Technical Presentations at the January 2013 Meeting

1.1  Antimicrobial Copper - a Simple Way to Reduce Contamination in Close Quarters?’, Mark Tur, CDA 

Following the chance observation that brass door knobs were less contaminated than stainless steel ones, and a subsequent clinical trial in 1983, investigations into the antimicrobial characteristics of copper and copper alloys (such as brass) have been ongoing. 

It is now recognised that copper is a powerful antimicrobial with proven rapid, broad-spectrum efficacy against the pathogens that threaten public health in both hospitals and the wider community, including MRSA, E. coli, Pseudomonas and – most-recently – norovirus and adenovirus. 

Norovirus cases peak in late winter, and can quickly decimate a workforce due to its highly-infectious nature.  Consequently, it is a matter of critical importance in close quarters such as offshore, shipping and office environments.  An incident reported in the Scotsman in December 2012 saw an oil platform evacuated following just five cases.  The next day, 55 of the crew were reporting symptoms. 

Clinical trials around the world have confirmed the benefit of deploying touch surfaces made from copper and copper alloys (collectively termed ‘antimicrobial copper’), which is to reduce microbial contamination and thus lower the risk of infections spreading, improving patient outcomes and saving costs.  These advantages should be transferable to other environments where items such as handrails, door handles and keyboards can be upgraded. 

Recent work shows antimicrobial copper may also reduce the spread of antibiotic-resistant organisms by destroying them before they can pass on genetic information, addressing a major concern in contemporary healthcare. 

Copper and more than 450 alloys have been registered by the United States Environmental Protection Agency as being permitted to market using public health claims in the US.  More information on this, available products and the science behind antimicrobial copper is available on www.antimicrobialcopper.org. mark.tur@copperalliance.org.uk 

[A pdf version of this presentation has kindly been provided for members, and can be obtained from the Secretariat]

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1.2 ‘25 years of Crevice Corrosion Testing of Stainless Steels, the Period After the Discovery of the Biofilm’, Ulf Kivisäkk, AB Sandvik Materials Technology (25th anniversary ‘hot’ topic)

During the last 25 years four larger test programs have been carried out in natural seawater in Europe. The outcome of the first exposures did not reflect the service experiences since for instanced 316L passed 6 months testing. The testing procedures were refined and especially the design of the specimen was improved and a specimen with PVDF crevice formers and a disc spring set up was developed. Other lessons learned were that if electrical connections should be used these should be made by using Pt or Ti wires. Further an adaptation of the flat specimen in order to suitable for tubular products was also made. 

The synthetic seawater according to ASTM D1141 does not take into account the formation of biofilm in natural seawater. A new synthetic seawater with biocapacity was developed where the use of an enzyme makes it possible to simulate the formation of a biofilm. The result of a 5 day test with this new synthetic seawater corresponds to an exposure of 6 months in natural seawater. 

During the last years filed testing of umbilicals has revealed that a biofilm seems not develop in larger confined areas which are in contact with the open sea. It should be noted that the biofilm is formed on the outside. The reason for this is unclear. 

The new synthetic seawater with bio capacity and the specimen set-up for both flat and tubular specimens are currently standardised within ISO.  

Reproducible crevice corrosion test procedures have been developed during the last 25 years and consistent results between laboratory testing and field testing has been achieved. It is known that environmental parameters influence the crevice corrosion resistance of stainless steel such as temperature, crevice geometry, type of seawater, oxygen content and the confinement. These aspects should be taken into consideration when crevice corrosion testing for seawater service is designed. 

 Figure 1. Crevice corrosion specimen with the disc spring set-up for tubular specimens developed in the Crevcorr project. 

[Ulf Kivisäkk, AB Sandvik Materials Technology, R&D, SE-811 91 Sandviken, Sweden]

 

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3.1    Corrosion Protection (Particularly by Organic Coatings) of Steel in Sea Water’, Douglas Mills, University of Northampton

 

The aim of on-site monitoring of an organic coating system is to be able to assess and get a numerical indication of its protection ability on any structure at that moment in time. A secondary aim is to assess how much protection is left in a paint system. The standard approach to monitoring of coated structures (or panels in a lab test) is to use the traditional method of visual inspection using some sort of rating scale e.g. ISO 4628, ASTM D610 (corrosion), D614 (blistering).  Disadvantages of this are it is qualitative (not numerical) and you only tend to see problems well after they have started. Also no prediction is possible. Electrochemical Methods are quantitative: Bacon, Smith and Rugg back in 1948 examined 300 coatings systems in sea water and measured their ionic resistance as a function of time using a DC measurement and found: > 100 Megohms/cm2 =good protection; 1 Megohm-100 Megohms =fair; < less than 1 Megohm  =poor. These criteria are still essentially the same as those used today.  The main methods available are DC Resistance (similar to B S and R) with advantages being it provides a single reading and is a simple method but disadvantages being that it is difficult to automate and highish voltages are applied.  Then there is Electrochemical Impedance Spectroscopy (EIS) where a sine wave (e.g. 20mv) is applied from say 10,000Hz to 0.01Hz and the resultant signals analysed using Bode and Nyquist plots.  Thirdly there is Electrochemical Noise Method (ENM) – which is described below.  These methods are well proven in the lab, but the challenge then is to transfer an Electrochemical Method and make it work in the field. For field application the technique needs to be non-intrusive, fast, accurate, simple to interpret and leave no indication that any measurement has been made (no long term change to the area examined).  ENM fulfils many of these criteria and with development could fulfil them all. In fact in-situ monitoring of ships coatings using EC techniques been already been done to a limited extent. In the US Navy J Murray and R Ruediseuli (NACE paper 2004) used EIS and ENM (current noise only) on an aircraft carrier in dry dock (see picture) .  And in the Dutch Navy T Bos and A Homberg used  ENM (NOCS arrangement which is discussed below) on submarines .

