General8212;This procedure is used for evaluation of the structural integrity of atmospheric storage tanks. The AE method can detect flaws which are in locations that are stressed during pressurization. Such locations include the tank wall, welds attaching pads to the tank, nozzle attachments, and welds attaching circumferential stiffeners to the tank. Among the potential sources of acoustic emission are:
In both parent metal and weld associated regions:
Cracks,
The effect of corrosion, including cracking of corrosion products or local yielding,
Stress corrosion cracking,
Certain physical changes, including yielding and dislocations,
Embrittlement, and
Pits and gouges.
In weld associated regions:
Incomplete fusion,
Lack of penetration,
Undercuts, and
Voids and porosity.
Inclusions:
Contamination.
In parent metal:
Laminations.
In brittle linings:
Cracks,
Chips, and
Inclusions.
Note 18212;Not all of these sources are typically encountered in field examination, some are detected under laboratory conditions.
Accuracy of the results from this practice can be influenced by factors related to setup and calibration of instrumentation, background noise, material properties and characteristics of an examined structure.
The outcome of this practice is to determine if the tank is suitable for service or if follow-up NDT is needed before that determination can be made.
Unstressed Areas8212;Flaws in unstressed areas and passive flaws (those that are structurally insignificant under the applied load) will not generate AE. Such locations can include the roof and certain welds associated with platforms, ladders, and stairways.
Passive Flaws (in Stressed Areas)8212;Some flaws in stressed areas might not generate acoustic emission during stressing. This usually means that the flaw has a higher stress tolerance than the examination stress.
Filling8212;Filling proceeds at rates which minimize AE activity caused by fluid flow and which allow vessel deformation to be in equilibrium with applied load. Hold periods are used throughout the filling schedule to evaluate AE activity produced by the loaded structure in the absence of fill noise.
Follow-up8212;Sources detected by AE should be examined using other NDT methods.
Background Noise8212;Excess background noise may distort AE data or render them useless. Users must be aware of common sources of background noise: high fill rate (measurable flow noise), mechanical contact (impact, friction, fretting) with the tank by objects, electromagnetic interference (EMI) (motors, welders, overhead cranes) and radio frequency interference (RFI) (broadcasting facilities, walkie talkies), leaks at pipe or hose connections, leaks in the tank bottom or walls, airborne particles, insects, or rain drops, heaters, spargers, agitators, level detectors and other components inside the tank, chemical reactions occurring inside the tank, and hydrodynamic movement of gas bubbles. This practice should not be used if background noise cannot be eliminated or controlled.
1.1 This practice covers guidelines for acoustic emission (AE) examinations of new and in-service aboveground storage tanks of the type used for storage of liquids.
1.2 This practice will detect acoustic emission in areas of sensor coverage that are stressed during the cou......
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