Analysis:A fatigue assessment was done based on Linear Static Structural-FEA to establish actual stress characteristics of the vessels by utilizing Elastic Stress Analysis to simulate Stress-Cycles and subsequent fatigue life using S-N curves. The controlling stress was the effective total equivalent stress amplitude, defined as one-half of the effective total equivalent stress range (PL+ P b+ Q + F) calculated for each cycle in the loading histogram..

Equipment: Hydrogen PSA Adsorber Vessel Wall-Nozzles-Skirt Structure. The designed fatigue life was set as per OEM (Original Equipment Manufacturer) to 870,000 cycles (20 operating years).

Problem: The hydrogen plant of a profitable refinery was faced with a daunting task of replacing 26 PSA vessels because the unavailability of a current / valid FFS based on history of actual operating conditions. As a result, the refinery would be mandated to replace 26 adsorber vessels within a short period causing loss of hydrogen production and a huge capital expenditure $$$.

Results-Conclusion: FEA based solution cyclic-stress solution established that the proved that these vessels have a higher fatigue design life of 1,696,500 cycles (39 operating years). This confirmed that the actual designed fatigue life was much longer than the estimate done by the OEM, as a result of which the PSA adsober vessels could continue to safely operate enduring a number of pressure cycle before end-of-life.

Benefits: This had a positive impact on cost projection and life-cycle-value analysis of these absorbers and also provided the basis for a phased replacement approach.