Technical Presentations at the January 2004 Meeting
1.1
‘No Corrosion in 40 years – A Mission Impossible?’,
Mike Dale (MACAW Engineering)
A case study was recounted identifying pipe material which
could withstand aggressive internal fluids for prolonged periods. The need for a
new pipeline arose from changes in waste water disposal regulations which forced
a hydrocarbon process plant operator to transport its effluent for treatment
before disposal. To ensure no leakage occurred into an environmentally sensitive
site with extremely limited physical access consideration of corrosion resistant
alloys were needed.
The effluent was based on produced water with high chloride
levels and heavy contamination with SRB’s and commensurate levels of H2S. A
programme of plant investigations and materials testing in actual fluids was
reported alongside an extensive literature review including offshore field
experience. Non-metallic materials were ruled out because of high solvent
contents, whilst carbon and 316L steels suffered rapid failure. Duplex steel
grades 2507 and 254SMO performed well and were recommended for consideration
within a specified operation envelope.
The pipeline was duly constructed from standard 25 Cr
Duplex steel and has been in successful operation for 4 years.
A Mission Not Impossible.
Recent process plant temperature difficulties sought
changes to the operational envelope and after consideration, in particular those
of critical pitting temperature, the requested changes were rejected in favour
of maintaining the original envelope of maximum temperature <35oC,
pH >5.5 and sulphide <20ppm.
Extension of the pipeline is planned and will encompass
more aggressive fluids, ~20% solvents and chloride >15%. Even under these
conditions the 25 Cr Duplex should not suffer and continue to perform. However a
3rd party developer was considered for the pipeline extension and
they propose to use carbon steel. We recommended that the existing Duplex
pipeline be protected by electrical isolation and fitted with non return valves
at points of contact for when the carbon steel portion of the extension fails.
The Mission Continues with a Twist.
For many decades, copper nickel alloy CuNi 90/10 has
extensively been used as a piping material for seawater piping systems in
shipbuilding, offshore, and desalination industries. In spite of the appropriate properties of the alloy, failure
cases have been experienced in practice. The
reasons for such difficulties are mostly attributed to the composition and
production of CuNi 90/10 alloys, to occurrence of erosion corrosion, as well as
corrosion damage in polluted waters. In this presentation, important points were
demonstrated which have to be considered to ensure a successful application of
alloy for this application. It
included metallurgical, design and fabrication considerations.
The important hydrodynamic considerations were presented for the
prevention of erosion corrosion. In
addition, commissioning, shut-down and start-up measures were compiled that are
necessary for the re- and establishment of the protective layer.
3.
‘The Use of Titanium in Naval Applications’,
John O. Fowler (Rolls Royce)
The
outstanding performance of Titanium and its alloys in seawater applications has
been established over many years, in a wide variety of onerous structural and
corrosive environments. This paper
describes the various material types, properties and forms together with an
overview of the chemical and mechanical behaviour of Titanium in naval service.
Design and manufacturing aspects are also considered in order to illustrate the most cost-effective use of the unique combination of properties offered by this material.