(57ak) Hazard Identification Tools for Complex Piping Systems

Petrochemical manufacturing sites’ logistics and outside battery limit (OSBL) facilities have some inherently different types of process safety hazards than inside battery limit (ISBL) process units. Logistics facilities include atmospheric tank farms, pressurized storage spheres or vessels, pipelines, docks, product loading racks, transfer switching valve manifolds, and so on. Many logistics facilities operate in unsteady state or semi-batch mode (e.g. fill to target level, then switch lineup, then transfer, etc.), and include some piping systems that alternate operation among multiple process services. By contrast, most ISBL facilities operate at steady-state, in one specific process service. Naturally, then, the techniques used for Process Hazard Analysis (PHA) and Hazard & Operability Study (HAZOP) for logistics areas should differ somewhat from the techniques used for ISBL process units.

A particular HAZOP challenge for complicated logistics facilities is the identification of misdirected flow threats. There are numerous alternative stream routings, sources, and destinations to consider. Typical consequences of misdirected flow threats may include non-safety issues such as off-specification product or minor operational upsets, but potentially also include major process safety top events like overfill or overpressure of storage vessels or tanks, or reactive hazard issues (e.g. inadvertently routing a more reactive stream into a process unit feed tank). Therefore, properly identifying the threats with highest potential consequences is just as vital as it is challenging.

This work draws upon some case studies of logistics facilities PHAs / HAZOPs from a large petrochemical manufacturing site. Several PHA / HAZOP methodologies & organizational strategies to identify potential misdirected flow threats are compared & contrasted. Although it is not possible to draw a generalized conclusion on which methodology would be the most effective for any given facility, the considerations highlighted in this work provide practical insight that may aide PHA / HAZOP facilitators and participants in choosing an approach that would enhance their ability to identify the most important threat scenarios for their facilities.