Compressed Air Preparation for Warmer Weather
Warmer, more humid weather means more moisture in compressed air systems. This can affect abrasive flow, blasting performance and equipment reliability if the air is not properly prepared.
A blasting system that has performed reliably throughout the cooler months can suddenly begin surging, blocking or feeding abrasive inconsistently as conditions become warmer and more humid. In many cases, nothing has changed with the blast pot or abrasive. Instead, the compressor is simply drawing more moisture from the surrounding air.
Throughout this blog, we look at where this moisture comes from, the problems it can cause and how correct compressed air preparation can help maintain consistent blasting performance.
Where Does the Moisture Come From?
All atmospheric air contains water vapour. A compressor draws this air in, compresses it and discharges it at a much higher temperature. As the compressed air travels through the airline, it begins to cool. The water vapour then condenses into liquid water. Without suitable air preparation, this moisture can continue downstream into the blast pot, hoses and associated blasting equipment.
An effective air preparation system helps manage this process by:
- Cooling the compressed air so moisture condenses before reaching the blast equipment
- Separating and collecting condensed water and other contaminants
- Draining contaminants from the compressed air system
Put simply, the objective is to make the moisture drop out of the compressed air early, collect it and remove it before it can affect blasting performance.
Why Moisture Problems Increase in Warmer Weather
Warm air can carry considerably more moisture than cooler air. A compressor operating on a humid 32°C day may therefore draw in significantly more water than the same compressor operating on a cool, dry winter morning. Once that air is compressed and begins cooling, the moisture must go somewhere.
Higher humidity can also reduce the available time between abrasive blasting and coating application. Freshly blasted steel is already vulnerable to flash rust, and moisture or contamination within the blast air can further increase this risk.
Signs of Moisture in Your Blast Air
Common signs that moisture may be entering the blasting system include:
- Abrasive clumping or bridging inside the blast pot
- Surging or spitting at the blast nozzle
- Inconsistent abrasive flow
- Blockages that temporarily clear after the pot is knocked or shaken
- Uneven blasting or inconsistent surface profile
- Flash rust appearing sooner than expected
- Moisture or oil detected during a blotter test
These symptoms can have several causes; however, the compressed air supply is one of the first areas worth checking, particularly during hot or humid weather. A blotter test completed in accordance with ASTM D4285 provides a quick method of checking compressed air for oil or water before blasting begins. This simple test can help identify contamination early and potentially prevent significant downtime or rework.
The Practical Cost of Wet Air
Moisture problems will often cost far more in lost productivity and rework than the equipment required to prevent them.
Wet or contaminated blast air can contribute to:
- Downtime while blockages are identified and cleared
- Wasted abrasive that has become damp or contaminated
- Reduced blasting performance and productivity
- Re-blasting where the required cleanliness or surface profile has not been achieved
- Flash rust developing before coating application
- Corrosion inside blast pots, valves and fittings
- Coating defects or failed inspections
On larger industrial, mining, defence or infrastructure projects, having to repeat even a relatively small section of work can quickly become costly.
ABSS Compressed Air Preparation Systems
SBI supplies ABSS Air Preparation Pre-Filter Systems, which combine compressed air cooling with moisture separation in a portable unit designed specifically for abrasive blasting applications. The systems can be positioned between the compressor and blast equipment and moved with the blasting setup as required.
Available sizes include:
- 200 CFM Air Dryer
- 300 CFM Compressed Air Pre-Filter System
- 500 CFM Compressed Air Pre-Filter System
- 1000 CFM Compressed Air Pre-Filter System
Correct sizing is important. The air preparation system needs to be matched to the compressor's actual output and the total volume of compressed air being used by the blasting equipment. An undersized system may not sufficiently cool and separate moisture from the compressed air at the required flow rate, limiting its effectiveness.
Blast Air and Breathing Air Are Not the Same
It is also important to distinguish between blast air preparation and breathing-air filtration. An air preparation system treats compressed air being supplied to the abrasive blasting equipment. It does not replace the breathing-air filtration equipment required for the blast operator. Air supplied to a blast helmet must pass through the appropriate breathing-air filtration and monitoring equipment. Blast-air preparation and breathing-air filtration perform different functions and should be treated as separate components within the blasting setup.
Prepare Your Compressed Air System Before the Heat Arrives
If blasting equipment has been operating reliably throughout winter, it can be easy to assume it will continue performing the same way as conditions become warmer. This is often when seasonal moisture problems begin to appear.
Before the warmer weather sets in, consider checking:
- Whether the compressor has suitable aftercooling and moisture separation
- That drains and separators are operating correctly
- That air lines are free from accumulated water
- That the air preparation system is correctly sized for the compressor and blasting setup
- That regular blotter testing forms part of site quality checks
A small amount of preventative preparation can be considerably easier and more cost-effective than dealing with a blocked blast pot or contaminated surface halfway through a hot working day.
At Spray Blast Inspect, we supply abrasive blasting equipment and compressed air preparation solutions for a wide range of industrial blasting applications. Our team can also assist with selecting an appropriately sized air preparation system based on your compressor output and blasting requirements.
written by Will Burge
Contact the SBI team for assistance with compressed air preparation and abrasive blasting equipment.