Location: Atlanta, Georgia

Client: Transportation Company

Contract Amount: $47,000

PROBLEM

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.

SOLUTION

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

psi).

Remtech conducted simulated vacuum failure demonstrations

that mirrored tank collapse signatures referenced by the Steel

Tank Institute, Underwriters Laboratory, and the actual tank

collapse.

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.

COST/BENEFITS

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 and site restoration.