Contractor Tip - Blast Cleaning Abrasives

• The SSPC/NACE Blast cleaning standards (Section 6) require both recyclable and expendable abrasive to be clean, dry and free of oil, grease and other contamination.  Your confirm this on the job site prior to turning on the air by testing the abrasive supply per the methods found in SSPC AB-1, AB-2, and AB-3.
• This means checking the abrasive for:
  • Oil (ASTM D7393) - oil and high performance prime coatings usually dont get along. If there's an oil leak in the "system" that's ignored, checking the abrasive supply for oil contamination can save a lot of abrasive consumption and the ensuing rework and cleanup, that would be at your expense.
  • Conductivity (ASTM D4940) - this is especially important for steel going into critical immersion service environments to ensure the abrasive is not salt contaminated
  • Train QC to perform and document these tests on every blasting day (required per SSPC QP-1)
  • Store the abrasive to keep it dry; allowing metallic abrasive to get wet can ruin an expensive drum of steel abrasive.  Allowing nonmetallic abrasive to get wet can reduce the effectiveness of the abrasive when it dries thus requiring more abrasive to get the job done and requiring the compressor to run longer than needed.  This is money unnecessarily falling out of your pocket.
  • Keep your air supply cool (in high humidity environments) and dry.  Perform the Blotter Test Daily (ASTM D4285)
• These are simple tests that can be easily performed in a few minutes by QC or the foreman before the start and during each blast shift.
• Nozzles:  Even if you diligently keep an eye on keeping the abrasive clean and dry and free of contamination, don't ignore the blast nozzle, which will also have an effect on productivity.
  • Use venturi nozzles which more than double the speed of abrasive hitting the surface with no increase in air 
  • Keep track of nozzle use hours vs mfg. life expectancy, if feasible
  • Check gaskets daily-a worn gasket allows the abrasive to damage the nozzle
  • Do not use nozzles worn to the next (1/16th) larger size
  • Measure nozzle orifice using a simple-to-use, inexpensive, measuring tool each blasting day
  • Replace any nozzle worn 1/16 inch beyond it original size or that shows any cracks on the jacket or liner
  • Worn nozzles demand more air - this decreases productivity and unnecessarily increases your operating fuel costs and wear and tear on your machinery
  • Besides wasting air supply, a worn venturi starts producing a straight bore pattern, which reduces production by requiring more abrasive and more fuel to run the system 

We hope this tip regarding getting the most out of your abrasive supply has been helpful.  Stay tuned for future tips such as air pressure, CFM, Blaster angle, standoff distance, hose size and other factors affecting blasting productivity.