Underwater Steel

By Web-searching on "corrosion resistant steels" you might find some ideas. Cor-ten is used on land/in air, but under water I don't know. Stainless is likely to be too costly. Can you fabricate your gratings and have them hot-dip galvanized?

it depends what you mean for water.. it's sewater? freshwater? brakish?

a stainless steel can do the job if it's freshwater with low chlorides, if it's water with high chlorides then you shloud select something more resistant like duplex or a copper alloy..

give us more info..

V.

corrosion & rust protection

It's for Sea water. Were planning to fabricate it and i can't find a material for the round bar that were going to used. It will be submerge all the time under water. Thanks for your reply.

Brass or carbon composite?

Copper-nickel is used as screens over intakes underwater on ships.

I think using the stainless steel pipe in sea water is prohibited due to the existing of chloride. I suggest to use either Nonmetallic piping, or lined metallic piping.

You specified steel for an intake, and you said sea water. How big is this intake? What is your cost objective? How long do you want it to live? How strong does it need to be?

The main concerns with the marine environment are corrosion and sea life. Even if you use corrosion resistant materials, this thing is going to be overgrown and clogged in fairly short order. You can mitigate this to some degree with things like anti-fouling paint, but only somewhat. You are still going to have to haul it out from time to time as the critters overcome the paint, and if you're going to have to pull it out of the water anyway?

Certainly you can use stainless steels to minimize corrosion and make it live a little longer, but you may find that with periodic maintenance and replacement, mild steel will be all you really need.

High nickel content compositions are best for an extended life subsea. Hot-dipped galvanized is grossly overrated for marine environments. Copper-based metals can reduce biological fouling.

Absolutely true, and I would certainly recommend cupro-nickel fasteners for attaching the thing. However, it is still going to become fouled and corroded and will need to be hauled out periodically for maintenance.

The question is, will the added cost of using cupro-nickel alloys offset the reduced cost of maintenance, as opposed to mild steel and a good anti-fouling paint? Kinda depends upon how much of a pain in the butt it's going to be to haul the thing out in the first place.

For example, if it's a ten hour procedure for an entire team of hard-hat divers, then indeed the alloy would be the way to go. But, if it's a 30 minute job for two SCUBA divers, then mild steel and anti-fouling paint might be the better choice.

I might point out that even warship hulls are normally made of mild steel, but we do haul 'em out about every two years, and even then they are always badly fouled. Something like this? I would suggest quarterly inspections at the very least.

I think using the stainless steel pipe in sea water is prohibited due to the existing of chloride. I suggest to use either Nonmetallic piping, or lined metallic piping.

I agree with you, but nobody seems to hear. Or they are too busy giving each other GA points.

There are a number of options

Titan or titanium stabilised ST St might work but is still susceptible to chloride corrosion (pitting).

Incolloy or inconel are better.

Hastelloy is better still and is available as wire or gauze.

Titanium is excellent. Sounds expensive but it isn't if there is not a lot of mass.

What we normally do for subsea structural infrastructure, is use an offshore grade carbon steel, special epoxy or glass flake paint system then put some sacraficial anodes - zinc or al/zinc. This can last 20 years. We sometimes use the other materials depending on criticality of the application.

Elastomers such as Neoprene are also OK in seawater.

for ultimate corrosion resistance, use titanium bar. you can contact me for additional information.

Use mild steel and get it hot dip galvanized and use a replaceable zinc anode

I've seen mild steel with a good coating of tar epoxy then anti fouling.

In addition add a cathodic protection system.

For the cost of some of the more exotic materials suggested, you can afford to replace a mild steel one several times over.

if you want to avoid any problem and spend more go with a superduplex (SAF 2507) but pay attention to possible galvanic corrosion with other elements if u don't want to spend to much now use a SS316L and plan for mainentance and replacement...

S

corrosion & rust prevention