Technical Presentations at the October 2004 Meeting
2.1 ‘Problems on Corrosion in Marine Piping Systems’,
Jian-Zhong Zhang & David Howarth (Lloyds Register EMEA)
Piping systems are the blood vessels
in the body of a ship, supporting various essential functions in respects
of safety, optimal operation and welfare of the crew and passengers, e.g.
ballasting operation, cooling system and fire system.
Failure of piping systems can lead to serious consequences;
therefore, there are various Ship Rules requirements for piping system
design and materials. However,
corrosion of piping system is still a commonplace and the resultant cost
for maintenance and repair is high.
Piping system corrosion involves
various materials and exposure media. Corrosion manifests itself in
various form, consequently, protection methods are more complicated than
the other parts of a ship. Piping
corrosion problems may result from inappropriate materials selection and
design, manufacturing, commissioning and maintenance.
In terms of materials selection, there
is no perfect solution. There
is always a balance between cost and performance, advantages and
disadvantages. Steel pipes
have low corrosion resistance, however, they are cheap and their
performance is more predictable. Stainless
steels and copper-nickel alloys are increasingly used in piping systems.
Corrosion resistance of these alloys depends on the quality of
passive film formed on the surfaces, therefore, to achieve their best
performance, much care and attention should be directed to promoting and
maintaining good quality of surface film.
If fail to do so, corrosion failures could occur more rapidly than
conventional materials.
Two common corrosion problems with the use of these alloys are
(1) galvanic corrosion resulted from coupling to conventional materials without appropriate isolation and
(2)
inappropriate fabrication, commissioning and maintenance.
Two piping system corrosion failures
were presented to illustrate the corrosion problems in ship piping
systems.
2.2
Keynote Lecture:
‘Corrosion Management’,
Derek Milliams (Advanced Corrosion Management Services Ltd)
A
model of corrosion management was presented that underlines the challenge
to materials and corrosion engineers to establish an effective information
flow loop involving all those concerned with the design, construction,
commissioning, operation, inspection and maintenance of equipment.
Such an information flow loop contains a number of essential
components:
Materials and corrosion design standards represent a wealth of
experience and should be exploited to the full to avoid the pitfalls of
the past.
Corrosion management manuals to feed forward information describing
the way the designers intend that a piece of equipment should be operated,
inspected and maintained in relation to its corrosion threats.
Inspection/Corrosion data bases to accurately store data, in a
readily recoverable form, and Data
analysis to make best use of the data collected using expensive staff
time, often at the cost of replacement of equipment and the associated
lost production.
Status reports on corrosion management, possibly on a yearly basis,
can be used to feed back information from inspection data analyses into
revised Corrosion management manuals to govern the future year’s
operation. Such reports can
also provide information to justify changes to Materials
and corrosion design standards for the future.
A
transparent and properly documented approach to Corrosion management can
provide a number of other benefits:
It can provide a means of deviation control in the operation of equipment and a basis on which to audit the technical integrity of equipment to aid the work of both managers and operational staff.
The
more accurate problem definition that can stem from time spent upon data
analysis allows the optimum use of existing technology when resolving
problems and the accurate focussing of research where new technology is
required.
Financially, a company’s attention to effective, properly documented, corrosion management can significantly reduce the life cycle cost of maintaining the technical integrity of their installations. At the same time, the evidence of effective corrosion management can also help to demonstrate to regulatory authorities that such a company is a responsible operator.
4.1
‘The
Vagaries of Corrosion Testing’,
Phil Dent & Chris Fowler (Bodycote Materials Testing)
The presentation covered the following areas:
- Test Methods, which should
be applicable to the required duty of the material, and should be
reproducible
- Temperature, with regard to service conditions
- Test Environment, including Biofilms, Partial
pressure of test gases, Autoclave control, Reliability of field water
analysis (contamination).
- Surface Conditions, which could include
Degreased, Pickled, Passivated, Machined and Sandblast / grit blast /
shot peened
- Specimen Location
/ Orientation / Size, where the location of test samples shall take
into account the manufacturing route and shall be representative of
the worst case field conditions, and where specimens should be as
large as possible within the limits of experimental equipment
- Stress Considerations
- Duration, which should be dependent on the problem, not on material delivery
- Evaluation, considering, for example: Weight loss, Pit depth (Occluded pitting), Crevice depth, Cracking
Conclusions:
- Corrosion testing is a complex science.
- Test methods need to be carefully selected.
- Test conditions should be chosen such that the
material properties are correctly evaluated.
- The industry needs to understand that corrosion is not an exact science.
4.2 ‘Modelling
of Marine Cathodic Protection Systems’, David Tighe-Ford (Royal
Military College, Cranfield University)
Dr David Tighe-Ford, Director of the
Warship CP Unit at the Royal Military College of Science, representing the
Institute of Marine Engineering, Science and Technology, gave a
presentation on the “Modelling of Marine Cathodic Protection Systems”.
This dealt with the physical scale modelling of impressed current
systems, illustrating many examples of its application to the control of
underwater hull corrosion and the associated non-acoustic electromagnetic
signatures.
It was shown how such modelling
provides “sea trials on dry land” in relation to system design and
evaluation, signature management and R & D studies for ships and
submarines. The critical
importance of system configuration was emphasised and the central role of
the reference electrode, which has been much neglected in the past.
At the end he suggested that the
Marine Corrosion Forum, the IMarEST and Lloyds Register could profitably
cooperate in producing a professional Code of Practice for the structured
procurement of optimum CP systems for ships and other marine structures. An approach based upon Design and Acceptance Protocols, based
upon a structured system analysis and design approach was suggested as a
basis for discussion.
He finished by mentioning that Warship
CP 2005, the Third International Symposium and Equipment Exhibition on
hull corrosion and non-acoustic signatures, will take place at RMCS,
Shrivenham, on 8 – 10 February 2005. Responding
to one question, he said that at present only physical scale modelling
offers studies of performance under way and the role of the reference
electrode, plus a research tool.