The inorganic components of seawater are well known and easily simulated by mixtures of the appropriate salts. The adoption of such mixes has the advantage that the buffering ability of seawater is simulated to some extent but leaves open the question of the role of the organic component of seawater, which is not simulated in any of the normal recipes available. It is always open to the experimenter to avoid the problem of simulating seawater by carrying out the test exposures in the sea itself. However seawater has such a variability that any exposure site or time of year will be inadequate in some unknown regard.
This paper describes our experience in holding water in the laboratory and of work relating to the influence of organic natural products on the corrosion of Kunife 10 (alloy CA706, 10Ni1.5FeCu alloy). To attempt to create a “modus operandi” for waters containing organic species, it is essential to first envisage their possible actions, for example, chelating action, inhibition, stimulation of transport, a reduction in ionic activity in solution leading to a change in the Pourbaix diagram, modification of crystal habits, or the formation of weak boundary layers. These aspects will be discussed in the paper.
A detailed study of the micro-organisms, which develop in tanks containing seawater over the period of their use as a stock of test medium and of the concomitent changes in water chemistry, has been made and will be reported. A more direct method of examining the effect of the organic component is to remove it from the water in order that it may be added back to synthetic mixes or used to augment the seawater itself. A system, which permits the removal and retention of high molecular weight compounds, will be described.
It is concluded that the organic material may have less influence on the corrosion of the Kunife alloy than on some other systems but that the techniques established to deal with organic components of seawater have been successful. In particular an influence of organic molecules on the cathodic process at low oxygen levels has been demonstrated.