I got this from another forum. It is a bit long, but I found it quite interesting, written by a materials and systems testing engineer for the Navy and "on-point".

A Lesson on Stainless Steel

Synopsis:

Rinse your rigging with fresh water often and keep out of freezing weather. Routinely inspect for rust and cracks before rigging the boat. Do not use rust converter which contain water based acid. Do not seal with wax as this deprived the SS of oxygen. If lubricant is required use lanolin based materials.

Detail:

Stainless steels are not indestructible materials, or resistant to corrosive attack. However, the family of stainless steels are excellent combatants of corrosion. With the correct selection of alloy and application of good design elements the few problems associated with corrosion in stainless steel can be conquered.

General Corrosion: General corrosion is an attack of the entire l surface. It is the least dangerous because rates of corrosion can be gauged and predicted. The general corrosion rates are low in many aggressive environments.

This can usually be cleaned with a greenie pad and is for exterior surfaces only.

Galvanic Corrosion: Galvanic corrosion occurs when two different ls are in electrical contact and submerged in the same corrosive solution. Stainless steels are grand ls and therefor seldom suffer increased corrosion rates as a result of galvanic corrosion.


Pitted Corrosion: Embedded iron may also increase pitting corrosion. This is one of the most common forms of corrosion seen on stainless steel. Iron particles deposited on the surface of stainless steel through mechanical contact with, usually carbon steels, quickly corrode and form a rust stain. If chloride ions are present this can increase an environment likely to cause pitting corrosion in the basic grades of stainless steel (see picture on previous page). Stainless steel fabricators are cautioned against using the same tools on stainless steels and carbon steels.

Crevice / Shielded Corrosion: Crevice / shielded corrosion occurs where the surface of stainless steel is Shielded therefore preventing the free access and availability of oxygen to the surface. The passive film tends to break down in these areas. Any conditions which give rise to a "crevice" should be avoided. This is the most prevailant form of rigging failure and occurs where the swaged fitting attaches to the cable. Usually a brown stain is evident at the jucture of the swaged furrel and the cable. An automotive dye-penetrant test can be performed on the swaged fitting to inspect for cracks. Bottom line: Replace if worried!

Stress Corrosion Cracking: Both pitting and crevice corrosion can lead to stress corrosion cracking under certain conditions. Stress corrosion cracking is a brittle fracture occurring in an otherwise ductile material. The austenitic crystal structure is prone to stress corrosion cracking whereas the ferritic crystal structure prevents its development.

For stress corrosion cracking to develop it requires the following three factors:

The presence of tensile stress. This can either be applied or residual stress occurring as a result of the l forming, fabrication and welding procedure. A minimum temperature. Generally stress corrosion cracking does not occur under 60 degrees ceicius.
The presence of a particular ion, eg. the chloride ion. It is often hard to quantify the exact chloride concentration needed, but localised concentration of chlorides will often initiate stress corrosion cracking. Eventually the progress of attack reaches such a degree that the yield stress of the material is exceeded due to the lack of residual sound material. High resistance to stress corrosion cracking 15 obtained by use of duplex stainless steels, stainless alloys and super ferritic stainless steels. Read VERY EXPENSIVE L!

Bottom line: rinse your rigging with fresh water and keep out of freezing weather. Inspect for cracks before rigging the boat. Do not use rust converter wich contain water based acid, D not seal with wax as this deprived the SS of oxygen. If lubricant is required use lanolin based materials.

Good luck.

Bob