PSI - Issue 14

Altaf Ali et al. / Procedia Structural Integrity 14 (2019) 273–281

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Author name / Structural Integrity Procedia 00 (2018) 000–000

For sample A-1, inclusion was observed in all three orientations but most clearly seen in shot 1. For sample A-2, LOP or root pocket was observed in shot 1 only. However, sample A-3 was prepared for porosity defect but as can be observed in all three shots of sample A-3 nothing has been found in radiography. Sample A-4 was prepared for incomplete weld which is clearly observed in shot 2. Obtained radiographs for sample FCW, TFWC, HWC, QWC are shown in Fig. 6 (b) above. As can be observed from all three shots, no defect was found in FCW sample and it was expected because this sample was welded at full current. For TFWC, a LOP has not been observed. In HWC and QWC, LOP is observed in all three shots. Generally, in actual practice, inclusion occurs near to the upper surface only and its size is comparable to tube thickness. Fig.7 (f) shows A-scan for sample A-1. As can be noted that surface echo has high amplitude and gets broadened. This broadening of surface echo comes out to be a characteristic nature of inclusion defects. Inclusion can be identified by A-scan only by analysing this broadening nature of surface echo. Some of the B-scan results are shown for reference in Fig.7 above. As can be noted, LOPs at various section locations have been detected at half skip distance. However, the amplitude range for all the results varies from -6 dB to 4 dB (all are not shown in Fig. 7). This may depend on various geometrical features of the defect like lack of penetration height, and inclination angle of LOP with the UT beam. To find this dependence is future scope of the present work. But, for comparison of obtained RT and UT results, various section locations along weld circumference can be used. Section identification scheme for both RT and UT is given below in Fig. 8 for any arbitrary weld section. A comparison of RT and UT results is given in Table 2. Results show that a good correlation has been obtained between RT and UT defect locations. Thus, UT poses to be a good alternative technique for present radiography technique. However, this work is to be extended further in future to study various geometrical features of LOP defect affecting UT signal response and hence to establish a criterion to qualify a UT indication as defect.

Fig. 8. (a) Section identification scheme for RT; (b) Section identification scheme for UT

Table 2. RT and UT results comparison Sample ID

RT results (Probable defect location) Inclusion detected in all three shots of radiographs Based on RT results a LOP type of defect has been observed with its probable section location 1-2 , 2 , 2 -3, 3-2, 3

UT results

A-1

In B-scan image big spot near to surface detected. In corresponding A scans surface echo gets broadened indicating inclusion detection Appreciable amplitude up to 6 dB has been recorded in sections 1.1, 1.2, 2.1, 2.2, 3. This also confirms to RT locations.

A-2

A-3 A-4

Nothing has been observed in RT

Not any appreciable amplitude observed

LOP has been observed in shot 1 and shot 2 & probable locations are 1-2 , 2 , 2-3

B scan images of section 3, 3.1 & 3.2 above show good detection of LOP at half skip. This confirms to RT sample section locations.

FWC

Nothing observed in RT Nothing observed in RT

Nothing appreciable observed in UT UT results show amplitude up to -3.5 dB LOP detected by UT at half skip distance.

TFWC

HFW

LOP detected