We did extensive testing of a pipe sand blasting system at a customer of ours. We tested with both the existing compressed air system as well as brought in a rental compressor to test the system while running at optimum blasting pressure.

The reason for this testing was that during discussions for new, more reliable and more efficient air compressor equipment, the question was raised about blasting pressure. We noticed that the existing air compressors are only rated for 100 PSI operating pressure (110 PSI max), and this is typically less than ideal for sand blasting. We suggesting running a test to determine whether or not operating the sand blasting system at a higher pressure would increase production.

Blasting Air Pressure

We increased the supply air pressure by about 40 PSI with the rental compressor. We took pressure readings at two points in the system, one was at the pressure gauge that was on the regulator feeding the blaster, and the other was a needle reading in the supply hose before the air/garnet mixture was fed into the blast nozzle. The needle reading is most critical, but the two readings were fairly proportional.

The following photos show the difference between the two systems:

Reading at the Regulator While Blasting

Existing Compressed Air Supply

101 PSIG
101 PSIG

Rental Compressed Air Supply

140 PSIG
140 PSIG

Existing Compressed Air Supply

74 PSIG
74 PSIG

Rental Compressed Air Supply

112 PSIG
112 PSIG

As you will see the existing compressed air supply system is giving a much less than desired compressed air pressure to the nozzle. For every 1 PSI over 100 PSI, you increase blasting efficiency by 1.5%! This is why nozzle pressure is so important, and directly affects production speed.

The blasting pressure was at least 26 PSI less than acceptable industry standards! This is costing huge production time and money.

Blasting Speed (Production Rate)

During this audit we tested two sizes of pipe, both with the existing compressed air supply as well as with the rental compressor supply air (approximately 40 PSI increase in pressure).

The first test was done with 16” x 42’ (165 SF blast area) pipe while using the existing compressed air supply:

Average Blast Time* 5:55/355 seconds
Rate of Blasting (Sq’/HR) 1,672

The second test was done with 16” x 42’ (165 SF blast area) pipe while using the rental compressed air supply:

Average Blast Time* 5:40/340 seconds
Rate of Blasting (Sq’/HR) 1,749

This test with 16” pipe only showed a 4.5% increase in time because the blasting trolley could not go any faster.

We decided to run 3 pieces of 30” pipe thru the system to see how that would change things, this is where the real improvement became obvious.

First test was done with 30” x 42’ (330 SF blast area) pipe while using the existing compressed air supply:

Blasting Time Going In: 7:14/434 seconds
Blasting Time Going Out: 2:35/155 seconds
Total Blasting Time: 9:49/589 seconds
Rate of Blasting (sq.ft./hr) 2,016

This blasting was not acceptable as per the “tape test”, and it should have been rerun or run at a slower rate of speed. We ran a second piece of pipe at these same trolley speeds but with the rental compressor supply pressure, and the blast quality was more than acceptable.

The third and final test was done with trolley speed going faster yet while still using the rental compressed air supply:

Blasting Time Going In: 4:31/271 seconds
Blasting Time Going Out: 2:40/160 seconds
Total Blasting Time: 7:11/431 seconds
Rate of Blasting (sq.ft./hr) 2,757

This final test of 30” pipe did prove to also be acceptable.

Below is a table summarizing the blasting production rates:

Case Study: Blasting Efficiency Report

*Acceptable but was noticeable cleaner than previous runs, may have been cleaner than necessary

Attached are photos of blasting 30” pipe at the different pressures:

Blasting @ 74 PSIG Nozzle Pressure

Case Study: Blasting Efficiency Report

Blasting @ 115 PSIG Nozzle Pressure

Case Study: Blasting Efficiency Report

You can see the difference in blasting effectiveness. Note the burn at the higher pressure and the sparks all the way around from when the garnet is bouncing around being more effective.

With the previous blasting rate of 1,672 sq.ft/hr being noted, we were able to achieve a vastly improved blasting rate of 2,757 sq.ft./hr at the higher nozzle pressure! This nearly a 40% increase in blasting production!

Conclusion & Recommendation

In conclusion, you can increase blasting speed by at least 40% by increasing your supply pressure by about 30%.

By increasing the air pressure by 40 PSI, we know that we will have an approximate 20% increase in the costs to produce the compressed air. Another study will be completed to confirm how much the increased costs in producing the additional pressure will offset the gains of increased production. Initial conversations had the customer very excited about increased production rates as this was the bottleneck in their production line.

Thank you very much to Blast-One out of Columbus, OH for their help in setting up this test.

Report Respectfully Completed By:

derrick-taylor

Derrick Taylor
Systems Engineer

Case Study: Blasting Efficiency Report