5.1 The damage-based design approach will permit an additional method of design for GFRP materials. This is a very useful technique to determine the performance of different types of resins and composition of GFRP materials in order to develop a damage tolerant and reliable design. This AE-based method is not unique, other damage-sensitive evaluation methods can also be used.5.2 This practice involves the use of acoustic emission instrumentation and examination techniques as a means of damage detection to support a destructive test, in order to derive the damage-based design stress.5.3 This practice is not intended as a definitive predictor of long-term performance of GFRP materials (such as those used in vessels). For this reason, codes and standards require cyclic proof testing of prototypes (for example, vessels) which are not a part of this practice.5.4 Other design methods exist and are permitted.1.1 This practice details procedures for establishing the direct stress and shear stress damage-based design values for use in the damage-based design criterion for materials to be used in GFRP vessels and other GFRP structures. The practice uses data derived from acoustic emission examination of four-point beam bending tests and in-plane shear tests (see ASME Section X, Article RT-8).1.2 The onset of lamina damage is indicated by the presence of significant acoustic emission during the reload portion of load/reload cycles. “Significant emission” is defined with historic index.1.3 Units—The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units which are provided for information only and are not considered standard.1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.1.5 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

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4.1 The methods and procedures used in mounting AE sensors can have significant effects upon the performance of those sensors. Optimum and reproducible detection of AE requires both appropriate sensor-mounting fixtures and consistent sensor-mounting procedures.1.1 This document provides guidelines for mounting piezoelectric acoustic emission (AE) sensors.1.2 Units—The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in non-conformance with the standard.1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

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5.1 General—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:5.1.1 In both parent metal and weld associated regions:5.1.1.1 Cracks,5.1.1.2 The effect of corrosion, including cracking of corrosion products or local yielding,5.1.1.3 Stress corrosion cracking,5.1.1.4 Certain physical changes, including yielding and dislocations,5.1.1.5 Embrittlement, and5.1.1.6 Pits and gouges.5.1.2 In weld associated regions:5.1.2.1 Incomplete fusion,5.1.2.2 Lack of penetration,5.1.2.3 Undercuts, and5.1.2.4 Voids and porosity.5.1.2.5 Inclusions:5.1.2.6 Contamination.5.1.3 In parent metal:5.1.3.1 Laminations.5.1.4 In brittle linings:5.1.4.1 Cracks,5.1.4.2 Chips, and5.1.4.3 Inclusions.NOTE 1: Not all of these sources are typically encountered in field examination, some are detected under laboratory conditions.5.2 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.5.3 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.5.4 Unstressed Areas—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.5.5 Passive Flaws (in Stressed Areas)—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.5.6 Filling—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.5.7 Follow-up—Sources detected by AE should be examined using other NDT methods.5.8 Background Noise—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 course of the examination. For flat-bottom tanks these areas will generally include the sidewalls (and roof if pressure is applied above the liquid level). The examination may not detect flaws on the bottom of flat-bottom tanks unless sensors are located on the bottom.1.3 This practice may require that the tank experience a load that is greater than that encountered in normal use. The normal contents of the tank can usually be used for applying this load.1.4 This practice is not valid for tanks that will be operated at a pressure greater than the examination pressure.1.5 It is not necessary to drain or clean the tank before performing this examination.1.6 This practice applies to tanks made of carbon steel, stainless steel, aluminum and other metals.1.7 This practice may also detect defects in tank linings (for example, high-bulk, phenolics and other brittle materials).1.8 AE measurements are used to detect and localize emission sources. Other NDT methods may be used to confirm the nature and significance of the AE indications (s). Procedures for other NDT techniques are beyond the scope of this practice.1.9 Examination liquid must be above its freezing temperature and below its boiling temperature.1.10 Superimposed internal or external pressures must not exceed design pressure.1.11 Leaks may be found during the course of this examination but their detection is not the intention of this practice.1.12 Units—The values stated in either SI units or inch-pound units are to be regarded as standard. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in non-conformance with the standards.1.13 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. Specific precautionary statements are given in Section 8.1.14 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

