Download Retrofit of Real Time Impressed Current Cathodic Protection

Retrofit of Real Time
Impressed Current Cathodic
Protection
MAKING LIFE EXTENSION A VIABLE OPTION
Andy Smerdon – CEO, Aquatec Group
Oceanology International, London, 16 March 2016
© 2016 Aquatec Group
Overview
• Introduction to Aquatec
• Cathodic Protection (CP) Primer
• The Problem
– Ageing Offshore Structures
• The Solution
– Retrofit CP System
– Real-Time CP Monitoring
– Controlling the System
© 2016 Aquatec Group
Aquatec Group Ltd
• Founded in 1990
• Headquartered in
Basingstoke UK
• Design and manufacture
all products and
engineered solutions
• Products sold worldwide
• ISO 9001, ISO 14001
BS OHSAS 18001
Customers in the offshore market
© 2016 Aquatec Group
Cathodic Protection Primer
© 2016 Aquatec Group
Steel in Sea Water
WHY DOES STEEL CORRODE IN SEA WATER?
• Galvanic corrosion – requires three conditions:
1.
2.
3.
Two dissimilar metals
Both immersed or in contact with the same electrolyte
An electrical connection or joining of the two metals
• The two dissimilar metals may be different – for example
steel and aluminium.
• They may be a single piece of the same metal with
metallurgical differences at the surface
© 2016 Aquatec Group
Corroding Steel
• Two similar steel plates welded together and immersed in sea
water fulfil the three conditions for galvanic corrosion because
the conditions at the surface vary according to depth and water
composition
• The following corrosive reaction takes place at more active
sites:
• The free electrons travel through the steel to less active sites,
where the following reaction takes place:
© 2016 Aquatec Group
Corroding Steel
• Recombination of these highly reactive ions at the active
surface produces the iron corrosion product ferrous
hydroxide:
• This reaction leads to current flow through the sea water
from the more active site (anode) to the less active site
(cathode), and the iron is depleted
© 2016 Aquatec Group
Control of Corrosion
FOUR METHODS
– Material selection – design
avoid galvanic cells
– Coatings
isolate metal from oxygen
– Environment
remove the oxygen
– Change the potential
cathodic protection
© 2016 Aquatec Group
Cathodic Protection (CP)
• CP controls corrosion of a metal surface by making all of
it work as the cathode of an electrochemical cell
• CP prevents corrosion by converting all of the anodic
(active) sites on the metal surface to cathodic (passive)
sites by providing free electrons (electrical current) from
another source.
• There are two types of CP…
© 2016 Aquatec Group
Sacrificial Anode CP (SACP)
• Sacrificial Anode CP
supplies the
protective current
through the
attachment of
preferentially
corrosive metals
(e.g. Zinc,
Magnesium,
The anode metal is sacrificed and depleted
Aluminium).
over the lifetime of the installation.
© 2016 Aquatec Group
Sacrificial Anode CP (SACP)
• Sacrificial Anode CP
supplies the
protective current
through the
attachment of
preferentially
corrosive metals
(e.g. Zinc,
Magnesium,
The anode metal is sacrificed and depleted
Aluminium).
over the lifetime of the installation.
© 2016 Aquatec Group
Impressed Current CP (ICCP)
• Uses permanent, non-corroding anodes supplied with an
external power supply
• Power supply acts
as ‘electron pump’
• Electrons are driven
from the anode to
the cathode
© 2016 Aquatec Group
ICCP In Practice
© 2016 Aquatec Group
The Problem
© 2016 Aquatec Group
The Problem
• Exploitation of offshore oil expanded in the 1970s.
• Platform design life based on estimates of reservoir yield
• 5-25 year life extensions now needed thanks to
–
–
–
–
Extended discoveries, satellite wells
Enhanced oil recovery techniques
Tax breaks for “brown field” development
Small lean operators taking over from majors
• Sacrificial CP on older platforms now depleted and
protection is failing
• Older ICCP systems often damaged or failing
• Regulators require reinstatement of
adequate protection levels
© 2016 Aquatec Group
An Example
• UK North Sea platform
• 38 years old
• Requirement for 15
year life extension
• ICCP selected as
optimum method
• Near real-time updates
of cathodic protection
potentials required for
closed-loop control
© 2016 Aquatec Group
An Example
• UK North Sea platform
• 38 years old
• Requirement for 15
year life extension
• ICCP selected as
optimum method
• Near real-time updates
of cathodic protection
potentials required for
closed-loop control
© 2016 Aquatec Group
The Solution
© 2016 Aquatec Group
The Solution
IMPRESSED CURRENT CATHODIC PROTECTION (ICCP)
• ICCP Anode Skids
• ICCP Power Supply
© 2016 Aquatec Group
Component Locations
Skid 2
3
60m
Skid 3
40m
2a
4
2
30m
PSU
1
J-Tube + JB
90m
5
Skid 1
45m
Skid 4
© 2016 Aquatec Group
How to Control the System?
