Wet blasting and dry blasting are abrasive cleaning methods that involve propelling small particles at a surface at high velocity to strip away rust, mill scale, contaminants and old coatings from a substrate. Both are fundamental forms of surface preparation and cleaning in industry for non-destructive testing / non-destructive examination (NDT / NDE), lining, coating, refurbishment and other purposes.
Here we look at the similarities and differences between the two.
Dry Blasting is similar to Wet Blasting but it does not use water or liquid, only air through a Venturi Nozzle.
The Main Advantages Of Dry Blasting
1) Efficiency. Dry blasting is an extremely efficient way of stripping away old coatings, mill scale, corrosion and other contaminants from metal surfaces. The resultant debris can be much easier to remove as waste.
2) Cost-effective. As it doesn’t involve additional equipment or the containment and disposal of water and wet waste, dry blasting is comparatively less costly.
3) Versatility. Dry blasting requires less equipment and preparation, and can be conducted in a wider range of locations. If dust is a concern, containment and extraction through the use of a temporary blast building or other suitable encapsulation can be considered.
The Main Disadvantages Of Dry Blasting
1) Health Hazard: The fine, abrasive dust released from dry abrasive blasting can cause harm to the operative or adjacent working parties if inhaled, or to local dust sensitive plant. This can however be effectively removed through use of Respiratory Protective Equipment, exclusion zones and encapsulation / containment.
2) Static Explosion Risk. Static build up during the dry abrasive blasting process the can create ‘hot sparks’ which can cause an explosion or fire in flammable environments. This can be manged by use of equipment shutdown, gas detectors and permits.
Wet blasting involves mixing a dry abrasive with water, either through:
• Water Injection Nozzles – where the abrasive is dampened before it leaves the blast nozzle.
• Halo Nozzles – where the abrasive is dampened with a mist as it has left the blast nozzle.
• Wet Blast Rooms – where the used abrasive and water are reclaimed, pumped and recycled.
• Modified Blast Pots – where the water and abrasive are both stored under either water or air pressure.
The Main Advantages Of Wet Blasting
1) Dust Reduction. Due to the use of water, wet blasting reduces the amount of dust produced by the abrasive blasting process. It is they key advantage of wet blasting. It protects the operative, adjacent working parties and any dust sensitive plant from fine, abrasive, airborne particulates and is particularly advantageous in open environments.
2) Hydrostatic Forces. The presence of water means that there is more mass at the point of impact. This means that you may require less abrasive. These forces also provide a suitable, feathered edge where if the new coating is to interface with a sound, existing coating.
3) Cleaning. With some types of wet blasting, you can strip the surface and clean it at the same time. This negates the need for a separate rinsing process to remove media fragments and soluble salts.
4) No Static Charges. Abrasive blasting can cause sparking, which can cause explosions / fires where flammable gasses / materials are present. Wet blasting does not completely remove sparks, but does create ‘cold’ sparks, essentially removing the static and thus reducing the risk of explosion.
The Main Disadvantages Of Wet Blasting
1) Water Consumption. A level of valuable water resource is consumed during the process, even more so depending on which method of Wet Blasting is used.
2) Water Mist. Although visibility can be increased due to the lack of airborne dust, visibility is still reduced somewhat due to the presence of return spray mist from the water.
3) Higher Costs. Water pumping, mixing and reclamation systems, plus the requirement for containment and drainage can increase the costs of wet blasting and the amount of equipment required.
4) Flash Rusting. Exposure to water and oxygen increases the speed at which a metal surface will corrode. To avoid this, the surface must be quickly and sufficiently air dried afterwards. Alternatively a rust inhibitor can be used to ‘hold’ the blasted surface from flash rusting, but is not always recommended and the surface is still required to be dried before painting.
5) Wet Waste. The water has to go somewhere. And so does the wet abrasive. This waste can be heavier and much more difficult to remove than its dry equivalent.
Find Out More
If you need to significantly protect an open environment or adjacent dust sensitive plant, then wet blasting may be the method for you. However, most other applications where the adequate environmental controls, containment and equipment are more than suitable for dry abrasive blasting.
At KUE Group, we are equipped to provide both wet and dry blasting solutions. Using our fleet of specialist vehicles and our temporary buildings on your site, or at our dedicated in-house facility, both methods have their uses. Please contact us today at firstname.lastname@example.org and let us help you advise you for the best solution for your surface preparation needs.