SPECIAL TOPIC : Actuation & Automation
A Look at Shape Memory Alloy Actuators
A general-purpose globe valve actuator using shape memory alloy ( SMA ) technology has been recently introduced to the industry . The introduction of this actuator was spurred on by a need in the energy sector for alternatives to methane-venting pneumatic equipment . The operation of venting pneumatic equipment that runs on pressurized methane , or fuel gas , is prevalent at natural gas well sites and facilities . Applications where the operation of pneumatic valve actuators and associated controllers vent methane into the atmosphere , include separators , gas injection , and blanket gas . With impending regulations that disallow the use of methane venting devices , the natural gas industry is challenged to find suitable non-emitting alternatives .
By Adam Nguyen , M . Eng , Automation Solutions Specialist - Kinitics Automation Limited
The Science of Shape Memory Alloys
Shape memory alloys ( SMA ) are a unique class of metal alloys that can be engineered to remember a specific physical shape . By harnessing this two-way shape memory effect , the shape of the material can be precisely controlled in a repeatable and predictable manner .
An assembly of SMA wires that work against a mechanical compression spring creates the basis for an SMA bundled wire actuator . By passing electric current through the SMA wires a shape memory effect is induced , which overcomes the spring force and causes the SMA wires to contract . When the actuator is coupled to the stem of a valve , the valve ’ s position can be controlled , Figure 2 .
Figure 1 : The KVA , an SMA bundled wire actuator , deployed at a natural gas production facility near Edson , Alberta .
Unique Features of Shape Memory Alloy Actuators
Fewer Parts , Single Moving Component
A distinction between an SMA bundled wire actuator and traditional motorized actuators is that the SMA bundled wire actuator has one moving part in its driveline . Globe valves controlled by motorized actuators require several components to translate the rotary motion generated by the motor to the linear motion of the valve stem . As a result , motorized actuators can exhibit backlash and require periodic maintenance such as lubrication or component replacement due to wear . The motorless design of the SMA actuator allows for minimal wear on mechanical components allowing for maintenance-free operation .
Mechanical Spring for Failure Closed
Like pneumatic actuators , an SMA bundled wire actuator uses a mechanical spring that is inherent to its design . The mechanical spring permits the SMA bundled wire actuator to return the valve to a known position in the event of power failure . The predictability of systems under failure events is an important property for many processes , especially for sites and facilities in remote locations where power can be unreliable . Though this behavior can be replicated with electric motors using a battery or capacitor as a power source backup , a limitation of this design is that the reliability of such systems is dependent on the proper functioning of the motor , the battery or capacitor backup , and associated controls that must detect and correctly respond to the fault condition . The feature can also be replicated in specialized motorized actuator designs that incorporate a pre-loaded spring .
This method however requires the use of active electrical clutches and brakes that need to be continuously powered . This may not be viable where power resources are limited .
Figure 2 : Shape memory alloy in valve actuator application .
4 Valve World Americas | September 2023 • www . valve-world-americas . net