• Existing SACP provides some residual protection
• ICCP must be set to supplement this
• Should not ‘over protect’ the steel as this can cause
damage
• Standard practice is to monitor the Cathodic Protection
potential
• Goal: to provide automated monitoring with remote
access
© 2016 Aquatec Group
Monitor CP Potential
– Maintains constant
potential
• Practical electrodes:
– Silver/Silver Chloride
+0.27 V re Hydrogen
– Zinc -0.77 V
– V2-V1  1.04V
Cathode (steel)
• Use reference electrode as datum to form half cell with
the cathode (steel structure)
V2
• Reference electrode
V1
Ag/AgCl
Zn
Sea
© 2016 Aquatec Group
Monitor CP Potential
• AQUAmodem 500CP real-time CP
potential monitor units
• Measure steel potential with respect to
Zinc & Silver/Silver Chloride electrodes
• Transmit data up to every 15 minutes
using acoustic telemetry
© 2016 Aquatec Group
Monitor CP Potential
• Steel case in contact with
cathode (steel platform)
through:
– Mechanical clamping
arrangement (ROV or diver
installed) 900mm clamp shown,
or
– Mechanical banding, or
– Friction welding
© 2016 Aquatec Group
Acoustic Telemetry: Pros & Cons
Pros
Cons
 Long range potential
 Slow
 Cheaper than long
cable runs
 Needs power:
especially for 2-way
 Cheaper to install
than cable
 Busy communication
channel
 Can be more robust  Acoustic path can be
than cable
problematic
© 2016 Aquatec Group
‘Send and Forget’ concept
• System Analogies
1.
2.
•
•
•
•
•
Static meter display - check when passing or on a schedule
Heartbeat monitor
- periodic tick shows system is healthy
- alarm and increased data when faulty
Measure data at preset rate
Transmit data infrequently if all is well
Increase update rate when alarm conditions are met
Transmission is automatic – no interrogation needed from
the surface
Only powered up when reading data or transmitting
© 2016 Aquatec Group
Monitor Units at Key Positions
Skid 2
3
60m
Skid 3
40m
M13
2a
Mobile
Rx
2
4
M12
30m
M11
PSU
M14
1
J-Tube & JB
90m
Skid 1
5
M9
M10
M8
M7
M6
M5
M4
M3
M2
M1
45m
Skid 4
© 2016 Aquatec Group
AQUAmodem 500CP Acoustics
•
•
•
•
•
‘Send and forget’ principle
Read data infrequently e.g. every 15 minutes
Transmit every hour unless alarm condition is detected
Transmit every 15 minutes if alarm is detected
Message collision avoidance:
– Two transmissions every update period
– Separated by random interval
• Message includes error checking and correction
• Decoding includes multiple validation stages to minimise
false alarms
• Range up to 600 m
© 2016 Aquatec Group
Closed-Loop Control
• Monitor all potentials
– continuously in near real-time
– using acoustics
•
•
•
•
Adjust current output on each skid
Calibrate system response
Control current on basis of measured potentials
Ensure adequate but not excessive protection
© 2016 Aquatec Group
PSU
Complete System
•
Fully integrated system
•
Monitoring
•
Impressed Current CP
•
Closed-loop control
JB
Monitor 1 of 14
Hydrophone
CP data to PSU
ICCP Anode Skid 1 of 4
Current from PSU
© 2016 Aquatec Group
What About Sacrificial?
•
Potential Monitoring
•
Current Monitoring
•
Sacrificial Anode CP
•
Data logging
•
Allows refinement of model
Potential Monitor
Hydrophone
Sacrificial Anode Skid
Return Current
Current Monitor + Data Logger
Sense Potential Drop
© 2016 Aquatec Group
AQUAmodem Op1
FOR REAL TIME DATA AND DATA RECOVERY
Optical Modem
for rapid data
download
© 2016 Aquatec Group
Summary
© 2016 Aquatec Group
Summary
• Retrofit CP solution for ageing offshore platforms and
pipelines
• Compact and efficient power supply
• Easily installed seabed equipment
• Acoustic comms removes need for cabled monitoring
• Real-time acoustics provides closed-loop control
• Capability for sacrificial current monitoring and
logged data retrieval
• A viable CP solution for life of field extension
© 2016 Aquatec Group
Thank you
Any questions?
© 2016 Aquatec Group