Corrosion resistant material

[ktowner]

I am currently looking for materials for certain components of a drive assembly I am working on that will be a salt water environment. The drive assembly will have a 1/2hp motor with double reduction worm gear reducer (200:1 ratio). It will have a wire cable pulling a mechanical assembly (don't know the weight). I have read that 316ss can be used in these environments but working on other projects in a similar environment, 316ss did not hold up at all. I am looking for other materials that could be used. I am new to this site. If I haven't given you enough info, let me know.
Here is a list of some of them:

Shafts - we normally use CRS 1045. I found a material called Aqualoy 22 that could possibly be used. I know its used for boat propeller shafts but I am not sure if it can be used for this application.

Cable - we normally use 316ss 3/16"diameter (7X19). I found a monel cable but I have no idea what the price of it will be. I need 6 sections 120' each.

Sprockets - we normally use a hardened steel (5/8" pitch - 30 teeth & 60 teeth). Any ideas on a material that would be strong enough but would withstand the environment.

Roller chain - 5/8" pitch.

 

[TVP]

What is the expected lifetime for this system? How exposed to salt water is it? Completely immersed? Partially? Is this natural seawater or something else? Temperature? As a rough starting point, Aqualoy 22 is reasonable. As you already noted, Type 316 is marginal in seawater, especially if you need long life. I'm not really all that knowledgeable about cable, but if duplex stainless steels are available, they should be considerably cheaper than monel. Sprockets and chains are difficult, since they are usually hardened martensitic steels. There are corrosion resistant martensitic stainless steels, but most of them are not really suited for seawater. You can start by comparing Type 420, 440C, Lescalloy BG42 to precipitation hardening stainless steels like 17-4, 13-8, etc.

 

[EdStainless]

Keep in mind that PH stainless grades like 15-7 and 13-8 are age hardening varieties of 316. So id 316 isn't good enough.....

Seriously, if you need more than a few months of life you need to be looking at super-duplex (25Cr), super-austenitic (6%Mo), and Ni based alloys.
There are a few other options Nickle aluminum bronze and Monel being two good ones for seawater service.
You will have to re0-think the strength/hardness levels that you are used to. You will need to beef things up in order to manage with weaker alloys in exchange for corrosion resistance.

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

 

[tomwalz]

Try HP Alloys

Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessors.com

Good engineering starts with a Grainger Catalog.

 

[ktowner]

Thanks for all the leads guys. We are currently using Super Duplex 2507 for some piping and some of the structural shapes for the mechanical skimmer that the drive will be pulling. I was wondering how tough it was to machine 2507, since these shafts will have to be machined for key ways.

TVP; These units will not be submerged but they will be sitting on the edge of the basin (3m above water elevation) that will be filled with seawater. The drive units will have a fiberglass cover over them. All exposure will be from the atmosphere. This will also be in a building. The water temp will be 22C normally with a Max temp of 32C. This unit will only be used during a red tide occurrence. These occurrences happen very randomly. This unit may sit for months before ever being used. We expect this unit to last for years.

thanks again everyone.

 

[cloa]

How many years- 5 or 20 or 30? I assume this equipment will have very little maintenance or will it get some?

 

[TVP]

Superduplex SS has terrible machinability-- high strength with high toughness makes for very gummy conditions in turning, milling, sawing, etc.