Stainless Steel 316 at Marina Sea Coast
Stainless Steel 316 at Marina Sea Coast
(OP)
I have a project on an island seashore. It is in a very harsh environment where it is very hot, high humidity and corrosive.
I use SST 316 machined parts as fixing brackets for anodized Aluminum Pipes (in direct contact).
I observed some Brown Rust Spots at the SST surface.
I want to know the following:
1- Can we consider this as a serious corrosion case.
2- What is the machining effect on SST 316? Do we need to have a polished surface if the rough machined surface may catch more corrosion.
3- Do we need to use some insulation between Aluminum and SST to avoid any galvanic corrosion, keeping in mind that size of SST bracket is very small compared to Aluminum.
4- Will the Acid Pickling and Passivationon be a helpful treatment for future jobs or do we need another coating?
5- Can we consider a guarantee (corrosion free product) of 15 years for SST 316 for such application.
I use SST 316 machined parts as fixing brackets for anodized Aluminum Pipes (in direct contact).
I observed some Brown Rust Spots at the SST surface.
I want to know the following:
1- Can we consider this as a serious corrosion case.
2- What is the machining effect on SST 316? Do we need to have a polished surface if the rough machined surface may catch more corrosion.
3- Do we need to use some insulation between Aluminum and SST to avoid any galvanic corrosion, keeping in mind that size of SST bracket is very small compared to Aluminum.
4- Will the Acid Pickling and Passivationon be a helpful treatment for future jobs or do we need another coating?
5- Can we consider a guarantee (corrosion free product) of 15 years for SST 316 for such application.





RE: Stainless Steel 316 at Marina Sea Coast
It is not uncommon for rust spotting on Type 316, particularly if the surface was ground or wire brushed with wheels previously used on steel or iron. Small particles of iron can get transferred to the stainless surface and corrode and initiate pitting on the stainless. Foreign material like dirt or salt deposits can also initiate staining. Keeping the surface clean, using a smooth finish (not a rough ground one)and passivating the stainless are all likely to reduce the occurrence of staining.
The atmospheric corrosion is usually cosmetic and not structurally significant. You might get a warranty against structural failure, but probably not against superficial staining and/or pitting because there are too many things that are too difficult to control in the service environment.
RE: Stainless Steel 316 at Marina Sea Coast
1. Keep sulfur content below 0.003%. This means no free machining versions of 316.
2. Pasivate the surface. There are not-too-toxic passivating solutions sold, usually citric acid based.
3. Minimize residual stress from fabrication.
If you want to guarantee for 15 years, you are at risk with 316. You may need to upgrade to 2205. The 316 may be saved by the aluminum acting as a sacrificial anode, but I would need to study the overall design before I would sign off on a life span.
RE: Stainless Steel 316 at Marina Sea Coast
If you don't mind a dull finish a pickling treatment would be the best.
I have seen many posts break off at their mounting from this kind of effect.
Corrosion never sleeps, but it can be slowed down.