It is a common phenomenon to make mistakes when specifying and using various stainless steel fasteners but there are some things to look into when using stainless steel fasteners. The primary thing to do is to select the right grade of stainless steel and the most commonly used grades are 316 and 304 but 316 is more corrosion resistant than grade 304 but the common rule is that the more corrosive the environment the more resistant the stainless screws needs to be and 316 is the most preferred especially if the fastener is visible it should be 316 since it is less likely to develop a brown discoloration or a tea stain.
These stainless steel threads also need to be lubricated before being assembled so as to reduce the risk of galling (this happens when the threads lock up) and the highest risk of galling is found in larger threads and only recognized lubricants should be used. The user needs to choose the right surface finish because the more polished the finish, the better the resistance to corrosion and there are some stainless products that have a brushed, satin or rougher finish which can be done on hinges, downpipes and fittings but the downside with this type of finish is that it traps small particles like salt which may damage the protective chromium layer on the stainless steel thus cause ‘tea-staining’ and give the material a rusty appearance.
Electropolishing or passivating (which forms an acid treatment) to improve corrosion resistance by thickening the natural occurring protective layer of chromium oxide that is formed on stainless steel and some stainless flat washers manufacturers passivate all their products and offer an option to electro-polish the same products on request. If the stainless steel products are on show they need to be cleaned to remove contaminants like salt and thus maintain the stainless steel appearance.
The person using stainless steel fittings needs to consider their exposure to rain water because stainless steel resists corrosion due to its naturally occurring chromium oxide which is a protective layer but when contaminants settle on the stainless steel they can damage this protective layer thus allowing oxygen to be in contact with the iron in the stainless steel causing it to rust. It is good to highlight that if the stainless steel is exposed to rainwater then the rainwater should wash off these contaminants thus restoring the stainless steel’s protective layer and thus if the steel is sheltered from the rain and it is in corrosive environment then the person should consider selecting a more resistant stainless steel grade, doing a polished or mirror polish and electro-polishing.