Surface treatment of fasteners

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Correct surface treatment of fasteners prevents corrosion and produces more secure joints

Rust damage can cause breakdowns due to load-bearing structural elements having been weakened through corrosion of various kinds.For this reason it is extremely important to select the right type of surface treatment for fasteners.

It is also important to take care when choosing materials.Always select fasteners made from a material that has the same or almost the same nobility as the material in which the bolt is being installed, if the joint is to be exposed to a damp environment.See combinations in the table.

If the steel bolt is installed in a more noble material, such as copper, the bolt will “sacrifice” material and speed up the corrosion attack on the bolt.

If the same steel bolt is installed in a less noble material, such as zinc, the situation will be reversed.The installation material will “sacrifice” material instead of the bolt.

Surface treatment of fasteners

The approximately lifetime of surface treatments in different environments is shown below.

Environment	Bright zinc-plating 10µm	Hot dip galvanisation 55µm
Indoors Countryside Small towns Cities Coastal atmosphere, West coast Industrial atmosphere, mild Industrial atmosphere, normal Industrial atmosphere, harsh	50 years 8 years 5 years 2 years 5 years 4 years 2 years 1 year	- 40 years 28 years 11 years 38 years 20 years 11 years 5 years

The approximate lifetime of A2 (stainless steel) in an industrial atmosphere is 25 years and in a coastal atmosphere 50 years. The approximate lifetime

Material composition

The table below shows how various materials work together from a corrosion perspective.

	Bright zinc-plating	Hot dip galvanisation	Alu	Cu/Ms	A2	A4
Bright zinc-plating Hot dip galvanisation Alu Cu/Ms A2 A4	++ + + - - -	+ ++ + - + ++	+ + ++ - + ++	- - - ++ - -	- + + - ++ ++	- ++ ++ - ++ ++

++ = Good
+ = Acceptable
- = Not good