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Overview - Why we Blast?

In shipyards we are blasting because the ship or the offshore structure oil rig is in a very corrosive environment. Seawater means salt, always wet and often, particularly in tropical areas, you’ve got warm conditions which aid the corrosion process even more.
We need an extremely rugged barrier to protect the steel from corrosion, because these assets are very expensive to build and when they are in service they are earning significant amounts of money. When they are out of service it means there are massive losses in production and losses in opportunity which results in losses to profits. We blast so that we get a great surface to put a coating onto as a barrier to the steel to protect it from corrosion and the best way to get a great surface for coatings is abrasive blasting.

DIFFERENT ABRASIVES USED IN SHIPYARDS

The most common types of abrasives used in the marine and shipyard industry are usually expendable abrasives when you are doing maintenance work or in a dry dock. Typically GMA garnet, copper slag, coal slag, crushed glass, staurolite, Chinese garnet, Indian garnet, South African garnet. The ones that are typically found to be the most popular are ones where they are able to clean the surface while removing the coating in a lesser time, e.g. faster coating removal. This is important because when it comes to marine coatings, because they are tough, rugged coatings, often in a maintenance situation, you are having to remove a thick coating. To remove a thick coating you often need a slightly coarser abrasive and even using higher pressures. When you talk about cleaning ship decks, oil rig decks, you are talking about taking off very thick coatings up to ¼” thick, so you need a coarser abrasive. You need to balance that with the disposal costs. Because there is often contaminants in the abrasive when you dispose of it and disposal can be a very expensive, you want to minimize your waste, so by using the optimum grain size, not too coarse but fine enough to keep those metering valves wound in, you minimize your abrasive consumption which reduces your disposal costs. Garnet has been found to be very popular for that, particularly with the new grades available, like GMA ToughBlast.

When blasting new ship construction the abrasive that is outstanding in its performance is GMA NewSteel Garnet. It has an extremely consistent particle size and shape, and will blast extremely fast.

Project Challenges

You are often working under tight deadlines which ship docking, the ship can only be out of the water for so many days, the old coating needs to be removed quickly, repaired and the ship put back into the water again so it can continue to operate. Every day the ship is out of the water it is not earning the owner money. The often un-spoken challenge is that because so much of the surface is inaccessible while it is in use, you can’t actually see the scope of the work and the condition of the existing coating while it is in the water, which means you don’t actually know until the ship is out of the water, or you are able to climb into the ballast tanks, to assess what the condition really is like. So you don’t actually know and it’s very difficult to prepare. You don’t know how much abrasive you need, what grade of abrasive you need, how many nozzles you need to put on it and you need to prepare for the worst, so that you are prepared for anything that you need to do. You don’t even know what grade the corrosion is.

If you are also doing repair work on the ship you need to have the boat out of the water, cut plates out and weld patches, all which add to the pressure of the painting at the end. While that fabrication work is going on you can’t paint, you have to wait for the welders to finish so that you can then come in and do the blasting and painting, and there may be some heavy delays. You may even need to be working at night which is quite difficult work.

The other thing that is tough about these types of projects is the confined space and the fact that you are in a severe corrosion environment. Because of that you can get very stringent quality controls. Some asset owners want every ‘i’ dotted and every ‘t’ crossed to ensure their coating life is maximized and hence their asset life is maximized. You might have inspectors running around. You are also dealing with the crew on the ship who have nothing else to do, so those staying with this ship look at you, check out what you are doing, ask you questions and waste your time. The other thing is if you run short and delay a docking there are massive costs incurred in the extra docking times, both from the shipyard’s point of view and the ship owner’s point of view. On slipways and in dockyards access is difficult. You might say yes, it’s in a dockyard, but you’re a long way away if anything is to happen. The equipment is always hundreds of metres away, it’s not like you’re in a blast room. Anything that needs to be brought onto the boat to work on the boat needs to be craned on and craned off, so you need to be very well organized to have the abrasive ready to be craned on all at once, the equipment to be craned into position all at the same time. Portable equipment really helps so you can actually get closer to where you are trying to work.

