Technical Presentations at the January 2007 Meeting
coatings fail through localized breakdown of the coating, or localized
initiation of corrosion, so the use of local techniques such as local EIS
or scanning techniques such as Scanning Kelvin Probe (SKP) or SVET can
provide useful insights into the failure process.
this work we have combined standard methods, such as EIS, with SKP and
Scanning Acoustic Microscopy (SAM), that can image blistering and
delamination beneath a coating, with good resolution. The work shows
how corrosion develops at a defect when coated steel is exposed to a
saline environment. Although failure begins by formation of an anode at
the defect and cathodic activity beneath the coating, our observations
show that new anodes develop driven by reduction of the deposited rust as
cathode. Analysis of potential maps to construct semi-quantitative
current distribution maps simplifies understanding.
This presentation focused on the challenges of controlling internal
corrosion within the North Sea oil industry.
The nature of interval corrosion in carbon steel flowlines was
outlined along with the traditional methods of chemical inhibiton.
The methods of application and the generic organic inhibitor
molecules which have served the industry over the past 15- 20 years were
challenge of environmental regulations for the North Sea were outlined.
This included an explanation of toxicity, biodegradation,
bioaccumulation, the methods used to measure these values and the values
which would result in a chemical being considered acceptable or not
acceptable to be applied on an offshore installation within the North Sea.
The presentation then focused on the development Nalco had made to modify
the chemical structures of some classic scale inhibitor molecules to
improve their toxicity, biodegration and bioaccumulation to meet
current/future regulations. The
performance results in terms of environmental data and corrosion
inhibition were presented for a currently marketed inhibitor used in high
temperature/high pressure field within the North Sea.
These results suggested it was possible to develop new molecules
that could meet environmental regulations and also perform as well if not
better than currently available corrosion inhibitor for control in carbon
[Nalco Ltd, Tern Place, Denmore Road, Aberdeen AB23 8JX. 01224 617000,
Based on the working experiences of the QinetiQ Corrosion Control team, the initial phases of a corrosion investigation were discussed, with emphasis on the collection of information regarding operating conditions and procedures. A range of analytical methods and equipment were reviewed, including electron microscopy, X-ray analysis, optical microscopy and chemical analysis. A number of generic causes of corrosion failure were proposed and the likely features of such corrosion identified. Examples of pitting corrosion and stress corrosion cracking around welds in stainless steels were used for illustration. The particular features of Microbially Influenced Corrosion investigations were examined. A case study was reviewed, where incorrect assembly of a seawater cooler header resulted in severe erosion-corrosion attack of a copper-10% nickel tube plate. The likely time-scale for the failure was estimated based on hydrodynamic calculations and literature on erosion-corrosion rates.