cathodic protection offshore
TRANSCRIPT
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Seawater pipeworkanti-fouling systems
Impressed current cathodicprotection systems
World leading technology for the offshore oil industry
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A single source solution for semi-
submersibles, FPSOs and FSOs
Cathelco and Jotun have combined orces to providea unique protection package or semi-submersibles,
FPSOs and FSOs. The strategic alliance provides a truly
comprehensive service or customers in the oshore
market worldwide.
Together, the companies provide a single source solution which can
combine ICCP hull corrosion protection with a high perormance
coatings package. I required, it can also include the provision o
seawater pipework anti-ouling systems to protect seawater li t pumps.
Through Cathelco you can have one point o contact or the entire
project backed by world leading expertise. On one hand, this draws on
Cathelcos record o experience spanning 50 years and over 20,000
installations on ships and oshore structures. On the other, it providesworld leading expertise in coatings technology based on Jotuns record
o quality and innovation.
Beyond this are the combined resources o two highly experienced
agent networks bringing sales and technical advice close to hand
wherever you are in the world.
Cathelco and Jotun working together to bring you a single source
solution combining cost-eectiveness, quality and long lasting reliability.
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Cathelco seawater pipework anti-ouling systems are designed
to prevent blockages caused by the growth o barnacles
and mussels in seawater lines. These can be expensive and
time consuming to remove, particularly in rigorous oshore
applications.
The Cathelco system is based on the electrolytic principle and
consists o a transormer/rectier which eeds an electrical
current to copper and aluminium anodes. In operation
the anodes produce ions which are carried throughout
the pipework system creating an environment in which
barnacles and mussels cannot settle or breed. The action
is assisted by aluminium hydroxide created by the aluminium
anodes which focculates the released copper. The highly gelatinous
copper aluminium hydroxide foc is carried throughout the system, spreading
into the slower moving areas close to the pipe surace where marine growth
larvae are most likely to settle. At the same time, a cupro-aluminium lm is built
up on the internal suraces o pipes to suppress corrosion
lOshore platorms seawater lit pumps protected using specially designed
anode units.
lSemi-submersibles anodes mounted in strainers or specially designed
electrolysis tanks.
lFPSOs anodes can either be mounted in seachests, strainers or electrolysis
tanks according to the requirements o the vessel.
Seawater pipeworkanti-fouling systems
Impressed current cathodicprotection systemsIn most cases, impressed current cathodic protection (ICCP) systems
are used in conjunction with specialised coatings to protect the
submerged suraces o semi-submersibles and FPSOs against
corrosion. Cathelco are in a unique position to oer advice on how
these systems can be combined or maximum eectiveness.
ICCP systems consist o a control panel/rectier connected to an
arrangement o anodes and reerence electrodes. In operation,the reerence electrodes measure the electrical potential at the
hull/seawater interace and a signal is ed back to the control panel
which raises or lowers the anode output accordingly. In this way, the
optimum level o corrosion protection is provided at all times.
lSemi-submersibles Specially designed ICCP systems or hybrid
systems using a combination o ICCP equipment and sacricial
anodes.
lFPSOs - ICCP systems or FPSOs using diver change reerence
electrodes and anodes.
lJack-Up Rigs Economical Minitek ICCP systems to protect jack-up
rigs when they are in transit.
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Pipework anti-fouling systems
for seawater lift pumps
Oshore structures are oten situated in relatively
shallow water where marine organisms breed moreprolically. This makes seawater pipework particularly
vulnerable to blockages which can have serious
consequences or the eciency o seawater cooling
and re ghting equipment.
Pump unit constructionCathelco pump protection anti-ouling units are designed to be
mounted at the bottom o pumps, oten inside the stilling tube or
caisson. They consist o special copper and aluminium anodes
housed within a steel ramework and ed with an electrical
current rom a transormer/rectier. The anode mounting rame
acts as the cathode, creating a completely sel contained unit
which is electrically isolated rom the pump using a specially
designed isolation kit.
Controlled dosingAlthough the seawater is dosed to higher concentrations than
sea-going vessels, this is sucient to prevent marine growth
and suppress corrosion within the pipework. The Cathelco unit is
automatically activated when the pump is switched on, however,
a low dosage is maintained at all times to keep the bottom o thepump and strainer area ree rom bio-ouling.
Anode lifeThe lie o the anodes is calculated to coincide with the scheduled
maintenance period or the pumps, typically at intervals o
between 2 and 5 years.
Deck mounted and tank systemsIn some cases it is not practical to t anode units within
stilling tubes due to lack o space or unusually high dosage
requirements. An alternative is to provide a deck mounted
electrolysis tank with a pipework system to distribute thedosed seawater to the bottom o each pump where it is carried
throughout the pipework by the seawater fow.
DC Cable
Control Panel
Caisson
Strainer
Pump
Electrode Unit
Waterflow
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ICCP systems forsemi-submersibles
Control PanelsCathelco oer a choice o
modular or thyristor control
panels. Modular panels can be
used on systems o up to 350
amps and have the advantage o
being lightweight and compact.
Thyristor panels can be used onsystems o up to 1,000 amps and
combine cost eectiveness with
rugged reliability. Both types o
panels incorporate computerised
output displays, alarms and
inormation systems.
