Technical Presentations at the July 2010 Meeting

1.1   Coatings for Control of Marine Fouling and Microbially Influenced Corrosion’, Bob Akid, Sheffield Hallam University 

Biotic sol-gel coating for the inhibition of marine corrosion and biofouling:  A unique anti-corrosion coating that inhibits the biofouling of metals in seawater that combines sol-gel technology and ‘protective’ microorganisms has been developed as an alternative to existing environmentally-damaging biocide/antifouling strategies [1, 2].   

The microbially-induced corrosion (MIC) of metals can result from biofouling and is promoted by the formation of destructive biofilms containing corrosion-causing bacteria. Sulphate-reducing bacteria are common to the marine environment and exacerbate corrosion by the formation of the corrosive metabolic by-product, H2S [3].  Since the biofilm bacteria are protected by a matrix of exopolymeric substances (EPS) [4], corrosion-causing biofilms are often resistant to destruction by biocides.  Paradoxically, biofilms that contain protective bacteria such as Paenibacillus polymyxa can actually inhibit corrosion [5].  P. polymyxa endospores can withstand exposure to a wide range of solvent concentrations and acid pH levels during sol-gel formulation and, following immobilisation of within the sol-gel coating provide enhanced corrosion inhibition when compared to that of sol-gel alone.   

A reduction in the formation of macroscopic biofouling and corrosion products has been observed on the surface of biotic sol-gel coated aluminium 2024-T3 panels immersed in estuarine seawater for six months when compared to those coated with the abiotic sol-gel.  Scanning electrochemical microscopy is being developed as a technique to investigate spatial distribution of redox-active compounds within the coatings in order to understand the protection mechanism of the coating.  Initial results have indicated a reduction in the adhesion of the corrosion-promoting bacterium, Pseudomonas aeruginosa [6] to the biotic coating, which could indicate a greater resistance to biofouling.   

[Akid R[1], Gittens J[1,2], Wang H[1], Greenfield D[1], Smith T.J[2].  [1] Materials and Engineering Research Institute, [2] Biomedical Research Centre and  Sheffield Hallam University, S1 1WB, UK] 

References 

1.       Akid R, Wang H, Smith T. J, Greenfield D, and Earthman, J. C, 2008, Advanced Functional Materials 18, 203-211

2.       Patent 0815731.5 (29.08.2008) Biological Functionalisation of a sol-gel coating

3.       Potekhina J.S, Sherisheva N.G, Povetkina L.P, Pospelov A.P, Rakitina T.A, Warnecke F, Gottschalk G, 1999, Applied Microbiology and Biotechnology 52, 639-646

4.       Korenblum E, Sebastian G.V, Paiva M.M, Coutinho C.M.L.M, Magalhaes F.C.M, Peyton B.M, Seldin L, 2008, Applied Microbial and Cell Physiology 79, 97-103

5.       Jayaraman A., Cheng E. T., Earthman J. C. and Wood T. K. 1997, Applied Microbiology and  Biotechnology 48, 11-17

6.       Videla H.A & Herrera L.K, 2005, International Microbiology 8, 169-180

 [Contact: Prof Bob Akid, Sheffield Hallam University, r.akid@shu.ac.uk]

1.2   The Sheathing of Hot Risers with CuNi’, Bernd Sagebiel, KME Germany AG & Co. KG 

A More Cost Effective Solution for Corrosion Protection of Hot Risers:  The splash zone of hot risers at offshore installations for gas and oil production is frequently subject to corrosion attack.  Corrosion protection has been successfully accomplished by sheathing the splash zone with Monel (NiCu 70/30).  However, in view of the high nickel prices the question arose, whether CuNi 90/10 could be a cost effective alternative to Monel.  This was supported by the fact that CuNi 90/10 has been already applied at some offshore structures with great success. 

As no experimental reports were available on the performance of CuNi alloys as sheathing material for hot risers in the splash zone, corrosion investigations were initiated to assess the limits of CuNi 90/10, CuNi 70/30 and NiCu 70/30 for this application.  Tubes of these alloys (three tubes for each set of experimental parameters) were heated internally to an inside temperature of 100 and 120 °C, respectively, and were exposed vertically for 1000 h  i) to a spray of artificial ASTM seawater kept at 50°C and ii) to ASTM seawater thermostated at 50°C.  In the last case the pipes were arranged  vertically in a way that the upper part of the tubes was above the water line forming a metal/water/air interface.  Both experimental setups were designed to image the corrosion situation in the splash zone of hot risers with special consideration of the temperature gradient and the formation of salt crusts. Corrosion loss was quantified by topographic scanning. 

In the 1000 h seawater spray test all alloys investigated experienced only general metal losses in the order of 2 to 4 µm regardless of the applied internal temperature.  Very small needle-like pits were found only under the salt crusts.  The pit depths were generally only 5 to 10 µm, the deepest pits amounted to 20 µm (CuNi70/30). 

