High Integrity Protection Systems

The American Petroleum Institute (API) and American Society of Mechanical Engineers (ASME) provide criteria for the protection of vessels and pipeline from excess pressure. In conventional design, a pressure relief device is used as the primary means of protection and a flare is used to safely combust the gases relieved during any overpressure event. However, community and regulatory authorities are demanding that industry reduce flaring. The need to balance safety and environmental requirements has resulted in the use of an alternative approach for overpressure protection — a safety instrumented system (SIS). API 521 and Code Case 2211 of ASME Section VIII, Division 1 and 2 allow the use of an SIS in lieu of a pressure relief device as long as the SIS meets or exceeds the protection provided by the pressure relief device. As SIS, their design must follow the safety lifecycle in the international standard IEC 61511. The required risk reduction results in the need for high SIS safety availability; therefore, these systems are often called High Integrity Protections Systems (HIPS).