Incurrent trend, the oil and gas industry is targeting operations in much deeperwaters and well depths resulting in high pressure and high temperature (HPHT)applications, creating a need for development of new technology. API 17Technical Report 8 (API 17TR8) provides the High Pressure High Temperature(HPHT) design guidelines. Design Verification of any HPHT equipment inaccordance with API/ASME using Finite Element Analysis is a mandatory processto undergo external certification like ABS, DNV etcAvariable bore RAM (VBR) enables a ram-type Blowout Preventer (BOP) to close andseal on more than one size pipe. VBR is a pressure controlling member placed ina BOP cavity intended to control the movement of well bore fluid.
The ratedworking pressure of the VBR design is 20,000 psi at temperature of 250°F.Theobjective of this work is to verify the design of the VBR closed on 7-5/8″diameter drill pipe for the failure modes like protection against plastic collapse:Global criteria 1 (Load Factor of 2.4) & Global criteria 2 (Load Factor 2.
1),protection against local failure (Load Factor 1.7), ratcheting criteria(loading and unloading of minimum three cycles) and hydrotest condition (LoadFactor 1.5) using elastic plastic materials in the model. Initially,a sensitivity study was performed for the full assembly model versus asimplified FEA model consisting of the critical components in the load path tounderstand the behavior. The study demonstrated that the results were similarin both the methods and the simplified model proceeded further for the designby analysis which reduces the complexity and a faster turnaround time. Analysiswas performed for the factored load cases required by ASME using 20 ksi borepressure, its associated end loads and rubber pressure.
Convergence is achievedwhich shows the FEA model is stable and satisfies the global criteria 1 & 2and hydrotest criteria. Accumulated strain limit damage value is less the 1.0which satisfies the requirement of protection against local criteria. Inratcheting criteria, the growth of plastic strain is zero, results there is adevelopment of elastic core in primary components which satisfies therequirement.