Reference ElectrodesReerence electrodes measure the electrical potential at
the hull/seawater interace and eed a signal back to the
control panel. They have zinc elements and are diverchangeable enabling them to be replaced rom the outside
o the hull by a diver.
AnodesA range o anode designs are available or oshore
applications. These include rod anodes, fush mounted
disc anodes and linear loop anodes which emit a powerul
current rom a relatively small surace area. All o the
anodes are diver changeable, simpliying replacement.
Diver change rod anodes
Reerence Electrode
Disc Anode
Rod Anode
Control Panel
Diver change disc anodes
Diver changereference electrode
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FPSOs generally have numerous seawater intakes serving
engine cooling, product processing, re ghting and a range oauxiliary services which can include the provision o a potable
water supply. It is essential that all o these unctions are
protected by an eective and reliable seawater pipework anti-
ouling system.
Seachest mounted anodesCopper and aluminium anodes can be mounted in seachests
i the scheduled drydocking period or the FPSO is less than 5
years, assuming there is sucient space availability.
Strainer mounted anodes
The advantage o strainer mounted systems is that the anodescan be changed at any time without the need or drydocking.
In these circumstances, Cathelco recommend that some o
the treated water is ed back to the seachests to ensure that
they are kept ree rom ouling.
Electrolysis tank systemsI the drydocking interval is greater than 5 years, an electrolysis
tank system may be the most practical option. In this case,
a eed is taken rom one o the seachests and pumped to
the electrolysis tank housing the copper and aluminium
anodes. The seawater is treated at a high dosage rate and
then distributed via pipework to multiple seachests where it is
diluted by the incoming fow and achieves a normal dosagerate to protect against bio-ouling.
lEective and reliable anti-ouling protection.
lAutomatic requires minimal attention.
lDoes not involve the use o chemicals.
lEnvironmentally riendly.
Marine pipework anti-foulingsystems for FPSOs
TYPICAL SEACHEST ANODE ARRANGEMENT
Valve
StrainerCathelcoAnodes
SeawaterCooling Line
To Heat Exchangers,Oil Coolers,Evaporators,Fire Pumps andAncillary Systems
TYPICAL STRAINER ANODE ARRANGEMENT
Power in
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ICCP hull protectionsystems for FPSOsand FSOsFPSOs require specially designed ICCP hull corrosion protection
systems because periods between drydocking are signicantly
longer than normal vessels. Other actors such as current creep on
anchor chains also have to be taken into consideration.
On a conventional ship there may be a 15% paint loss over a 5 year
period, but on an FPSO paint loss may exceed 80% ater a 20 year
operational period at sea. Thereore, the skill in designing an ICCP
system or an FPSO relies on understanding these dierences and
using equipment which meets the demand or long lasting reliability.
Cathelco systems use diver change anodes and reerence
electrodes which can be changed rom the outside o the hull,
simpliying replacement. There is also the option o using Jotun
diver change circular anodes and reerence electrodes which are
designed with vulcanised rubber coatings to create a watertight seal
with the coerdam or easy installation and replacement.
As FPSOs are stationary in the eld they are tted with orward and
at systems, providing a 50/50 current output, unlike conventional
vessels which have higher current demand around the stern.
As with all oshore acilities demanding the highest levels o
perormance, reliability and saety, Cathelco hull protection systems
have a minimum 1.5 times redundancy actor built into the design,
subject to specication.
Through a comprehensive understanding o cathodic protection and
technical innovation in equipment design, Cathelco are maintaining
their position as leaders in hull protection or this ast developing
area o oshore production.
Diver change linear loop anode
Diver change rod anodes
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Systems for offshore
vessels
Cathelco seawater pipework anti-ouling
systems have been tted to numerous
oshore supply vessels, tugs and re
ghting crat throughout the world. On
smaller vessels, space saving control
panels and a range o anode designs
simpliy installation. ICCP hull corrosion
protection systems are also available oroshore vessels, oering reliable, long
term protection at an economical cost.
Subsea pipeline corrosion
protection surveys
Corrintec, a division o Cathelco,
specialises in subsea pipeline corrosion
protection surveys using trailing wire
and ROV techniques. They gather and
analyse data concerning the status o
cathodic protection systems enabling
clients to make inormed decisions
about maintenance.
Jotun Marine Coatings
In more than 50 countries, Jotun
Marine Coatings, assists and advises
customers on the most eective
solutions to the prevention o corrosion
and ouling.
Jotun is active in every aspect o
coating technology. This expertise is
built on investment, innovation and
the practical knowledge earned in the
protection o more than 15,000 vessels
and oshore platorms throughout the
world.
Cathelco Ltd, Marine House, Dunston Road,
Chesterfeld S41 8NY United Kingdom
Telephone: +44 (0) 1246 457900
Fax: +44 (0) 1246 457901
Email: [email protected]
Web: www.cathelco.com
We recommend Jotun coatings
Worldwide Service NetworkOur worldwide network o sales and service centres can provide
immediate advice and assistance on the complete range o
Cathelco products. Agents contacts details are available on our
website:www.cathelco.com
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