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Acoustic emission (AE) testing on a layered steel vessel was performed during a pressure test. A comparison of both conventional feature-based AE and Modal Acoustic Emission (MAE) was carried out. Most of this paper deals with the results obtained with this latest-generation transducer, especially some applications of MAE technology. On site, high priority was assigned to source location to provide maximum support to the Radiographic Testing measurements that were scheduled to begin immediately after the AE pressurization activities were completed. Acoustic Emission technique was capable of determining the location of the source cluster. In addition to that by using the Modal AE, the waveforms were further analyzed for additional characterization and location refinement. MAE results described in this paper include source location refinements, source-sensor distance measurements used to validate the linear nature of the discovered source cluster, and the demonstration that wave propagation characteristics (at least for the discovered cluster) were like those of an unrestrained plate having the same thickness as a single layer of the layered vessel. [ABSTRACT FROM AUTHOR]

Different types of pressure equipment are widely used in oil refining and petrochemical processing. A lot of these were made from carbon steels and have been used for a few decades. Long-term operation under extreme conditions causes defect initiation and growth in the microstructure of the equipment materials. The defects, which grow due to work loads, may damage the entire structure and may lead to the failure of the entire industrial unit. Consequently, the development of new nondestructive evaluation methodologies which allow the assessment of the condition of materials comprising the pressure equipment after long-term operation in the refinery industry is very important. The methodologies development is possible as a result of complex destructive laboratory tests combining different experimental techniques. The paper presents results obtained from the complex destructive tests with acoustic emission (AE) recording on real pressure vessel (capacity of 2.6 m3) after long-term operation in the refinery industry. The vessel has been operated in crude oil distillation unit for over 40 years. A lot of corrosion damages were present on the inner surface of the vessel shell as a result of long-term operation. The material's microstructure of some shell plates was coarse-grained, which arose from improper heat treatment during plates manufacturing. The hydraulic pressure test with AE recording of the pressure vessel was shown that AE method allowed to detect of local plastic deformation processes and early stage of crack initiation in overheated and corrosion degraded shell's material. The results of the conducted investigations form the basis for the developing of a complex methodology for assessment of the technical condition of pressure equipment in the refinery industry. The investigations, presented in this paper, were realised within the project of LIDER VII Programme financed by the National Centre for Research and Development of Poland. [ABSTRACT FROM AUTHOR]

Application of Modal Acoustic Emission (MAE) method to evaluate the health of the pressure vessels has been established in standards and procedures. Most of these standards ask for broadband transducers with certain level of flatness in the frequency response of the sensor in a specific frequency range with certain level of sensitivity so that the captured traveling waves' energy gets a fair representation from all the different modes present in that frequency range. In this paper the PKBBI sensor, developed by MISTRAS Group Inc, as required by these standards, is characterized. The results of some example real applications have been presented and analyzed to further evaluate the capabilities of this sensor. The PKBBI sensor shows superior performance in the MAE analysis versus the conventional sensors. Spectrograms of the waves have been overlaid to the group velocity curves to evaluate and analyze the acoustic emission modes and how they can be utilized to extract valuable information on the traveling path, medium, and source classification of acoustic event. [ABSTRACT FROM AUTHOR]

This paper discusses results of two AE tests performed of the pressure vessel within a 5-year period. The AE testing capabilities in detecting the lamination defects are demonstrated. This experience also shows the capabilities of AE technique for condition monitoring of large metallic industrial facility with structural defects evolving with time. This approach allows us to define the main trends in defect development process and to make a decision about what kind of inspection should be performed while facility is under operation or intermittently stopped. [ABSTRACT FROM AUTHOR]

Several regulatory rules, such as the Best Practices Guideline (GBP) [1], exist for acoustic emission (AE) testing of pressure vessels in France and the rest of the world and allow AE testing based on two techniques (zonal location and planar source location methods). However, the analysis criteria of data recorded during the testing lack adequate basis. This work highlights inconsistencies in analysis methods defined in these guides or codes based on modelling calculations in Part 1 of this study [2], while this paper shows, from a real case (AE testing of a 2000 m³ spherical storage tank), that the results of an AE test cannot be reproducible due to a lack of strictness in the application rules of AE. Thus, depending on the testing configuration used, some emissive defects can be detected or missed. This study may also be used as a basis for defining a new AE testing standard specifically and quantitatively defining a methodology of analysis based on a different approach from those used currently. Today, the CETIM may apply this new testing methodology based on significant feedback enabling a greater reproducibility and sensitivity of AE testing. [ABSTRACT FROM AUTHOR]

