Modelling safety critical BOP closing times for arbitrary BOP control systems
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There are presently no recommended practises, defined by standards, for closing time calculation of Blow Out Preventers (BOPs), when designing BOP control systems. As the closing time is a safety critical design parameter for BOPs and BOP control systems, this paper proposes a model for calculating this value. A guideline is included in order to recreate an equivalent model, applicable for most BOP control system designs. Models are constructed and compared to an equivalent prototype system, comparing closing times and pressure trends throughout the closing function. The model assumes that the BOP control system has hydraulic pressure supplied from an accumulator bank, where the interfacing BOP is a blind/blind shear ram. The models consider closing operations for both situations of drill pipe (DP) being either present or not in the bore. The modelling is done primarily using simple hydro mechanics and thermal mechanics in conjunction with API16D. All data sources, as far as practical, are published and per-reviewed literature. Results from the model are promising for BOP closing times without DP in the bore. Inaccuracies were found when comparing to a BOP with DP present in bore. However the model does require some preliminary information about the BOP in order to give accurate predictions. In addition the model is not applicable for systems using rotating machinery as pressure source or where there are several independent pressure sources.