seams, visual inspection, and ID measurement, hardness testing and thickness mapping, and wet fluorescent magnetic particle inspection (WFMPI) at blister boundaries. Key findings: Cracks observed in the L-seam and C-seam at blistered zones. Localised thinning from 32 mm to 10-11 mm. WFMPI showed no significant external surface cracks. Vessel failed
Figure 2b V-38 blisters and crack
redirected the incoming flow away from the wall, resulting in smoother flow patterns and significantly reduced wall impact. Results showed localised flow turbulence and wall shear stress contributing to wet H₂S corrosion and hydrogen ingress. The absence of stainless-steel cladding exacerbated the problem. Based on these insights, the nozzle orientation was modified to 90° with increased projection of the inlet distributor from the wall (216 mm to 400 mm) and implemented during plant turnaround, which is expected to minimise wall erosion and wet H₂S corrosion, thereby extending equipment life and improving overall reliability of the rich amine flash drum. Mitigation measures and engineering controls Several mitigation options were evaluated to address the hydrogen blistering observed in
Level I FFS based on API 579-1/ASME FFS-1 guidelines. In the bottom dish and zone 1 above it, there were no blisters, but near to the inlet nozzle, zones 2 and 3 showed blisters. The zone above the inlet nozzle was also free from blisters. CFD analysis and root cause elucidation CFD simulation of the vessel inlet distributor was carried out by BPCL R&D (CRDC) using vessel drawings, stream properties, and flow details. A CFD study was conducted using the actual drum geometry (see Figure 3 ). Simulations evaluated the internal flow patterns for three nozzle orientations: 180°, 90°, and 45°. The results showed that the existing 180° orientation led to direct jet impingement of H₂S- rich amine on the vessel wall, causing localised turbulence and corrosion. Flow impingement closely corresponded to the location of the blisters. In contrast, the 90° orientation
Velocity: Magnitude (m/s)
>1
0 0.111 0.222 0.333 0.444 0.556 0.667 0.778 0.889
250mm
Figure 3 CFD velocity vector plot showing impingement zone
Refining India
25
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