No passwords, No popups, No cost, No AI
we earn from your eBay & Amazon purchases

Home /
T.O.C.
Fun
FAQs
Good
Books
Ref.
Libr.
Adver-
tise
Help
Wanted
Current
Q&A's
Site 🔍
Search
curated with aloha by
ted_yosem
Ted Mooney, P.E. RET
- Pine Beach, NJ
finishing.com -- The Home Page of the Finishing Industry


  pub
  The authoritative public forum
  for Metal Finishing since 1989

-----

Galvanized but unpainted doors rusted in one year




My question concerns the limitations that galvanizing provides. I am involved with a job on the South Texas Coast. The hollow metal frames were provided as galvanized and also some as galvannealed. The frames were onsite and installed for over a year prior to being painted. There is much rust showing now on the frames and it is even coming through on frames that have been painted. These frames were not provided with bituminous coating because it was not specified. My question is does galvanizing alone provide assurance against rust or is there some standard as far as how soon it needs to have a coating applied ?
On this same project there is widespread rust surfacing including on stainless steel items.

Michael Rouse
- Spring, Texas
April 15, 2009



April 17, 2009

Rust forming on galvanized steel within a short time like that suggests something anomalous.

You didn't mention (maybe don't know?) if this is pregalvanized sheet made into doors or post fabrication hot dip galvanizing.
The former is very smooth, but has a thin zinc coating compared to the latter, but the latter lasts longer.

Under "normal" atmospheric conditions, galvanizing should last many decades. In low pollution areas perhaps 80-100 years, in coastal or higher pollution areas, at least 20.

But galvanizing has a weakness (don't we all?), and that's acid. It cannot withstand acid, and acidic conditions can erode it within weeks at worst.
Acid conditions can occur with a few specific conditions, including (but not limited to) cow excrement, moist peat soils, acid from chemical plants, certain fertilizers, heavily polluted moist conditions (acid rain), certain plant leaves accumulations, etc.

Other than galvanizing in these conditions, its hard to see how it would rust quickly.
Painting galvanized steel will make it last longer (you need to pretreat fresh galv. to get the paint to stick).

You mentioned galvanneal. This is a much thinner coating, closer in zinc thickness to zinc plating than hot dip galv. The thinner the zinc the less corrosion protection duration you'll get. With plating, you might get 10-12 microns thickness. Galvanneal 15-25? Hot dip galv. 100 microns. Life expectancy is directly proportional to thickness.

That you have stainless rusting suggests a highly corrosive environment. (Guess that would be 304 stainless grade?)

geoff_crowley
Geoff Crowley
Crithwood Ltd.
Westfield, Scotland, UK
crithwood logo


none
adv.
this text gets replaced with bannerText
spacer gets replaced with bannerImages



(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:

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


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