The other thing is, particularly on slipways, the ship is on an angle so what you might think is normally a nice work area, the ship is actually on a slope on the slipway so you need to work on a different angle to what you would normally work and you may need to install stairways, ladders etc, to access where you need to work.

THE BEST BLASTING EQUIPMENT

High production equipment could be anywhere from a 6.5 cu ft pot right through to multi-outlet megablast machines, 8 ton, 20 ton, 50 ton blast machines. The reason is you’ve got a lot of blasting happening in a close proximity and to save filling up multiple blast pots, you can fill up a megablaster with your day’s worth of abrasive, or even a week’s worth of abrasive and not having to worry about depressurizing and refilling that pot. The best equipment to use is high production equipment utilizing 1½”-2” valves. Because your blast pot may be a long way away from the blasting surface, you need to use upgraded size hoses, so 1½” maybe 2” hoses and high performance nozzles, particularly where you have open blasting. You might be using a hyper nozzle when blasting the outside and inside the ship tanks, you want the large hose sizes to keep the performance up, but when it gets to the confined areas inside a tank you may be using a short nozzle to blast.

Inside submarines you will find some very tight confined areas, inside ballast tanks and inside ship holds, there are a lot of confined areas and you will need very fast response deadman times normally using an electric deadman. You need good lighting and you need great flexibility because you are doing a lot of blasting behind the areas of a flange or somewhere you can’t see easily. You need to get in and under to properly blast clean the surface and put the coating on properly which requires a lot of twisting of the blast hose and a short nozzle to get into that area. As it is a confined space you want safety at the top of your chart for the operator.

Coating Types and Equipment

Many different coatings are used in the Marine environment. For marine structures it has to be ultra high builds. For shipbuilding we are talking about epoxies and anti-fouls on the outside. On the inside of tanks we are talking about solventless epoxies, even surface tolerant epoxies of a thickness of around about 20-40 mils. We have some areas on offshore oil rigs where we are talking Passive Fire Protection (PFP) coatings, then there are the decks which is always a very thick, often rubbery non-skid coating. There is often an aggregate dropped into that coating to add to the non-skid characteristics.

The best painting equipment to use is usually airless sprayers. You may be using plural component sprayers for some of the high build epoxies, some of the solventless epoxies and certainly for the PFP coatings. One of the most common sprayers for any shipyard is the Graco 60:1 NXT and becoming more popular is the Graco 45:1 and 70:1 XL pump which provides extra volume so you can run multiple guns over longer distances.

Environmental and Safety Considerations

Because you are close to the water you don’t want contaminants falling into the water or getting into the waterways. There have been many cases where abrasive contamination, coating contamination has got into the waterway and massive fines have been issues. Even severe environmental damage has happened.

You will also have the issue of noise, a lot of shipyards have other workers nearby and also residential areas nearby and that means that there are a lot of people who can hear you blasting, because blasting is a noisy exercise. The other major issue is dust. If your neighbors can see any dust, you may be driven to blast at night and then that makes the noise problem even worse because residential areas with a lot of noise generates a lot of complaints from neighbors. So dust, noise and contamination are key environmental concerns.

On the inside ships you are working around a lot of trades you could have welders nearby, you could have flammable areas nearby, electrical hazards, fall hazards, confined space hazards etc, so you need watchers. There have been situations where workers have died because they have been overcome by paint fumes in a ship’s hold. There have been instances where a blast hose has blown up under a blaster’s arm and blasted his lung open and the poor man died because the blast hose was worn out. You need to be right on top of your game. You need to make sure that your hoses are properly tested, they have good life in them, the rubber is not too thin, you have good access, good lighting, you don’t have the issue of flammable areas, you have good ventilation. Some of the most hazardous areas are actually working on the inside of a ship where there are not a lot of people available, so if the equipment malfunctions the poor operator is left in a dangerous situation.

On the outside of ships you need cherry pickers and access equipment to actually get access to the outside of the boat. Sometimes you will get automated equipment but most of the time you are actually doing it by hanging on to a nozzle.

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Ships and Marine Blasting