Rust problem? The answer lies in removing all of the salt

Few can have failed to observe how much more difficult it is to prevent rust problems from recurring once they have appeared on a steel surface. No matter how hard one tries with brushing or sand blasting, the rust often comes back at the same place shortly after treatment. Most of us have seen and experienced this seemingly incurable phenomenon and it is all down to the fact that there are residual salt levels remaining in the surface of steel, even where ship?s sides are washed with low pressure fresh water after sand blasting. The salt is still present in the steel surface in much the same concentration as earlier, i.e. 20-25 milligrammes/cm2.

The usual explanations of why rust returns so quickly varies from “the original paint is much better” to “old rust isn?t removed carefully enough” and “wrong paint has been used”. However, in recent years detailed tests and research have shown that the real explanation is that, unless all salt is removed, the rust will soon return.

The solution

The removal of old paint, rust and salt with water

jetting

will result in practically salt free surface. Several paint manufacturers therefore demand water

jetting

of the steel surfaces prior to painting if the guarantee is to be valid. It is therefore important to have an efficient, compact water

jetting

machine that can be handled easily around the ship to remove rust salt and old paint in a secure and fast way.

When pitting has started, it is important to get the pitting pocket empty of electrolytes and salt remnants to stop them from spreading through the steel. Since the pitting holes can be narrow, it is hard to reach down into the bottom except when using water

jetting

. The extreme water jet with a speed of up to 680 m/s will clean out every trace of electrolyte and rust debris and will then be ready to be coated with fresh primer and paint to completely fill up the holes thereby preventing corrosion from re-appearing.

There is also the added problem of new flash rust forming after cleaning with water, while salt in the air or seawater will re-enter the surface. It is therefore vital to prime and repaint the steel as soon as possible. If hot water is used for water

jetting

, the heat will be transferred from the water to the steel and the steel plate will dry immediately after cleaning. Oil and grease will also be removed completely and the bare steel surface will offer a good key for the new primer and top-coat.

Advantages of water

jetting

Water

jetting

gives exact defined small border zones against the old intact coating. This is particularly important with small patches of rust on the surface since it allows the good undamaged paint to remain and maintenance to be less extensive. The cleaned surface becomes practically free from salt, rust and electrolytes and the newly applied paint will be as good as the original. Water

jetting

also avoids having to cover up adjoining areas to protect them from abrasive contaminations such as sand and paint remnants, which, under current legislation, must be treated as special waste because of the mixing with old and, often, poisonous paint. When using water

jetting

, the resultant waste is only 1.5% of that from sand blasting.

Because of the modest amount of water used when water

jetting

, one should only use freshwater. Unlike sand blasting, water

jetting

can be carried out in all kinds of weather and, when the surface is dry, can be painted immediately without any risk of contamination from sand and paint dust particles. For shipyard painters, the working conditions are also better because of absence of dust.

The PC answer

The problems with traditional water

jetting

machines or ultrahigh pressure cleaners are that they are large, costly and only suitable for cleaning large areas and are awkward for small jobs. As a result of customer feed-back from specialists working for ship owners and oil companies, Speeder AS has designed a range of compact ultrahigh pressure cleaners called the PC (Personal Cleaner). According to the Norwegian company, these ?Speedclean? units are reasonably priced and light in weight, only 65 kg, and measure only 0.5 x 0.7 metres.

The air powered motor can be used anywhere, even in hazardous areas. To optimise the safety and durability of the cleaner, the company has designed the new unit to be without pressure when not

jetting

. This is achieved by a remote controlled air valve in front of the air motors so they start and stop by using this valve. When this valve is closed the ultra high pressure hose and pump are compl-etely free from pressure. Consequently, Speedclean ultrahigh pressure cleaners are fitted with less expensive seals, hoses and other components, and have an external protective hose enclosing the ultrahigh pressure hose thereby making the whole unit fail-safe.

Revolution in water

jetting

Said to be the most important innovation of ?Speedclean? is the development of a new linear solution, where the nozzle is moving back and forth by means of a little air driven linear motor that pushes directly on the nozzle. A very simple, efficient, reliable and effective patented solution which will enable the operator to easily limit the area to be cleaned without wasting time

and energy when using the normal rotating nozzle.

The Speedclean system is claimed to be three times faster than the traditional rotating nozzle.

Because it is possible to use the right angle to get the jet in under rust and old paint, the enormous speed pressure

in the water will peel of or shatter away everything that needs to be removed in a very efficient way. Another interesting aspect is that with the rotating nozzle much of the energy is wasted in fine misty droplets which never reach the steel plates. This is not the case with the linear movement since the water is not rotating.

This new ultrahigh water jet solution is set to impact the industry. Other techniques such as sand blasting are already being superseded by water

jetting

and there is every possibility that the Speedclean system will do the same to traditional water jet systems. With an efficiency improvement of more than 300 % compared with rotary nozzle water

jetting

, the investment costs are reduced to a fraction while the running costs are considerably less. Speeder has taken out a patent for the linear solution.