Technical Presentations at the October 2006 Meeting
2.1
‘Low Signature Impressed Current Cathodic
Protection Systems - Recent Developments - Future Concepts’, Barry
Torrance (Aish Technologies Limited)
After
a brief introduction to present Impressed Current Cathodic Protection (ICCP)
technology and its purpose in minimising corrosion, this paper reviewed
recent developments in ICCP equipment and its contribution to (a) hull
condition management, and (b) corrosion-related signature management.
It also looked
forward to some future concepts.
The
topics are grouped broadly into ‘corrosion reduction’ and ‘signature
reduction’ areas, but there is much interaction between the two.
This interaction can be managed with computer control.
The
paper emphasised the need for corrosion and signature management to be
built into the design of a vessel right from the start, rather than being
almost an afterthought.
Topics covered:
Hull Condition Management
Corrosion-Related
Signature Management
Equipment Overview
Computer Controlled Multi-Zone systems
Active bonding of moving parts
System Modelling
Condition Based Maintenance
Accuracy and Reliability of ICCP information
Fine-Grain ICCP
Damage location
High-Immunity Reference Electrodes
Own-Ship Signature Display
Diver-Safe ICCP
(Similar
paper previously presented at: ‘Underwater
Defence Technology Europe’, Amsterdam, June 2005; ‘Recent Advances in
Cathodic Protection’, University of Manchester, February 2006; NACE
/ CB&I John Brown Limited Evening Technical Meeting, May 2006)
2.2
Keynote Lecture:
‘Application
of Physical Scale Modelling to the Evaluation of a ship’s ICCP Systems’, Horst-Friedrich Arendt (ex-Bundeswehr Technical Centre for
Ships and Naval Weapons, Germany)
The
purpose of this fundamental study was to establish optimum cathodic
corrosion protection system configurations for ship hulls. Comprehensive
surveys were conducted in order to develop a better understanding of the
electro-chemical processes occurring on a ship hull in a seawater
electrolyte. The results obtained show that the performance of a system
can only be evaluated when it is installed on a real object. However, once
installed the location of the impressed current anodes and the reference
electrodes cannot be changed if the potential distribution over the
underwater hull is not optimal. Hence, a procedure had to be established
that permits the development and optimisation of system configurations for
future objects.
A
validated, experimental laboratory technique using scale ship models was
established to determine the fundamentals of cathodic corrosion protection
and to develop a theoretical understanding of the underlying mechanisms.
The findings obtained in practice could be applied to the models. The
model studies were conducted in a systematic manner and under defined
conditions in German standard (DIN) artificial seawater and in a natural
electrolyte.
The
experiments clearly showed the functional correlation between the
geometric configuration of the reference electrodes on the hull and the
locations of the anodes. The results reflect the interrelationships
between the electro-chemically more positive bronze propeller and the
steel. The configuration developed in the course of the experiments
provided an optimum distribution of the protection current over the entire
hull model.
The data from the model study were applied to the design features of the Class 123 Frigate. Subsequently, the efficiency of this procedure was evaluated on a real object in a real electrolyte.
The
results obtained clearly demonstrate that physical scale modelling is a
rational, scientific method for the evaluation and design of impressed
current cathodic protection systems.
4.1
‘Long
range guided wave inspection for oil pipelines and offshore risers’,
Prof Peter Cawley (Imperial College, London)
This
presentation considered the attraction
of guided waves for long range inspection and the problems to be overcome.
It then looked at examples of use: pipes in chemical plant,
offshore and target applications and sensitivity.
Typical
Ranges (in each direction, using standard transducers) are as follows:
·
In ideal
conditions: 80m
·
Typical
30 year old pipe with little internal or external corrosion: 40m
·
Typical
30 year old pipe with some general corrosion: 20m
·
Typical
pipe wrapped in factory applied foam:15m
·
Heavily
corroded pipe or pipe that is bitumen wrapped: 5m
·
Six
welds
·
The
first flange or the second bend or branch
Note:
these ranges can be doubled by using low frequency transducers
Target
Applications are those requiring rapid, full
coverage screening of pipes. Especially
cost effective in locations with difficult access, such as sleeved road
crossings, corrosion under insulation, wall penetrations, pipe racks and
rope access. Can detect
cracks and general metal loss (greater than 5% of the cross-sectional
area).
The
conclusions were:
·
Long range guided wave inspection now in routine commercial use worldwide
·
Particularly valuable for screening long lengths of pipe and for testing
inaccessible areas
·
Increasing use offshore and new applications subsea
·
Dry coupled piezoelectric array very quick to attach and gives reliable,
reproducible results with minimal surface preparation
·
Permanently attached arrays now available