• Federal Highway Administration >
• Publications >
• Research Publications >
• 04124 >
• 06a.Cfm >
• Lab & Field Testing of AUT Systems for Steel Highway Bridges

Lab & Field Testing of AUT Systems for Steel Highway Bridges

6. RESULTS

Laboratory evaluation and field testing of the P-scan system in parallel with both RT and manual UT was performed on 10 laboratory specimens and 46 field specimens. The results produced from this testing illustrate the potential benefits of implementing AUT.

LABORATORY RESULTS TC "LABORATORY RESULTS"

The results of the laboratory evaluation are summarized in table 6. The first column of table 6 indicates the specimen identification code. The second, third, and fourth columns indicate the inspection method performed on each specimen. "Rejected" or "Accepted" indicates that the specimen was either rejected or accepted, respectively, by the employed inspection method. "Ind." stands for indication, and the angle (q) indicates the transducer's refracted angle. The indication characteristics in the fourth column (i.e., indication rating (d), length (L), depth (Z), x-position, and y-position) are obtained from P-scan images. These characteristics are compared with the UT acceptance-rejection criteria in tables 6.3 and 6.4 from the AASHTO/AWS D1.5M/D1.5: 2002 Bridge Welding Code⁽¹⁾ to determine whether the indication should be accepted or rejected.

The category 1 laboratory specimens were rejected by all three inspection methods (table 6). Figure 10 shows the radiographic image of laboratory specimen S033. Figure 12 shows the P-scan images of the toe and root cracks in specimen S033. The radiographic image provides the spatial dimensions of the defects (i.e., length and position), while the P-scan images provide three-dimensional information (including length, depth, and global position). Specimen S034 (figure 33) contained two manufactured cracks. This 12.7-mm- (0.5-inch-) thick plate contains a longitudinal crack in the weld (figure 34) and a transverse crack in the weld (figure 35). Both cracks were detected by RT and manual UT. Figure 36 shows the radiographic image of specimen S034. The two cracks can be seen clearly. The transverse crack in specimen S034 was detected by manual UT when the weld was inspected in the transverse direction. The P-scan system detected only the longitudinal/centerline crack in specimen S034 (figures 37 and 38). The photographs, radiographic images, and P-scan images of the remaining laboratory specimens that contained rejectable defects are shown in figures 39 through 71.

The results provided in table 6 showed that the indication rating (d) given by the P-scan system varied from the conventional UT rating in some cases. This variance may be caused by one of the following parameters:

• High sensitivity of P-scan system.
• Manual versus computer determination of spatial characteristics of defects (including sound path and time of flight).
• Attenuation.
• Slightly varying scanning patterns.
• Operator variability.

Table 6. Inspection results of laboratory specimens.

*AUT is not configured to detect transverse cracks.
1 inch = 25.4 mm

Table 6. Inspection results of laboratory specimens (continued).

*Under the provisions of table 6.3 in the AASHTO/AWS D1.5: 2002 Bridge Welding Code (i.e., class B and class C flaws shall be separated by at least 2L), Ind. 1A, Ind. 1B, ... are considered as a single defect, Ind. 2A, Ind. 2B, ... are considered as a single defect, etc.

1 inch = 25.4 mm

Figure 41. P-scan images of laboratory specimen S125: From TSC side of centerline.

Figure 42. P-scan images of laboratory specimen S125: From BSC side of centerline.

Figure 43. Laboratory specimen S126: Top view of joint.

 

Figure 44. Laboratory specimen S126: Radiographic image showing discontinuities in the weld.

Figure 45. P-scan images of laboratory specimen S126: From TSC side of centerline.

Figure 46. P-scan images of laboratory specimen S126: From BSC side of centerline.

Figure 47. Laboratory specimen S132: View of joint.

 

Figure 48. Laboratory specimen S132: Radiographic image showing discontinuities in the weld.

Figure 54. Laboratory specimen S133: Radiographic image showing discontinuities in the weld.

Figure 55. P-scan images of laboratory specimen S133.

Figure 57. Laboratory specimen S135: Top view of joint.