The paper describes a method of pressure testing of a vessel made from austenitic steel type AISI 304. The method of acoustic emission was used as a non-destructive inspection tool. On the outer surface of the vessel was placed a network of AE sensors comprising the entire volume of the vessel. In normal operation, this pressure vessel operates under cryogenic conditions (-160 ° C). During the pressure test with nitrogen, increased emission activity was registered, especially in the cylindrical part of the vessel. The individual emission events were not located in sub-sources (clusters), but were distributed throughout the shell volume. This caused a complication in evaluation of the pressure vessel according to the current valid standards for the evaluation of the AE signals. By further analysis has been found that the registered AE signals were induced by phase transformation of austenite to deformation-induced martensite, including the reverse process at local sites. [ABSTRACT FROM AUTHOR]

This is a tutorial article and covers the physical principles encountered in the field of acoustic emission (AE). This is followed by instrumentation and signal analysis methods. The second half is devoted to structural AE testing that relies on source location methods with detailed presentation of case histories. Three test setup examples and results on fiber-reinforced wind turbine blades and pressure vessels are provided. [ABSTRACT FROM AUTHOR]

Relative to potential use of acoustic emission (AE) to monitor pressure testing of large steel pressure vessels, in-plane pencil lead breaks (PLBs) were carried out on the open end of a remnant of such a vessel. This remnant had an inner diameter of 58 in. (1473 mm), a wall thickness of 3.3 in. (84 mm) and a total cylindrical length of 125 in. (3175 mm) ending in a head welded to the cylindrical section. The cylindrical section did not have a monotonic wall, but instead it was made of 11 layers (10 at about 0.277 in. [7 mm] thick, and the inside one of about 0.47 in. [11.9 mm] thick) to create a layered pressure vessel (LPV). Due to the presence of the multiple interfaces between layers, a question arose as to whether a sensor mounted on the outer layer was relatively less sensitive and had different frequency content for sources on the inner layers in comparison to sources on the outer layers? The PLB study used four pairs of different types of AE sensors. The sensor types included: i) strong resonance at a single frequency region; ii) multiple resonance frequencies; iii) and iv) broadband response with different frequency responses. Each sensor pair was acoustically coupled, one on the outside surface and one directly below on the inside surface. The sensors were located at 66 in. (1676 mm) (20 times the wall thickness) from the PLB points. This distance was considerably less than the helical path of about 214 in. (5436 mm). Considering PLBs on the ends of the different layers, Part 2 focused on identification of Lamb modes of wave propagation in the AE signals from the four sensor types. In addition, by use of superimposed group velocity curves on frequency versus time results, the peak intensity in the frequency versus time domain for the outside sensor types was studied relative to determination of the presence of dominant full thickness propagation or dominant single layer propagation. For PLBs on the outer most layers, both single layer propagation and full thickness propagation were present in some of the outer sensor signals. [ABSTRACT FROM AUTHOR]

Relative to potential use of acoustic emission (AE) to monitor pressure testing of large steel pressure vessels, in-plane pencil lead breaks (PLBs) were carried out on the open end of a remnant of such a vessel. This remnant had an inner diameter of 58 in. (1473 mm), a wall thickness of 3.3 in. (84 mm) and a total cylindrical length of 125 in. (3175 mm) ending in a head welded to the cylindrical section. The cylindrical section did not have a monotonic wall, but instead it was made of 11 layers (10 at about 0.277 in. [7 mm] thick, and the inside one of about 0.47 in. [11.9 mm] thick) to create a layered pressure vessel (LPV). Due to the presence of the multiple interfaces between layers, a question arose as to whether a sensor mounted on the outer layer was relatively less sensitive and had different frequency content for sources on the inner layers compared to sources on the outer layers? The PLB study used four pairs of different types of AE sensors. The sensor types included: i) strong resonance at a single frequency region; ii) multiple resonance frequencies; iii) and iv) broadband response with different frequency responses. Each sensor pair was acoustically coupled, one on the outside surface and one directly below on the inside surface. The sensor pairs were located at 66 in. (1676 mm) (20 times the wall thickness) from the PLB points. This distance was considerably less than the helical path of about 214 in. (5436 mm). Considering PLBs on the ends of the different layers, Part 1 focused on changes in the character of the AE signals from the four sensor types. Comparisons for each sensor type were made of the amplitudes of the outside sensor relative to those of the inside one. In addition, as the PLB was moved to different layers, the changes in the signals and frequency content of the different sensor signals were studied. Except for one sensor type, the outer sensor peak signal amplitudes relative to the inner sensor peak signal amplitudes changed significantly as the PLB layer moved from the outer layers to the inner layers. In addition, the signals and frequency content also varied with changes in the PLB layer. The results represent a lower bound due to the potential for some increased transmission between layers when an LPV is pressurized to significant levels. [ABSTRACT FROM AUTHOR]

