Download Rio Tinto Dampier Salt Operations Mistaken

PROJECT PROFILE
PROJECT PROFILE
Rio Tinto Dampier Salt
Operations Mistaken Island
Mooring Dolphin Repair Project
Introduction
The Rio Tinto Dampier Salt Limited
mooring dolphins were constructed
in 1971 in conjunction with the load
out wharf and ship-loader platform
at Mistaken Island in the Burrup
Peninsular Archipelago, 1250km north
east of Perth and 21km northwest
of Karratha in Western Australia.
The dolphins or ship berthing
stations are used for the shipping of
up to 4.2 million tonnes of salt per
annum. The dolphins comprise seven
reinforced concrete platforms 7.5m
long x 4.57m wide by 1.55m to 2.15m
deep supported by ten steel encased
reinforced concrete driven piles.
Situated in a severe marine
environment, the reinforced concrete
dolphins have been subject to 40 years
of chloride attack associated with
saltwater windblown spray and splash.
Some of the dolphins had previously
been conventionally patched
repaired in 1984 and 2009, but it was
recognised in 2010 that dolphins
3, 4 & 5 were in need of further
remediation using cathodic protection
(CP). Invitations to tender were
called in March 2011 and following
a detailed review of submissions,
Duratec Australia was awarded the
works in May 2011 on the basis of its
alternative proposal which included
design and installation of a Hybrid CP
system, (the first in Western Australia),
which satisfied the need for a simple,
cost effective, robust, long-term
reinforced concrete protection system
in this environment.
Hybrid CP – Background
Many reinforced concrete structures
suffer attack from ingress of water
soluble salts into the concrete and
or carbonation of concrete due to
atmospheric exposure leading to loss of
passive alkaline conditions surrounding
the embedded reinforcing steel. The
associated corrosion of the reinforcing
steel is an electrochemical process and
the most effective means of arresting
this process is to apply electrochemical
treatments. One recently developed
preventative treatment is called Hybrid
Cathodic Protection. This technology
is a combination of electrochemical
treatments using both an impressed
current and a galvanic anode cathodic
protection phase. An impressed current
is applied to the reinforced concrete
for a short period, (7-10 days), during
which propagating acid corrosion
sites are neutralised to re-passivate
the reinforcing steel. The system then
reverts to a galvanic anode system
providing a relatively low current to
maintain the passive condition of the
reinforcing steel and prevent long term
further corrosion. This simple cost
effective corrosion control process is
robust, rapidly inhibits corrosion, can
be applied in shutdown conditions,
requires no long term power supply,
requires no long term maintenance
and can easily be monitored. For these
reasons the client chose to adopt this
treatment for the Dampier Salt mooring
dolphins.
The Contract
The initial contract works included
the following on mooring dolphins
3, 4 and 5:
Remediation of the reinforced
concrete including design supply,
installation and commissioning of
Hybrid CP;
Hawser rail replacement; and
Removal of existing fenders and
the assembly and installation of
replacement fenders.
In addition, the contract required
the following works on all seven
mooring dolphins:
Existing mooring hook removal and
replacement; and
Installation of access bridge
mounting plates.
A further contract was also awarded
which involved the following
refurbishment works on dolphins
3, 4 and 5:
Removal of ancillary steelwork and
marine growth from all ten piles of
each dolphin; and
Surface preparation and installation
of a heavy duty marine pile
protection system to the steel piles
for 5.8m below the soffit.
Details of the Works
Concrete Remediation
and Hybrid CP Installation
The works commenced in June 2011
with the shutdown of all ship loading
for a period of eight weeks. Work
was performed around the clock
commencing with removal of existing
fenders using a barge mounted crane
and installation of fully encapsulated
scaffold access platforms on dolphins
3, 4 and 5. Delaminated cover
concrete removal was performed
using the hydro-demolition technique
employing the use of a filter-cloth
debris capturing system and waste
water quality monitoring throughout
to satisfy environmental requirements.
Dolphins on a moonlight nightshift.
Original dolphin condition.
p.38 CORROSION & MATERIALS
Original soffit condition.
Original fender hook condition.
Low tide access condition.
