Technical Presentations at the January 2009 Meeting

1.1   ‘Optical 3D Surface Metrology’, Brian Kyte, Alicona 

The InfiniteFocus system is ideal for the study of the effects of all types of corrosion and engineered surfaces.  It is now in use in many corrosion laboratories around the world. 

Its operating principle is Focus Variation.  This moves the focus plane of a known objective lens vertically over a surface which in conjunction with Smartflash illumination builds up a 3D full colour model of the surface to be examined. 

Large areas up to 100mm square can also be imaged using the built in X-Y stage, artefacts that can be caused by multiple imaging are avoided by the alignment of the 3D data points as opposed to stitching.  The resultant 3D model can then be used to measure features on the surface of the object. 

Measurement Capabilities include 

  • Profile including Ra and “virtual cross sectioning of the surface
  • Area, including “S” parameters
  • Volume
  • Pit measurement
  • Material removed from a surface
  • Contour measurement
  • 2D measurement

Using these measuring tools enables quantification of corrosion damage with high resolution visualisation permitting examination of features such as crack initiation sites. 

The viewable image is made up of 3D data points that can also be exported into other 3D analysis packages for further investigation. 

Contact: Brian Kyte, Alicona Uk Ltd, Lime Tree House, 15 Lime Tree Walk, Sevenoaks TN13 1YH, [email protected], tel: 07984596015, 

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1.2  ICCP and Anti Fouling’, Steve Ellis, Cathelco 

The presentation gave an introduction to the Cathelco Group Companies compromising:- Cathelco, Cathelco Jotun, Corrintec, MPSL, F.A.Hughes, Wilson Taylor and Morgan Berkeley. 

The next section highlighted the problems of corrosion and the need for corrosion control of submerged hulls.  The principles of ICCP and Sacrificial anodes were then covered including the arrangement of an ICCP system and detailed description of all the components of the ICCP system. 

Further types of ICCP system were also introduced including systems for Bow and Stern thruster Tunnels, Aluminium Hulls and Aluminium Waterjets, summarised by a list of advantages of ICCP systems over Sacrificial anodes. 

On Antifouling systems the problem of bio-fouling was discussed including the bio-fouling sequence and the problems, maintenance requirements caused by marine growth within pipework systems.  The Cathelco copper dosing Anti-fouling system was then introduced with an explanation of the process and the components required. 

In summary, ICCP systems in conjunction with coating systems:-

q       Totally prevent hull corrosion

q       Are cost effective

q       Are low maintenance

Marine pipework Anti-fouling systems:-

q       Prevent blockages and restrictions

q       Make major savings in pipework maintenance and renewal costs

q       Prevent engines from overheating and reduce fuel usage

Contact: Steve Ellis, Cathelco Corrintec, Marine House, 18 Hipper Street South, Chesterfield S40 1SS, Tel: +44 1246 246700, [email protected], 

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3.1    ‘Response of 70-30 CuNi to conditioning pre-treatments and sulphide exposure’, R Oakley & J. Galsworthy, QinetiQ 

An investigation of the behaviour of 70/30 copper-nickel tube alloy under conditions of sulphide exposure was undertaken after occurrences of rapid pitting corrosion in naval seawater cooled heat exchangers, believed to have been induced by microbial sulphide generation. 

The response of copper-nickel alloy surfaces to various pre-conditioning practices prior to exposure to seawater was studied, covering short chemical pre-treatments using sodium dimethyl-dithiocarbamate (SDD), benzotriazole (BTA) or ferrous sulphate solutions and longer term conditioning with static or flowing freshwater or clean seawater.  The experimental programme used the Linear Polarisation Resistance method supported by mass loss measurements to determine the resistance of copper-nickel pre-conditioning surface films towards corrosion induced by the high localised levels of sulphide believed to be induced by microbial activity. 

It was found that none of the pre-conditioning treatments employed provided immunity to corrosion due to high levels of sulphide in seawater, but that some treatments did improve or accelerate the formation of corrosion protective films on 70/30 copper-nickel alloy surfaces when subsequently exposed to sulphide-free seawater.

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3.2   Mathematical Modelling of Interactions Between Impressed Current and Sacrificial Anode Cathodic Protection Systems in Offshore Installations’, Robin Jacob, Corrosion Consultancy & Cristina Peratta & John Baynham, CM BEASY 

Recent oil and gas developments have involved operations in deep waters, with installation depths greater than 2000 m becoming commonplace.  For such developments, the most practical approach has been to use a floating production storage and offloading [FPSO] system, with produced fluids transferred from the well heads through manifolds, flow lines and a riser system to the FPSO.  Designing Cathodic protection [CP] systems to protect the individual components of such a development can be problematic without an appreciation as to how they will interact once the entire asset is commissioned.  This is particularly true where impressed current [ICCP] systems are fitted to the FPSO hull, with sacrificial anodes on the subsea equipment. It can also be further complicated where responsibility for the various structures lies with different parties. 

For a recent deep-water project, a computer modelling study was commissioned to provide information on the performance of the CP systems protecting each of the components and in particular the interaction currents flowing between the FPSO and the riser system.  The principal aim was to ensure that the ICCP system on the hull of the FPSO could be operated in such a manner as to reduce interaction with the sub sea sacrificial anodes to a minimum throughout the operating life of the field.  As CP monitoring data becomes available from the field, the model will be further refined and developed as a working tool for the field Operations group to utilize as input to Risk Based Inspection and maintenance planning. 

The presentation describes the strategy and rationale behind the modelling programme and some of the major lessons learned.

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