added prior to cutting to prevent buckling. A hydrogen bake-out at 350°C for eight hours was done to eliminate atomic hydrogen from weld zones. Gas cutting was used for plate removal, followed by bevel preparation and dye penetrant testing (DPT) on both old and new bevels. Root pass, back-chip, and final welds underwent DPT. Post-weld heat treatment (PWHT) was conducted circumferentially, as per WRC Bulletin 452. PAUT scans were done before and after PWHT to ensure no defect propagation during thermal cycles. Inlet distributor modification: CFD simulations identified that liquid splashing on the shell from the inlet distributor was the primary cause of localised HIC. To mitigate this, the distributor nozzle was extended from 216 mm to 400 mm. A deflector elbow was added to redirect the flow downward. Splash plates were incorporated to break kinetic energy and prevent direct wall contact (see Figure 5 ). These modifications were integrated into the vessel’s revised datasheet. This engineering control is crucial in reducing high-velocity impingement and turbulence, minimising the risk of future hydrogen blistering. Final actions included: Patch repair per ASME PCC-2 Article 201 (see Figure 6 ), PWHT as per WRC Bulletin 452, eight-hour hydrogen bake-out at 350°C, and an inlet nozzle extension to 400 mm with deflector plates to prevent splashing. Lessons learned and recommendations Key takeaways include: Internal cladding (SS316L) should be standard for rich amine service vessels. CFD should be used during design to avoid impingement, related failures. Early signs of HIC in upstream equipment (VH V10, VH V30) should trigger wider inspection. Periodic inspection, including PAUT and metallography, is essential even without visible damage. Feed distributors must avoid direct wall contact and promote smooth flow dispersion. Recommendations: Retrofit existing vessels with cladding, apply CFD-based design
review, update material specifications and inspection protocols. Conclusion The failure of the rich amine flash drum (V-38) due to hydrogen blistering and HIC was the result of high-velocity amine impingement in a non-cladded carbon-steel vessel. While previous inspections showed no visible damage, the absence of internal protection and flawed flow distribution ultimately led to severe damage. A combination of CFD, FFS, and advanced NDT confirmed the root cause. A targeted patch repair and inlet modification enabled the unit’s safe continuation until full vessel replacement. This case underscores the importance of proactive design, inspection, and simulation in mitigating wet H₂S corrosion in refinery equipment. Figure 6 Welded patch area before and after PWHT
VIEW REFERENCES
Avinash Sankpal sankpalavinash@bharatpetroleum.in Arun Kumar kumararun@bharatpetroleum.in Aman Kumar Sahoo amansahoo@bharatpetroleum.in Prashant Nandanwar nandanwarpt@bharatpetroleum.in Abdul Quiyoom abdulquiyoom@bharatpetroleum.in
Refining India
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