The major fouling organisms on the surfaces of UNS $31600, UNS N08028, UNS N08825, UNS N06030 and UNS C71500, have been identified along the shores of the Arabian Gulf in Kuwait. The corrosion rate of the alloys was also determined as a function of immersion time by the weight loss method. The exposure period covered both the summer and winter seasons at which the average seawater temperature was 35°C and 22°C respectively. With the exception of the UNS C71500, all the other alloys were heavily fouled with greenish, brownish and reddish type of algae and different sizes of barnacles. The limiting factor for performance in seawater has been shown to be crevice corrosion, but UNS N08028, UNS N08825 and UNS N06030 were unaffected by localised corrosion for a period of 9 months.
Marine corrosion and fouling are interrelated, and in tum, depend upon the interaction of metals with the biotic and natural aquatic environment. While the effects of chemicals and physical factors are widely studied and documented, the information available on the role of fouling organisms with respect to the development of corrosion processes is not entirely exhaustive and is often conflicting. Each environment has its own biotic and physiochemical characteristics.
Immediately following immersion, dissolved organic material is adsorbed onto the metallic surface imparting a net negative charge to the surface ~'2. The surface almost immediately becomes covered with non-cellular organic films of different composition and concentration. All of these micro- organisms produce copious mucilage giving rise to the characteristic 'slime' associated with the thin fouling layer, which itself may influence the subsequent settlement of micro-and-macro-fouling organisms 3. There are two morphological types of macro-fouling, soft and hard. Soft foulers comprise flexible, sometimes compressible organisms that lack a rigid external skeleton, and include all seaweeds, soft corals, sponges, anemones, tunicates, hydroids and some bryozoans. Hard fouling organisms possess a hard external skeleton in the form of shell, plates or dwelling tube, and include moluses, solitary and aggregate tubeworms, barnacles and the crustose algae.
Pitting corrosion often occurs under deposits or in crevice sand although the weight lost is small, this type of corrosion can rapidly produce holes, and may initiate stress cracks which will then propagate 4. Large differences in the oxygen concentration at the metal surface may be created by the larger (macro) fouling organisms s. It is likely, therefore, that local oxygen concentration cells may be created when there are gaps in fouling layers or between two adjacent species.
The growth of marine microorganisms along Kuwait's shores is accelerated by the following factors: the location of Kuwait near the Shatt A1-Arab, which is a reproduction ground for many biological species; the moderate climate (i.e., the warm sea) year-round, which sustains biological growth; and the amount of nutrients in the Gulf seawater. In addition, pollutants from refineries, power plants and raw sewage may have deletrious effects on metallic structures.
The work described in the present paper represents a study of corrosion behaviour of UNS $31600, UNS C71500, and high grade alloys in natural Arabian Gulf seawater over a period of 9 months. The contributory roles of fouling and seawater characteristics in subsequent corrosion processes is examined. The metals were exposed along the different test locations in Arabian Gulf sea.
Special non-conductive racks made of plexyglass to hold the metallic panels were constructe