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Titanic Science
Part 1
Implications to Maritime Steel Structures.
Written by Dr. D. Roy Cullimore, (M); University
of Regina, Lori Johnston, (V); Droycon
Bioconcepts Inc.
Click any image to enlarge
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ABSTRACT
Since the sinking of the RMS Titanic in 1912,
there has occurred a growing mass of iron-rich bioconcretious
structures called rusticle's, 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 rusticle's 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 ¼”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 rusticle's 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 rusticle's 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 rusticle's 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. |
Rusticle Determination
Since the discovery of the RMS Titanic in 1985, there have been
a number of opportunities to examine and study this deep-sea
wreck. The ship sits in under approximately 4000 meters of 10C
water, with pressures in excess of 6000psi. One of the first
features that stood out in the images of the ship was the mass
of rust-like growths, coined rusticle's (Pellegrino, 2000).
These occurred as a growing mass of iron-rich bioconcretions
on the steel surfaces of this once elegant ship. These bioconcretions
were first noted growing on the outside and within the ship’s
structures. The scale of these growths led to the adoption of
the term “rusticle” as a derivation of two words,
“rust” and “icicle”. The term “rust”
was elected because the growths had a predominantly rusty colour
while the texture resembled flakes of rust growing on steel
(Cullimore, 1999). The most dramatic, but not necessarily the
largest growths, hung over the sides of the hull and parallel
the structure of icicles.
In character and form, these growths resemble the speleothems
that have been observed in natural limestone caves. These rare
speleothems, originally considered to be secondary mineral growths,
appear to be of subaqueous origin, and show many similarities
to the deep oceanic growths observed at the RMS Titanic. In
their simplest form, both the rusticle's and the speleothems
could be described as elongate structures, incorporating organic
filaments coated by, or included in, a shell of iron oxide and/or
calcite. In the Lechuguilla Cave, New Mexico, the speleothem
growths are described as hanging down in ways that closely resemble
the rusticle's at the RMS Titanic (Davis, Palmer and Palmer.
1990). These cave growths are irregular, consisting of iron
oxide stalactites and calcite encrusted columns. They are all
of ancient origin (greater than 100,000 years) and are now dry
and inactive. Microscopic examination reveals that the speleothems
are primarily iron oxide deposits covering organic filaments.
These encrustations were deposited via oxidative reactions that
may have been initiated by bacteria. Other unusual cave features
related to rusticle's in form, but not based on iron oxides,
include pool fingers. These stalactiform subaqueous growths
are calcite-encrusted organic strings, interconnected by curved
bridge structures. In Wind Cave, South Dakota, hollow subaqueous
calcite speleothems known as “helictite bushes”
that grow in an upward branching pattern, have been identified.
These growths again, closely resemble rusticle's and pool fingers.
They include fossil bacterial traces, but may be more closely
related to the submarine “white smokers” than to
either rusticle's or the pool fingers (Davis, 1989, 1991; LaRock
and Cunningham, 1995).
The bioconcretious rusticle's vary in colour, texture, size
and form. The variations of colour, particularly the brilliant
orange-brown colour of the rusticle's, is due to the highly
oxidized ferric iron content. Closer examination of the rusticle's
by Pellegrino and Cullimore (1997), Wells and Mann (1997) and
Mann (1997) revealed that the rusticle's are complex structures
involving water channels, reservoirs, complex iron plate-like
structures, thread-like spans, porous matrices and ducts connecting
to the outside. Within the rusticle structure, there appears
to be a number of different microbial strains occupying specific
sites. These were identified using the Biological Activity Reaction
Tests (BART™, Droycon Bioconcepts Inc., Canada) to include
sulfate reducing bacteria (SRB), iron related bacteria (IRB),
heterotrophic aerobic bacteria (HAB), denitrifying bacteria
(DN), and archaeobacteria, together with a range of fungi. Six
different forms of rusticle's were noted, however all bore the
common characteristics of diverse and site-focused bacterial
consortia.
The supporting structures appeared to be dominated by a mesh-like,
heavily mineralized matrix in which goethite was dominant. The
presence of goethite in rusticle's was confirmed by Garzke et
al, 1997. In addition, iron oxide sulfate complex, known as
green rust (Fe+23.6 Fe+30.9(O--, OH-, SO4--)9) was found (Garzke
et al, 1997). A large hanging rusticle, recovered from the ship
in 1996, was analyzed by electron diffraction x-ray, which revealed
that iron was the dominant atom within the range of atoms tested.
