An Innovative Ultradeepwater Subsea Blowout Preventer (SSBOP) Control System Using Shape Memory Alloy Actuators

Abstract

Abstract API RP16E1 mandates that minimum acceptable Blowout Preventer (BOP) control system response times are 60 seconds or less for an annular preventer and 45 seconds or less for a ram type preventer. Norsok standard2 response time for closing rams when located at seabed is 30 seconds, or 45 seconds for annuli greater than 20 inches. As drilling moves to deep water, conventional BOP actuation technologies based on full or partial hydraulics (hydraulic, electrohydraulic or multiplex electrohydraulic systems) are unable to meet this standard because of the long hydraulic fluid communication path between the offshore platform and the BOP stack on the sea floor. This paper presents an innovative undersea Blowout Preventer (BOP) using Shape Memory Alloy. The goal of this project is to develop innovative fast-response BOPs using only Nickel Titanium (Nitinol) Shape Memory Alloy (SMA) as the actuator. Nitinol SMA has a long fatigue life and high corrosion resistance. As a solid-state actuator, it is capable of up to 5% strain recovery or 72,500 psi restoration stress with many cycles. It can be actuated by electrical heating, thereby replacing hydraulic actuation and hydraulic lines with electric cable. With significantly fewer components, the SMA system will dramatically reduce total cost and will increase operation reliability. The new device could easily be retrofitted to existing conventional subsea control system so that other methods can also be used as a backup. Most important, the innovative all-electric BOP will provide much faster response than its hydraulic counterpart and will improve safety for subsea drilling. To demonstrate the feasibility of such a device, a proof-of-concept prototype of a BOP with SMA actuation has been designed, fabricated, and tested at University of Houston. The BOP actuator uses strands of SMA wires to achieve large force and large displacement in a remarkably small space. Experimental results demonstrate that the BOP can be activated and fully closed in less than 15 seconds. The concept of this innovative device is illustrated, and detailed comparisons of the response time for hydraulic and Nitinol SMA actuations are included. This preliminary research reveals the potential of smart material technology in subsea drilling systems.