cathodic protection offshore

7/27/2019 Cathodic Protection Offshore

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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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cathodic protection offshore

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