Low-Profile Phased Array Probes and Application

Abstract: The low-profile phased array probe is a new type of special probe. In this paper, the low-profile phased array probe is compared with the conventional phased array probe of the same specifications, which reveals features of the low-profile phased array probe in terms of small size, high precision and low noise. Because of these superior characteristics, the low-profile phased array probe is very suitable for the testing of butt welds of small diameter tubes. Therefore it has been widely used in petrochemical and electric power industries.

Key words: low-profile phased array probe, acoustic beam focusing, small diameter tube, butt weld.

1. Characteristics of Low-Profile Phased Array Probe

Low-Profile phased array probe is a new type of special probe, with the appearance shown in Fig. 1. The central part is the probe array, and on both sides are the assembly hole and water injection channel respectively. The method mainly comprises the following steps: performing physical focusing on a passive aperture which cannot be subjected to electronic focusing control by bending the array in the passive aperture direction; and combining the electronic focusing in the array direction, realizing a fine focal column at a designed testing depth, so as to obtain a narrower acoustic beam and achieve higher testing precision, signal-to-noise ratio and resolution. The characteristics of the low-profile phased array probe are recognized in depth by comparing with the conventional phased array probe of the same specifications as follows.

1.1?Beam Focusing

The low-profile phased array probe is a curved array probe which is physically bent by a plurality of elements in a passive aperture.

While the conventional phased array probe is a planar array, Fig. 2 shows the planar array shape and sound field distribution diagram of the conventional phased array probe, and Fig. 3 shows the curved array shape and sound field distribution diagram of the low-profile phased array probe. The comparison of the two figures shows that the curved array effectively solves the defocusing issue of the acoustic beam through the combination of mechanical and electronic focusing, and reveals that the acoustic beam focusing of the low-profile phased array probe is superior to that of the conventional phased array probe.

1.2?Testing accuracy

A/B/C represents the combination of 3 types of probes and wedges. See Table 1 for the respective names and models. They are for testing φ1.5 artificial flaws of the special test block DL. See Fig. 4 for the shape and size of test block, Fig. 5 for the schematic diagram of testing method, and Fig. 6 for the testing map. See Table 2 for the flaw measurement value and error of testing result.

By measuring the flaw size and calculating the difference, the flaw measurement accuracy of low-profile probe and conventional probe is compared. It is proved that the testing accuracy of code C, that is, the combination of low-profile probe and arc wedge, is much higher than that of code A and B, namely the combination of conventional probe and wedge.

1.3?Signal to noise ratio

Use the same method as 1.2 above to detect the φ1.5 flaw on DL test block. See Fig. 7 for the spectrum of testing results and Table 3 for signal-to-noise ratio.?

The signal-to-noise ratio (SNR) of the low-profile probe is much higher than that of the conventional probe.

1.4?Technical indicators

The specification and overall size, performance index, wave and spectrum comparison difference of low-profile and conventional phased array probe are tested respectively. Table 4 below shows the specification and overall dimension of the two probes, Table 5 shows the performance index of7.5L16 -0.5-9, Fig. 8 shows the wave and spectrum of 7.5L16 -0.5-9, Table 6 shows the performance index of 7.5SL16-0.5-10-R35E, and Fig. 9 shows the wave and spectrum of 7.5SL16-0.5-10-R35E. ?

Through the comparison of the external dimensions and performance indicators of the two probe specifications, in terms of external dimensions, the external size of the low-profile probe is 26*22*10, while the conventional probe of the same specification is 15*28*28, with the height difference up to 18mm. The low-profile phased array probe with the height 10mm is very suitable for detection under narrow spatial conditions of pipes. In terms of performance indicators, the -20dB pulse width of the low-profile phased array probe is smaller than that of the conventional probe, which is conducive to improving the testing resolution.

2. Application of Low-Profile Phased Array Probe

The low-profile phased array probe is the best choice for ultrasonic phased array testing of small diameter pipe butt welds, and its small volume, especially the characteristic of only 10mm in thickness, addresses the issue that many pipelines in petrochemical and power plants cannot be detected in a narrow space due to compact arrangement; meanwhile, the curvature of the small diameter pipe is large, and its focusing function reduces the incident surface of acoustic beams and reduces the divergence of acoustic beams on the arc surface of the pipeline; in addition, the wall thickness of the small diameter pipe is thin, and the acoustic path generated by ultrasonic beams in the pipe wall is short. Higher resolution and signal-to-noise ratio are required for testing in the near-field region, which is exactly the advantage of low-profile probes. Due to the superior characteristics of low-profile phased array probes, they are widely used in phased array testing of butt weld with small pipe diameters. The number of butt weld interfaces tested by SIUI testing equipment has reached over 100,000, and various flaws such as incomplete penetration, incomplete fusion, inclusion and porosity have been found, so as to eliminate potential safety hazards in time.

Fig. 10 shows the complete set of phased array testing equipment for butt welds of small diameter tubes, and its typical configuration is shown in Table 6. Fig. 11 shows the application of the equipment in petrochemical plants.

References:

[1] Li Yang, Application of Phased Array Ultrasonic Testing Technology in Small Diameter Pipe Butt Weld Testing in Offshore Engineering Nondestructive Testing, 2013, 35 ?(09) :41-44.

[2] Li Yan, Ultrasonic Phased Array Testing of Small-Diameter Thin Wall Pipes. Nondestructive Testing, 2012, 36 (03):1-4.?