Tube trailers are used in the distribution of industrial gases. The tubes, which are seamless steel, measure 22-in. diameter, about 1/2-in. wall, and 34 ft long. The U. S. Department of Transportation mandates periodic re-tests of tubes every 5 yr. Acoustic emission re-tests have been substituted for hydrostatic re-tests. This paper presents an analysis of flaws using fracture mechanics methods and establishes a maximum allowable flaw depth. It describes the acoustic emission test method and presents some typical results. Also, some discussion of the hydrostatic re-test is included.

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