Aluzinc vs Painted Steel in Chloride Rich Environment

[btimm]

Good morning all,

I am an electrical engineer working on a project in a very corrosive environment. I don’t have details about the chemicals that are present but I know that they include chlorides. I also know that the plant makes extensive use of acids and produces several salts. I can probably get further details on some of these if required but I am limited by a confidentiality clause so I can’t share the type of plant.

Banned materials on the plant include: galvanized steel; zinc, aluminium, chrome, nickel and nylon. Their preferred materials are painted steel (wet spray, 200 micron) and GRP.

The MV switchgear that we have selected makes extensive use of aluzinc, which has not yet been tested on the plant. As usual on these projects we don’t have time to conduct these tests before manufacturing begins.

I understand that aluzinc’s corrosion resistance is orders of magnitude better than that of normal galvanized steel but what I really need to know is how it stacks up against painted steel.

As I mentioned before I am an electrical engineer so materials and corrosion are something of a mystery to me. I would appreciate it if anyone could give me any information on this topic or link me to documents that I can pass on to our client.

Thanks for the assistance,
Bevan

 

[TVP]

btimm,

You will need to understand the details of this application in much greater detail than you described above in order to make any meaningful comparison. What exactly are the parts that you intend to have coated with aluzinc? I presume that you mean an Al-Zn-Si coating that is preapplied to the steel sheet by continuous hot dip galvanizing? Do you know the thickness of this coating? If it is truly Aluzinc®, the trademarked product from ArcelorMittal, then it comes in standard offerings from 13 micrometers minimum per side, to more than 26 micrometers per side.

What exactly is the environment that these parts will be subjected to? Continuously immersed in some type of process fluid containing chlorides, salts, and acids? Temperature? Concentration of these species? If not continuous immersion, then what?

In general, if zinc coatings are not allowed to be used, then Al-Zn-Si coatings are going to be questionable. Organic coatings provide corrosion protection by a different mechanism than Zn or Al based coatings (barrier vs. sacrificial), so the performance depends a great deal on the particular details of the application. I strongly encourage you to obtain the necessary details from your customer and to work with a competent corrosion specialist (hired consultant or otherwise) in order to make the appropriate decisions. Trust me, I won't be the only person on this forum that suggests this.

 

[CoryPad]

Well said TVP.

 

[strider6]

i've seen in some project that Aluzinc is proposed as a substitute for Galvanized Steel for external atmospheric application but never for immersed or under pressure service.

S



Corrosion Prevention & Corrosion Control

 

[EdStainless]

I don't think that you stand a chance. In environments that are that corrosive the anodic coating gets consumed so fast that soon you are left with no protection. A good coating over the AluZinc may be a good option.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube