Stainless steel sculpture and salt water

Dennis A. Baltuskonis <dbaltusk [at] trinity__edu> writes

>Texas Gulf coast city is having a recurring problem with a large
>"stainless steel" sculpture installation and would like to hear of
>extended actions to take toward maintaining the pieces.  The artist
>allegedly used an "inferior" grade of stainless steel, which does
>exhibit signs of rust within a year of each "cleaning".  The
>sculpture piece is located directly across from the sea wall and is
>therefore exposed year round to the gulf coastal salt water
>environment. ...

The Australian Stainless Steel Development Association (ASSDA) has
done a lot of work on the not dissimilar problem of SS handrails
beside the sea especially down the east coast of Australia.  There
is a document at

    <URL:http://www.assda.asn.au/data/portal/
        00007704/content/00773001080526001671.pdf>

        **** Moderator's comments: The above URL has been wrapped
        for email. There should be no newline.

which describes the requirements to minimise rusting (called Tea
Staining) by having at least 316 (marine grade) stainless, getting
the roughness less than 0.5 micrometre Ra (or CLA in the older
terminology) and passivating the surface with nitric acid after the
last mechanical removal of the surface material during fabrication.
Nitric does not usually change the appearance of stainless steels
such as 304 or 316 although if the surface is a very bright mirror
polish, it may cause some fogging.  It does not sound as though the
statue has a mirror polish!  The document also recommends regular
cleaning with warm water and detergent very much along the lines of
"if it was a window, would you clean off the deposits?".

There is not enough information supplied but if the stainless steel
was 304 and not 316, I would expect rust staining in days or weeks
rather than months.

ASSDA has also put out some suggestions for cleaning which include
using phosphoric acid  (possibly similar to the OSPHO) or oxalic
acid (used for removing iron stains from bore water) or sulphamic
acid (often used to clean SS cookware) and even nitric acid.  If
abrasion is needed, then I assume this list is likely to be rather
more careful about changing the appearance than the fabricators to
whom we normally provide advice. Hope this helps,

Graham Sussex


                                  ***
                  Conservation DistList Instance 18:10
                 Distributed: Thursday, August 5, 2004
                       Message Id: cdl-18-10-002
                                  ***