Emerson Actuator Works Faultlessly After 20 Years in Arduous Offshore Duty

Since 1989, offshore installations in the English sector of the North Sea have been required by law to install Emergency Shutdown (ESD) valves to isolate the installations from oil and gas pipelines. A Bettis valve actuator − specially designed by Emerson Process Management − installed at that time has just been decommissioned after 20 years of faultless service. Used in extremely arduous duty, the actuator is being decommissioned because the valve has been re-sized due to the reduced flow rates of the field.

Installed in a riser emergency shutdown system, the Bettis TRQ actuator was designed specifically for the application. With a torque rating of 67,800 Nm (600,000 in-lb), the spring return actuator was the most powerful of its type at that time. Its unique quad design required four cylinders and two spring units to overcome the enormous valve stem forces of the 20in Class 900 valve and to meet the stringent client safety factor requirements. Two of the cylinders have 50 cm (20 in) pistons and two have 40 cm (16 in). The actuator weighs over 5.08 tonnes (5.6 tons) and is over six meters (20 feet) in length.

The regulations introduced in 1989 also covered inspection and testing of ESD valves, including the requirement to perform a partial stroke test of the valve at intervals not exceeding 6 months. The installed Bettis TRQ actuator was one of the first with this diagnostic capability. Partial stroke diagnostic tests have been able to prove satisfactory operation over this actuator's lifetime, avoiding the need to remove the actuator from the line for maintenance.

Emerson has developed its actuator technology significantly over the two decades since this actuator was installed. The company has supplied actuators providing over 226,000 Nm (2,000,000 in-lb) of spring end torque, and has the capability to supply a unit providing 565,000 Nm (5,000,000in-lb) torque output.

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