A tank shipped with an interstice on which a vacuum is drawn:

A tank shipped with an interstice on which a vacuum is drawn:

• A. Must still have a soap water test of the entire exterior surface to check for potential leaks before it is installed
• B. Need not be subjected to the pre installation air/soap test provided the tank arrives within limits designed by the manufacturer
• C. Must be hydrostatically tested before installation
• D. Must have the vacuum increased to 15 Hg of vacuum for a period no less than 1 hour and not decay beyond manufacturers allowable pressure loss.

Answer: (B)

When a tank is shipped with an interstice under vacuum, the tightness of that interstice is validated by the manufacturer’s tested limits. If the tank arrives within those approved limits, there’s already evidence that the interstice and shell are leaking-free to the standard the manufacturer sets. In that case, performing a pre-installation air/soap test on the exterior would be redundant because the key acceptance criteria—leak-tightness of the interstice and shell—has already been demonstrated by the shipped unit. The soap test specifically checks for bubbles along the exterior surface to show leaks, which isn’t necessary here since the manufacturer’s limits have been met and the interstice vacuum has served as the leakage indicator. If the unit had not met those limits, additional testing would be required, but with compliance, the extra test isn’t needed.

When a tank is shipped with an interstice under vacuum, the tightness of that interstice is validated by the manufacturer’s tested limits. If the tank arrives within those approved limits, there’s already evidence that the interstice and shell are leaking-free to the standard the manufacturer sets. In that case, performing a pre-installation air/soap test on the exterior would be redundant because the key acceptance criteria—leak-tightness of the interstice and shell—has already been demonstrated by the shipped unit.

The soap test specifically checks for bubbles along the exterior surface to show leaks, which isn’t necessary here since the manufacturer’s limits have been met and the interstice vacuum has served as the leakage indicator. If the unit had not met those limits, additional testing would be required, but with compliance, the extra test isn’t needed.