Balancing Mechanical and Instrumented Protections in Brownfield Projects

There are many oil and gas facilities around the world that were built at a time when current acceptable engineering requirements were different from today's acceptable engineering best practices and requirements.  As a result, many of the existing facilities are grandfathered from new regulations unless major changes in design or services are initiated.  From the operating company’s perspective, this also implies that older facilities may not be at same acceptable risk levels as newly built facilities.  This paper will describe utilizing overpressure and overfilling protection methods commonly employed by industry (such as ISO/EN 4126, API 521, IEC 61508 / 61511, ISA 84.01 etc.) on brownfield projects for mechanical and instrumented protection systems to achieve an acceptable operating company risk levels on brownfield projects.  One way to achieve this is by balancing both prescriptive and risks based approaches to establishing acceptance criteria that takes into account operability and reliability framework necessary for the operating company to justify the engineering solutions.  Some of the issues this paper intends to deal with include pressure relief with header tie-ins and modifications to flare or vent recovery systems, safety instrumented systems independence and physical separation from process control systems, and issues related to location and infrastructure challenges.