Vacuum box testing of welds, among other applications, is used to test the bottom of storage tanks during tank erection.
You'll find plenty of information on the matter in the following standards:
API 650: Standard for oil and oil products storage tanks
AWWA D100: Welded steel tanks for water storage.
API is the American Petroleum Institute: www.api.org
AWWA is the American Water Works Association: www.awwa.org
Giovanni S. Crisi
Sao Paulo - Brazil