International Workshop on Advanced Research

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International Workshop on Advanced Research
Development of Coatings for Corrosion Protection
of Offshore Oil Gas Operation Facilities,
Marine Pipeline and Ship Structures   Organized
by Colorado School of Mines in cooperation with
MMS   Practical Experience Paper Presented by
Anil Mewara, Manager Offshore Operations, MODEC
International LLC, Houston
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Introduction Our practical experience of one
MODEC operated ship shaped FSO located in the
Southern Gulf of Mexico. Over the past couple of
years, concern has been expressed that locating
FSO/FPSOs in U.S. waters is not safe from
pollution point of view. MODECs experience with
operating our FSO in GOM has been quite
successful over the past six years without any
incident of oil pollution and has an excellent
HSE record.
The very concept of FPSOs is based on exploiting
marginal oil fields and it is customary for all
our clients to demand an FPSO that will operate
in one location for 15 to 20 or even 25 years
WITHOUT DRYDOCKING. Either zero or minimal few
hours every month, the downtime does not allow
the contractor any freedom.
Right from FEED study, the contractor must ensure
optimum corrosion protection for the operational
life. thickness of steel plating, still retains
the integrity of the hull over the entire life
expectancy.
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TAKUNTAH General Information and
Capabilities TAKUNTAH was converted to an FSO
in Singapore in 1997/98. Fatigue analysis over
the designed life extension of 15 years resulted
in renewal of about 1200 tons of steel. During
conversion, ballast tanks were completely coated.
Cargo tanks were partially coated underdeck and
at the bottom, to a height of 3.0 and 1.0 meters
respectively. Cargo piping system was designed
with extra thickness and were coated on the
inside.
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In the 68 months of operations, 715 tankers have
been loaded for an export quantity of 400 million
barrels of crude. For many continuous periods of
a month or more, frequency of tankers has been
every 28 hours.   Inspite of such high
commercial demands, MODEC is proud of the fact
that there has been no downtime and no incident
of oil pollution in over 2000 days of continuous
operations. TaKuntah is maintained in class and
operates in compliance with all applicable
Mexican and International Maritime Regulations
including the ISM code.
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Brief details of Corrosion Protective
Systems   Paint Systems Ballast Tanks Full
coated. Sacrificial anodes installed. One
Stripe coat 500 Microns Epoxy holding primer
50 Microns Coal tar epoxy system 2 coats x
150 Microns/coat Slop Tanks Fully coated.
Sacrificial anodes installed. One Stripe Coat
500 Microns. Epoxy holding primer 50
Microns Coal tar epoxy 2 coats x 150 Microns
each  
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Cargo Tanks Partial coated (top bottom 3.0
and 1.0 meters respectively) Hull
Topsides 4 coat system (275 mic. Total
thickness) as follows Zinc silicate 75
mic. Micaceous iron oxide epoxy 2 coats x
125 mic/coat Polyurethane 50 mic   Hull
Wind/Water Area 5 coat system (490 mic. Total
thickness) as follows Epoxy primer 40
mic Glass flake epoxy 2 coats x 150
mic/coat Micaceous iron oxide epoxy 100
mic Polyurethane 50 mic
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Hull Under Water 6 coat system (865 mic total
thickness) as follows Epoxy primer 40
mic Glass flake epoxy 2 coats x 150
mic/coat Coal tar epoxy 75 mic Self
polishing copolymer anti fouling system 3
coats x 150 mic/coat Deck Area Epoxy coating
system 2 coats x 250 mic/coat Piping External
Coal tar epoxy 2 coats x 150 mic/coat Internal
Glass flake epoxy 2 coats x 200 mic/coat
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Remarks Side and bottom plating were inspected
without detecting damage. Paint coat in good
overall condition. No relevant marine growth was
found
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Remarks The welds were sample inspected on the
forward, amidship and after including both sides
of the hull. No relevant damage was found.
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Remarks Both bilge keels were thoroughly
inspected. No relevant damage was found.
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Impressed Current System For Hull Wilson
Walton Aquamatic III Lead/silver Anodes fitted
on both sides of hull in forward/
amidships/stern areas. These anodes were
fitted over specially coated areas with
di-electric coating. Marine Growth Protection
system Cathelco anti-fouling and
ferro-injection system for seachests and SW
pipes.
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Remarks All the seachests were inspected and the
dirt was removed. No relevant damage was found.
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Corrosion Control During Operations In
recognisition of the 15 years designed life
expectancy, following controls are exercised
during operations A. ICCP and Cathelco readings
are monitored daily and monthly log is sent to
technical department of supplier for their
appraisal and recommendations if any are duly
complied with. B. At every periodical tank
inspection, coating is touched up wherever it
may be disturbed. Surface is prepared by hand
tools. In this regard, particular attention is
paid to the aftermost bay and area just below the
suction bell mouth, which is subject to
cavitation. During conversion, the bell mouth
was raised by 2 inches to gain access for this
maintenance. C. At every periodic inspection
inside the tanks, thickness gauging is carried
out and readings compared with original readings
from the conversion yard. By and large, coatings
are found better than 99 intact and thickness
readings do not show any deterioration.
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D. Tank anodes are inspected for any wastage.
Having been fitted in already coated areas, the
wastage so far is noted to be negligible. E. Acidi
c attack, that can be caused by the presence of
H2S gas released by the Maya crude cargo on the
upper parts of cargo tanks, is minimized by
causing dilution with fresh inert gas and
purging. F. PV valves and self closing devices on
the tank vent pipes for ballast tanks are
maintained in good condition to prevent ingress
of fresh air into tanks. G. The in out
lengths of anchor chains are measured for
thickness at every five yearly interval to check
on undue wastage. At last recording, this
wastage was noted to be less than 2 on the
diameter. H. Maintenance of deck plating and
fittings above deck are continuous maintenance
items and are descaled and touched up or coated
as necessary. I. The exterior of the hull,
where accessible, is touched up with paint as
necessary.
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Remarks Max. of wastage detected less than 3
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J. The glass flakes coating in way of fenders,
does provide extra protection against
abrasion. K. The inaccessible underwater areas of
hull are inspected with the help of divers every
2.5 years. Obviously no maintenance by way of
recoating is possible. However, at such
inspections, it has been noted that the
extensive coating system applied at the
conversion yard is by and large fully intact.
Where superficially disturbed, it is noted that
substrata of paint coating is quite intact still.
At last underwater inspection carried out by
divers and monitored on deck with video cameras,
in March 2003 (i.e. 5 years after drydocking),
showed that there was hardly any sea growth
barnacles etc. This indicates that anti-fouling
coats are still effective. We have no delusions
that this can continue for another 10 years.
However, we feel confident that corrosion
if/when it starts will not cause the integrity
of hull to be unduly effected.
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L. It may be added that the rudder and propeller
areas which are isolated from the ICCP system,
are extensively covered with barnacles. This for
an FSO/FPSO is inconsequential as at the end of
their life, they will be towed away. M. During
such underwater inspection, particular attention
is paid to the seachests and their external
gratings. If necessary, gratings are removed to
the deck and recoated. Anodes inside the tanks,
are noted to be quite active and when needed,
they can be replaced.
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Remarks In good overall condition.
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Remarks In good overall condition.