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Aluminum vs Stainless Steel Cable Winders

01/11/2012 10:35 AM

My boat lift has an aluminum drum winding up a stainless steel cable. I do not have the specifications on either material. Both are subject to salt water environment.

Aluminum is close to the "Active" Stainless Steels in the Galvanic series but is more distant to the "Passive" Stainless Steels. This suggests that it will react with "Passive" SS more rapidly than with the "Active" SS.

If the lift manufacturer used an "Active" Stainless, is it an acceptable way to avoid corrosion? If he used a "Passive" Stainless, can I expect problems?

How can I tell if the cable is "Active" or "Passive" Stainless Steel?

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#1

Re: Aluminum vs Stainless Steel Cable Winders

01/11/2012 11:04 AM

"The corrosion state of steel can be classified as passive, active, or indetermi-nate, depending on the difference in potential between the steel and reference elec-trode. The potential difference is determined by setting up an electrochemical cell between the steel and a reference electrode, and measuring the voltage drop between the electrodes using a voltmeter."

Both stainless steel and aluminum vary widely in properties according to composition...

http://www.tnb.com/contractor/docs/cabletray_us_revised_lr.pdf

Good reference...

http://www.iri.ku.edu/publications/SM65.PDF

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#2

Re: Aluminum vs Stainless Steel Cable Winders

01/11/2012 12:11 PM

For there to be appreciable galvanic corrosion over time the lift would need to be left in the water continuously. The lift is usually stored out of the water.

To have Galvanic corrosion both metals need to be in the electrolyte. Are they?

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#3
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Re: Aluminum vs Stainless Steel Cable Winders

01/11/2012 12:24 PM

Man you can tell you don't live near the beach....Holy Crap, I'd show you a picture of my brand new wheels( ok 1.5 yr ) but I'm too heart broken....Yes they were coated with epoxy...The point is you can slow it down, but you can't stop it...

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#4
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Re: Aluminum vs Stainless Steel Cable Winders

01/11/2012 1:07 PM

Well don't live right on the beach but there is plenty around. There is a difference between the causes of corrosion. We test the hardware we use for corrosion resistance before placing them on our products. If he is concerned about galvanic corrosion in the lift he maybe looking at the least likely parts. The spool axle may be steel. If it is a motored lift. There could be other parts more likely to corrode then the ss cable and alu spool.

Sorry for your heart break but is the damage to the wheels really galvanic?

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#5
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Re: Aluminum vs Stainless Steel Cable Winders

01/11/2012 1:46 PM

No actually I wouldn't characterize it as galvanic in nature but rather atmospheric, talking about the wheels specifically...But in the case of dissimilar metals touching in a corrosive atmosphere the corrosion process is greatly accelerated, as you probably well know...As to what parts in this lift may be more at risk, who can say without detailed info....In any case if there are any two dissimilar metals touching, there should be proactive maintenance...

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#6
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Re: Aluminum vs Stainless Steel Cable Winders

01/11/2012 1:56 PM

I understand that he is worried about galvanic corrosion. Both the dissimilar metals would have to be immersed in the electrolyte. Most lifts around here the winch assembly is well out of the water.

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#7
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Re: Aluminum vs Stainless Steel Cable Winders

01/11/2012 2:17 PM

Not to split hairs, but immersion into an electrolyte is not necessary to make a battery, which is what's happening here.

All you need is an damp, electrolytic path between the two dissimilar metals.

The real question to ask is how long does the electrolyte remain in contact with the metals, and for what service is the winch intended?

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#8
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Re: Aluminum vs Stainless Steel Cable Winders

01/11/2012 10:34 PM

Good point Lyn.

Salty air + dew and condensation = electrolyte. The boat lift I have has a lot of problems between the SS304 cable and the aluminum pre- threaded drum.

Without covering the cable and drum with a greasy impermeable compound I will have to replace the Alu in about 4 years. (diameter 3") Lithium grease helps to break up the transfer. Apply it thick.

The same happens to alu masts with SS screws and bolts in it. Again, cover the joint.

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#9
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Re: Aluminum vs Stainless Steel Cable Winders

01/11/2012 10:46 PM

Sounds like good advice to make the best of a bad situation.

My question is: Why did the boat lift manufacturer not use stainless steel winders, other than for economic considerations? What advantage do aluminum winders have in this situation, other than they are cheaper and more readily available than stainless steel 316 winders?

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#10
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Re: Aluminum vs Stainless Steel Cable Winders

01/11/2012 11:23 PM

That is something you need to ask the manufacturer. He needs to sell his product and there is competition. Same winders in stainless steel will be 4 times more expensive, but that is an economic consideration. I think it is about the cheapest way, unless he uses plastics or zamac like in garage door drums. Boats are heavy, expensive and he wants not too much liability. Besides that, the cable likes a softer seat. Stainless on stainless tends to seize too. (friction damage)

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#11
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Re: Aluminum vs Stainless Steel Cable Winders

01/12/2012 12:08 AM

Galvanic corrosion out-of-but-in-proximity-to bodies of salt water can easily occur in two phases. Tiny particles of salt from aerosols produced by wind and wave action settle on the surfaces in question. Then moisture from the atmosphere (dew, fog, or mist) condenses on those surfaces. The result is similar to that of complete immersion in an electrolyte; it just takes longer.

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#12
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Re: Aluminum vs Stainless Steel Cable Winders

01/12/2012 4:34 AM

Not necessarily longer. In the tropics it goes faster in the (wet) air than in the colder water. Temperature has a lot to do with electrolysis activity. In the air (and sun) the temperature is mostly higher than in the water.

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#13

Re: Aluminum vs Stainless Steel Cable Winders

01/12/2012 10:41 AM

Most suppliers of boating gear offer units of varying corrosion control. If you live on a quiet lake, you buy the one with the least protected versions. If you are on lovely tropical island in the middle of the ocean, you buy the most fully protected design.

Did you, "Cheap Out," here ?

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