Revamps 2022 Issue

Summary A life assessment of a PSA vessel has been carried out to analyse the effect of peaking measurements, with the intent of developing a life management plan that helps the future safe operation of the PSA vessels and minimises the need for internal inspection. Based on the outcome of the analysis covered in this study, the recommended steps for the life management and inspection strategy are suggested as follows: Step  At half design life, review fabrication tolerances for peaking, misalignment, and plate tolerances. Review construction records to determine if the vessels have been subjected to rolling after fabrication, and conduct peaking measurement, preferably by laser scanning, on the weld seams (including circumferential welds). Step  Determine the stress associated with peaking and other anomalies using stress analysis, including the stress associated with the inlet/outlet nozzle and manway. Step  Use an appropriate fatigue assessment method to determine the consumed life fraction based on the stress profile. Step  Conduct advanced ultrasonic inspections on welds (longitudinal and circumferential) and conduct external sur- face inspections on the nozzle and manway welds. Step  As the consumed life fraction approaches 80% (Step 3), conduct a fracture mechanics-based fatigue anal- ysis based on the stress profile from the laser scan and the FEA, and crack-growth parameters that include the effect

of hydrogen charging. Use the half-life (i.e. remaining crack growth life divided by two) to determine the future inspec- tion frequency. Step  If cracks are discovered during the inspection (Step 4), employ a fracture mechanics approach to esti- mate remaining fatigue life and apply a half-life inspection strategy to determine when vessels should be taken out of service for repair. References 1 The American Petroleum Institute and The American Society of Mechanical Engineers, Fitness-for-Service API 579-1/ASME FFS-1 (API 579 Second Edition). © API Publishing Services June, 2016. 2 British Standards Institution BS 7910:2015 Guide to methods for assessing the acceptability of flaws in metallic structures, 2019. 3 British Standards Institution BS 7608:2014 Guide to fatigue design and assessment of steel products. 4 McIntyre P, Pumphrey P H, CEGB Research TPRD/L/MTO386/M86, The rate of fatigue crack growth in pressure swing adsorption vessel material under simulated operating condition, Journal of Pressure Ves- sel Technology, April 2015, Vol. 137 /021406-1. 5 Davies R, Hewrine S, Chapman J, Fatigue cracking of adsorber on hydrogen PSA unit, Ammonia Technical Manual 1996.

Annette Karstensen is a Fitness for Service and Fracture Mechanics Specialist at Becht. She has more than 25 years’ experience trouble - shooting integrity projects, covering engineering components that re- late to hydropower, fossil power, and petrochemical plants.

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Revamps 2022