Motivated by the emerging hydrogen mobility uses, especially the need for storing a high amount of energy in a small and lightweight volume, type IV composite pressure vessels have become a state-of-the-art technology for high pressure hydrogen. They comprise a non load-bearing liner, generally made of plastic and assembled with metallic bosses, around which a carbon fibre-epoxy composite is wound. Though such vessels can already be operated safely, there is a lack of knowledge concerning their residual performance after a mechanical impact. There is a need for associated nondestructive examination (NDE) methods, able to assess whether a cylinder is still fit for service after impact. The FCH-JU funded pre-normative research project HYPACTOR was set up to investigate the damage created in type IV pressure vessels by mechanical impacts, and then the use of Acoustic Emission to build rejection criteria during inspection. The methodology was to combine several AE tests on healthy and impacted vessels and correlate the results with residual performances. The developed criteria were applied to a wide database of Type IV composite vessels with different sizes, design specifications and working pressures. The validation was carried out on 114 hydraulic tests on healthy and impacted vessels. Results have demonstrated a capacity to differentiate damaged cylinders from healthy ones, with some small influence of the number of pressure cycles between impact and inspection. [ABSTRACT FROM AUTHOR]

Acoustic emission (AE) is widely used in order to evaluate the integrity of many types of structures, such as pressure vessels, reactors, storage tanks, concrete structures, aerospace structures. Several regulatory rules exist for AE testing (AT) around the world and allow AE testing based on two operational modes (zonal location and planar source location methods). However, the different regulations have not always produced the same rules and requirements, leading to different results. The method called CATS has been developed by the author, based on knowledge and experience, to be a universal tool that can evaluate any configuration of AT (a structure, an array of sensors, attenuation characteristics, data acquisition characteristics), with a same methodology. This tool/methodology should help all the users of this technique to measure in a numerical scale, the degree of performance of an AE testing, giving a clear view on what we can detect, and where (the degree of coverage of a structure). [ABSTRACT FROM AUTHOR]

The use of modal acoustic emission testing and analysis techniques to determine the quality of newly manufactured vessels and to detect and analyze damage in vessels that are in service can provide the required confidence in the safety of high pressure composite (HPC) pressure vessels operated at pressures up to 103 MPa (15,000 psi). These vessels are made of composite materials, such as carbon fibers embedded in a resin matrix, the fiber content being approximately 60% by weight. A practical method for distinguishing fiber break and matrix cracking events by a combination of energy and frequency is described and a new rolling ball impact energy calibration technique provides a method for comparing source energies with wave energies. Background energy oscillation appears to give detailed insight into failure progression. Fiber-bundle tip vibration can reveal the presence of already broken fiber bundles. The curvatures of cumulative events and energy curves quantitatively measure pressure vessel stability and are used in the current ASME code as accept-or-reject criteria for HPC pressure vessels. These tools are useful for manufacturing acceptance, in-service testing, quality control, fatigue, stress rupture and composite repair applications. [ABSTRACT FROM AUTHOR]

We propose an acoustic emission based method to predict the local stress exposure of a fiberreinforced material. This approach uses a stepwise increased load profile as common in testing procedures of fiber-reinforced pressure vessels. We apply an artificial neural network to establish a relationship between acoustic emission criteria evaluated for each load cycle and the globally applied load ratio. The acoustic emission training database for this neural network is obtained from lab-scale experiments, such as tensile tests, bending tests, double-cantilever-beam tests, endnotched- flexure tests and lap-shear tests. We present the application of this neural network to burst tests of three small-scale pressure vessels (560 mm length) and two large-scale pressure vessels (2600 mm length) for burst pressure prediction. In all cases, the deviation between predicted and measured burst pressure is less than 3.0%, with a maximum prediction uncertainty of 9.8%. In addition, we present a segmentation technique, which allows evaluating the acoustic emission criteria for sub-volumes of the full structure. This is based on precise source localization of the acoustic emission signals using artificial neural networks. The local prediction of load ratios allows evaluating the stress exposure of the structure as function of the applied load cycles. The resulting concentrations of stress exposure are compared to in situ camera analysis during the tests, strain gage measurements and post mortem analysis of the vessels. In all cases, good agreement with the prediction of the local load ratio is found. [ABSTRACT FROM AUTHOR]