Werner Hoyt, marine engineer and shipbreaking expert with over 30 years experience working with naval ships sent the following email to the No Ship Action Group on 9/2/2011:
“And the Saga of the HMAS Adelaide continues. Estimated costs so far to reef in excess of $3100/ton and she is not yet reefed.
With the news on problems with the Ex Canberra breaking up the No Ship Action Group (Residents of Avoca Beach NSW) have a good chance of stopping the reefing.
What is happening to HMAS Canberra in an active environment will happen on a similar scale of time for the Adelaide
The increased turbulence at Avoca will do several things:
1. As the vessel paint exfoliates due to corrosion propagating between the paint and metal flaking it off, surface area available to drive galvanic corrosion processes increases.
Essentially the ship has become a giant battery discharging through the water.
A positive feed back loop is in place. Corrosion rates increase, increasing available surface areas to support the galvanic process until the point in time there is no longer contact between the aluminum in the superstructure and the steel of the hull.
2. Result is a faster breakup of the vessel.
3. The good news here is that fibre glass will not be washing up on Avoca’s beaches.As a result of the tribunal’s orders all fibre glass insulating material was to be removed at substantial cost. The effect of this will be to expose surfaces of the ship to the environment sooner, more available oxygen for corrosion.
4. The bad news. The galvanic corrosion process will rapidly corrode away locations where aluminum lockers and electronic cabinets were mounted. This will make these heavy items susceptible to moving/falling over if the ship shifts in it’s reefed position endangering divers.
Lighter aluminum lockers freed of their attachments will be flushed out of the hull due to the more dynamic (turbulent) environment and soon wash up on Avoca’s beaches.
Why has this happened? It is a basic difference in ship construction.
Ships with aluminum superstructures reefed prior to HMAS Canberra were assembled by inserting a dielectric material between the steel and the aluminum and huck bolted (riveted) together and isolated electrically.
The HMAS Canberra and HMAS Adelaide were constructed utilizing an explosion bonded steel and aluminum bi-metalic joint. This provides 100% conductivity between the superstructure and the hull driving the galvanic corrosion process.
The ship is a giant galvanic corrosion cell. Essentially once immersed in sea water the ship becomes a giant battery discharging through the sea water.
This was not seen in earlier reefing sites because the riveted joint provided an extremely high resistance connection comparatively between the hull and superstructure of the ship.
This difference results in corrosion activity that takes place in 1.5 years versus 20 to 60 years or more previously experienced in earlier reefings.
Best of luck mates cleaning the mess up if HMAS Adelaide is reefed. Dearly hope that wiser heads ultimately prevail here.
Sincerely,
Werner F. Hoyt, PE
Program Manager
Ship Recycling Programs
Source:
Email: avoca@noship.com.au
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