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4.1 The purpose of the AE examination is to analyze how an examination object is withstanding the applied load, or if it is suffering from some latent damage. Consequently the emission activity must be evaluated in relation to the applied load.4.2 The applied load (on the examination object) may include mechanical forces (tension, compression or torsional), internal pressure and thermal gradients. It may be short to long, random or cyclic. The applied load may be controlled by the examiner or may already exist as part of the process. In either case the applied load is measured along with the AE activity.4.3 Possible applications include the determination of part integrity, quality control assessment of production processes on a sampled or 100 % inspection basis, in-process examination during a period of applied load of a fabrication process (for example, spot welding, bonding, soldering, pressing, etc.), proof-testing after fabrication, monitoring a “region of interest” (or concern) of a structure (for example, bridge joint or repair, vessel, pipe), and re–examination after intervals of service.1.1 This guide covers techniques for conducting acoustic emission (AE) examinations of small parts. It is confined to examination objects (or defined regions of larger objects) where there is low AE signal attenuation throughout the examination region. This eliminates the consideration of complex attenuation factor corrections and multiple sensor and array placements based on overcoming signal losses over distances.1.2 The guide assumes a typical AE examination as one where there is a controlled or measured stress acting upon the part being monitored by AE. Particular emphasis is placed on sensor and system selection, sensor placements, stressing considerations, noise reduction/rejection techniques, spatial filtering, location determination, use of guard sensors, collection of AE data, AE data analysis and report. The purpose of the AE examination is to analyze how an object under evaluation is withstanding the applied load.1.3 Possible applications of this guide includes materials characterization, quality control of production processes, proof testing after fabrication, evaluating regions of interest of larger structures and retesting after intervals of service. The applied load may include mechanical forces (tension, compression or torsional) internal pressure and thermal gradients.1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.1.5 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

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5.1 Due to safety considerations, the Compressed Gas Association (CGA) and others have produced guidelines which address in-service inspection of NGV fuel containers (see 2.2 – 2.4). AE examination is listed as an alternative to the minimum three-year visual examination which generally requires that the container be removed from the vehicle to expose the entire container surface. The AE method allows “in-situ” examination of the container.5.1.1 Slow-fill pressurization must proceed at flow rates that do not produce background noise from flow of the pressurizing medium. Acoustic emission data are recorded throughout a pressurization range (that is, 50 % to 100 % of AE examination pressure).5.1.2 Fast-fill pressurization can be used if hold periods are provided. Acoustic emission data are recorded only during the hold periods.NOTE 1: Fast-fill pressurization is less appropriate for carbon (or graphite) composites due to the lower sensitivity of carbon fibers to stress rupture compared to other fibers.5.1.3 Background noise above the threshold will contaminate the AE data and render them useless. Users must be aware of the following common causes of background noise: high fill rate (measurable flow noise); mechanical contact with the vessel by objects; electromagnetic interference (EMI) and radio frequency interference (RFI) from nearby broadcasting facilities and from other sources; leaks at pipe or hose connections and airborne particles, insects, rain and snow. This practice should not be used if background noise cannot be eliminated or controlled.5.2 Sensitivity is influenced by factors that affect elastic wave propagation, sensor coupling and signal processor settings.5.3 It is possible to measure AE from AE sources that cannot be verified by other NDE methods.1.1 This practice provides guidelines for acoustic emission (AE) examination of filament-wound composite pressure vessels, for example, the type used for fuel tanks in vehicles which use natural gas fuel.1.2 This practice requires pressurization to a level equal to or greater than what is encountered in normal use. The tanks' pressurization history must be known in order to use this practice. Pressurization medium may be gas or liquid.1.3 This practice is limited to vessels designed for less than 275 bar [4,000 psi] maximum allowable working pressure and water volume less than 1 m3 or 1000 L [35.4 ft3].1.4 AE measurements are used to detect emission sources. Other nondestructive examination (NDE) methods may be used to gain additional insight into the emission source. Procedures for other NDE methods are beyond the scope of this practice.1.5 This practice applies to examination of new and in-service, Type II, filament-wound composite pressure vessels.1.6 This practice applies to examinations conducted at ambient temperatures above 20°C [70°F]. This practice may be used at ambient temperatures below 20°C [70°F] if provision has been made to fill to the tank's rated pressure at 20°C [70°F]. Also that the test temperature must not exceed the glass transition temperature of the matrix material.1.7 Units—The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in non-conformance with the standard.1.8 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. Specific precautionary statements are given in Section 8.

