Corrosion Prevention during transport and storage
For this second column I said I would write about corrosion prevention during transport and storage. This topic was suggested to me by a couple of things that have come to my attention recently. Firstly I was asked by a diesel engine manufacturer about how to prevent corrosion during transport to the user (including a sea voyage) and secondly, as mentioned in my column last time, is the "Corrosion Intercept Technology" which it is claimed keeps my guitar strings in pristine condition until I open the packet. A third related matter came up in talking to the producers of this Journal, Jonathan et al at Square One when I visited recently. I was told how the aluminium plates which used to be used as Masters for printing the journal (and are still used for printing other work) corrode in the workplace air and have to be discarded after about three years. So this whole area is important and is perhaps not given the attention it deserves.

There are various remedial approaches. One is controlling the environment by removing the corroding species. A common example would be the use of dessicants and that is certainly commonly adopted with small items like cameras (a little bag of "dessicant" inside the packaging). For bigger items humidity control of the room can be used (keeping it below 30%). Also there is a need to keep dust levels low e.g. by filtering (the corrosion that affects items in one's attic is largely caused by dust!). Alternatively one might control the environment by removing the oxygen (in that connection I remember when Power stations were mothballed, it was common to flood with nitrogen). There is also, of course, the barrier approach e.g. containing the item in an inpenetrable plastic bag or similar. There are also temporary protectives which might be a plastic film applied to a product which would then be removed at the time of use either by dissolution or just by stripping off physically. However one can also be pro-active and use VPIs (Vapour Phase Inhibitors). My memory is that these were typically volatile amines and their aim was to reinforce the oxide or air formed film on items.

So what can be done in the case of the examples we started this column with? Obviously a diesel engine is a big item and would be transported in some sort of crate or box. As it would probably be difficult to provide a controlled atmosphere, a dessicant might help along with effective barrier packaging (someone can tell me if I'm wrong!). The "Corrosion Intercept Technology" one is interesting, how are they doing this? There is no doubt that guitar strings do tarnish in the air (which leads to a duller sound) that is one reason why they have to be replaced every year or so even when the instrument is not played. No obvious dessicant was in the bag. Perhaps some form of VPI has been impregnated in the plastic film. Or maybe they rely on an unusually good barrier process (as we know plastic films normally let oxygen through. Thus, the whole 'CIT claim is unclear, but I think you would agree it is a good phrase!).

Regarding the aluminium plates could something be done here? A dust filtered controlled humidity room may be difficult to achieve. VPIs could be useful although how effective commonly available VPIs would be for aluminium is open to question. Maybe a reader can help?

In relation to this, I have just come back from EuroCorr 2005 held in Lisbon (I will talk more about this conference in the next issue). At this event there was an interesting presentation written by Digby McDonald about containers for storage of nuclear waste underground in Nevada. The plan is to use Alloy 22 which is basically a high nickel alloy like Incoloy with a fantastically low corrosion rate. So this is a rather different example! Instead of a few months (the diesel engine), year or so (guitar strings) or several years (the aluminium plates), the length of time these nuclear waste containers might be expected to last without significant corrosion might be 10,000 years. Bit of a challenge! Maybe in my next article I'll talk about "predicting corrosion"!

Anyway, anyone who wants to share anything on what I have written above please contact me at Douglas@harrbridge.freeserve.co.uk.

(If you do you'll get a chance to see your name in print or be anonymous just as you wish).
Dr Douglas Mills
Technical Secretary