Painted into a corner

Shipyards and ship repairers could be forced to use new spray painting equipment to comply with pollution control legislation. As the size and complexity of modern commercial vessels has grown, so has the surface area that needs to be coated, and so have the demands placed on spray painting equipment. And there has been a […]

Shipyards and ship repairers could be forced to use new spray painting equipment to comply with pollution control legislation.

As the size and complexity of modern commercial vessels has grown, so has the surface area that needs to be coated, and so have the demands placed on spray painting equipment.

And there has been a corresponding rise in concern about resulting pollution. Because of the large areas to be covered and the fact that, in the UK, ships are generally painted in the open air, spray drift and contamination is increasingly becoming an issue.

Most paints and coatings used to protect ships and offshore structures from the corrosive effects of the marine environment are designed to be applied by large-scale industrial spray painting equipment. Shipyards say only this type of machine, often linked to multiple spray guns, is capable of painting large structures quickly enough to avoid production bottlenecks.

Applying marine paints and coatings to ships using long line, multi-gun, high-pressure airless spraying equipment is the most widely used technique, and is quick and efficient.

But coatings manufacturers and the UK’s Environment Agency are increasingly concerned about environmental problems associated with the use of this type of equipment.

Airless spray painting equipment is particularly suited for applying the kind of high solids content, highly viscous paints and coatings used in shipbuilding and the offshore industry. It works by atomizing the product as it passes through the nozzle of the spray gun. In order to be effective this process takes place at very high pressures of up to 120bar.

There are other types of spray painting equipment, such as air-assisted sprayers, but these tend to be slower. They are usually only used on smaller areas of a vessel where a more aesthetic finish is required, or for applying specialised coatings.

John Lewis, technical services manager at coatings manufacturer Jotun-Henry Clarke, explains that high-pressure airless techniques produce a very fine spray mist.

Because the mist is produced at high pressures, when the coating strikes the target surface a phenomenon known as ‘bounceback’ occurs. This can cause airborne paint to travel up to more than half a mile from its point of application.

The phenomenon is a major problem at British yards, says Eric Burkes, an inspector with the Environment Agency’s North East region.

The main problem in shipyards used to be discharges to water, says Burkes, but in the last two to three years the environmental hazards associated with spray painting have grown. He says a number of yards on Tyneside are on notice that they will be prosecuted if further instances of pollution occur.

On Tyneside, says Burkes, marine paints and coatings applied using high-pressure airless techniques frequently travel beyond the confines of the shipyard. On a number of occasions, particularly during windy weather, spray mist has crossed the River Tyne and damaged property and vehicles.

‘The problem is often exacerbated by poor training, or by inappropriate use of high-pressure spraying equipment,’ says Burkes. ‘Contractors may be under pressure to complete a job, or finish a section before the end of a shift, and it is not unknown for them to turn up the pressure on the pump in order to try to complete their work more quickly. In fact, this often has the reverse effect as coatings are not applied correctly, and the level of pollution increases as a result.’

Another big factor in the rising concern over the effects of spray painting in the UK is that, unlike many of their European counterparts, British yards have been slow to move to construction under cover in specially designed halls.

But specialist makers of spray painting equipment believe new techniques they have developed can be as efficient as high-pressure airless systems. The new processes have an equally high transfer efficiency, they say, and provide a much higher level of control of the application.

‘High-pressure airless equipment is well-suited for use on large, uninterrupted areas,’ says David Gill, managing director of Accuspray International, ‘but its days are limited. We need to bring pressures down, and eliminate bounceback.’

Accuspray has developed a high volume low pressure (HVLP) spray gun which, it claims, can apply coatings to large surfaces with the speed and efficiency of high-pressure airless systems, but without the bounceback. It is to launch a painting machine based on the HVLP process.

HVLP equipment uses volume rather than pressure to atomize paints and coatings, eliminating much of the problem of drift associated with high pressure systems.

CoverCat Spray Systems in Middlesbrough has developed another type of airless system for continuous application to large areas using long lines and multi-gun assemblies. The CoverCat 452 heats the product before it is sprayed to ensure atomization. This reduces wastage and consumption, says CoverCat.

Other manufacturers are developing similar low pressure systems, or hybrid equipment which uses a combination of pressure and volume to atomize the product.

The Environment Agency says there are several good reasons why shipyards should adopt more environmentally sound spray painting techniques, apart from the cost if they are found guilty of breaching pollution regulations.

Low pressure equipment is easier to control and more accurate, says the agency. With the cost of applying coatings to some large vessels running into millions of pounds, it makes environmental and commerical sense for yards to re-examine the painting equipment they use.