During the 1000 h water exposure heavy salt crusts grew on the surface of the tube part above the water line due to the internal heating to 100 and 120 °C, respectively.  The metal loss below the salt crusts was widely general and ranged at 100 °C internal temperature between 10 and  30 µm, and the deepest local penetrations between 15 and 30 µm.  Below the waterline no corrosion attack was visible except some single tiny micropits with depths in the order of 10 µm.  The general corrosion loss was below 2 µm.  At 120°C internal temperature the general material loss ranged between 10 and 25 µm, the deepest local penetrations amounted to 80 µm, but generally were in the order of 15 to 40 µm.  Below the waterline no corrosion attack  could be documented (metal loss <2µm). 

Thus, basically all CuNi alloys investigated can be recommended as sheathing material for corrosion protection of hot risers in the splash zone.  With CuNi 90/10 a cost efficiency of more than 50% could be achieved as opposed to NiCu 70/30. 

[G. Schmitt1, R. Feser2, C. Kapsalis2,3, K. Steinkamp3, B. Sagebiel3, 1 IFINKOR-Institute for Maintenance and Corrosion Protection Technology, Kalkofen 4, D-58638 Iserlohn, Germany, gue.schmitt@t-online.de, 2 Laboratory for Corrosion Protection, South-Westfalia University of Applied Sciences, Frauenstuhlweg 31, D-58644 Iserlohn, Germany, feser.r@fh-swf.de, 3 KME Germany AG &Co KG; Klosterstr. 29, D-49074 Osnabrück, klaus.steinkamp@kme.com;  bernd.sagebiel@kme.com] 

Note:  a pdf version of the paper on which this is based, or the presentation, has kindly been provided for members, and is available from the Secretariat.

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3.1   ‘Use of Arctec (Al-Ti) and Prosion (AlZnIn) Alloys for Thermal Spraying onto Steel for Protection against Corrosion’, Chris Wheatley, CJ Wiretech Limited 

LSM in Rotherham, UK, together with CJ Wiretech Limited have developed two new series of aluminium alloys for thermal spraying onto steel for protection against corrosion. These are available as wires for arc spraying or powders for HVOF spraying or Coldspray.  

The first series is based on aluminium plus a small addition of titanium and is called Arctec Spray. The titanium promotes extreme wear resistance in the sprayed layer whilst allowing the material to behave as well in aggressive conditions, from a corrosion standpoint, as pure aluminium (TSA). The wear resistance causes the material to be non-slip when it is sprayed and for a long period of time afterwards. Pedestrian floor-plate testing at the Ceramic Research Association predicts that Arctec will remain of low slip potential for pedestrians for 21 years, assuming 1000 footfalls per day. For vehicular traffic it is necessary to test in all combinations of vehicle and environment. Sprayed Arctec has been tested successfully on the deck on an aircraft carrier, on manhole covers for use in roads to prevent accidents with motorcycles, on steps of coaches of trains and on a loading ramp for fork-lift trucks. In the future applications will be found on oil platforms for walkways and ladders.  

Prosion is an alloy of aluminium-zinc-indium. The alloy itself has been known for many years as a cast anode in marine environments but is now available as a solid homogeneous wire for arc spraying. The indium is added as an activator to prevent the well-known ‘passivation’ condition found with aluminium in mildly aggressive environments. ZRA measurements showed that the cathodic current protecting a bare steel sheet reached as high as four times that of pure aluminium in the same conditions. This high degree of protection arises because the alloy exhibits a potential which is 100mV lower than aluminium, thereby significantly increasing the driving force for CP. This has allowed sprayed Prosion to be used in the CP of reinforced concrete where the ionic path has a much higher resistance than in metals. Future work at Sheffield Hallam University will follow the effect of spraying concrete test slabs with Prosion under different application conditions. Meanwhile, Prosion also lends itself to spraying directly onto steel as it forms the typical barrier protection found with pure aluminium but also acts more readily and more reliably in the CP of steel under all marine/salty conditions. 

3.2    ‘The Role of QA/QC in Corrosion Failures - a Case Study’, Roger Francis, RA Materials 

Following an emergency shutdown on an offshore platform, a leak developed in an oil cooler on one of the seawater injection pumps.  The cooler had 90/10 copper-nickel tubes (1/4” od) with 60/40 brass tube plates and gunmetal water boxes.  A single tube had leaked just after the inlet tube plate.  The water boxes had divider plates showing the heater to be a 3-pass unit, but severe erosion corrosion had occurred on the dividers and water had clearly been by-passing some of the stages, causing low flow in some of the tubes. 

Examination of the tubes showed that they had poorly adherent corrosion products and extensive chatter marks from the drawing process.  These were not involved in the current failure but might have exacerbated attack under other circumstances.  The tubes had a thick deposit of lead/tin solder in the inlet, which was covered in lead/tin corrosion products.  Downstream of this was deep pitting with copper crystals at the bottom.  This was where the leaking tube had perforated.  At the temperature of the cooler (~50°C), this suggests ammonia induced hot-spot attack.  In the open North Sea there is no ammonia pollution, but ammonium chloride is used as an activator in many soldering fluxes. 

It is suggested that the failure was caused by inadequate washing off of soldering flux after sealing in the tubes.  The excessive solder deposits in the tube mouths suggest that the heat exchanger and/or the solder bath were not hot enough to enable the solder to run out after sealing. 

This demonstrates a lack of application of QA/QC procedures during manufacture.  Checking of the tubing prior to construction and suitable inspection after manufacture would have prevented this failure.

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