Tank Blasting Project Sites

Internal and External maintenance of tanks.

Overview - Why we Blast?

With fuel storage it is very important that the internals of the tanks are coated. The reason for that is that fuel and oil is lighter than water, so all the water drops to the bottom of the storage tank and it is very corrosive. The bottom area of a tank is often contaminated with "chlorides" other words, "salt", particularly in crude tanks so it is very, very corrosive. What that means is the tank floor and normally 3 ft up the walls is coated.

It is crucial that surface preparation is top class, to avoid re-work and costly "tank-downtime" to re-coat a failed tank floor. And, it may be the Contractor who pays!

Where are the heavy corrosion areas on a Tank?

The reason that corrosion is an issue is because of the moisture in the fuel and moisture in the oil. The moisture in the crude oil often contains seawater, which is highly contaminated with chlorides, this is very corrosive to steel and you will find the tank floor is the most rapid deteriorating area which needs to be blasted frequently. On the underside of the roof you can get condensation and it is another cause of corrosion.

A floating roof tank sits right on top of the oil so it’s not so much of a problem underneath, but the actual top side of the floating roof. The reason that this is an issue is because a lot of water builds up there and the water actually runs inside the tank. The top of a floating roof tank collects rainwater and because they are often located in a marine environment, casing premature corrosion damage due to chlorides. Water can pool in there for a long time so you have puddles of salty water causing corrosion issues.

Why good surface preparation is critical

The maintenance of internals of tanks and good surface preparation is crucial because of the fact that the fuel and oil in the tank is expensive.  To take a tank out of service to repair it is very costly so you want to minimize the time between having to empty the tank to inspect it and repair it. So if you can decrease the time it means a massive cost saving to the facility and that’s what we are all about – reducing the cost of corrosion control.

Good surface preparation is crucial to get excellent coating lift to minimize the maintenance time and out of service production costs associated with tank repair.

The ideal abrasive for Blasting Storage Tanks

The most common types of abrasive used are GMA Garnet, Coal Slag and Copper Slag. Sometime with large flat floors we use shot blast machines with steel grit and shot, but that is only cost effective in limited circumstances.   The abrasives that are better than others, generally achieve a more consistent finish, a high quality service cleanliness and a more consistent profile, the best abrasive available is GMA Garnet.  Part of the reason for that is you often have some coating failure.  The tank floors can be ¾- 1” or 1¼” thick plate you will get some pitting.  The GMA Garnet has the right amount of fine grains in it to actually clean out the pits properly, so there are not corrosion deposits left in the pitting.

Tank surface preparation setup

The basic equipment requirements.

Coating Types and Equipment

Many different coatings types are sprayed... On the inside of the tanks we are typically seeing solvent-less epoxies or high solid epoxies straight onto the steel. This means you need a higher class of blast which is normally SP5, minimum SP10. Typical coating thicknesses are 20-30 mils, even 40-60 mils quite often. The reason for this is to reduce the environmental effect of having solvents in the coating.

The Painting Equipment we typically see is a 60:1, 70:1 or 80:1 pump running one or two guns with large tips. Typically you are wanting to run a 27-31 thou tip. The biggest contractors are using large plural component heated sprayers for their solvent-less epoxies to minimize coating wastage but also to give the best atomization and coating coverage finish inside when you are coating.

Project challenges

One major uncontrollable challenge is the inclement weather. There are not many ways to handle weather issues, except to use a Dehumidifier and to ensure that your blasting equipment is high production to ensure you can make use of every hour of favorable weather.  Using a dehumidifier is a key part of doing the internals of a storage tank, because you want to blast for several days at once you need to make sure that the weather conditions are favorable.  You need to be very organized because the tank is out of service so the days on the job are crucial, so if you can save time you’re far better off, but if you run over time you often end up with penalty rates. 

The access around the tanks is often a challenge because you have to go around and bund the walls and run extra hoses.  Because you often have equipment one side of the tank you may not be able to get to the other side of the tank.  The tank could be 250 ft across so you’re having to run hoses all the way in and around across the tank which means you’re having to cope with pressure loss in blasting and also painting. Work in refineries also needs to be rated equipment.  If you are working in a construction area it is very muddy and you have equipment getting bogged. 

Proper Ventilation

An abrasive blasting enclosure site that doesn’t have adequate ventilation will quickly become a dusty, hazardous haze, hindering productivity and safety.

Working in confined environments such as tanks by law requires good ventilation. In some instances the coating that is being removed will contain hazardous substances (in the majority of cases this will be lead-based pigments). As these substances are considered toxic, specialized systems will be required. It is essential for the safety and productivity of the blasting team involved to maintain conditions during the blasting process that allow them to keep blasting.

Good ventilation will:

  1. Reduce the dust level inside the tank, improving the visibility and allowing the blasters to blast without any visual hindrance. It is important to have the duct work from the ventilation system positioned close to where the operators are working. This keeps the work area around them the clearest ensuring maximum visibility.
  2. Look after your blaster’s personal safety by quickly drawing any hazardous dust or fumes from the area where the workers are blasting. This is important as many of the old coatings contain lead or other harmful products which can damage the lungs and be harmful to blasters long and short term health.

Reduce clean up time after blasting is finished. By moving the air and dust out of the area it does not settle back down over the newly blasted surface. This helps to prevent the freshly blasted surface from being recontaminated.

Internal Lighting

The major advantage of having good lighting on a blasting site is the safety of personnel. By reducing injury’s you are protecting staff from long term health issues and protecting the project from potential legal allegations.

Having the correct lighting will also allow the blaster to achieve a cleaner surface first time. This means that there will be less re-working and reduced need to go back and clean up patches that were not cleaned to the correct specification. Good visibility leads to a much higher quality job and therefore no repainting due to coating failure. When the inspector checks the job for surface profile any areas of poor blasting can get very expensive.

Lighting options can be installed high lighting or helmet attachments to assist the blaster directly.

Safety Warnings and Legal Obligations

Always remember that a tank is a confined space, you need watchers, people with intrinsically safe radios and communication systems.  You need to get people in through manholes, manways, as well as get past ductwork hoses, so it’s a tight access environment.  You need to make sure your people are safe, and make sure you’ve got people checked in and checked out.

Want more information?

Get in contact with a BlastOne consultant to review how to improve your profits and enhance your project performance.