The Breakdown of P&ID Non-Engineering Items

What Are P&ID Non-Engineering Items?

P&ID non-engineering items refer to the elements included in a piping and instrumentation diagram that don’t directly represent physical process equipment or instrumentation. Instead, they support readability, navigation, and interpretation—ensuring the diagram functions as a complete, user-friendly document.

These features may not control or measure flow, but they’re essential for cross-referencing, layout clarity, and revision tracking.

Off-Page Connectors (OPCs)

When a pipeline continues onto another drawing, OPCs are used to indicate that continuation point. They ensure logical process flow is maintained across multiple sheets in a large system.

Each OPC typically includes:

• The destination drawing number (e.g., where the pipeline picks up again)
• A four-digit line reference number that matches the corresponding P&ID
• A brief service description (e.g., “Product Transfer to Tank Farm”)

This is especially important in large projects where systems span dozens of drawings.

Annotations

Annotations are simple, non-graphic additions like:

• Text boxes, labels, or notes that offer design clarifications
• Safety and operational instructions
• Unique conditions or installation guidance

These elements help readers understand specific design decisions or risks without cluttering the core diagram.

Segment Breakers

Segment breakers indicate a change in a pipeline’s:

• Material or specification
• Pressure or temperature class
• Insulation or trace heating
• Geographical area

They allow long pipelines to be broken into logical sections without losing detail, making it easier to interpret design intent and compliance zones.

Bunds and Walls

While P&IDs are not true geographical representations, some layouts—especially in chemical and storage facilities—include simplified depictions of bunds, walls, or containment zones.

These are used to:

• Show where pipelines cross safety boundaries
• Indicate whether a line goes through or over a bund wall
• Align pipework with fire protection or spill containment design

Example: A tank outlet line going over a bund wall is drawn with an arc or elevation note, while a line going through may be drawn as a straight continuation with a bund penetration note.

Revision Bubbles

Keeping track of drawing changes is critical, especially during design, commissioning, or site updates.

Revision bubbles are small circular markers placed on the diagram near modified areas. They include:

• A revision number or letter (e.g., A, B, C or 1, 2, 3)
• A link to the revision history table in the P&ID border, where a full description of the change is recorded

This helps engineers, project managers, and contractors quickly identify what has been updated—reducing errors and keeping everyone aligned.

Why Include P&ID Non-Engineering Items?

Although these items don’t directly relate to process equipment or control, they’re essential for:

• Drawing navigation across multiple sheets
• Design clarity and decision traceability
• Safe implementation of modifications
• Regulatory compliance and version control

Well-managed P&ID non-engineering items improve usability for all stakeholders—from control room operators to EPC contractors.