Location: Atlanta, Georgia
Client: Transportation Company
Contract Amount: $47,000
A transportation company engaged a tank vacuum testing
company to comply with the UST integrity testing requirements.
During the test a loud pinging noise was observed. A second
vacuum tank testing company was engaged and applied 0.84
inches of Hg vacuum and reported that the tank was tight.
Remtech was engaged to determine if the tank had been
damaged during testing by the initial testing company.
Remtech exhumed the underground storage tank by vacuuming
the tank pit overburden and gravel backfill with a vacuum truck.
The tank bottom collapse signature was 30 ft long, 55 inches in
width with a vertical deflection of 5.5 inches. The collapse
signature mirrored a single-lobe tank buckle shape referenced in
UST publications prepared for the Steel Tank Institute.
The interior of the tank was cleaned and ground down at test
points. Tank shell thicknesses were recorded with a
Panametrics NDT 37 DL Plus with a Single Element Transducer
and Ultragel II couplant. The original testing company’s vacuum
testing equipment had a vacuum relief setting of 5.5 psi and
allowed a maximum vacuum pressure of 4 psi.
Remtech used the Roark Equation that predicted a collapse
vacuum for this tank of - 2.729 psi (specified by Underwriters
Laboratory Standards UL 58 and UL 1746). Recognized
industry potential collapse pressures (range from -1.16 psi to <-3
Remtech conducted simulated vacuum failure demonstrations
that mirrored tank collapse signatures referenced by the Steel
Tank Institute, Underwriters Laboratory, and the actual tank
Flexure of UST tank shells weakens the steel and contributes to
premature failure. Remtech prepared a root cause engineering
report that concluded that the vacuum testing was responsible
for damaging the tank.
The vacuum tank testing company was using a maximum vacuum
of 4 psi that exceeds the predicted failure vacuum. The testing company reimbursed the transportation company for damages.