Full Vacuum Vs Half Vacuum (FV Vs HV)

Full Vacuum

FV - for vessels having steam as a signifacant component during normal operation (e.g. amine regenerators)
- for vessels operating under full or partial vacuum during normal operation
- for vessels that require steamout as part of routine operation

Half Vacuum
HV - for vessels that require steamout during maintenance only and does not have steam during normal operation

Thanks doct9960

Boiler and Pressure Vessel engineering - FV versus Half FV for BPVD?:

Interconnection tag number is P&ID.

Interconnection tag number is P&ID is called OPC.

"Interconnections (OPC) – are shown between lines (piping OPC) and instrument signals (Instrument OPC) present on two different P&ID sheets. Sometime these interconnectors are also assigned with a unique tag number. For easy identification of the connections between two P&IDs. A connector present on two different drawing connection a line or a signal carries the same tag number."

Credits: Piping and Instrumentation Diagram – P&ID | Enggcyclopedia:

LOC acronym

In Chemical Engineering plant terms, we always talk about Loss of containment. So the acronym LOC is used in HAZOPs regularly to indicated "loss of containment".