Technical Presentations at the October 2009 Meeting

1.1   ‘Galvanic Corrosion Performance of High Strength Copper-nickel Alloys in Seawater’, Julian Wharton, University of Southampton 

High strength copper-nickel alloys (Cu-Ni-Mn-Al-Nb) alloys have been widely used for marine applications due to their excellent resistance to seawater corrosion, high inherent resistance to biofouling and good fabricability.  However, in-service experience has shown that these alloys may encounter variable performance worldwide, i.e. due to local environmental conditions.  In particular, the corrosion performance of high strength Cu-Ni alloys may be affected by the seawater environmental factors, which include biofouling, temperature, salinity, and dissolved oxygen content.  This work reports an investigation into the galvanic corrosion performance between two wrought high strength copper-nickel alloys, Cu-15Ni and Cu-19Ni, with regard to the influence of surface oxide films/deposits and biofouling when immersed in seawater.  Analyses of galvanic currents, coupled and decoupled potentials routinely monitored for two years are presented.   

[R.C. Barik1, J.A. Wharton1, R.J.K. Wood1, K.R. Stokes1,2
1 National Centre for Advanced Tribology at Southampton (nCATS), School of Engineering Sciences, University of Southampton, Highfield, Southampton, SO17 1BJ, UK
2 Platform Sciences Group, Dstl Porton Down, Salisbury, Wiltshire, SP4 0JQ, UK]

 

  1.2  ‘Novel Treatment of Accelerated Low Water Corrosion on Harbour Structures’, Barry Lamb, BAC Corrosion Control Ltd

Accelerated Low Water Corrosion (ALWC) is a particularly aggressive form of microbiologically-induced localised corrosion affecting steel piling and other immersed structures, which is most commonly found close to the level of the Lowest Astronomical Tide (LAT).   

To mitigate this, cathodic protection (CP) and/or coatings are currently used in combination with surface sterilisation.   

However, it is expensive and difficult to apply conventional coatings to existing corroded structures under water to prevent further corrosion.   

In some cases, a calcareous film, a deposit of Calcium Carbonate (CaCO3) and Magnesium Hydroxide (Mg(OH)2) produced on steel structures has been proved to be an effective and an inexpensive substitute for a conventional corrosion control coating.   

When deposition conditions are appropriately controlled, it provides corrosion protection for steel in seawater. 

BAC Corrosion Control Ltd (BAC) and partners Mott MacDonald and The University of Manchester have developed a patented treatment, LATreatTM, to counter the problem of ALWC by applying a calcareous deposit in a controlled process.  The process can be used to treat local areas where ALWC is occurring. 

LATreatTM is an electrochemical process which works in a similar way to CP simply using the seawater and electricity to generate all the necessary active agents. 

The treatment comprises three optimised stages, Cleaning, Sterilisation and Coating which are typically carried out sequentially using BAC control equipment located within easy access of the structure to be treated. 

At present the endurance of the calcareous film is being studied both in the laboratory and the field.  The treatment should be commercially available in mid 2010.  A Patent has been filed for the process.

[barryt.lamb@bacgroup.com, 01952 208506]  

Note: This presentation is available in pdf format to staff of MCF member companies.  Please contact the Secretariat for details.

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  4.1  ‘Corrosion in Seawater Cooling Systems’, Clive Tuck, Lloyd’s Register EMEA

A number of typical instances of corrosion in seawater cooling systems on board a ship were considered and explanations were given as to the possible causes of deterioration.  The examples shown included corrosion of heat exchangers (copper based shell and tube type and titanium plate type), pumps, pipework and items which were subject to galvanic corrosion.

Attention was drawn to the recently published DEF STAN 02-781 ‘Protection of Seawater System Pipework and Heat Exchanger Tubes in HM Surface Ships and Submarines’  which gives details of the best methods of conditioning copper alloy pipework for seawater use.  Microbial-influence and biofouling have been found to be important factors in accelerating corrosion in seawater cooling systems.  Also, seawater flow needs to be matched to the materials used and free of turbulence, particularly with respect to the pump speeds employed.

Conclusions from an analysis of the main causes of corrosion were: 

        -  Ensure that adequate quality control standards are set for equipment and components

 -  Make sure that the design takes account of possible galvanic corrosion issues –

    dissimilar metals need to be electrically separated

 -  Pre-conditioning (passivation) of CuNiFe has to be effectively carried out

 -  Set up and regularly carry out a maintenance programme for heat exchangers

 -  Ensure that the anti-fouling system is effective and switched on at all times  

 

 4.2  ‘Development of Corrosion Fatigue Testing in Sour Oilfield Environments’, Dean Horspool, Exova/University of Birmingham 

The development of flexible pipelines and risers has been a key driver in allowing the oil and gas industry to develop fields in deeper and deeper waters, utilising floating production technologies.  During service, the annulus environment located between the two polymer layers of the pipe may become corrosive.  Permeation of corrosive species from the produced fluids along with permeation and subsequent condensation of water in the annulus of the pipe may result in the development of an acidic aqueous environment. 

If this situation occurs in service the integrity of the carbon steel tensile armour wires located in the annulus may be at risk.  As such, it is the aim of the current research project to investigate the effect of simulated corrosive oilfield environments on the fatigue life of the tensile armour wire component of the pipe.  

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