No registration or passwords; no pop-up ads -- just aloha, fun, & answers.
(as an eBay Partner & Amazon Affiliate earns from qualifying purchases).
Home /
T.O.C.
Fun
FAQs
Good
Books
Ref.
Libr.
Advertise
 
Help
Wanted
Current
Q&A's
Site 🔍
Search
pub  Where the
world gathers for metal finishing
Q&As since 1989



-----

Corrosion of galvanized steel in a Marine Environment




Q. How far away does a galvanized steel exterior product need to be located from the ocean before the rusting effects become negligible?

I manufacture a galvanized steel rail that is polyester powder coated.

And what is meant by MARINE grade powder coat? Is this actually in the paint or in the pretreatment of the metal?

Thank you.

Joe Garcia

2006


A. Hello.

My understanding is that you have selected galvanising as your primary source of protection (galvanic) for your steel substrate. You have then chosen powder coat as your aesthetic coating to make it look nice. All zinc coated steel (galvanized steel) will react with oxygen and moisture to allow the zinc to become sacrificial to the steel and thus form zinc oxide. With a powder topcoat this reaction will still occur, only it will happen under the powder. This will continue relatively unnoticed for a period of time, after which two things will occur. The zinc oxide (also known as white rust) will form on the powder surface making it unsightly. The second part is that the powder will eventually lift and peel. Here is where you need to consider both pretreatment and choice of powder for marine applications. To diminish the formation of zinc oxide the article should be pretreated with either a chromate conversion or zinc phosphate prior to powder application. Whilst there are different grades of powder it is important to select a powder that has a higher resin quality and quantity (these may be known as marine grade). A further step would be to apply a powder primer, based on epoxy technology, underneath the polyester powder topcoat to further slow the ingress of moisture to the substrate.

To provide a short answer to your question, yes you can get a marine grade powder that will perform better, but it will only ever perform as well as the pretreatment applied.

Regards,

Michael Lind

2006




(No "dead threads" here! If this page isn't currently on the Hotline your Q, A, or Comment will restore it)

Q, A, or Comment on THIS thread -or- Start a NEW Thread

Disclaimer: It's not possible to fully diagnose a finishing problem or the hazards of an operation via these pages. All information presented is for general reference and does not represent a professional opinion nor the policy of an author's employer. The internet is largely anonymous & unvetted; some names may be fictitious and some recommendations might be harmful.

If you are seeking a product or service related to metal finishing, please check these Directories:

 
Jobshops
Capital
Equipment
Chemicals &
Consumables
Consult'g, Train'g
& Software


About/Contact  -  Privacy Policy  -  ©1995-2024 finishing.com, Pine Beach, New Jersey, USA  -  about "affil links"