Characterization of leak rates in thermoplastic barrier valve seals under high static and cyclic pressure loads

The article focuses on characterization of leak rates under high static and cyclic pressure loads in thermoplastic barrier seals used in gas lift valves. The objective of the study is to validate the seal design for gas lift valves and check if its sealing material would meet the stringent leakage requirements laid out in the Statoil standards. The Statoil has a stringent leakage requirement of ≤2 sccm with gases and a pressure drop of ≤1% of the applied pressure differential with liquids. For convenience of the study only the barrier check valve portion of the actual gas lift valve is tested. It includes a spring, check dart, a portion of the flow bore, a portion of the nose (housing the dart) and the check seal. For leak tests at pressures up to 2000 psi, a standard nitrogen bottle was used and for higher pressures up to 10,000 psi, a boost pump was employed. In addition, the test rig was designed to generate accelerated cyclic loads to study the effect of it on leakage characteristics of the seal. Finite element analysis (FEA) on the seal design under 100 and 10,000 psi validated the stress-strain states in seal and predicted the sealing contact pressures. It was observed that the new seal design satisfies the Statoil requirements after an initial pressure cycle. In addition, it is observed that leak rates are unaffected by the accelerated loading cycles.