Significance and Use
5.1 Phased array ultrasonic testing (PAUT) is an advanced examination technique used for enhanced flaw detection, sizing, and imaging as compared to conventional UT employing single-element transducers. PAUT utilizes multi-element (array) probes in which groups of elements are pulsed with pre-calculated time delays (“focal laws”) for each element (“phasing”). The resulting constructive and destructive interference allows for electronic steering, shaping, and focusing of the sound beam.
5.2 Though primarily a method of generating and receiving ultrasound, phased arrays are also a method of scanning and imaging. The two basic types of scans are the Linear or Electronic scan (E-Scan) and the Sectorial or Azimuthal scan (S-Scan). In the E-Scan, which emulates a manual scan, multiple sound beams are created at the same refracted angle. The beam is electronically translated along the active axis of the array by sequentially adding an element on one end and dropping an element off the other end of the active group of elements within the probe, with time multiplexing coordinated by the instrument’s on-board processor. In the S-Scan, which is unique to phased arrays, the sound beam is electronically swept through a range of user-defined angles by sequentially changing the time delays applied to each element. Because the beam angle is no longer solely dependent upon the wedge angle, more complete data can be obtained and more complex geometries can be examined versus conventional UT. With their distinct features and capabilities, phased arrays require special set-ups and standardization, as addressed by this practice. Commercial software permits the operator to easily make set ups without detailed knowledge of the phasing requirements.
5.3 Phased arrays can be used in different ways: manual or encoded linear scanning; and different displays or combinations of displays. In manual scanning, the dominant display will be an S-scan with associated A-scans. S-scans have the advantage over E-scans in that all the specified examination angles can be covered at the same time.
5.4 The main advantages of using phased arrays for ultrasonic weld examinations are:
5.4.1 Increased control of beam characteristics, including capability for focusing and steering the beam;
5.4.2 Faster scanning and increased probability of detection due to multiple lines/angles acquired and displayed in a single pass;
5.4.3 Increased ability to examine complex geometries and areas with limited access;
5.4.4 Better imaging from the true depth S-scan;
5.4.5 Digital data storage capability, which is intended to enable auditing, archiving, and off-line post-processing, re-processing, and comparison of data from different examinations;
5.4.6 Rapid and reproducible set-ups with electronic instruments.
Scope
1.1 This practice describes ultrasonic techniques for examining welds using phased array ultrasonic methods (see Note 1 and Note 2).
1.2 This practice uses angle beams, either in S-scan or E-scan modes, primarily for butt welds and Tee welds. Alternative welding techniques, such as solid state bonding (for example, friction stir welding) and fusion welding (for example, electron beam welding) can be examined using this practice, provided adequate coverage and techniques are documented and approved. Practices for specific geometries such as spot welds are not included. The practice is intended to be used on thicknesses of 9 to 200 mm. Greater and lesser thicknesses may be examined using this practice if the technique can be demonstrated to provide adequate detection on mockups of the same wall thickness and geometry.
1.2.1 Extreme caution should be used when attempting to size indications using phased array. It is likely that without proper procedures, indications can be oversized due to beam divergence, multiple virtual probes returning signals from the same indication, etc. For more guidance, see 12.4.
1.3 Units—The values stated in SI units are to be regarded as standard.
Note 1: This practice is based on experience with ferrous and aluminum alloys. Other metallic materials can be examined using this practice, provided reference standards can be developed to demonstrate that the particular material and weld can be successfully penetrated by an ultrasonic beam.
Note 2: For additional pertinent information, see ASME BPVC Section V, Article 4, Guide E2491, Practice E317, and Practice E587.
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.
