The weld shown in Figure 1 failed during a cyclic loading test. The subsequent investigation involved:
1. Weld Examination: The specimen was cut perpendicular to the weld, as shown in Figure 1, to view the weld at different locations. The vessel's shape made it impossible to use NDE methods such as X-Ray. The fracture has been darkened for emphasis.
2. Stress Analysis: The most plausible failure mechanism was determined to be fatigue failure. This conclusion was confirmed by a cycle-life prediction using stress values generated from the FEA (Figure 2).
3. Physical Testing: Similar vessels were pressure-tested to further confirm the theoretical results found in Step 2.
4. Design Revisions: The proposed design solutions mitigated the effect of cyclic loading.