Fasteners that are planned to be used in an aggressive environment are subject to special requirements. First of all, it should not cause corrosion of the elements that it also fastens. The marine environment causes two types of corrosion.

 

Galvanic corrosion.

This type of corrosion occurs when two types of metal immersed in an electrolyte come into contact. Salt water is an excellent electrolyte. Some types of metals should not be used together, since some alloys corrode faster in the presence of others.

As an example, you can take a galvanized bolt that cannot be combined with stainless steel parts, just as it is better not to connect aluminum with brass products.

 

chemical corrosion.

The occurrence of this type of corrosion is provoked by chemical action with an external aggressive environment (sea water, humid air). The impact of salts accelerates the process of corrosion development. They prevent the formation of oxide films that give a protective effect on metal surfaces.

The consequences of such corrosion can be catastrophic, so it is very important to choose the right fastener metals and protective coating. It is also worth remembering that stainless steel also has vulnerabilities.

Metals in the marine environment

Stainless steel.

In the marine environment, the oxide layer on the surface of the steel is destroyed quickly, and when there is a lack of oxygen, it is not restored. Corrosion resistance depends on the amount of chromium in steel. Steel A2 (304) with a chromium content of more than 17% has high stainless properties.

When choosing fasteners of this type from A2 steel, an important point must be taken into account. For example, take a bolt that attaches the skin to the ship's hull below the waterline. Its head has access to oxygen, which is why it can restore the oxide layer, while the bolt shaft is in an environment of chlorides and acids. Without a protective film, it corrodes like ordinary steel and forms a galvanic couple with the cap. Fasteners made of A2 steel, installed above the waterline, where there is access to oxygen and there is no constant contact with water, it behaves normally.

In order to increase corrosion resistance in aggressive liquids, molybdenum is added to A2 steel, after which it is designated A4 (316). Fasteners made of such steel can work for a long time in a marine and chloride environment and in acetic acid vapors.

Steel and galvanized.

No non-galvanized mild steel fasteners may be on board. Zinc coating provides excellent corrosion resistance. For maximum long service life in the marine environment, the protective layer must be at least 10 µm. A similar result is achieved by hot dip galvanizing.

Copper.

When building boats, ship nails with copper washers are used, they are very resistant to corrosion, elastic and easy to mount, but many companies abandoned them with the advent of fiberglass hulls. Also, the non-standard sizes used in the repair of the skin disappeared from the sale.

Brass and bronze.

Bronze fasteners are more capable of resisting corrosion in salt water or marine environments and can last for decades.

For durability, lead, tin, silicon and other alloyed elements are added to brass. This multi-component alloy is used in the manufacture of marine fasteners.

You can get advice and buy fasteners by making an application on our website or by calling us at (048) 736-04-94, (048) 736-04-84.