Technical Presentations at the October 2010 Meeting
the purpose of this short presentation, suppression of MIC will only be
considered in ship and off shore lubrication systems, fuel systems, and
cooling water systems, and in ship bilge and ballast water.
There are other specific locations where MIC can be occurring in
the marine industry and the general issues discussed today will largely be
applicable there also.
there are several categories of practical antimicrobial strategies,
housekeeping to prevent ingress of contaminating microorganisms
by creating an unfavourable environment for microbial growth and activity
application of physical procedures to kill or remove microbes
application of anti-microbial chemicals
of corrosive agents involved in MIC
system design ensures that water and sludge can readily be removed, that
there are no dead legs or surplus pipes/tanks where undisturbed growth
could occur, and that clean and ‘dirty’ fluids can be segregated so
that no cross contamination occurs.
housekeeping will vary according to particular systems and materials but
could include regular and thorough removal of water from fuels and oils,
prevention of stagnation and prevention of cross contamination.
environments can be created by avoiding the use of or by depleting
essential microbial nutrients, and also by manipulating parameters such as
pH, temperature, water activity (relative humidity) and Redox
When MIC occurs spontaneously where it has not occurred before, it
is usually because there has been an inadvertent change in one of these.
For example, if a lower concentration of anti-freeze is used in a
coolant, this may change its water activity from one which suppresses
microbial growth to one which actively sustains it.
removal of microbes can be as simple as filtration (of microbial
aggregates only), or by any cyclone, centrifuge, or settling device which
can utilise the high density (c. 1.05 g/cm3) of microbes
compared to water or mineral oils, to separate and segregate them.
Physical disinfection methods can be UV (water systems only), but
are more often batch or in line heating.
Other exotic methods exist, such as hard irradiation and
ultrasound, but are theoretical rather than practical on a large scale.
use of anti-microbial chemicals introduces a host of technical and
Technically they must be appropriate to the target organism,
compatible with the fluids and materials in the system treated, have
appropriate regulatory approvals, and endorsed by machinery and systems
designers, and last but not least, capable of safe use and safe disposal.
There is no wonderful magic chemical bullet which kills all of the
microbes all of the time, and active chemicals and appropriate
concentrations and formulations of them, must be selected and applied
according to particular circumstances.
or removing microbes does not necessarily stop MIC and it mat be necessary
to remove corrosive agents such as acids or hydrogen sulphide.
choice of strategies may seem bewildering, more so if several strategies
are deployed at the same time.
The choice will be discussed in relation to the marine MIC
locations outlined above.
There is no guarantee of success and monitoring for microbes and
MIC with on-site tests, to validate efficacy of the strategies
implemented, should be an integral part of MIC suppression in systems at
indicates that the introduction of eco-friendly fuels, lubricants and
additives is increasing risk of microbial growth and MIC and it should be
anticipated that new problems will arise, as they have done several times
over the last few years.
This presentation looked at the potential for savings in three main areas, by means of examples and case studies. Causes and remedies for the corrosion-related signatures: Power Frequency ELFE (Extremely Low Frequency Effect), Shaft-Related ELFE, Underwater Electric Potential and Corrosion-Related Magnetic were discussed. Typical cost comparisons were made between 1-zone and 3-zone ICCP systems.
By specifying an ICCP system with a relatively large number of anodes and running the anodes at a relatively low maximum voltage, it is possible to enhance:
· SURVIVABILITY by reducing corrosion-related signatures
· AVAILABILITY by reducing the amount of time out of service due to corrosion
· SUSTAINABILITY by reducing a vessel’s carbon footprintOVERALL COST due to reduced running costs and corrosion-related maintenance/repair costs.
Erosion-corrosion causes problems to
many industries due to the synergistic interaction between these
processes. A semi-empirical
model developed at the University of Southampton has been used to evaluate
erosion-corrosion of stainless steel UNS S31603.
It was found that the model predicted high synergistic interaction,
indicating that the accelerated corrosion due to oxide film removal was
not the only synergy mechanism present.
The aim of this work was to study the microstructure of UNS S31603
subjected to erosion-corrosion to inform the modelling process.
Electrochemical noise measurements were performed to study the
effect of velocity, sand size and sand concentration on the corrosion
current. The rise in current
levels during solid particle impact was due to the erosion enhanced
corrosion synergistic effect.
Post-test analysis was done using SEM,
FIB and TEM. SEM analysis on
the surface revealed that each particle impact cuts into the material to
form lips and craters and these features start to overlay each other after
a short period. The
generation of surface roughness due to this process is believed to affect
the adherence of the passive film and generates microgalvanic sites on the
metal surface. Micro-cracks
were observed running from the surface into the subsurface along with
embedment of particles and oxide film.
The density of cracks was observed to be significantly lower in the
pure erosion sample compared to the erosion-corrosion sample, indicating
that the corrosive fluid accelerates crack propagation. Physical models
have been developed to explain these mechanisms.
Rajahram*, T.J. Harvey, J.C.Walker, S.C.Wang, R.J.K. Wood; National Centre
for Advanced Tribology, School of Engineering Sciences, University of
Southampton, UK. *: [email protected]]
The copper-30% nickel alloy has been
used for submarine seawater cooler tubes for many years.
The alloy forms a thin, adherent, cuprous oxide when exposed to
clean, oxygenated seawater which can offer corrosion resistance.
The deliberate formation of this protective surface layer on new or
cleaned tubes prior to service is known as 'conditioning'.
Recent leaks in new and cleaned cooler tubes have been experienced
after only short periods of operation.
These tubes have been found to contain deep, isolated, penetrating
pits. The effectiveness of
conditioning treatments and the nature of the corrosion have been
Influenced Corrosion (MIC) has been suggested as the cause. This paper
presents some of the studies conducted in support of this problem. It
includes the evaluation of various conditioning treatments and other
studies to improve the understanding of the observed problem.
© Copyright QinetiQ limited 2010 [John C. Galsworthy and Robin S.
Oakley, QinetiQ ltd. Cody Technology Park, Farnborough, GU14 0LX, UK]