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5.1 This test method is used where high accuracy of velocity or continuous discharge measurement over a long period of time is required and other test methods of measurement are not feasible due to low velocities in the channel, variable stage-discharge relations, complex stage-discharge relations, or the presence of marine traffic. It has the additional advantages of requiring no moving parts, introducing no head loss, and providing virtually instantaneous readings (1 to 100 readings per second).5.2 The test method may require a relatively large amount of site work and survey effort and is therefore most suitable for permanent or semi-permanent installations.1.1 This test method covers the measurement of flow rate of water in open channels, streams, and closed conduits with a free water surface.1.2 The test method covers the use of acoustic transmissions to measure the average water velocity along a line between one or more opposing sets of transducers—by the time difference or frequency difference techniques.1.3 The values stated in SI units are to be regarded as the standard.1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. Specific precautionary statements are given in Section 6.1.5 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

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5.1 The AE examination method detects damage in FRP equipment. The damage mechanisms that are detected in FRP are as follows: resin cracking, fiber debonding, fiber pullout, fiber breakage, delamination, and bond failure in assembled joints (for example, nozzles, manways, and so forth). Flaws in unstressed areas and flaws that are structurally insignificant will not generate AE.5.2 This practice is convenient for on-line use under operating stress to determine structural integrity of in-service equipment usually with minimal process disruption.5.3 Indications located with AE should be examined by other techniques; for example, visual, ultrasound, dye penetrant, and so forth, and may be repaired and tested as appropriate. Repair procedure recommendations are outside the scope of this practice.1.1 This practice covers acoustic emission (AE) examination or monitoring of fiberglass-reinforced plastic (FRP) tanks-vessels (equipment) under pressure or vacuum to determine structural integrity.1.2 This practice is limited to tanks-vessels designed to operate at an internal pressure no greater than 1.73 MPa absolute [250 psia, 17.3 bar] above the static pressure due to the internal contents. It is also applicable for tanks-vessels designed for vacuum service with differential pressure levels between 0 and 0.10 MPa [0 and 14.5 psi, 1 bar].1.3 This practice is limited to tanks-vessels with glass contents greater than 15 % by weight.1.4 This practice applies to examinations of new and in-service equipment.1.5 Units—The values stated in either SI units or inch-pound units are to be regarded as standard. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in non-conformance with the standard.1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.1.7 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

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3.1 Acoustic emission data is affected by several characteristics of the instrumentation. The most obvious of these is the system sensitivity. Of all the parameters and components contributing to the sensitivity, the acoustic emission sensor is the one most subject to variation. This variation can be a result of damage or aging, or there can be variations between nominally identical sensors. To detect such variations, it is desirable to have a method for measuring the response of a sensor to an acoustic wave. Specific purposes for checking sensors include: (1) checking the stability of its response with time; (2) checking the sensor for possible damage after accident or abuse; (3) comparing a number of sensors for use in a multichannel system to ensure that their responses are adequately matched; and (4) checking the response after thermal cycling or exposure to a hostile environment. It is very important that the sensor characteristics be always measured with the same sensor cable length and impedance as well as the same preamplifier or equivalent. This guide presents several procedures for measuring sensor response. Some of these procedures require a minimum of special equipment.3.2 It is not the intent of this guide to evaluate AE system performance. Refer to Practice E750 for characterizing acoustic instrumentation and refer to Guide E2374 for AE system performance verification.3.3 The procedures given in this guide are designed to measure the response of an acoustic emission sensor to an arbitrary but repeatable acoustic wave. These procedures in no way constitute a calibration of the sensor. The absolute calibration of a sensor requires a complete knowledge of the characteristics of the acoustic wave exciting the sensor or a previously calibrated reference sensor. In either case, such a calibration is beyond the scope of this guide.3.4 The fundamental requirement for comparing sensor responses is a source of repeatable acoustic waves. The characteristics of the wave do not need to be known as long as the wave can be reproduced at will. The sources and geometries given in this guide will produce primarily compressional waves. While the sensors will respond differently to different types of waves, changes in the response to one type of wave will imply changes in the responses to other types of waves.3.5 These procedures use a test block or rod. Such a device provides a convenient mounting surface for the sensor and when appropriately marked, can ensure that the source and the sensor are always positioned identically with respect to each other. The device or rod also provides mechanical loading of the sensor similar to that experienced in actual use. Care must be taken when using these devices to minimize resonances so that the characteristics of the sensor are not masked by these resonances.3.6 These procedures allow comparison of responses only on the same test setup. No attempt should be made to compare responses on different test setups, whether in the same or separate laboratories.1.1 This guide defines simple economical procedures for testing or comparing the performance of acoustic emission sensors. These procedures allow the user to check for degradation of a sensor or to select sets of sensors with nearly identical performances. The procedures are not capable of providing an absolute calibration of the sensor nor do they assure transferability of data sets between organizations.1.2 Units—The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

