Fundamental to most acoustic emission 270 acoustic

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fundamental to most acoustic emission 270 Acoustic Emission Testing P ART 1. Acoustic Emission Testing of Spheres and Other Pressure Vessels
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tests. Loading techniques vary according to the service conditions anticipated for each vessel. 1. For inservice pressure vessels, the load is based on the maximum operating pressure. 2. In the case of new or repaired vessels, the hydrostatic or pneumatic test load is the basis for the test. 3. In some cases, testing will require a hybrid loading combining two or more hydrostatic, pneumatic, operating and pressure test loads. 4. Filling a thin wall (low pressure) column for a hydrostatic test may cause it to exceed the maximum test pressure at the bottom. 5. In spheres, the liquid level and density contribute both to the load on the bottom hemisphere and to the support legs. 6. A hydrostatic pressure test is specified for some vessels but detection of service related damage (such as stress corrosion cracking) at the operating pressure is required. 7. Some vessels are rated for a higher working pressure. Examples of loading schemes for typical pressure vessel tests are given below. The starting pressure may need to be lower if the maximum operating pressure is uncertain. Acoustic emission from environmental cracking such as stress corrosion cracking occurs predominantly within a few percent of the operating pressure. Care is needed to ensure that shallow cracks in particular are not blunted and that data are not lost because of starting the test at too high a pressure or exceeding the operating load when preparing (by filling or other means) for a test. Two pressure cycles are often needed because of shakedown effects. Evaluation criteria for the second loading (if required) are more severe and these results belong in the inspector’s report. In this case, the operating pressure varied greatly over the height of the column. A staged test was designed to take into account the effective operating pressure in three different zones. These covered the 90 to 110 percent inservice test range and a final pressure loading was incorporated to provide additional data at the maximum service load. Figure 1 shows three loading schemes. Figure 1c shows a complex fill and pressure test regime used for a series of liquefied petroleum gas spheres. The combined test was designed so that the spheres were subjected to combined loads beyond any that they could experience during operation. Test Procedure Description Test procedures for acoustic emission testing during hydrostatic pressure testing differ among companies but most address the following basic elements. Preparation The need to apply the correct load means that acoustic emission testing is highly dependent on proper planning and preparation. The inspector needs to know many details about the vessel to be tested, including any history of damage or repair, recent load history and operational details. Such details are important for specifying the transducer placement, loading procedure and, to some extent,
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  • Fall '19
  • Nondestructive testing, Hydrostatic test, Acoustic Emission

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