Cathodic protection of splice bolts from area-wide galvanized coating??

[VoyageofDiscovery]

If an entire area is galvanized and a specific item within this area does not have coating, such as A490 bolts at a bolted splice connection, is this an issue for corrosion of the bolts?

 

[Dhurjati Sen]

Sure its an issue. Some protection of the non-galvanized part is required in the form of painting or a rubber washer.

Regards.

DHURJATI SEN

 

[VoyageofDiscovery]

Don’t the bolts become cathodic relative to the galvanizing in the surrounding area?

 

[Dhurjati Sen]

There may not be any galvanic corrosion but general corrosion would occur, hence some protection is required.



DHURJATI SEN

 

[Chumpes]

hello Voyageofdiscovery

1/ I am not aware of the grades of material that are covered by the specification ASTM A490 (document was withdrawn in 2014). Corrosion mechanisms always have to relate to a material and the answer may be very different depending on the type of corroding material...

--> Are you talking about carbon steel bolts ??

2/ A bolt (hypothesis : carbon steel CS) of small surface exposed to an electrolyte, with an electrical connexion to a large CS surface coated with zinc, would benefit from cathodic protection (CP) from the sacrificial zinc coating when temperature remains below (roughly?) 60°C (memories).

3/ even benefiting from cathodic (galvanic) protection, the CS bolt may still suffer slow generalized idiomorphic corrosion (so called generalized corrosion by Dhurjati Sen).

4/ in my opinion, even benefiting from CP provided by the sacrificial zing coating, cathodic protection of the CS bolt has to come with a coating that limit the current demand and the consumption of the zinc coating. Moreover, if bolts can be seen as critical parts that should not fail, then additionnal measures versus corrosion may be even more justified and a organic coating should consequently be applied on the bolt.

CP experts on the forum may have clear bibliographic references to provide and that may justify the application of a coating on the CS bolts even benefiting from cathodic protection...

regards

 

[EdStainless]

What about galvanized hardware?

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P.E. Metallurgy, Plymouth Tube

 

[VoyageofDiscovery]

Thanks all, looks like some paint or additional coating is necessary.

FYI
A490 bolts are not to be hot dip galvanized. Also see chemical composition below:

http://www.portlandbolt.com/technical/specifications/astm-a490/