United States Department of Transportation
i
Testing and Recommended Practices to Improve Nurse Tank Safety: Phase IV
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2022-06-01
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[PDF-1.73 MB]
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Edition:Final Report, October 2018–September 2020
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Abstract:A selection of agricultural anhydrous ammonia nurse tanks was examined using phased array (PA) ultrasonic technology and acoustic emission (AE) monitoring to determine what effect is produced in the tanks during hydrostatic pressure testing (“hydro testing”). Tanks were selected to cover a variety of manufacturing ages and conditions, included those that received post weld heat treatment (PWHT) and those that did not; pre-1999 tanks with thicker steel; post-1999 tanks with thinner steel; and a new tank. Before hydro testing, tanks were examined using PA to locate existing cracks. This included re-testing 20 previously studied tanks, and 1 new tank. (An older tank was also included for testing to failure.) Next, the tanks were monitored for AE during the hydro test. The majority of tanks (16) showed no change at all due to the hydro test. Seven tanks did show slight differences and were re-examined using PA. These differences could be attributed to a variety of reasons including formation of new cracks, growth of existing cracks, better detectability of existing cracks due to the increased sensitivity of the PA equipment, or enhanced detection of an existing crack due to expansion/cleaning of the crack during the hydro test. A single crack was strongly suspected as having been initiated due to the hydro test, and it was at a probe minimum (PM) value in length, far below what calculations show is dangerous. The limited changes seen indicate that hydro testing does little or no harm to the tanks.
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