Tuesday, September 30, 2014

Dilemma Between P&ID and Safe Chart

The due dates for Piping and Instrumentation Diagram, P&ID and Safe Chart always is a conflict personally for me and generally for a project. This is because due date for P&ID is more critical deliverables compared to Safe Chart. However, Safe Chart is a checklist practice to be done on P&ID to evaluate requirement on safety devices/devices. This is developed conjunction with of API RP 14C where clear guidelines are provided where to provide all the safety devices/devices.

With this Safe Chart, we able to identify which equipment need relevant safety devices, Low alarm, Low Low trip, High alarm, High High trip, check valve, etc. This is very crucial because it gives minimum requirement and acts as basis when developing P&IDs. The P&IDs being developed will be based on minimum requirement and at least will have some idea on minimum safety devices to be installed on related equipment before it is used for design review and later for Hazard and Operability (HAZOP).

Development of safe chart should be earlier than P&ID so that most of the safety devices requirement can be captured but producing P&ID earlier than safe chart becomes common practice nowadays. The issue with this practice is that if the design is done for detailed design or EPCC and instrument items are bought during development of safe chart. As highlighted earlier, priority of issuing documents is more weighed to P&ID and sometimes issuance of safe chart could be during IFC/AFD of the P&ID. With this scenario, safe chart might be developed based on existing P&ID and not really based on API RP 14C guideline which sometimes some crucial safety devices might be missing in both P&ID and safe chart.

Safe chart is normally developed based “Safety Analysis Checklist (SAC)” which is available in API RP 14C where give items to be checked such as will pressure safety device (PSH, PSL, and PSV), flow safety device (FSV), level safety devices TSH and TSL), temperature safety device (TSH), and not limited to what only available in this SAC but additional input may be added based on design review and HAZOP. Hence, by applying this checklist, most of the criteria which considered as critical will be captured even before design review or/and HAZOP. However, the dilemma is there in design house consultants where requirement to issue Safe Chart not really consistent among phases of project, among projects, and/or clients/consultants.

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