Immersion testing seawater

When the sacoglossan Placobranchus ocellatus was immersed in seawater containing 14C sodium hydrogen carbonate, 14C label was incorporated into both 9,10-deoxytridachione (Structure 2.124) and the photorearrangement product photodeoxytridachione (Structure 2.125).242 In Elysia viridis, sodium [l-14C]propionate was incorporated into elysione (Structure 2.126), an ichthyotoxic metabolite found in the mollusc s mucus secretions.237 Attempts to repeat this propionate labeling experiment in Elysia timida and to test the putative role of acetate in the biosynthesis of 15-norphotodeoxytridachione (Structure 2.127) were unsuccessful.237 243 The metabolites shown in Structures 2.124, 2.125, 2.126, and 2.128, some of which were toxic, were present in the mucus secretion of Elysia timida, consistent with a defensive role.243 The hypothesis that these complex pyrones function as suncreens242 has been disputed.243... 

Media considerations. SCC tests can be divided into those conducted in natural environments, such as atmospheric exposure tests and seawater immersion tests, and those which are conducted under laboratory conditions or other fabricating operations. The principal disadvantage of atmospheric exposure tests is the comparatively long time required for their completion however, they are reliable since they can reflect the projected use. There is a standard practice for evaluating stress-corrosion cracking resistance of metals and alloys by alternate immersion in a solution of NaCl 3.5%, pH 6.5. For spray testing, ASTM B-117, 2003 states the relevant conditions for conducting the test. (ASTM G44)4... 

There is a specific terminology used for hypothesis tests. One migjit ask, for example, whether the rate of corrosion obtained for an aged steel coupon immersed in seawater is equal to that found in city drinking water. 

Immersion tests in distilled water, tap water, and seawater have shown that chromized steels exhibit high corrosion resistance to these solntions. After 8 h testing in a salt spray fog at 35°C, chromized steel was less affected than alnminized steel, galvanized steel, or a 17% Cr steel. 

For marine applications, pH-stable EAPs have been investigated. Double-stranded PANI has been coated onto A1 alloys (458) immersion tests in simulated seawater showed improved corrosion resistance as compared to control samples (epoxy coating) (459). Recently, poly(bis-dialkylamino)phenylene vinylene) (BAM-PPV) was shown to adhere to A1 alloy in an immersion test using simulated seawater (pH 8) to retard corrosion (460,461). Quantitative evidence was obtained to show corrosion inhibition as compared to noncoated A1 alloys. 

While many laboratory tests for resistance of metals to stress corrosion cracking have been developed, only a few tests are amenable to actual in-situ testing in seawater. These primarily consist of the exposure of statically stressed type test specimens such as described in ASTM G 30, G 38, G 39, and ISO 7539-2, ISO 7539-3, and ISO 7539-5. In addition, welded specimens such as described in ASTM G 58 are excellent for evaluation of the stress corrosion resistance of weldments in simple immersion tests. Evaluation of corrosion fatigue is usually limited to laboratory testing. 

Pantai Teluk Kalong was selected in this research due to widely application of Al-Mg-Si alloy in the shipping, marine, oil and gas industrials surrounding the area. The values of physicochemical properties of seawater such as salinity, dissolved oxygen, pH and temperature were monitored during the immersion test. Average selected physicochemical data of the seawater used are reported in Table 2. 

The EDS spectrum in Figure 8 presents the elements exist in Al-Mg-Si alloy after immersion test. It shows the presence of sodium (Na) and chlorine (Cl) in the specimen surface. Seawater predominantly consists about 3.5% of sodium chloride (NaCl) and many other ions. Chloride ions are very strong, and could easily penetrate the passive film, and dissolution of the aluminium substrate occurs and results in corrosion. 

The use of SEM-EDS techniques provide good insight into the surface corrosion products grown on Al-Mg-Si alloy during the immersion test in seawater with and without the natural products as corrosion inhibitors. The SEM results indicate that the natural products (NH, VL and TS) absolutely minimized the corrosion products on the specimen surfaces. They also protect the passive film from dissolution in aggressive solution like seawater. 

Tests in outdoor testing stations have shown that cladding provides an effective protection for many years, whether exposed to weathering or immersed in seawater [29]. The consumption of the cladding avoids corrosion of the underlying core (Figure B.5.5). 

Over the past 50 years, many results of immersion tests in seawater have been published [20, 21]. Table D.3.4 summarises the maximum pitting depths after 5 and 10 years... 

Immersion tests in seawater at many places, some of which have exceeded 10 years, as well as more than 50 years of experience with marine applications of aluminium demonstrate that casting alloys without copper of the 40000 series A-S7G (42100), A-SIOG (43100) the 50000 series A-G3T (51100), A-G6 (51300), as well as wrought alloys of the 5000 and 6000 series have an excellent resistance to corrosion in the marine environment and seawater. 

For marine applications, pH-stable EAPs have been investigated. Double-stranded PANI has been coated onto A1 alloys (458) immersion tests in simulated seawater showed improved corrosion resistance as compared to control samples... 

The literature on corrosion testing of aluminum alloys in seawater is extensive. Summaries of information are provided in Ref 28 and 29, and in most of the Selected References. Table 8 lists results of 10 year immersion testing of various alloys in the form of rolled plate exposed in three locations. Similar data for extruded products of several 6xxx alloys and one 5xxc alloy are given in Table 9. Direct cotrparison of the data in Tables 8 and 9 is provided in Table 10, in which corrosion is expressed in terms of average weight loss, and in Fig. 10, which illustrates the decel-... 

Water Tests. In colorfastness to water, ISO 10S-E01, the test specimen is placed in contact with the chosen adjacent fabrics, immersed in water, and placed wet between glass plates and left for 4 h at 37°C. After drying, the effect on the test specimen and stain on adjacents are assessed. The test, colorfastness to seawater, ISO 10S-E02, is the same as EOl but uses 30 g/L anhydrous sodium chloride solution instead of water. To test for colorfastness to chlorinated seawater/swimming baths water, ISO 10S-E03, the specimen is immersed in sodium hypochlorite solution containing either 100, 50, or 20 mg of active chlorine per Hter at pH 7.5 for 1 h at 27°C, rinsed, dried, and assessed. 

This thin-film-composite membrane has been found to have appreciable resistance to degradation by chlorine in the feed-water. Figure 2 illustrates the effect of chlorine in tap water at different pH values. Chlorine (100 ppm) was added to the tap water in the form of sodium hypochlorite (two equivalents of hypochlorite ion per stated equivalent of chlorine). Membrane exposure to chlorine was by the so-called "static" method, in which membrane specimens were immersed in the aqueous media inside closed, dark glass jars for known periods. Specimens were then removed and tested in a reverse osmosis loop under seawater test conditions. At alkaline pH values, the FT-30 membrane showed effects of chlorine attack within four to five days. In acidic solutions (pH 1 and 5), chlorine attack was far slower. Only a one to two percent decline in salt rejection was noted, for example, after 20 days exposure to 100 ppm chlorine in water at pH 5. The FT-30 tests at pH 1 were necessarily terminated after the fourth day of exposure because the microporous polysul-fone substrate had itself become totally embrittled by chlorine attack. 

Media Considerations SCC tests are conducted in (i) natural atmospheres (ii) seawater immersion, and (iii) laboratory or other fabrication conditions. Atmospheric exposure tests take a long exposure time, but are reliable as they... 

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