Concrete and steel condition after cover concrete was removed
by hydro-demolition.
Reinstated cover concrete.
Old fender removal by barge.
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PROJECT PROFILE
The exposed reinforcing steel was
replaced or augmented where greater
than 20% loss of section occurred.
All reinforcement was checked for
electrical continuity, with isolated
areas requiring welding in place
of 6mm bar to make good. While
the reinforcement was exposed,
negative cable connections were
made along with the installation of
permanent reference cells. This was
closely followed by dry spray gunite
application of cover concrete to
restore the original surface profile and
when sufficiently cured, core drilling
and installation of 20mm studs
for fender cone and chain anchor
points. Mooring hook removal and
replacement works were performed
concurrently during these works.
Progressive installation of the design
approved Hybrid CP system followed
involving the following procedures:
Drilling and initial soaking for 24hours
of anode holes 30mm dia. x 150mm
deep in vertical faces and soffit;
PROJECT PROFILE
Installation of anodes in alkaline
paste backfill;
rogressive powering of each
P
zone using a temporary TR at
12 volts for 10-12 days with current
recorded daily;
Passage of a minimum charge of
50KCoulombs/m2 rebar area in each
zone with the aim of re-passivating
the reinforcement;
Once the applied charge criteria had
been met, the system was converted
to galvanic mode with the rebar
negative connection connected to
the titanium wire connection in the
junction box. The galvanic current
achieved was between 2 and 3mA/m2
of reinforcement; and
Backfilling of titanium wire slots with
cementitious repair mortar.
Evaluation of the system performance
was assessed against a corrosion rate
criterion based on the Stearn Geary
Equation with a targeted corrosion rate
of less than 2mA/m2 of steel which
is equivalent to a corrosion rate of
2mm section loss in 1000 years. This
criterion has been recently adopted by
the latest European Standard BSI EN
ISO 12696:2012 Cathodic Protection of
Steel in Concrete. This was measured
by recording the galvanic current
of each subzone and completing an
instant-off and depolarisation test,
(similar to ICCP), utilising these figures
to calculate actual corrosion rates.
Corrosion rates so obtained were all
below the 2.0mA/m2 target.
Pile Protection Application
Pile surface preparation and
wrapping was undertaken using
a specialist diving contractor and
installation of the Denso Seashield
Series 200FD heavy duty marine
system. This was complemented by
a conventional abrasive blast surface
preparation and the application
of Interzone 954 high-build epoxy
protective coating system applied in
the complex geometry zones.
New Fender Installation
On completion of these works
installation of the new pre-assembled
fender units was performed using
a 35m barge with 20 tonne lifting
capacity to place the 10.5 tonne
units comprising:
New mooring hooks were installed.
a team environment. There were many
challenges which the project team had
to face. These included:
Major logistics working on multiple
dolphins separated by water;
Front fender panel;
Fender rubber cone;
Fender cone flange plate; and
Support and link chains.
New fender at work on dolphin 3.
Access restrictions;
Working 12 hour shifts 24/7 for
8 weeks;
Working over water;
Co-ordinating multiple tasks in
limited space and access only by boat
with a large workforce;
Difficult weather conditions including
wind and high temperatures;
Precision works on concrete
structures; and
High tidal range;
Operating in a sensitive marine
environment.
Underwater works;
Project Summary
A project like this can only
be delivered by sound project
management and the commitment
of the entire workforce including
specialist subcontractors to working
collaboratively and harmoniously in
It was with a strong team approach that
despite these challenges all of the works
were completed safely, on time and
within the eight week shutdown and
without incident.
Acknowledgements
Our thanks go to the project
management team at Rio Tinto DSL,
Infracorr Consulting, and Bhagwan
Marine, Seaforce, the Duratec Project
Management team and work crew and
subcontractors who all contributed
to the successful delivery of this
remediation project.
Completed Dolphin 5.
Hybrid CP installation on vertical face.
Hybrid CP installation on dolphin soffit.
Some piles were coated and partially wrapped where the geometry
did not allow full wrapping.
Piles wrapped in the Denso Seashield system.
p.40 CORROSION & MATERIALS
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