the exposure to seawater fog. 

Protective film formation. The good corrosion resistance in seawater offered by copper-nickel alloys results from the formation of a protective oxide film on the metal surface. The film forms naturally and quickly, changing the alloy s initial exposure to seawater. In clean seawater, the film is predominantly cuprous oxide, with the protective value enhanced by the presence of nickel and iron. Cuprous hydroxy-chloride and cupric oxide are often also present. ... 

Components where exposure to seawater and high mechanical stresses are required Oil and gas production where hydrogen sulfide and elementary sulfur exist at temperatures in excess of 150°C... 

Figure 11.8 Welded assemblies of aluminum Alloy 7005 with Alloy 5356 filler metal after a one-year exposure to seawater. (Reproduced with permission from Daubert Cromwell.)...

Formation of bis- and triscatechol complexes in the byssal threads after exposure to seawater (pH 8). Reprinted from Waite et al. [121], Copyright 2011 National Academy of Sciences of the United States... 

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