High temperature shape memory alloy actuators through mechanical treatments for an oil & gas down-hole valve

ABSTRACT Shape memory alloy actuators, with their simple operation through heating, and high solid state strain and force output are ideally suited to a range of robust engineering applications within the oil & gas industry, such as down-well flow control valves. Because reservoir temperatures can reach up to 250°C for very deep wells, a range of alloys with high transition temperatures are required. For a specific ‘single-shot’ valve application, with an operational temperature requirement of 110°C, a robust shape memory alloy (SMA) actuator, capable of delivering a stroke of 2 mm with high force output (4 kN), was developed and tested from Nitinol alloy H (Ni:Ti ratio of 49.5%:50.5%). The inducement of mechanical stresses within nickel-titanium alloys can influence the transitional temperature range of the alloy. This characteristic was exploited to raise the martensitic-to-austenitic transition temperature (A p ) of the alloy from 90°C to 130°C, through the application of large compressive cold-working stresses (equivalent to 10% compressive strains). The actuator acted as an electrically-activated trigger within a hybrid SMA-hydraulic valve. Once activated the actuator releases a high pressure seal allowing stored hydraulic pressure to operate the main mechanism of the valve. The operation of the SMA actuator and complete valve assembly, inclusive of battery pack and control electronics to activate the SMA, was successfully tested within a test-well environment at depths up to 900 meters and under hydrostatic pressures of 7,500 psi (51 MPa). The reliability of the valve and the SMA actuator demonstrates the applicability of this technology to down-hole oil & gas applications. Keywords: Shape memory alloy, high temperature, hydraulic actuation, oil & gas, down-hole valves