Failure Mechanisms
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Material or Machine Problems
Material or Machine Problems
Recently the company I work for did a floor scan on a tank. Several areas where identified, and repaired. Another floor scan was preformed, and several more areas where noted. (This time I watched.) Again, areas where marked and repaired. Upon compleation of the repairs and inspections, a hydro test was performed. Hydro was acceptable. (No leaks within 24hrs.)
After water was emptied from tank, tank was put back into service, and product was put into the tank. Tank was about half way full and started to leak. A few days later during the inspection, through holes where observed in one area of the tank floor.
The question I have is: Could the MFE Unit have missed these indications during scaning? (I know that the area was scaned, because I saw it scaned.) If so how?
Could something have happened in the material that would have coused this? (No top side corrosion noted on floor. Failure was from bottom side.) The only thing that was different between the hydro-test and when product was put in the tank was two heating coils where turned on. (To about 250 degrees F.)
If anyone has any ideas, let me know.- 1 Reply
Does happen occaisionally. Have used technique very successfully, but have missed holes. Was the through hole surrounded by underside corrosion? Sensitivity correct? Scanning technique good enough to cover 100%? What diameter of hole through floor? Anywhere near floor plate lap joint that may have caused sensors to be raised up or tilted? Near annulus plates? A big worry but it does happen.
Forgot to ask, were you using MF leakage or straight forward ultrasonic testing? I presumed MFL.
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