1. Use the Correct Pressure and Volume
To clean down to bare metal the grit must hit the surface with sufficient force. The right combination of air pressure, air volume and blast equipment components will quickly remove the scale from the pipe. We recommend 100 psi from a 100+ CFM (cubic feet per minute) compressor.
2. Use the Right Nozzle and Hose
A ¼" nozzle used with medium size grit achieves the best result for our purpose. The nozzle restricts the passage of air and grit. The compressed air speeds up as it passes through the nozzle, accelerating the abrasive in the air stream. As the inside of the nozzle wears, the mixture slows down and loses force. When the operator notices a loss of production it is time to replace the nozzle.
PLCS recommends a 25' x ½" ID blast hose for good results. Using a longer hose and bending or looping it will cause a drop in pressure. Friction against the walls of the blast hose will slow the grit velocity. Try not to use a longer blast hose than is necessary.
3. Use Proper Technique
The media valve at the bottom of the tank determines how much abrasive grit mixes in with the air going to the nozzle. Use far less grit than air, so it feels like 10% grit to 90% air. When first starting to blast keep the media valve closed and run air only for a few minutes to clear the hose of any residual grit and remove any moisture from the hose. Then open the media valve a little at a time to introduce a small amount of grit into the airstream. You will notice when the optimum amount of grit is in the airstream because it is cleaning most efficiently and you can hear a steady abrasive flow. Too little abrasive causes a high-pitched sound and too much an erratic pulsing. Experiment until optimal flow is achieved.
During the blasting operation keep the nozzle about 2 to 3 inches from the pipe surface at a slight angle from straight on. Move the nozzle with a smooth constant stroke. Do not whip the nozzle back and forth, or concentrate in one area, both will result in a lack of productivity.
Always use clean, dry air and grit. At the end of each work day empty the blast hopper and blow out any residual grit from the hose by operating the blaster until only air is exiting the hose. If grit is left in the blaster overnight, humidity will cause the grit to clump together, clogging the nozzle and making it close to impossible to use the next day.
Use a high quality compressor air line water separator to prevent any moisture from entering the blast hose. Also there must be no oiler on the air line from the compressor. Moisture and oil impedes the overall blasting operation and will discharge onto the pipe. This will affect the adhesion of the sealant to the pipe and may result in a failed repair. As always, follow gas company procedures and be sure the operator is equipped with the proper respirator fed by an approved clean, dry breathing air source.Happy blasting!
Unique Products for the Gas Distribution Engineer
Over the years US gas companies have installed millions of Normac and Dresser Style 90 compression couplings throughout their distribution systems. These coupling have offered a very easy way to join two pieces of ¾" to 2" pipe together but they have not always been trouble free. Despite material and manufacturing improvements, the basic design of compression couplings has not changed. They rely on elastomers and compression as sealing mechanisms. The safety problem that exists with these couplings falls into two major failure categories, which are pipe pullout or leakage. Typical pullout causes include damage from third party, cyclic fatigue from changing seasons, ground movement or improper installation. Leakage generally occurs when the rubber seals begin to degrade over time due to old age or change in gas quality. Nevertheless, these issues are not going away and must be mitigated. 