The relationship was (dominant atom first): Fe > Na >
S > Cl > Ca > Mg > Si > P > Mn. There was
a considerable variation in the elemental composition for the
various samples analyzed, reflecting the heterogeneous nature
of the structures within the rusticle's Where goethites dominate
the structure, the iron (Fe) concentrations would be very high,
while other components within the rusticle (e.g., the water
channels and porous regions) would have lower iron levels. Rusticle's
also vary widely in size and form. Video imagery reveals rusticle
sizes ranging from tiny tubercles or encrustations to massive,
braided or rope-like bioconcretions, exceeding 3-4 meters in
length. The rusticle's form also varied from flat, plate like
growths to convoluted and intricate growth patterns .Relevance
of Rusticle Activities to the Maritime Industry
The investigations to-date on the rusticle's has revealed that
they are capable, under suitable conditions, of extracting iron
from steel at significant rates. This biological extraction
has the potential to seriously compromise the physical structure
of a ship. The time frame for such compromise would appear to
be based on the visual evidence. This evidence has been gathered
from various sunken vessels (e.g., Bismarck, Yorktown, Derbyshire
and the RMS Titanic), located at various sites around the world.
There remains the potential for the covert growth of rusticle's
within ships during the normal operational life span. Covert
growth would mean that the rusticle's would thrive at sites
within the body of the vessel, particularly those that are not
commonly inspected, and where conditions are conducive for growth.
In a ship’s structure, areas that are most vulnerable
include welded areas and areas that have severe stress concentrations.
(Mansour, Wirsching, Lucket, Plumpton and Lin. 1997). It is
estimated that 2 bulk tankers are lost every month, with 45%
of these losses due to heavy weather and structural damage.
This category is further described as “strained crack
in hull”, concluding that structural failure is the major
cause for the rising number of bulk carrier losses. This can
be seen from the December 12, 1999 sinking of the Erika during
a storm off the French coast. The 25-year-old tanker Erika broke
in two, spilling about 15,000 tons of fuel oil, polluting 250
miles of beaches, killing or maiming 300,000 sea birds. The
classing agency for the tanker, RINA, reported the initial findings
into the cause of the accident pointed to a small structural
failure in hull structure. This structural failure led to further
cracking and finally to the collapse of the hull (Hauley, Barbara.
2000). These structural failures can be a result of corrosion
and fatigue cracking. This, in conjunction with biological attachment
from within the tanker itself, can result in the loss of a ship’s
integrity (Ma, Orisamolu, Bea and Huang. 1997).
A range of factors would be important in considering the potential
for these rusticle's to grow rapidly enough to compromise the
normal life-span and sea-worthiness of the ship. These factors
could include, but are not necessarily limited to, suitability
of steel surfaces on which rusticle's can form and function,
a high level of humidity or a water saturated environment, oxidative
conditions, greater than 1.4% salt concentration in the water,
temperature gradient, turbulence, nutrients, electrically charged
surfaces and neglect. A typical example of a condition where
these rusticle's could infest and compromise the integrity of
the ship would be between hulls and in compartments where there
would be a confined environment in which conditions could become
conducive to growth.
The most likely sites for a rusticle infestation to occur would
require a number of variables to be achieved. These would include
surfaces or areas where the steel is poorly protected with paint,
embrittled by stress, electrically charged in any way, involved
in rhythmic movement of water over the site, positioned on a
temperature gradient, and/or areas where available water contains
sufficient nutrients to support growth. Where a site is not
subjected to regular inspections for example, on a monthly basis,
and/or the rusticle growth is suppressed through the use of
biocides or physical removal, the rusticle growths can then
begin to extract iron from the steel and weaken the afflicted
steel structures. It is a common practice to presume that the
appearance of rusty encrustations are merely the result of physical-chemical
activity and are an inevitable part of the normal deterioration
that may be expected. Traditionally, the appearance of rust
within an enclosed chamber has not been viewed as a living mass
that is “eating” away at the steel, but rather that
the rust is an inevitable chemical event for which solutions
may be ineffective over the long term.
In the water well industry, it is now acknowledged that the
bulk of the plugging and clogging events that occur down a well
are actually biologically derived. Comparable studies have revealed
that it is the same groups of bacteria that are involved in
these events both down in water wells and deep down at the site
of the RMS Titanic. Similar rusticle structures are observed
at both sites. The question therefore becomes whether steel
fabricated ships floating on the surface, or the RMS Titanic,
a splintered steel structure lying on the ocean’s floor,
are subject to the same bacterial challenges as water wells,
which involve steel structures set into the ground water. The
arrival of non-indigenous organisms, such as the Zebra Mussel
(Dreissena polymorpha), plaguing North American water systems
appears to have arrived as covert passengers in or on water
going vessels. |
part 2 cont...click
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