Technical Presentations at the January 2007 Meeting

2.1  ‘Organic coatings, using results for Scanning Kelvin Probe and Scanning Acoustic Microscopy’, John Sykes, Oxford University 

Organic 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. 

In 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. 

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2.2  The challenge of Developing Environmentally Friendly Corrosion Inhibitors for North Sea Application’, Myles Jordan and Neil Feasey, Nalco Ltd 

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 highlighted. 

The 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 steel flowlines.

[Nalco Ltd, Tern Place, Denmore Road, Aberdeen AB23 8JX. 01224 617000, [email protected]]

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4.1     ‘Corrosion failure investigation techniques’, Robin Oakley, QinetiQ

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.

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