The Impact of Bioconcretious Structures (Rusticles) for the RMS Titanic: Implications for Maritime Steel Structures

摘要

Since the sinking of the RMS Titanic in 1912, there has occurred a growing mass of iron-rich bioconcretious structures called rusticles, on the steel surfaces of the ship. Recording the growth rates has only been possible since the ships discovery in 1986, but a cycle has been established in which iron and other elements are being biologically extracted from the steel into these rusticle structures and exported into the oceanic environment as biocolloids. The rate of biological extraction by the rusticles is critical in the determination of ship structural integrity. To ascertain the effects of rusticle activity, three grades of steel (A6, AH36 and EH36) were employed as 6″ x 1″ x 1/4" coupons. These coupons were arranged on IPSCO steel test platforms and placed at sites on and around the RMS Titanic wreck site in August 1998. They remain at the site and are due to be recovered during a subsequent expedition. Laboratory studies indicate that rusticles can be grown on steel, under a variety of conditions, including the application of anodic or cathodic charges. Radiographic analysis has revealed that the iron movement into and throughout a rusticle is focused along narrow pathways within the internal structures. Methodologies have been developed to strip the encrusted rusticle growths from the steel to allow evaluation of the rate of the biological removal of iron from the steel using a patented Blended Chemical Heat Treatment™ process. Laboratory studies indicate that the rusticles are able to extract iron, phosphorus and sulfur from embrittled steel, particularly at anodic sites. A methodology has been developed to manipulate biological growth rates and extraction mechanisms through the use of variable charges. The evaluation of rusticles has direct application to the shipping industry relating to the structural integrity of submerged steel structures including tankers, pipelines, and offshore drilling rigs. This breakdown will negatively impact the environment, particularly oceanic organisms, through toxic releases.