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1.1 This practice provides guidelines for continuous monitoring of acoustic emission (AE) from metal pressure boundaries in industrial systems during operation. Examples are pressure vessels, piping, and other system components which serve to contain system pressure. Pressure boundaries other than metal, such as composites, are specifically not covered by this document.

1.2 The functions of AE monitoring are to detect, locate, and characterize AE sources to provide data to evaluate their significance relative to pressure boundary integrity. These sources are those activated during system operation, that is, no special stimulus is applied to produce AE. Other methods of nondestructive testing (NDT) may be used, when the pressure boundary is accessible, to further evaluate or substantiate the significance of detected AE sources.

1.3 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.

1.4 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 and health practices and determine the applicability of regulatory limitations prior to use. For specific precautionary statements, see 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.

5.1 Acoustic emission examination of a structure requires application of a mechanical or thermal stimulus. In this case, the system operating conditions provide the stimulation. During operation of the pressurized system, AE from active discontinuities such as cracks or from other acoustic sources such as leakage of high-pressure, high-temperature fluids can be detected by an instrumentation system using sensors mounted on the structure. The sensors are acoustically coupled to the surface of the structure by means of a couplant material or pressure on the interface between the sensing device and the structure. This facilitates the transmission of acoustic energy to the sensor. When the sensors are excited by acoustic emission energy, they transform the mechanical excitations into electrical signals. The signals from a detected AE source are electronically conditioned and processed to produce information relative to source location and other parameters needed for AE source characterization and evaluation.

5.2 AE monitoring on a continuous basis is a currently available method for continuous surveillance of a structure to assess its continued integrity. The use of AE monitoring in this context is to identify the existence and location of AE sources. Also, information is provided to facilitate estimating the significance of the detected AE source relative to continued pressure system operation.

5.3 Source location accuracy is influenced by factors that affect elastic wave propagation, by sensor coupling, and by signal processor settings.

5.4 It is possible to measure AE and identify AE source locations of indications that cannot be detected by other NDT methods, due to factors related to methodological, material, or structural characteristics.

5.5 In addition to immediate evaluation of the AE sources, a permanent record of the total data collected (AE plus pressure system parameters measured) provides an archival record which can be re-evaluated.