Processing facilities isolation valves

All fixed fire suppression system control valves should be located out of the fire hazard area but still within reach of manual activation. For high hazard areas (such as offshore facilities), dual feeds to fire suppression systems should be considered from opposite areas. For onshore facilities, firewater isolation valve handles should not be contained within a valve pit or a below grade enclosure within the vicinity of hydrocarbon process facilities, since heavy process vapors travel from the process and may settle inside. 

Isolation valves may be located near the property line, the edge of a process unit, or the liquid outlet of a vessel. Valves should be installed on all hazardous materials lines entering or leaving the facility to ensure the facility can be isolated in the event of a spill or fire. Similarly, valves should be located at or near the battery-limit of each unit or outside dike walls for the same reasons and for safety and ease of access. 

Processing facilities have experienced several serious pipe trench fires. Contributing to the size of the fires were inadequate or plugged drains, lack of isolation valves, pipelines on the ground, or inadequate fire stops along the length of the trenches. Pipe trench fires can result in significant business interruption. 

PFD Acronym for Process Flow Diagram. A facility engineering drawing depicting the process without showing instrumentation and minor isolation valves. Use to show flow quantities and conditions at various points in the process. 

Some facilities may simply isolate a process with valves, blinds, and flanges, then draw a vacuum or apply an inerting blanket. The restart may be straightforward. 

When possible, firewater mains should be arranged in loops around process facility and tank farms. Shutoff valves should be located to allow isolation of system segments for maintenance while stiU providing water for all facilities. The minimum water rate with a section of pipe out of service should be at least 60% of the design rate at design pressure for that area. A firewater header should be provided in each process facility area to serve hose stations. 

Pressure relief valves are a critical safety item in almost all process facilities. Pressure relief valves simply must work. This means that they must never be blocked in from the equipment item(s) that they are protecting. Yet their very criticality means that relief valves will have to be routinely isolated and/or removed from the system that they are protecting so that they can be maintained and tested— both for the pressure at which they open and, more rarely, for their flow capacity. 

Listed across the top of the matrix are the various shutdown valves in the facility. A mark in each box indicates the function performed by each device to assure that it protects the process component. By comparing the functions performed by each device to the mechanical flowsheet, it is possible for an auditor to quickly ensure that the process component is indeed isolated. 

Other guidelines cited in Reference 5 suggest methods for estimating additional release factors such as release duration or inventories. It should be noted that the above methods are again only approximations. Site-specific designs and process conditions should be evaluated. For example, some facilities may have few, if any, emergency block valves available to isolate a release. Other facilities may be designed for rapid isolation. 

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