Wire Rope Rust

[patholahan]

I have a sample of air craft cable 1/4" (7x19) galvanized that is used to hold boats out of the water (fresh water). It has developed some surface rust after 3-5 days in use and I'm wondering how the material properties will diminish and at what rate. Should the rusted wire rope be replaced, or is the rust a normal reaction around wet and corrosive environments?

 

[unclesyd]

What is the cable material Carbon Steel or Stainless Steel?

Was the cable lubricated?

 

[hydromech]

It is often the case that ferrous particles get stuck to the rope and when the rope is exposed to moisture, it is those particles that rust. This give the appearance that the rope is rusting.

Hydromech

 

[patholahan]

The cable is made of carbon steel. To my knowledge, it was not lubricated beyond the galvanized coating.

The rust seems to be mostly concentrated to the grooves in between the strands.

 

[unclesyd]

Galvanized coatings are notorious for for cracking, especially if pulled over too small a sheave or drum. The supplier of the cable can give you a minimum sheave size. If this is the cause of the galvanized coating you should see if where the cable is flexing.

The galvanized coating should protect the wire for some time before it affects the strength of the cable.

I would keep a watch on cable and if you see any broken stands start thinking about replacement. Broken strands are indications that the cable is starting to fail.

I would also look at getting a good penetrating spray on cable lubricant and apply it at least twice a year. Check
with the local marine supply store.

I would definately look at an eventual SS replacement.

 

[patholahan]

Good ideas. However, I've just found out that they application of this galvanized cable is not new. They've been using the same type of cable without issues for a long time. Even over salt water they have not seen the rust form that quickly. My question is how do I know if the galvanized coating is thick enough or even present at all. Are the wire ropes generally coating by the individual strands, or once they are all wound together?

 

[unclesyd]

Unless something has changed a flexible wire rope will have individual strands galvanized with some types like guy wires can be galvanized after forming.

There is no simple test to determine the thickness of the zinc.
As I sated above you should be able to get some life from the cable if you use a penetrating lubricant.

Since the company states that this cable is used all over I would ask them why it is rusting in your case. A replacement might be in order.

 

[unclesyd]

Made a sashay by the docks this weekend and noticed that they were soaking a cable in Prelub 19. This reminded me that this material was used by the Navy and others. If you can find a source of supply for the aerosol this might be they way to go. You might have to order a case and sell the extra to the neighbors

http://www.purelube.com/products/wire_rope_lubricants/low_viscosity.htm