The ElMag ultra-low frequency corrosion control system, which was originally developed by Ecospec Global Technology, has been fitted in the seawater-cooled stern tube cavity of a fleet of tankers operating in the US
The ElMag system mitigates metal corrosion problems in the seawater-cooled stern-tube cavity with the presence of super duplex stainless steel shaft and carbon-steel cavity housing. It is the only system that can actively generating magnetite.
This protective magnetite layer can only be formed traditionally with chemicals for treating steel surfaces submerged in closed-loop water systems, or under high temperature and pressure.
However, ElMag with the innovative use of ULF, is able to provide protection to steel or metals in water at ambient temperature, using very low power and without using chemicals.
Its unique feature is its self-repairing characteristic: if the protective layer is damaged, the ElMag system will produce a new protective layer, unlike traditional coatings which need to be physically restored.
The magnetite layer is not susceptible to interference corrosion, allowing it to provide corrosion protection on a 24/7 basis.
Cathodic protection and coatings are the traditional solutions for controlling dissimilar metal corrosion, pitting corrosion, and hard to-reach areas such as crevices.
In the stern-tube void, there are several different types of metallic materials in the same area: mild steel for the housing, duplex stainless steel for the shaft, and steel/noble metal for the bearings. Due to the variant nobility inherent in each type of metal, even the best coating is not able to effectively control corrosion. Another common solution is to mount sacrificial anodes but their effectiveness is limited.
Over time, the surfaces of these anodes tend to disintegrate leaving fragments in the water of the stern tube cavity, which may end up in the cervices, possibly damaging the stern tube bearing.
In freshwater-cooled stern tubes, chemicals are usually added to protect this area against corrosion. Such chemicals present in the water tend to leak out into the sea together with the water defeating the objective of adopting a water-cooled instead of an oil-cooled system to prevent undesirable substances from being released into the sea.
The ElMag system being a chemical free solution, will not pose such problem.
First installed in Sembcorp Marine’s Admiralty Shipyard in Singapore in August 2014, the ElMag system yielded positive results after more than five years in operation when the stern tube was inspected.
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