The following comments regarding corrosion are made with particular reference to balustrading.
316 grade is usually regarded as the standard “marine grade" stainless steel, however in a marine environment and up to 5000 metres from exposed surf beaches, 316 can exhibit surface corrosion, usually visible as brown staining (commonly referred to as “tea staining”). This is particularly associated with crevices and/or a rough surface finish.
Tea staining on 316 grade can be minimized by -
- Avoiding ferrous metal contamination. Use tools dedicated to working only stainless steel. (For the same reason, never use steelwool as a cleaner),
- Specifying a surface finish with an Ra value (surface roughness) of less than 0.5 micron,
- Electro-polishing to achieve a further reduction in Ra value of approximately 0.2 micron,
- Regular washing with clean water containing a salt free surfactant (household dishwashing detergents usually contain salt, added as a thickener),
- Avoiding installations that are not subject to regular rain washing,
- Ensuring that the design of the job permits good drainage to avoid contaminant concentration (especially salt).
Stainless steel typically exhibits a much lower Yield Stress (or Proof) as a percentage of its Ultimate Strength than mild steel.
Yield Stress (defined as the stress at which a 0.2% permanent deformation occurs) is typically 40 – 45% of Ultimate Strength for stainless steel. This compares with 60 – 65% for mild steel.
Part size for size, the Yield Stress will be approximately the same for both materials, however the Ultimate Strength of the stainless steel part will be nearly double that of the mild steel part.
The links below provide access to a wealth of information on history, grades, characteristics and properties of stainless steel.