In-service Defect Assessment Annular BOP Case Studies And Safety Assessment Software System Development

Well control is the focus of safety work in oil and gas development work. Blowout preventer (BOP) is a core component of well control equipment, BOP shell is the main component of BOP. However, defects such as cracks, pits and porosities may appear on BOP shell during BOP casting and the service process, these defects will produce expansion in the long-term service and cause pressure leakage which can’t ensure the safety production. Therefore, it is very necessary to do safety assessment for the defects.At present, safety assessment for the BOP shell depended on working site engineering personnel experience to a great degree. There is an urgent need for soft system of safety assessment for a BOP shell defects in order to make the evaluation results more reliable, more reasonable, and more accurate and improve the evaluation efficiency. This Paper has been carried out researches in the following fields.(1) The mechanical model of the annular BOP was established according to elastic-plastic mechanics——thick cylinder.(2) On the basis of GB/T19624-2004"Safety Assessment for In-service Pressure Vessels Containing Defects", conventional assessment, fatigue assessment scheme of BOP shell surface defect and volume defects were established, concrete algorithm of all parameters were given. They have provided a theoretical basis for the development of the software system.(3) The two kinds of3D entity model of FH35-70annular BOP manufactured by HYDRIL and SHAFFER companies were established by using mechanical design software PRO/E. and the force situation of hydrostatic condition on them was simulated based on the finite element analysis software ABAQUS platform, it can be seen from the finite element result that maximum equivalent stress and displacement appears on inner cavity upper part of the annular BOP shell, and proved that they are safe.(4) Analytical solution of the crack stress intensity factor was calculated according to fracture mechanics.(5) The numerical solution of stress intensity factor of an axial inner surface crack was calculated. In order to simulate the crack tip singularity better,20nodes was used in the whole model, the mesh was refined the cracks around the area, the mesh was refined around the area and1/4unit was set in the two rows units around the crack. Crack stress intensity factor at maximum depth of and both ends of the crack were obtained by viewing the results. The error was3.82-5.21%by comparing the numerical solution and analytic solution, which verified the correctness of the mechanics model of annular BOP established.(6) Because the real crack is irregular, they can be characterized for shapes according to defects characterization rules.(7) The paper presented a framework of software system of safety assessment for BOP shell defects in view of the reality problems. A set software system based on the framework has been developed. The system not only has function of the defect data management, BOP basic data management. But also make conventional assessment and fatigue assessment for defects quickly and accurately.