The Chairman (Clive Tuck) opened the meeting.  

2.2      ‘Welding Issues with Copper Alloys’, Mike Gittos & Chris Punshon (TWI), presented by Briony Lee  

3.   OPEN FORUM

1.   John Fowler asked whether anyone had experience of exposed carbon fibre (in epoxy) against nickel aluminium bronze in seawater.  It was suggested that insulation might be looked at, although there was a consensus that insulating with epoxy was difficult.  Information has been gathered by DERA on the subject, but this largely concerns carbon fibre corroding aluminium.  There is a DERA report which advocates the use of glass, although this would cause loss of other benefits. 

2.   Barry Torrance (Aish) mentioned that his company had been doing experimental work on small signal frequency responses between ICCP elements, and invited anyone interested to discuss this with him after the meeting. 

3.   Derek Bates (DRB Materials) had been looking at aluminium extrusions for the marine industry.  These were anodised in a chromic acid bath, and there were resulting patchy anodised areas with some black and some shiny.  This was not acceptable to clients, and a solution had not yet been found.  Clive Tuck (Langley) said that this was a common problem, particularly seen on the thicker parts and welds of aluminium extrusions (AlMgSi) after colour anodising.  It is caused by high iron content.  This influences the size and distribution of the Al-Fe-Si phase particles which come out on grain boundaries.  It was therefore necessary to be selective about the source of the aluminium.  Even if the overall average iron content of differently sourced samples might be equivalent, the micro-structural form of the iron is a controlling factor.  The effect is also seen if there is a high copper content, although it becomes less if a small amount of nickel is present in the AlMgSi alloy. 

4.   Mike Lawrence (KBR) asked whether there was an acceptable method for the preconditioning of a Cu-Ni pipework cooling system if it had been run with less than perfect seawater and left damp for a while.  In such a case, once in service, it could already be corroded.  Is there any solution which can be washed through to improve the situation?  Wilhelm Schleich (KME) mentioned that there were standards available: 

NES 781 Issue 3 Sep 1990 and VG 85004-8:1995 (in German).  Both standards deal with NaDDTC-treatments of the CuNi-Systems.  (This NES covers the process and procedure to be used to prevent excessive corrosion of ships sea water system and heat exchangers due to use of sulphide polluted sea-water during construction).  In general, the content of both standards is similar. However, the NES prescribes an electrochemical method for the evaluation of the treatment quality, but the VG limits the evaluation to visual means only.  

As to prolonged exposure of Cu-Ni pipe to polluted seawater, the Royal Navy heat treat Cu-Ni to improve its oxide film, and use resistance polarisation sensors to control iron anodes which are used to produce iron dosing of the system.

4.    TECHNICAL PRESENTATIONS  (part 2):  

4.1   ‘Long-term and Accelerated Corrosion Performance of Cast Nickel Aluminium Bronze in Seawater’, Robin Oakley and John Galsworthy (QinetiQ)  

Part 1 :  ‘Long-term and Accelerated Corrosion Testing Methods for Copper-Based Alloys in Seawater’, R.S. Oakley^a*, J.C. Galsworthy^a, K.R. Stokes^b, G.S. Fox^a   [a QinetiQ Ltd, Cody Technology Park, Farnborough, Hampshire, UK. GU14 0LX; b Defence Science Technology Laboratory, Porton, Salisbury, Wiltshire, UK. SP4 0JQ]

4.2    ‘Learning from Failures’, Derek Bates (DRB Materials Technology Ltd)