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3.1 Degradation in sensor performance can occur due to dropping, mechanical shock while mounted on the test structure, temperature cycles, and so forth. It is necessary and desirable to have a simple measurement procedure that will check the consistency of sensor response, while holding all other variables constant.3.2 While test blocks of many different kinds have been used for this purpose for many years, an acrylic polymer rod offers the best all-around combination of suitable acoustic properties, practical convenience, ease of procurement, and low cost.3.3 Because the acoustic properties of the acrylic rod are known to depend on temperature, this practice requires that the rod, sensors, and couplant be stabilized at the same working temperature, prior to application of the practice.3.4 Attention should be paid to storage conditions for the acrylic polymer rod. For example, it should not be left in a freezing or hot environment overnight, unless it is given time for temperature stabilization before use.3.5 Properly applied and with proper record keeping, this practice can be used in many ways, such as:3.5.1 To determine when a sensor is no longer suitable for use.3.5.2 To check sensors that have been exposed to high-risk conditions such as dropping, overheating, and so forth.3.5.3 To get an early warning of sensor degradation over time.3.5.4 To obtain matched sets of sensors and preamplifiers.3.5.5 To verify sensors quickly but accurately in the field, and to assist troubleshooting when a channel does not pass a performance check.1.1 This practice is used for routinely checking the sensitivity of acoustic emission (AE) sensors. It is intended to provide a reliable, precisely specified way of comparing a set of sensors or telling whether an individual sensor's sensitivity has degraded during its service life, or both.1.2 The procedure in this practice is not a “calibration” and does not give frequency-response information.1.3 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.1.4 This practice does not purport to recommend one sensor manufacturer over another nor does it imply that one type of sensor will react differently from another when using this procedure.1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.1.6 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

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5.1 EMAT techniques show benefits and advantages over conventional piezoelectric ultrasonic techniques in special applications where flexibility in the type of wave mode generation and where no fluid coupling is desired. EMATs are highly efficient in the generation of surface waves.5.2 Since EMATs are highly efficient in the generation of surface waves, and since acoustic techniques utilizing surface waves are proven effective for detecting surface and near-surface discontinuities, they should be considered for any applications where conventional penetrant testing and magnetic particle NDT techniques are effective but undesirable.5.3 Since EMAT techniques are non-contacting, they should be considered for ultrasonic testing where applications involve automation, high-speed examinations, moving objects, applications in remote or hazardous locations, applications to objects at elevated temperatures, or objects with rough surfaces.5.4 The purpose of this practice is to promote the EMAT technique of the ultrasonic method as a viable alternative to conventional PT and MPT methods for detecting the presence of surface and near-surface material discontinuities.5.5 The use of EMATs and the selection of appropriate operating parameters presuppose a knowledge of the geometry of the component; the probable location, size, orientation, and reflectivity of the expected flaws; the allowable range of EMAT lift-off; and the laws of physics governing the propagation of ultrasonic waves. This procedure pertains to a specific EMAT surface inspection application.1.1 This practice covers guidelines for utilizing EMAT techniques for detecting material discontinuities that are primarily open to the surface (for example, cracks, seams, laps, cold shuts, laminations, through leaks, lack of fusion). This technique can also be sensitive to flaws and discontinuities that are not surface-breaking, provided their proximity to the surface is less than or equal to the Rayleigh wave length.1.2 This practice covers procedures for the non-contact coupling of surface waves into a material via electromagnetic fields.1.3 The procedures of this practice are applicable to any material in which acoustic waves can be introduced electromagnetically. This includes any material that is either electrically conductive or ferromagnetic, or both.1.4 This practice is intended to provide examination capabilities for in-process, final, and maintenance applications.1.5 This practice does not provide standards for the evaluation of derived indications. Interpretation, classification, and ultimate evaluation of indications, albeit necessary, are beyond the scope of this practice. Separate specifications or agreement will be necessary to define the type, size, location, and direction of indications considered acceptable or non-acceptable.1.6 Units—The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard.1.7 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.1.8 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

