CHARACTERISTICS OF CATHODIC PROTECTION AND CALCAREOUS DEPOSITS FOR TYPE 316L STAINLESS STEEL IN SIMULATED DEEP SEA CONDITIONS

摘要

Throughout the past three decades, cathodic protection (cp) technology for offshore structures has seen significant progress with regard to both design and materials. Most studies upon which these improvements are based have concentrated on carbon steels and ambient temperature conditions. Presently, however, there are an increasing number of deep sea structures for oil production; and more sophisticated alloys such as stainless steels and are being utilized for certain components. In the present study, Type 316L stainless steel specimens (UNS 31603) were galvanically coupled to indiumactivated aluminum anodes through various size resistors to establish different levels of cp. The exposures were in natural seawater that was either at ambient south-Florida temperature or maintained at 5℃ to simulate deep sea conditions. Cathode potential and current density were routinely monitored, and upon termination of the exposures the nature of calcareous deposits was characterized using scanning electron microscopy and energy dispersive x-ray analysis. The optimum potential for protection of SS 316L after 90 days was estimated as -1,020 to -1,060 mV/SCE at ambient temperature which is more negative than for carbon steel (-1,000 mV) and -1,100 mV/SCE at 5℃,. The optimum slope parameter was 2.3Ωm2 at ambient and 0.91Ωm2 at 5℃.Implications of these findings with regard to cp of offshore structures are discussed.