Emerson Process Manageent designed and installed a Bettis valve actuator that was recently decommissioned after 20 years of faultless service in the offshore installation in the English sector of the North Sea.
Since 1989 and by law, offshore intallations require emergency shutdown (ESD) valves to isolate the installations from oil and gas pipelines.
The recently decommissioned Bettis TRQ actuator was installed in a riser emergency shutdown system. At the time of installation, the spring return actuator was the most powerful of its type, with a torque rating of 67,800 Nm (600,000 in-lb). Its unique quad design required four cylinders and two spring units to overcome the large valve stem forces of the 20 in. 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 1989 regulations also required inspection and testing of ESD valves every six months. The installed Bettis TRQ actuator was one of the first to have diagnostic capabilities and the partial stroke diagnostic tests performed throughout the years have been able to prove satisfactory operation over this actuator's lifetime. This preventive measurement, allowed the actuator to be kept in place, avoiding the need to remove it from the line for maintenance.
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