Finite element method modeling for flexible coupling of gas turbine compressor package installed in one of PT. Pertamina Hulu Energi Offshore North West Java (PHE ONWJ) facility has been completed. The model delivered result which is in acceptable level of accuracy as compared to manufacturer operating guideline as well as follows in general to guidance of API 671 widely used as industrial code and standard for coupling.
The scope of modeling is including the static and dynamic analysis for both perfectly aligned (used as base reference) and for misaligned condition. The scope covers as well the cyclic stresses which in turns determining the disc pack life time. The major challenge on the modeling is mainly to vary the degree of misalignment and how to distribute the additional load to the flexible part of the coupling causing deformation of disc pack.
The static analysis modeling reveals that the stresses are still below the yield point when aligned perfectly even in high vibration situation, but when it reaches up to 0.1 degree of misalignment with maximum torque the Von-Misses stress has exceeded the yield. The dynamic analysis shows that for similar 0.1 degree the fatigue factor of safety also has exceeded API 671 requirement.
Following the actual coupling failure events, the model has successfully indicated the location of highest stress correlated to crack initiation as compared to actual cracks found in existing discs specimen. The model has been validated as well with the result of material analysis of the damaged flexible discs showing that the failure occurred due to over misalignment.
In addition to manufacturer manual description, the model is capable to recommend maximum angular misalignment that need to be monitored during compressor operation and provide basis to calculate safety factor to comply API 671 guideline.
As oil and gas exploration and production company which focus on possible highest energy efficiency of its operating platforms — which all is located offshore, the work leads a way in integrity management of turbo-machinery equipment in order to maximize running time and minimize production shutdown.