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5.1 Real-time detection and assessment of cracks and other flaws in concrete structures is of great importance. A number of methods have been developed and standardized in recent decades for non-destructive evaluation of concrete structures as well as methods for in-place evaluation of concrete properties. Review of some of these methods can be found in ACI 228.2R-13, ACI 228.1R-03, and ACI 437R-03. They include visual inspection, stress-wave methods such as impact echo, pulse velocity, impulse response, nuclear methods, active and passive infrared thermography, ground-penetrating radar and others. These methods in most of the cases are not used for overall inspection of the concrete structure due to limited accessibility, significant thickness of concrete components, or other reasons and are not applied for continuous long-term monitoring. Further, these methods cannot be utilized for estimation of flaw propagation rate or evaluation of flaw sensitivity to operational level loads or environmental changes, or both.5.2 In addition to the previously mentioned non-destructive tests methods, vibration, displacement, tilt, shock, strain monitoring, and other methods have been applied to monitor, periodically or continuously, various factors that can affect the integrity of concrete structures during operation. However, these methods monitor risk factors that are not necessarily associated with actual damage accumulation in the monitored structures.5.3 Monitoring the opening or elongation of existing cracks can be performed as well using different technologies. These may include moving scales (Fig. 1), vibrating wire, draw wire, or other crack opening displacement meters, optical and digital microscopes, strain gages, or visual assessment. However, this type of monitoring is only applicable to surface cracks and requires long monitoring periods.FIG. 1 Moving Scale Crack Opening Monitor5.4 This guide is meant to be used for development of acoustic emission applications related to examination and monitoring of concrete and reinforced concrete structures.5.5 Acoustic emission technology can provide additional information regarding condition of concrete structures compared to the methods described in sections 5.1 – 5.3. For example, the acoustic emission method can be used to detect and monitor internal cracks growing in the concrete, assess crack growth rate as a function of different load or environmental conditions, or to detect concrete micro-cracking due to significant rebar corrosion.5.6 Accuracy, robustness, and efficiency of AE procedures can be enhanced through the implementation of fundamental principles described in the guide.1.1 This guide describes the application of acoustic emission (AE) technology for examination of concrete and reinforced concrete structures during or after construction, or in service.1.2 Structures under consideration include but are not limited to buildings, bridges, hydraulic structures, tunnels, decks, pre/post-tensioned (PT) structures, piers, nuclear containment units, storage tanks, and associated structural elements.1.3 AE examinations may be conducted periodically (short-term) or monitored continuously (long-term), under normal service conditions or under specially designed loading procedures. Examples of typical examinations are the detection of growing cracks in structures or their elements under normal service conditions or during controlled load testing, long term monitoring of pre-stressed cables, and establishing safe operational loads.1.4 AE examination results are achieved through detection, location, and characterization of active AE sources within concrete and reinforced concrete. Such sources include micro- and macro-crack development in concrete due to loading scenarios such as fatigue, overload, settlement, impact, seismicity, fire and explosion, and also environmental effects such as temperature gradients and internal or external chemical attack (such as sulfate attack and alkali-silica reaction) or radiation. Other AE source mechanisms include corrosion of rebar or other metal parts, corrosion and rupture of cables in pre-stressed concrete, as well as friction due to structural movement or instability, or both.1.5 This guide discusses selection of the AE apparatus, setup, system performance verification, detection and processing of concrete damage related AE activity. The guide also provides approaches that may be used in analysis and interpretation of acoustic emission data, assessment of examination results and establishing accept/reject criteria.1.6 Units—The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.1.7 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.1.8 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

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