Stainless Steel & Brass - Galvanic Corrosion

[Ranman]

Can anyone describe to me the rate of galvanic corrosion between partnered 304 stainless steel and brass in freash water? Is there anything I can do to slow the rate of corrosion?

[gcarter]

Can anyone describe to me the rate of galvanic corrosion between partnered 304 stainless steel and brass in freash water? Is there anything I can do to slow the rate of corrosion?
Randy, it's the zinc in the brass that's the problem.
If you replace the brass w/bronze, it will slow down considerably.
It's the same reason you never use brass in salt water.

[Ranman]

I re-looked at my info and noticed that the material is actually SAE 841 Bronze.

Oh crap, the SS is 316 as well.


The reason I ask is because I am mating a 3/8" 316 SS dowel pin and a bronze flanged sleeve bearing (bushing) for 3/8" shaft dia in a marine application that will call for considerable submersion. Will the parts last or will thay fuse together in no time? The previous sleeve bearing was nylon and did not last long.

[CHACHI]

I re-looked at my info and noticed that the material is actually SAE 841 Bronze.

Oh crap, the SS is 316 as well.


The reason I ask is because I am mating a 3/8" 316 SS dowel pin and a bronze flanged sleeve bearing (bushing) for 3/8" shaft dia in a marine application that will call for considerable submersion. Will the parts last or will thay fuse together in no time? The previous sleeve bearing was nylon and did not last long.Randy, how about using Delrin for the bushing?

Ken

[DonziJon]

Your question is fairly "broad" in that it doesn't describe the application. As a general rule, SS and Bronze in intimate contact doesn't seem to be a problem, either in a salt (marine), or fresh water environment.

Straight inboards not uncommonly have SS or Monel propeller shafts, with Bronze propellers, keyed to the shaft with brass key stock without any problems. There may also be a "sacrificial" anode collar on the shaft just in case.

Now if you're using a "tapered" SS dowel pin and are concerned that the pin could not be driven out at a later date, ....even that probably wouldn't be a problem because 99% of the pin is in a bore and not in contact with the electrolyte (water). In that case just smear some Anti- Seize compound or Silicone Seal on the pin before driving it into the bore. This acts as an electrical insulator between the two metals. SS screws are routinely used in fastening hardware to aluminum masts, using silicone seal on the screw when making the assembly. John

[techspecial]

I know this won't answer this specific question...but.
It's always good to review the basic principles this time of the year here where we're ready to put the boats back in.
I think this article concisely sums it all up
www.boatus.com/seaworthy/galvanic/default.asp

[Ranman]

Your question is fairly "broad" in that it doesn't describe the application. As a general rule, SS and Bronze in intimate contact doesn't seem to be a problem, either in a salt (marine), or fresh water environment.
Straight inboards not uncommonly have SS or Monel propeller shafts, with Bronze propellers, keyed to the shaft with brass key stock without any problems. There may also be a "sacrificial" anode collar on the shaft just in case.
Now if you're using a "tapered" SS dowel pin and are concerned that the pin could not be driven out at a later date, ....even that probably wouldn't be a problem because 99% of the pin is in a bore and not in contact with the electrolyte (water). In that case just smear some Anti- Seize compound or Silicone Seal on the pin before driving it into the bore. This acts as an electrical insulator between the two metals. SS screws are routinely used in fastening hardware to aluminum masts, using silicone seal on the screw when making the assembly. John

This answers my question very well. The application is a swim ladder. I lost the bottom rung of the swim ladder on the Formula and am in the process of fabbing a new rung. The rung is simply 1" SS tubing bent into a "U" shape with 2 3/8" pins mounted outboard at the tips of the "U". The pins act as a hinge point and are sprung into the main body of the ladder using two flanged sleeved (previously white plastic) bushings and rotate allowing the bottom rung to fold. I am replacing the flanged sleeves with bronze ones that are readily available from McMaster Carr (they don't offer them in SS). The bottom ladder rung will be submerged anytime the swim ladder is deployed and the whole ass'y is obviously in a wet area.

I thought that some boats use SS shafts mated to bronze props which is why I thought this would work. I am going to use the bronze sleeves and see how the ladder does this season. I jhust wanted to make sure this wasn't a big no no. Thanks again for the info.

[Pismo]

If it is clean fresh water then there will be little galv corrosion.