When the stainless premium is justified - and when it is wasted money.
Stainless steel costs several times mild steel for the same shape. The choice depends on environment and hygiene.
Use stainless where there is moisture, chemicals, salt air, food contact, or a wipe-clean requirement. This includes commercial kitchens, food areas, coastal structures, mining and marine environments, and visible architectural work.
Use mild steel (galvanised or painted) for internal, dry, hidden structural work such as beams, frames and guards that never see water.
Stainless steel typically costs several times mild steel for the same shape. The premium is recovered in environments where mild steel would rust or need constant repainting. For dry, hidden structural work, galvanised or painted mild steel is the lower-cost option.
304 suits interior and light exterior use. 316 suits coastal, mining and harsher exposure. Match the grade to the exposure.