3. Scanning tests of welding seams
(1) Calibration of AUT systems: The adjusted AUT scanning device was plated on the calibration block to calibrate one by one in accordance with the simulated focus law to ensure that the amplitude of the strip scan signal of each channel was between 70% and 99% in the dynamic calibration.
(2) Scanning of AUT welding seams: After the calibration was done, 5 artificially defective welding seams on a pipe with a diameter of 114.3 mm would be scanned one by one.
(3) Reference line drawing: Placed the AUT scanning device at the defect of the welding seam. Walked back and forth to find the highest wave position of the defect, and marked the highest wave position of the defect and travel direction of the AUT scanner with a marker; drew a reference line for the defect location. The reference line drawing is as shown in Figure 6.
Figure 6 The schematic diagram of the defect reference line
(4) Macro slicing: According to the defect reference line, 25 artificial defects detected by AUT were cut one by one, and the relevant defect slices were shown in Figure 7.
Figure 7 Slicing of related defects
4. Comparative analysis of data
Performed data analysis on the AUT scan map of 5 artificial defected welding seams one by one, and recorded the relevant starting point, length, height, depth, type and other parameters of the defect one by one. Compared and analyzed with the macro slicing data. Comparative analysis of AUT and macro slice data is shown in Table 2. It can be seen from Table 2 above that for the 5 artificial defected welding seams numbered W01, W02, W03, W04 and W05, there was a deviation between -1 mm and 0.8 mm for the defect height value evaluated by AUT and macro slicing evaluation. The minimum deviation value was 0.1 mm, and the maximum deviation value was 1 mm.
Table 2 Comparative analysis of AUT and macro slicing data
| Welding items |
Wall thickness |
Defected items |
Locations |
AUT data |
Slice data |
Height |
| Defected types |
Starting point |
Length |
Height |
Depth |
US/ |
Height |
Depth |
|
| W01 |
6.4 |
1 |
The cover surface |
Lack of fusion |
20 |
13 |
0.9 |
1 |
DS |
0.7 |
1.2 |
0.2 |
| W01 |
6.4 |
2 |
The cover surface |
Lack of fusion |
93 |
15 |
0.7 |
1 |
US |
0.8 |
1.1 |
-0.1 |
| W01 |
6.4 |
3 |
The cover surface |
Lack of fusion |
171
|
10
|
0.9
|
1
|
DS
|
1.1 |
2 |
-0.2 |
| W01 |
6.4 |
4 |
The filling |
Lack of fusion |
236 |
23 |
2.9 |
4.2 |
US |
2.2 |
3.6 |
0.7 |
| W01 |
6.4 |
5 |
The filling |
Lack of fusion |
313 |
22 |
2.3 |
2.5 |
DS |
2 |
3 |
0.3 |
| W02 |
6.4 |
1 |
The filling |
Lack of fusion |
16
|
23 |
2.8 |
4 |
DS |
2 |
3.4 |
0.8 |
| W02 |
6.4 |
2 |
The root |
Lack of fusion |
95
|
13 |
1 |
6 |
C |
1.3 |
6 |
-0.3 |
| W02 |
6.4 |
3 |
The root |
Lack of fusion |
164
|
18 |
0.5 |
6 |
C |
1.5 |
6 |
-1 |
| W02 |
6.4 |
4 |
The root |
Lack of fusion |
241
|
16
|
0.5 |
6 |
C |
1.2 |
6 |
-0.7 |
| W02 |
6.4 |
5 |
The middle of the welding seam |
Lack of fusion between layers |
312
|
21 |
1.8 |
4.1 |
C/V |
2.2 |
4.2 |
NA |
| W03 |
6.4 |
1 |
The middle of the welding seam |
Lack of fusion between layers |
23
|
7
|
0.9
|
4.2 |
C/V |
2.9 |
4.2 |
NA |
| W03 |
6.4 |
2 |
The middle of the welding seam |
Gas holes between layers |
100
|
5 |
0.8 |
4.2 |
C/V |
2.8 |
4.3 |
NA |
| W03 |
6.4 |
3 |
The cover surface |
Lack of fusion |
162
|
23
|
1.3 |
1.3 |
DS |
0.9 |
1.4 |
0.4 |
| W03 |
6.4 |
4 |
The cover surface |
Lack of fusion |
264
|
12
|
1.5 |
1.5 |
US |
0.7 |
1.2 |
0.8 |
| W03 |
6.4 |
5 |
The cover surface |
Lack of fusion |
371
|
13 |
1.2 |
1.2 |
D/S |
0.9 |
1.3 |
0.3 |
| W04 |
6.4 |
1 |
The filling |
Lack of fusion |
16
|
22
|
2.1
|
2.5
|
D/S |
1.9 |
3.3 |
0.2 |
| W04 |
6.4 |
2 |
The filling |
Lack of fusion |
92
|
17
|
2.5
|
4.2 |
US |
1.8 |
3.9 |
0.7 |
| W04 |
6.4 |
3 |
The filling |
Lack of fusion |
160
|
21
|
1.7
|
2.5 |
D/S |
1.4 |
3.2 |
0.3 |
| W04 |
6.4 |
4 |
The root |
Lack of fusion |
239
|
17
|
1
|
6
|
C |
1.4 |
6 |
-0.4 |
| W04 |
6.4 |
5 |
The root |
Lack of fusion |
315
|
14
|
0.7 |
6 |
C |
1.2 |
6 |
-0.5 |
| W05 |
6.4 |
1 |
The root |
Lack of fusion |
22
|
17
|
0.5
|
6
|
C |
1.4 |
6 |
-0.9 |
| W05 |
6.4 |
2 |
The middle of the welding seam |
Lack of fusion between layers |
92
|
21
|
1.5
|
4.8
|
C/V
|
1.9
|
4.1 |
NA |
| W05 |
6.4 |
3 |
The middle of the welding seam |
Dense gas holes |
173
|
12 |
1.5 |
5 |
C/V |
1.3 |
4.0 |
NA |
| W05 |
6.4 |
4 |
The middle of the welding seam |
Dense gas holes |
236
|
16 |
1.1 |
4.4 |
C/V |
1.4 |
4.2 |
NA |
| W05 |
6.4 |
5 |
The root |
Lack of welding |
313
|
17
|
0.6 |
6 |
C |
1.3 |
6 |
-0.7 |
5. Conclusion
According to the requirements of relevant standards for inspecting carbon steel pipelines, the defect height and quantitative accuracy of AUT detection process does not exceed ±1 mm. In the experiment, AUT inspection, data analysis, and reference line drawing were carried out one by one for artificial defect welds of the processed 5 pipes with a diameter of 114.3 mm (4 inches) and a wall thickness of 6.4 mm in this article, and then the 25 artificial defects were subjected to a macroscopic slice test one by one. Through data analysis, AUT detection technology could effectively detect 25 artificial defects processed in a welding seam on thin-walled pipe with a diameter of 114.3 mm (4 inches) and a wall thickness of 6.4 mm, and the greatest quantitative deviation of the height of the defect was 1 mm, which met the requirement for the defect height quantitative accuracy required by the carbon steel pipeline's inspection standard (±1 mm). Therefore, the AUT detection technology can be applied to inspecting the thin-walled carbon steel pipeline of 4 inches.
