In the fast-changing Non-Destructive Testing (NDT) industry, Standard Test Blocks serve the very important purpose of standardizing and calibrating test equipment to ensure that it is functioning properly. These blocks are non-representative tools, meaning that they are not manufactured from, or machined to represent, actual parts. Rather, they consist of simplified design and contain manufactured targets such as side-drilled holes, flat bottom holes, angles, radii, steps and other geometric features.
Within the discipline of Ultrasonic Testing (UT), Test Blocks allow the technician to calibrate instruments for both angle beam and normal incident (straight beam) inspections. The blocks are used to set metal distance and sensitivity settings, determine the beam exit point and refracted angle of angle beam transducers, evaluate system resolution, and more.
For years, standards organizations such as ISO, ASTM, ASME, and AWS have issued codes governing the manufacture of Standard Test Blocks for conventional UT. These blocks perform perfectly for simple pulse-echo systems, but their effectiveness is limited for newer Phased Array Ultrasonic Testing (PAUT) systems that employ multiple elements in a single transducer. Phased array technology is now widespread in the industry, but codes governing the manufacture of calibration blocks for PAUT are surprisingly lacking. As a result, there are many different ways to approach a PAUT calibration.
As a trusted manufacturer of Standard Test Blocks for over 40 years, the staff at PH Tool has been in on the design changes since the introduction of PAUT into our industry. There are several differences to note between a PAUT test block and one that is used for conventional UT. The general trend, however, is for the blocks to get bigger (i.e. longer, thicker, wider, etc.,) with more “targets” (holes, other geometric features or discontinuities for the UT equipment to evaluate.)
The spacing between targets often increases as well. The more generous spacing helps to eliminate “ghost images” that would otherwise appear from adjacent holes if they were located too close to one another. A perfect example of this can be seen in the Phased Array Calibration and Sizing (PACS)® Block, an innovative design that was jointly developed by PH Tool and Mark Davis of the University of Ultrasonics at the time.
Much like a traditional IIW-Type Block, the PACS® integrates features used in establishing beam exit point, beam angle, metal path calibration, and sensitivity, with the important addition of allowing for angle corrected gain (ACG) in depth and in metal path for phased array equipment. The side-drilled hole reflectors are offset from each other over the 18.000 inch (457.2mm) block length to afford improved access over a wide range of sector angles or long linear scan lengths. The traditional IIW-Type Block is not suited to this function.
Fig. 1: Traditional IIW-Type 1 Block
Fig. 2: Phased Array Calibration and Sizing (PACS)® Block
Another example of advances in PAUT test block design are the Extended Range Variable Wall (ERVW) line of ASME-compliant piping calibration blocks, jointly designed by PH Tool and Holloway NDT & Engineering Inc. These blocks feature multiple wall thicknesses and specially machined diameters to cover a much wider range of pipe sizes than traditional blocks. Three blocks weighing just 30 lbs cover the majority of pipe from 3 to 20 inches, and replace 24 standard blocks.
The ERVW-line of blocks are available in both side-drilled hole and notch variants, and configurations for both circumferential and axial scanning.
Other examples/trends in PAUT test block design include:
- Curved scanning surfaces to simulate pipe OD or ID.
- Vertical stacks of side-drilled holes used to determine inspection sensitivity, beam angle, screen height linearity
- Angles cut into the end of blocks to help deflect sound away from corners
- Switch from EDM Notches to SDHs as an “omnidirectional” reflector for setting DAC/TCG
- Tighter control on raw material “cleanliness” and anisotropy
We hope this piece has helped to clarify some of the trends in Phased Array UT block designs. The PACS® Block is just one of many solutions that PH Tool offers for PAUT applications. Other examples include the new “PAUT IIW Block” from ISO 19675, other blocks in the PACS® Family like the Mini PACS®, PACS® Notch Block, and AWS PACS® Block, Phased Array NAVSHIPS Block, ASTM E2491 Assessment Block, and PAUT Pipe Calibration Blocks for ASME Sec V requirements. PH Tool will also make custom blocks to meet your exact specifications. Large bar and tubular reference standards can also be made for large-scale inline PAUT inspection systems used in primary metals manufacture. To learn more about test blocks for phased array UT, or to request a quote, please contact PH Tool Technical Sales.
For more than 40 years, our team of toolmakers, machinists, and management staff has supplied the NDT industry with high-quality test blocks and reference standards, featuring our EDM notches, flat-bottomed holes, and other "perfect imperfections."
We’ve spent decades earning a reputation for supplying our customers with products and services that are second-to-none. We look forward to answering your questions and teaming with you on your next project.