Swaged Alloy Ferrules on Wire Rope Slings for subsea use

[Ussuri]

Generally for rigging used in subsea environments we used steel ferrules at the end terminations.

However, it is possible to use alloy ferrules but only if the wire rope is not submerged for any length of time. This is because the sea acts as an electrolyte turning the ferrule into an anode, causing it to corrode.

Does anyone have any guidance on how long it would take for the strength of the ferrule to be compromised? Has there been any research done on this subject?

Any thoughts or comments would be appreciated.

 

[StephenA]

I wonder why you would want to take such a risk? Unless there is a log of the time spent submerged for each ferrule under water and the amount of wire rope and / or steel structure that it is protecting it is impossible to say.

We generally use spelter sockets or the steel ferrules that you have mentioned unless the lift is a one off use such as lifting concrete diffuser domes into position.

Stephen Argles
Land & Marine

http://www.landandmarine.com

 

[Ussuri]

We acquired a project with a very very limited schedule (a few days) and had to get some large rigging made up quickly. The problem was they rigging manufacturer could not get steel ferrules in time for us to meet the mobilisation date, only alloy. I dont think spelters were considered. The penalties for not meeting the date were quite high.

The job required the rigging to stay subsea for a short period of time so alloy ferrules may be suitable, albiet risky.

I dont know how long they can be left though, and thats the problem. Ideally we wouldnt touch alloy ferrules with a barge pole but the client has effectively tied our hands.

 

[StephenA]

We have wrapped or painted the alloy ferrules in the past that sort of isolates them electically but I cannot give any guarantees.

The worst is if the rigging is attached to a steel structure which the ferrules try to protect and then you loose the ferrule in a few days.

Have you time to change to spelters?

What about adding anodes?

Stephen Argles
Land & Marine

http://www.landandmarine.com