5.1 APR technology is used for detection, location and identification of internal diameter (ID) flaws-indications and blockages in tube bundles.

5.2 Reliable and accurate examination of tube bundles is of great importance in different industries. On-time detection of flaws reduces a risk of catastrophic failure and minimizes unplanned shutdowns of plant equipment. Fast examination capability is of great importance due to reduction of maintenance time.

5.3 APR examinations are performed for quality control of newly manufactured tube bundles as well as for in-service inspection.

5.4 Performing an APR examination requires access to an open end of each tube to be examined.

5.5 Flaws that can be readily detected and identified include but are not limited to through-wall holes, ID pitting, erosion, blockages, bulging due to creep and plastic deformation due to bending.

5.6 APR can be applied to tube bundles made of metal, graphite, plastic or other solid materials with straight and curved sections. The APR technology has been found effective on tubes with diameters between 12.7 mm [¹/₂ in.] to 101.6 mm [4 in.] and lengths up to 18 metres [60 feet].

5.7 Closed cracks on ID surface, without significant geometrical alternation on ID surface, may not be detected by APR.

5.8 APR technology can be used for flaw sizing when special signal and data analysis methods are developed and applied.

5.9 In addition to detection of flaws and blockages, APR technology can be applied for assessing tube ID surface cleanliness, providing valuable information for equipment maintenance and improving its performance.

5.10 Other nondestructive test methods may be used to verify and evaluate the significance of APR indications, their exact position, depth, dimension and orientation. These include remote visual inspection, eddy current and ultrasonic testing.

5.11 Procedures for using other NDT methods are beyond the scope of this practice.

5.12 Acceptable flaw size can be calculated using methods of fracture mechanics, numerical modeling, or both. These calculations are beyond the scope of this document.

1.1 This practice describes use of Acoustic Pulse Reflectometry (APR) technology for examination of the internal surface of typical tube bundles found in heat exchangers, boilers, tubular air heaters and reactors, during shutdown periods.

1.2 The purpose of APR examination is to detect, locate and identify flaws such as through-wall holes, ID wall loss due to pitting and/or erosion as well as full or partial tube blockages. APR may not be effective in detecting cracks with tight boundaries.

1.3 APR technology utilizes generation of sound waves through the air in the examined tube, then detecting reflections created by discontinuities and/or blockages. Analysis of the initial phase (positive or negative) and the shape of the reflected acoustic wave are used to identify the type of flaw causing the reflection.

1.4 When proper methods of signal and data analysis are developed, APR technology can be applied for sizing of flaw/blockage indications.

1.5 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 standards.

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.