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Life of galvanised steel in highly corrosive environment

May 31, 2011

Hi,
We have been asked to provide a whole life cycle cost comparison between galvanised mild steel and grade 316L (1.4404) stainless steel. The products are recessed manholes to take pavement blocks on footpaths. I'll have to do this for other streetscape products at a later date also.

The project is in the Middle East - daytime temperatures from May to September are 46C (115F) to 54C (129F) degrees, nighttime 35 °C (95F). For the rest of the year temperatures are more bearable 25C/77F day and 18C/65F night.
The construction site is right on the coast - it has actually been reclaimed from the sea. Lots of salt in the air
Humidity apparently reaches 85% in the mornings reducing to 50-60% in afternoons
I don't have a measure for the salt content in the air but apparently it is very high.
There are regular strong winds and sandstorms.

For Galvanised Steel, we could galvanise to 70 microns or to 140 microns, but most of our competition will just comply with the European Norm and aply 70 microns.

In these extreme conditions is stainless the only thing we should use, or would you believe that a 70 micron coating of galvanised would survive for 20/30/40/50 years?

I would appreciate your opinions on the issue of Stainless 316L vs Galvanised Steel in these conditions.

Shane Curtin
Fabrication Employee - Wexford, Ireland

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The UK and Ireland Galvanizers association has published a book on sustainability in galvanized products, and that has data that you could use.
If you are able to get 70u on manhole covers you might do well. I think you might more likely get 100u.
The standard calls for average of 85u, not 70. (but you didn't state material thickness, might be 70 for thin steel)

Geoff Crowley
Crithwood Ltd.
Westfield, Scotland, UK

First of two simultaneous responses -- June 3, 2011

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Second of two simultaneous responses -- June 6, 2011

Dear Sir,

www.galvinfo.com:8080/zclp/

You will find a calculator for predicting zinc coating life at this website. I believe the calculator is developed by the IZA (International Zinc Association).

Regards,

CS Leong
- Selangor, Malaysia