Corrosion simplified and solved

We are so used to corrosion on ships that no-one raises an eyebrow at the rust-stained hulls in any port or dock. It is, apparently, considered to be the way of things.

It is true that steel will rust. But with the knowledge and resources at our disposal we have long passed the point when we should have recognized that this is a problem, and solved it.

Corrosion on ships is rarely recognized as a failure of the coating, but that is precisely what it is. The first job of a hull coating is to prevent the gradual weakening and destruction of marine assets that is caused by corrosion. It remains a massive problem for shipping despite coating repairs every few years, eating up valuable days in drydock. Not only that, but current coating compounds also leak a million ton of toxic material into our oceans every year.

Corrosion is not some unavoidable fact of life. The basics of the subject have been well known for centuries, but they are worth reiterating. The iron in a steel hull is, effectively, trying to return to the state in which it was taken as an oxidised ore. Three things are needed for rust to form: metal, water, and oxygen. Energy, the galvanic difference between metals, stimulates the process, and impurities in the metal, seawater, water vapor, acids, salts, carbon dioxide and stresses hasten it.

While cathodic protection slows the corrosion on a ship, total prevention is only achieved by preventing metal, water and oxygen from coming into contact with eachother. That is the primary job of a coating. The problem is simply that most coatings fail poorly in that task.

One reason for their failure is the permeability of zinc primers, epoxies and antifouling coatings usually used. Water can get through and behind the layers of coating where it can start the corrosion process while accelerating it by causing coating delamination. This is the sequence of coating degradation which opens the door for further corrosion.

A second reason is the use of heavy metals in coating systems such as copper. These have a high galvanic differential with the steel of the hull. In practice we see copper-based coatings degrade very quickly – their difference in potential is the highest we encounter on ships. The fact that zinc, epoxy and antifouling, all of which have different surface tensions, are used together, further aggravates the problem.

Permeability, different surface tensions, poor adhesion and heavy metals are the four main factors that lead to an inferior protection on the ship hull.

It is not difficult to see that if a coating has no heavy metal content and therefore can avoid potential differential, is impermeable to water and achieves superior adhesion, the problem is solved. If the steel hull is isolated from its surroundings, then galvanic activity and corrosion are canceled.

Our range of coating systems has achieved this.

Observation over twenty years on hundreds of ships protected with our coating systems, reveals a distinct absence of hull corrosion on any of them. We do not find corrosion on these hulls.

With our glass-flake coating systems we have the solution. Their superior adhesion, impermeability and toughness fully isolate the steel hull. Even heavy corrosive environments in port or in seawater fail to touch the anodes or the steel surface of the hull. In fact, anodes become superfluous on an Ecospeed hull.

Environmentally our coatings are a vital solution because they contain no heavy metals, no zinc and no pesticides or other biocides. Extremely high concentrations of these elements are already found in the sediments around ports, estuaries and even far out at sea. It is clear that using them on ship hulls is not sustainable.

The subject of hull fouling is dealt with in a previous article – but it should be mentioned here that anti-fouling coatings have already caused one international marine catastrophe with the extensive use of TBT, and are creating further catastrophes if their use is continued. The attachment of marine organisms to ship hulls seems to be little affected by the currently available anti-fouling materials, but the marine environment suffers severely from their accumulating toxicity.

Simple mechanical removal of these organisms from a hard, non-toxic surface is the obvious and most workable solution, provided the coating is designed to withstand this.

We have seen more than 20,000 ships  over the last fifty years – after some time they all have corroded, rough, degraded and inefficient hulls.

An amazing discovery we frequently make is that, on inspection of ships coated with our systems, we never see corrosion of any significance, even when there has been small impact damage. Not after two years, not after five years, not even after ten years. This proves that with an inert coating there is no influence on the steel, even when exposed to seawater.

The conclusion is simple: the majority of the coating systems in general use today do not protect the hull sufficiently. They should be replaced with coatings that can do the job.

Contact us for more information
+ 32 3 213 5318
info@subind.net

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