Organic Coatings used on ships are built up normally on a freshly blasted surface. A primer is applied, then an intermediate coat and then a top coat.  If above the water line, the top coat will be UV resistant, below the waterline this is less essential.  The latter area may have an antifouling coat (or several coats). Typical coatings used are based on Epoxy and Polyurethane. Typical systems for the hull might be 120 mm each coat; total thickness 500mm (systems for superstructure might be half that thickness). The total wetted area on an aircraft carrier might be >8000m2! Note: effective monitoring of the coatings on ballast tanks and other steel items on ships is also very important. 

The ENM method uses 3 electrodes – two Working electrodes (WE) and one reference (Ref).  The voltage is measured between WE and Ref, the current between the two WE, normally at the same time.  Data is gathered typically over about 4 mins at 0.5 sec intervals (512 data points).  A ZRA and data logger are needed and ideally also a computer and a suitable data processing programme like Cottis’s EANALIZ. There is commercially equipment available e.g. from ACM, Gamry, CML.  Noise Resistance (Rn)  =Standard Deviation of Potential Noise/Standard Deviation of Current Noise.

There are three common arrangements of ENM: Salt bridge (only suitable in Lab), Single Substrate (suitable outside and well verified) and NOCS– see picture  (needs no connection to the substrate and is still being improved). Murray and Ruedisueli’s work used ENM (current only).  Problems encountered included long run required to connect to hull (13 metres of cable), attaching probe/sensor was time consuming, and with only Current Noise measured they had no criteria (e.g. B S and R) to compare values against. Another factor was uncertainty about time to leave the cell/sensor contacting the coating to establish equilibrium.  

Work in my lab has gone some way to address these problems. The NOCS method gets around the problem of connecting to the substrate, the probe (copper pad (see diagram above))  can be attached to any surface using tape or magnets. And the system actually measures Rn.  A perceived disadvantage of NOCS is that three areas are measured at once and if they have different resistances it is difficult to find out which area dominates.  A recent paper (Mularczyk Mills and Picton) given at EMCR (Maragogi) conference in Nov 2012 addresses this. It appears by varying the way the three electrodes are attached to the box that any lack of homogeneity can be spotted and, in ideal cases, individual values can be obtained.  Not fully addressed yet is the final problem of time to equilibrium for thick (e.g. ship’s hull) coatings.  But it appears possible that because of the exponential nature of the process of diffusion of water and ions into the coating.  If several sequential Rn measurements are obtained over time, extrapolation to the steady state value will be possible without needing to leave the sensor in place for many hours.     

So it appears promising that the ENM method can be developed (bigger pads, battery operation etc) for use, fairly routinely, to monitor and assess the state of painted steel items on ships.     [Douglas J. Mills, University of Northampton, Douglas.Mills@northampton.ac.uk]

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3.2   Marine Corrosion during 25 Years of the MCC/MCF’, Roger Francis, RF Materials 

The author discussed the establishment of the MCC/MCF in the mid 1980’s and presented an idiosyncratic view of some of the early corrosion problems that were discussed.  Six different issues were discussed, describing the problem as it was then and some of the research results.  Each one was followed by a discussion of where this issue is at the current time.  The issues were: 

1.       High Alloy Stainless Steels for Seawater Cooling Systems. 

2.       Galvanic Corrosion of High Alloy Stainless Steels in Seawater. 

3.       Selective Phase Attack of NAB. 

4.       Hydrogen Embrittlement under CP, Subsea. 

5.       External Chloride SCC of Hot Stainless Steel Pipes. 

6.       Thermally Sprayed Aluminium Coatings. 

Some of these are no longer issues, or have limited impact, while others are still the subject of much research.  The author pointed the audience to EFC publication No.63, An Introduction to Marine Corrosion, which covers all the issues in the above six items and where information to avoid problems can be found. 

Finally the author described a couple of failures, where elementary mistakes led to corrosion catastrophes.  Such mistakes are still made and the author urged all the audience to help disseminate the information in the EFC publication No. 63, knowledge of which could help avoid future failures.

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