PSI - Issue 60

Sreerag M N et al. / Procedia Structural Integrity 60 (2024) 20–35 Sreerag M N/ Structural Integrity Procedia 00 (2023) 000 – 000

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Table-5: Comparison of FE computed failure pressure for different cases of cirseam weld FE Model with uniform properties at shell and c/s weld region (Conservative)

FE model with parent metal properties and weld properties at c/s weld region (Realistic)

Property

Failure pressure (ksc)

% diff. with respect to PM failure pressure

L/s weld region

Failure pressure (ksc)

% diff. with respect to PM failure pressure

PM

97.37 90.97 88.80 79.68 76.80

-

-

-

R0 R1 R2 R3

7.03 9.65

R0 R1 R2 R3

97.66 97.61 97.33 97.23

0 0 0 0

22.22 26.78

4.3. Discussion of results

 In rolled and welded shells having inferior weld properties, the dilation of the shell is governed by superior parent metal properties whereas the instability criterion is governed by the reduced weld properties.  In L/s weld, if conservative model was used the difference in failure pressure with and without using weld properties is only of order of 1%. However, in case of cirseam weld, the difference in failure pressure with and without using weld properties is very high. So, while estimating the failure pressure for cirseam weld, it is always necessary to consider the effect of parent metal properties. 5. Effect of weld repair length on the failure pressure In the previous section, weld properties were assumed for entire weld length. But actually, Virgin weld conditions (R0 weld) exists for all long seam welds (i.e., for full length of long seam weld of shell with weld bead width of 30mm) or for all cirseam welds (i.e., 360° circumference with weld bead width of 30mm). The shells after completion of all cirseam weld are heat treated (Aged). After this, if at any stage an acceptable defect is found in the weld region, defect is removed by local repair. First the gouge length is worked out based on the size and location of defect. Then material is gouged and welded again. To attain mechanical properties, this local repair region is locally aged (local heat treatment). Weld repair process leads to further reduction in property. i.e. The weld properties R1, R2 and R3 are for small local length and not for the entire long seam (axial length) or cirseam (circumference). In this section the effect of this repair on the failure pressure is studied for long seam weld and cirseam weld. 5.1. Effect of repair length in long seam weld For studying this, FE model similar to one described in section 4.1 is used. In the model, fig 4, the region away from the weld, the parent metal property is used. In the entire long seam weld region for a weld bead width of 30mm, virgin weld properties(R0) are used. The repair properties are simulated in the virgin weld region by specifying the axial length.

Fig 4: Typical FE model simulating the virgin long seam weld with weld repair and parent metal