Practical Examples of Alternate Overpressure Protection Systems: An Owner's Perspective

In 2007 API 521/ISO 23251 [1] published guidance on the use of High Integrity Protective Systems (HIPS). In 2009, the Dow Chemical Company (Dow) updated its internal work process to apply Dow’s risk based work processes to HIPS design, application and evaluation. The overall result is an efficient process that links together the existing work processes for conventional relief design, Layers of Protection Analysis (LOPA) and Safety Instrumented Systems (SIS).  This produces a risk based method for applying and designing protection layers into a HIPS. For additional details, refer to ”High Integrity Protection System Design Using a Risk Base Approach” by Robert J. Stack, AICHE 2010 spring meeting 6^th Global Congress on Process Safety.

HIPS is used to mitigate overpressure scenarios when: 1) a conventional PRD is not practical or possible, 2) a conventional PRD will not be reliable or 3) a conventional PRD will work but will result in high treatment cost.  In addition, HIPS can also used to limit the required relief size by limiting the operating window of the process.  The purpose of this paper is provide several practical examples on the use of HIPS within Dow and to describe some of the challenges and associated strategies to insure successful implementation and sustained process safety performance.