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A Piping and Instrumentation Diagram (P&ID) is the schematic diagram that shows the piping, equipment, instrumentation, and control systems of a process plant, including the interconnections between them. It is one of the most heavily referenced documents throughout a facility's life — used in design, construction, commissioning, operations, and maintenance — and one of the most common sources of document control problems when revisions are not properly managed.
Across oil, gas & LNG, chemical & process, utilities, pharmaceutical, shipping, and mining & metals, the P&ID is the reference document that operators, maintenance engineers, and safety teams turn to first when they need to understand how a system is actually built and controlled.
A P&ID shows the physical sequence of piping, valves, and equipment along with the instrumentation and control loops that monitor and regulate the process — pressure transmitters, control valves, safety interlocks, and their signal paths. Unlike a process flow diagram (PFD), which shows the overall process at a conceptual level, a P&ID captures the level of physical and instrumentation detail needed to actually build, operate, and maintain the plant.
P&IDs are revised constantly throughout a project — during design development, in response to vendor data, and to capture field changes during construction. An outdated P&ID in circulation is a genuine safety and operational risk: maintenance work planned against the wrong revision can miss a safety interlock or misidentify an isolation point. This is why P&ID status and revision control is one of the most safety-critical aspects of document management on a capital project, and why as-built P&IDs are a mandatory component of any document handover package.
Every tagged item that appears on a P&ID — a valve, an instrument, a vessel — should correspond to an entry in the Master Tag Register (MTR). This linkage is what allows a maintenance planner or operator to move from a P&ID drawing to the underlying tag data, technical attributes, and maintenance history for any piece of equipment shown on the drawing, and back again.
A PFD shows the overall process at a conceptual level — major equipment, primary flow paths, key operating conditions — and is typically produced earlier in the design process. A P&ID adds the full instrumentation, control, and piping detail needed for construction and operation. Both documents typically need to remain consistent with each other and with the tag register as a project progresses.
Sharecat keeps P&IDs linked to their associated tags in the Master Tag Register, with clear revision and status tracking so that operations and maintenance teams can be confident they are working from the correct, current version of a drawing. This closes one of the most common and safety-relevant gaps in engineering document management: P&IDs that are technically available but disconnected from the tag data and revision history that make them trustworthy to use.
What does P&ID stand for?
Piping and Instrumentation Diagram (sometimes also expanded as Process and Instrumentation Diagram). It shows the piping, equipment, instrumentation, and control systems of a process plant and how they are interconnected.
What is the difference between a P&ID and a PFD?
A process flow diagram (PFD) shows the process at a conceptual level with major equipment and flow paths; a P&ID adds full piping, instrumentation, and control detail needed for construction, operations, and maintenance. See the comparison above.
Why is P&ID revision control important?
Because maintenance and operations decisions are made directly against the P&ID. Working from an outdated revision can mean missing a safety interlock, an isolation point, or a field change — making P&ID status control a safety issue, not just a documentation one.
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27001
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