Is Hot Dipped Galvanized Necessary For Submerged Steel Shackles

[rutman]

I have an application where steel shackles are used in a deep ocean mooring. We have used plain and painted steel shackles with good results. Now the push is to use hot dipped galvanized shackles. Is this necessary or will the hot dip quickly corrode away after several months?

 

[SJones]

Will there be cathodic protection applied?

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

 

[rutman]

We do not use cathodic protection. The shackles are oversized to compensate for corrosion over time. We normally see a 4 to 5 year deployment life with no problems.

 

[SJones]

Then why change? Is it to reduce the corrosion allowance? The life of the galvanising will, of course, be dependent upon the applied thickness, but will be more than a few months, particularly in quiescent deep water. There will be voluminous corrosion product that could hinder disassembly for retrieval.

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

 

[rutman]

The believe is that the galvanize coating will provide corrosion protection, but my experience with hot dipped galvanize in the phototrophic zone is that it quickly corrodes away. It is somewhat slower in the lower, colder depths. My concern is it worth the additional cost? Disassembly is not a problem.

 

[strider6]

These tables show the corrosion rates of Zinc and Zinc-Coated Steel in Sea Water:

http://www.galvanizeit.org/aga/about-hot-dip-galvanizing/how-long-does-hdg-last/in-water

http://www.galvanizeit.org/aga/abou...last/in-water/water-corrosion-data//#seaWater

hope this help

V


Corrosion Control

 

[mshimko]

Galvanizing provides what is essntially a very thin sacrificial anode, with the emphasis on "very thin".

The service life of sacrificial anodes (in this case - galvanizing) is determined (partly) by the mass of anode material.

Since galvanizing provides a very thin layer, with little mass (relatively speaking), I wouldn't recommend it, and in generall, I oppose sacrificial cathodic protetion in immersion when the CP is provided by coatings of any type.

 

[unclesyd]

Every shackle I've seen used underwater has been HDG for marine service. Take a look the Peerless-ACCO offerings of marine chain and hardware.

http://www.peerlesschain.com/downloads/peerless-acco-2010.pdf#p

age=19

 

[unclesyd]

Here is the link in the proper format.

http://www.peerlesschain.com/downloads/peerless-acco-2010.pdf#page=19