Safety and reliability improvement of valves and actuators in the offshore oil and gas industry

Abstract

Valve failure is a major risk and a costly phenomenon in the offshore sector of the oil and gas industry. It results in severe negative consequences, such as a loss of assets, a loss of production due to plant shutdowns, and health, safety, and environmental (HSE) issues, such as hydrocarbon (oil and gas) spillage. Improving the safety and reliability of the valves and connected actuators is necessary to limit the occurrence of failure. This paper focuses on three aspects of improving valve and actuator reliability: material selection, design optimization, and boosting the safety integrity level (SIL). The first and second aspects are applicable only to valves, but the third targets both valves and actuators. Using value engineering as a systematic material selection approach shows that 25 Cr super duplex is an optimum material for valves in process services, such as valves for hydrocarbons and chemicals, if the hydrogen sulfide content in the oil is below the limit given in ISO 15156. A case study using a wall thickness and weight reduction approach—according to ASME sec.VIII instead of ASME B16.34—on large, heavy oil export pipeline ball valves is reviewed in this paper. A finite element analysis has been performed to ensure that the thickness of the valve is sufficient to withstand pipeline loads. Insufficient valve thickness can jeopardize the mechanical integrity of a valve and causes valve failure. SIL calculation is a major step in improving the safety and reliability of safety critical valves. A method of SIL calculation is implemented as per the IEC 61508 standard for oil export pipeline valves with an emergency shutdown function. Utilizing leakage monitoring and partial stroke testing increases the SIL along with safety and reliability.