PROPERTY
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STAINLESS STEEL (316)
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GALVANISED STEEL
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COMPARISON
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Mechanism of protection
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A protective oxide layer which self-repairs in the presence of oxygen, granting long-term corrosion resistance. |
A protective zinc coating is applied to the steel during manufacturing. When damaged, surrounding zinc cathodically protects the exposed steel. |
The stainless steel protective layer is more durable and is able to 'heal' itself. Stainless steel protection does not diminish with material loss or thickness reduction. |
Appearance
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Wide range of finishes available from very bright electropolished to abrasive linished. Appealing high quality look and feel. |
Spangles possible. Surface not bright and gradually changes to a dull grey with age. |
Aesthetic design choice. |
Surface feel
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Very smooth and can be slippery. |
Coarser feel which becomes more apparent with age. |
Aesthetic design choice. |
Green credentials
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May be re-used in new structures. Valuable as scrap after lifetime of structure - high recycling rate because of collection value. |
Carbon steel generally scrapped at end-of-life and is less valuable. |
Stainless steel is extensively recycled both within manufacturing and at end-of-life. All new stainless steel contains a substantial proportion of recycled steel. |
Heavy metal run off
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Negligible levels. |
Significant zinc run off especially early in life. |
Some European highways have changed to stainless steel railings to avoid zinc contamination of environment. |
Lifetime
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Indefinite, provided surface is maintained. |
Slow general corrosion until zinc dissolves, red rust will appear as zinc/iron layer corrodes, and finally the substrate steel. Repair required before ~2% of surface has red spots. |
Clear life-cycle cost benefit for stainless steel if extended life intended. The economic break-even point can be as short as six years, depending on the environment and other factors. |
Fire resistance
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Excellent for austenitic stainless steels with reasonable strength and deflection during fires. |
Zinc melts and runs which may cause failures of adjacent stainless steel in chemical plant. Carbon steel substrate loses strength and suffers deflection. |
Stainless steel offers better fire resistance and avoids risk of molten zinc if galvanised is used. |
Welding on site
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Routine for austenitic stainless steels, with care about thermal expansion. Welds can be blended into surrounding metal surface. Post-weld clean up and passivation essential. |
Carbon steel readily self-weldable but zinc must be removed because of fumes. If galvanised and stainless steel are welded together, any zinc residue will embrittle the stainless steel. Zinc-rich paint less durable than galvanising. In sever marine environments, a crusty rust can appear in three to five years and steel attack at four years/mm afterwards. |
Short-term durability similar but zinc-rich coating at joins required upkeep. In severe conditions, galvanised will get rough rust - even holes - and possible hand injury especially from unseen seaward side. |
Contact with damp porous material (e.g. wooden wedges) in a salty environment
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Likely to cause rust stains and crevice attack, but not structural failure. |
Similar to storage stain leading to rapid zinc loss and longer term due to perforation. |
Not desirable for either, but in long term can cause failure at base of galvanised poles. |
Maintenance
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Can suffer tea staining and micro-pitting if not adequately maintained. |
Can suffer general zinc loss and subsequent corrosion of the steel substrate if not adequately maintained. |
Rain in open areas or washing in sheltered areas is required for both. |