Volume 1, Number 2 April 2002
TNT Tips:
Penetrant Dye Removal
After penetrant dwell time comes the job of removal Ñ not a bad job on smooth surfaces, but tough on rough or irregular surfaces. The old lint free rag just doesn't get it.When you encounter the problem areas often found on as-welded surfaces, machined parts with sharp inside corners, or parts with depressions or pits, try this. Clean the part using the normal method and then finish the problem areas with a commercially available cotton swab or with a cotton swab on a toothpick. If you run into an inspector or customer who finds this method unacceptable, place the lint free rag on the part and use the swab to push it into the problem area.
This method also helps in precleaning and removing water following water washable or post emulsification operations. Lint free paper towels can be pushed into tight spots better than thicker items.
George R. Henke
Napa, California
Cotton Swab and Nonaqueous Developer
In recent years, many companies have replaced solvents such as acetone, trichloroethane, and carbon tetrachloride with alcohol for various reasons. While alcohol is less flammable, does not present as severe a hazardous waste disposal problem, and doesn't have the toxicity associated with more volatile solvents, neither does it evaporate as quickly. This can be annoying when performing penetrant inspections.Standard practice when confirming indications detected with color contrast penetrant systems is to remove a suspect indication with a solvent moistened wipe, allow the solvent to evaporate, and reapply developer to the area. A discontinuity indication will generally reappear as the developer dries, confirming the indication. If a low volatility solvent such as alcohol is used, evaporation time is significantly increased. I find that spraying nonaqueous developer onto a cotton swab and wiping the indication saves time. It removes the indication, cleans the surface, and reapplies developer in one step.
Carrier and Particulate Pooling
Many times when testing splines of shafts or grooves on a gear, the accumulation or pooling of magnetic particles and carrier make the interpretation more difficult.I find that by using an air nozzle with about 5 lb (2.3 kg) of air pressure, the carrier can be removed while the particles stay intact on the indication. The indication jumps out, making it much easier to interpret.
John Morris
Houston, Texas
[ The NDT Technician ]
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